[ { "id": "authors:yepmh-n6488", "collection": "authors", "collection_id": "yepmh-n6488", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230725-48998000.5", "type": "article", "title": "Activation of light alkanes at room temperature and ambient pressure", "author": [ { "family_name": "Zhang", "given_name": "Haochen", "orcid": "0000-0002-2774-5868", "clpid": "Zhang-Haochen" }, { "family_name": "Li", "given_name": "Chunsong", "orcid": "0000-0002-8016-1896", "clpid": "Li-Chunsong" }, { "family_name": "Liu", "given_name": "Wenxuan", "orcid": "0009-0006-0583-0793", "clpid": "Liu-Wenxuan" }, { "family_name": "Luo", "given_name": "Guangsheng", "orcid": "0000-0003-3273-4511", "clpid": "Luo-Guangsheng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Xu", "given_name": "Bingjun", "orcid": "0000-0002-2303-257X", "clpid": "Xu-Bingjun" }, { "family_name": "Lu", "given_name": "Qi", "orcid": "0000-0002-0380-2629", "clpid": "Lu-Qi" } ], "abstract": "Light alkane activation under mild conditions remains a substantial challenge. Here we report an aqueous reaction system capable of selectively converting light alkanes into corresponding olefins and oxygenates at room temperature and ambient pressure using Cu powder as the catalyst and O\u2082 as the oxidant. In ethane activation, we achieved a combined production of ethylene and acetic acid at a rate of 2.27\u2009mmol\u2009g_(Cu)\u207b\u00b9\u2009h\u207b\u00b9, with a combined selectivity up to 97%. Propane is converted to propylene with a selectivity up to 94% and a production rate up to 1.83\u2009mmol\u2009g_(Cu)\u207b\u00b9\u2009h\u207b\u00b9, while methane is converted mainly to carbon dioxide, methanol and acetic acid. On the basis of catalytic experiments, isotopic labelling experiments, spectroscopic insights and density functional theory calculations, we put forward mechanistic understandings in which the C\u2013H bond is activated by the surface oxide species generated during the oxidation process, forming alkyl groups as key reaction intermediates.", "doi": "10.1038/s41929-023-00990-9", "issn": "2520-1158", "publisher": "Nature Publishing Group", "publication": "Nature Catalysis", "publication_date": "2023-08-14" }, { "id": "authors:0exvf-ets94", "collection": "authors", "collection_id": "0exvf-ets94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220520-388227000", "type": "article", "title": "Selective Enhancement of Methane Formation in Electrochemical CO\u2082 Reduction Enabled by a Raman-Inactive Oxygen-Containing Species on Cu", "author": [ { "family_name": "He", "given_name": "Ming", "orcid": "0000-0001-5392-503X", "clpid": "He-Ming" }, { "family_name": "Chang", "given_name": "Xiaoxia", "orcid": "0000-0001-6598-6083", "clpid": "Chang-Xiaoxia" }, { "family_name": "Chao", "given_name": "Tzu-Hsuan", "clpid": "Chao-Tzu-Hsuan" }, { "family_name": "Li", "given_name": "Chunsong", "orcid": "0000-0002-8016-1896", "clpid": "Li-Chunsong" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Xu", "given_name": "Bingjun", "orcid": "0000-0002-2303-257X", "clpid": "Xu-Bingjun" }, { "family_name": "Lu", "given_name": "Qi", "orcid": "0000-0002-0380-2629", "clpid": "Lu-Qi" } ], "abstract": "The role of oxygen-containing species on Cu catalysts in the electrochemical CO\u2082 reduction reaction (CO\u2082RR) remains unclear due to the difficulty in its stabilization under reaction conditions. Co-electrolysis of CO\u2082 with an oxidant is an effective strategy to introduce oxygen-containing species on Cu during the CO\u2082RR. In this work, we present concrete evidence demonstrating that an oxygen-containing species is able to not only enhance the rate of the CO\u2082RR but also tune selectivities for certain products. Co-electrolysis of CO\u2082 with H\u2082O\u2082 on Cu selectively accelerates the CH4 production rate by up to a factor of 200, but with only a slight enhancement of C\u2082\u208a products. Combined investigations using in situ Raman spectroscopy with density functional theory calculations reveal that a Raman-inactive Cu oxide species is responsible for the improved CH\u2084 production. Results reported in this work highlight the possibility of enhancing Cu-based CO\u2082RR catalysts by introducing stable oxygen-containing catalytic structures.", "doi": "10.1021/acscatal.2c00087", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2022-05-20", "series_number": "10", "volume": "12", "issue": "10", "pages": "6036-6046" }, { "id": "authors:xkgp7-s7d20", "collection": "authors", "collection_id": "xkgp7-s7d20", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210308-132156702", "type": "article", "title": "Selective Activation of Propane Using Intermediates Generated during Water Oxidation", "author": [ { "family_name": "Zhang", "given_name": "Haochen", "orcid": "0000-0002-2774-5868", "clpid": "Zhang-Haochen" }, { "family_name": "Li", "given_name": "Chunsong", "orcid": "0000-0002-8016-1896", "clpid": "Li-Chunsong" }, { "family_name": "Lu", "given_name": "Qi", "orcid": "0000-0002-0380-2629", "clpid": "Lu-Qi" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "Electrochemical conversion of light alkanes to high-value oxygenates provides an attractive avenue for eco-friendly utilization of these hydrocarbons. However, such conversion under ambient conditions remains exceptionally challenging due to the high energy barrier of C\u2013H bond cleavage. Herein, we investigated theoretically the partial oxidation of propane on a series of single atom alloys by using active intermediates generated during water oxidation as the oxidant. We show that by controlling the potential and pH, stable surface oxygen atoms can be maintained under water oxidation conditions. The free energy barrier for C\u2013H bond cleavage by the surface oxygen can be as small as 0.54 eV, which can be surmounted easily at room temperature. Our calculations identified three promising surfaces as effective propane oxidation catalysts. Our complementary experiments demonstrated the partial oxidation of propane to acetone on Ni-doped Au surfaces. We also investigated computationally the steps leading to acetone formation. These studies show that the concept of exploiting intermediates generated in water oxidation as oxidants provides a fruitful strategy for electrocatalyst design to efficiently convert hydrocarbons into value-added chemicals.", "doi": "10.1021/jacs.1c00377", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2021-03-17", "series_number": "10", "volume": "143", "issue": "10", "pages": "3967-3974" }, { "id": "authors:spfj4-gjz37", "collection": "authors", "collection_id": "spfj4-gjz37", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200803-093757604", "type": "article", "title": "Oxygen induced promotion of electrochemical reduction of CO\u2082 via co-electrolysis", "author": [ { "family_name": "He", "given_name": "Ming", "orcid": "0000-0001-5392-503X", "clpid": "He-Ming" }, { "family_name": "Li", "given_name": "Chunsong", "orcid": "0000-0002-8016-1896", "clpid": "Li-Chunsong" }, { "family_name": "Zhang", "given_name": "Haochen", "orcid": "0000-0002-2774-5868", "clpid": "Zhang-Haochen" }, { "family_name": "Chang", "given_name": "Xiaoxia", "clpid": "Chang-Xiaoxia" }, { "family_name": "Chen", "given_name": "Jingguang G.", "orcid": "0000-0002-9592-2635", "clpid": "Chen-Jingguang-G" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cheng", "given_name": "Mu-jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Xu", "given_name": "Bingjun", "orcid": "0000-0002-2303-257X", "clpid": "Xu-Bingjun" }, { "family_name": "Lu", "given_name": "Qi", "clpid": "Lu-Qi" } ], "abstract": "Harnessing renewable electricity to drive the electrochemical reduction of CO\u2082 is being intensely studied for sustainable fuel production and as a means for energy storage. Copper is the only monometallic electrocatalyst capable of converting CO\u2082 to value-added products, e.g., hydrocarbons and oxygenates, but suffers from poor selectivity and mediocre activity. Multiple oxidative treatments have shown improvements in the performance of copper catalysts. However, the fundamental underpinning for such enhancement remains controversial. Here, we combine reactivity, in-situ surface-enhanced Raman spectroscopy, and computational investigations to demonstrate that the presence of surface hydroxyl species by co-electrolysis of CO\u2082 with low concentrations of O\u2082 can dramatically enhance the activity of copper catalyzed CO2 electroreduction. Our results indicate that co-electrolysis of CO\u2082 with an oxidant is a promising strategy to introduce catalytically active species in electrocatalysis.", "doi": "10.1038/s41467-020-17690-8", "pmcid": "PMC7395777", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2020-07-31", "volume": "11", "pages": "3844" }, { "id": "authors:5rrfe-wz511", "collection": "authors", "collection_id": "5rrfe-wz511", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190806-124541228", "type": "article", "title": "Mechanism and kinetics for both thermal and electrochemical reduction of N_2 catalysed by Ru(0001) based on quantum mechanics", "author": [ { "family_name": "Chen", "given_name": "Liang-Yu", "clpid": "Chen-Liang-Yu" }, { "family_name": "Kuo", "given_name": "Tung-Chun", "clpid": "Kuo-Tung-Chun" }, { "family_name": "Hong", "given_name": "Zih-Siang", "clpid": "Hong-Zih-Siang" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "The conversion of N_(2(g)) to NH_(3(g)) is an important industrial process that plays a vital role in sustaining the current human population. This chemical transformation relies heavily on the Haber\u2013Bosch process (N2 thermal reduction, N_2TR), which requires enormous quantities of energy (2% of the world supply) and extreme conditions (200 atm and 500 \u00b0C). Alternatively, N_(2(g)) can be reduced to NH_(3(g)) through electrochemical means (N_2ER), which may be a less energy intensive and lower-capital approach since the H atoms come from H_2O not H_2. However, N_2ER efficiency is far from satisfactory. In order to provide the basis for developing a new generation of energy efficient processes, we report the detailed atomistic mechanism and kinetics for N_2ER on Ru(0001) along with a comparison to N2TR. We obtained these results using a new electrochemical model for quantum mechanics (QM) calculations to obtain free energy surfaces for all plausible reaction pathways for N_2ER under a constant electrode potential of 0.0 V_(SHE). For both processes, the elementary steps involve several steps of breaking of the NN bonds, hydrogenation of surface N_2H_X or NH_X, and NH_3 release. We find similar energetics for the NN cleavage steps for both systems. However, the hydrogenation steps are very different, leading to much lower free energy barriers for N_2ER compared to N_2TR. Thus, N_2ER favors an associative route where successive hydrogen atoms are added to N_2 prior to breaking the NN bonds rather than the dissociative route preferred by N_2TR, where the NN bonds are broken first followed by the addition of Hs. Our QM results provide the detailed free energy surfaces for N_2ER and N_2TR, suggesting a strategy for improving the efficiency of N_2ER.", "doi": "10.1039/c9cp03187a", "issn": "1463-9076", "publisher": "Royal Society of Chemistry", "publication": "Physical Chemistry Chemical Physics", "publication_date": "2019-08-28", "series_number": "32", "volume": "21", "issue": "32", "pages": "17605-17612" }, { "id": "authors:w355h-yxq78", "collection": "authors", "collection_id": "w355h-yxq78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190730-090851748", "type": "article", "title": "Computational and experimental demonstrations of one-pot tandem catalysis for electrochemical carbon dioxide reduction to methane", "author": [ { "family_name": "Zhang", "given_name": "Haochen", "orcid": "0000-0002-2774-5868", "clpid": "Zhang-Haochen" }, { "family_name": "Chang", "given_name": "Xiaoxia", "orcid": "0000-0001-6598-6083", "clpid": "Chang-Xiaoxia" }, { "family_name": "Chen", "given_name": "Jingguang G.", "orcid": "0000-0002-9592-2635", "clpid": "Chen-Jingguang-G" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Xu", "given_name": "Bingjun", "orcid": "0000-0002-2303-257X", "clpid": "Xu-Bingjun" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Lu", "given_name": "Qi", "orcid": "0000-0002-0380-2629", "clpid": "Lu-Qi" } ], "abstract": "Electroreduction of carbon dioxide to hydrocarbons and oxygenates on copper involves reduction to a carbon monoxide adsorbate followed by further transformation to hydrocarbons and oxygenates. Simultaneous improvement of these processes over a single reactive site is challenging due to the linear scaling relationship of the binding strength of key intermediates. Herein, we report improved electroreduction of carbon dioxide by exploiting a one-pot tandem catalysis mechanism based on computational and electrochemical investigations. By constructing a well-defined copper-modified silver surface, adsorbed carbon monoxide generated on the silver sites is proposed to migrate to surface copper sites for the subsequent reduction to methane, which is consistent with insights gained from operando attenuated total reflectance surface enhanced infrared absorption spectroscopic investigations. Our results provide a promising approach for designing carbon dioxide electroreduction catalysts to enable one-pot reduction of products beyond carbon monoxide and formate.", "doi": "10.1038/s41467-019-11292-9", "pmcid": "PMC6659690", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2019-07-26", "volume": "10", "pages": "Art. No. 3340" }, { "id": "authors:ppp1n-6sk54", "collection": "authors", "collection_id": "ppp1n-6sk54", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190418-104651423", "type": "article", "title": "Effectively increased efficiency for electroreduction of carbon monoxide using supported polycrystalline copper powder electrocatalysts", "author": [ { "family_name": "Li", "given_name": "Jing", "clpid": "Li-Jing-CHEMENG" }, { "family_name": "Chang", "given_name": "Kuan", "clpid": "Chang-Kuan" }, { "family_name": "Zhang", "given_name": "Haochen", "orcid": "0000-0002-2774-5868", "clpid": "Zhang-Haochen" }, { "family_name": "He", "given_name": "Ming", "clpid": "He-Ming" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Chen", "given_name": "Jingguang G.", "orcid": "0000-0002-9592-2635", "clpid": "Chen-Jingguang-G" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Lu", "given_name": "Qi", "orcid": "0000-0002-0380-2629", "clpid": "Lu-Qi" } ], "abstract": "Many electrocatalysts can efficiently convert CO_2 to CO. However, the further conversion of CO to higher-value products was hindered by the low activity of the CO reduction reaction and the consequent lack of mechanistic insights for designing better catalysts. A flow-type reactor could potentially improve the reaction rate of CO reduction. However, the currently available configurations would pose great challenges in reaction mechanism understanding due to their complex nature and/or lack of precise potential control. Here we report, in a standard electrochemical cell with a three-electrode setup, a supported bulk polycrystalline copper powder electrode reduces CO to hydrocarbons and multicarbon oxygenates with dramatically increased activities of more than 100 mA cm^(\u20132) and selectivities of more than 80%. The high activity and selectivity that was achieved demonstrates the practical feasibility of electrochemical CO or CO_2 (with a tandem strategy) conversion and enables the experimental exploration of the CO reduction mechanism to further reduced products.", "doi": "10.1021/acscatal.9b00099", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2019-06-07", "series_number": "6", "volume": "9", "issue": "6", "pages": "4709-4718" }, { "id": "authors:j76hd-2qh79", "collection": "authors", "collection_id": "j76hd-2qh79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190125-155529881", "type": "article", "title": "Csp^3-Csp^3 Bond-Forming Reductive Elimination from Well-Defined Copper(III) Complexes", "author": [ { "family_name": "Paeth", "given_name": "Matthew", "clpid": "Paeth-M" }, { "family_name": "Tyndall", "given_name": "Sam B.", "clpid": "Tyndall-S-B" }, { "family_name": "Chen", "given_name": "Liang-Yu", "clpid": "Chen-Liang-Yu" }, { "family_name": "Hong", "given_name": "Jia-Cheng", "clpid": "Hong-Jia-Cheng" }, { "family_name": "Carson", "given_name": "William P.", "clpid": "Carson-W-P" }, { "family_name": "Liu", "given_name": "Xingwu", "orcid": "0000-0002-8564-1151", "clpid": "Liu-Xingwu" }, { "family_name": "Sun", "given_name": "Xiaodong", "clpid": "Sun-Xiaodong" }, { "family_name": "Liu", "given_name": "Jinjia", "clpid": "Liu-Jinjia" }, { "family_name": "Yang", "given_name": "Kundi", "clpid": "Yang-Kundi" }, { "family_name": "Hale", "given_name": "Elizabeth M.", "clpid": "Hale-E-M" }, { "family_name": "Tierney", "given_name": "David L.", "clpid": "Tierney-D-L" }, { "family_name": "Liu", "given_name": "Bin", "clpid": "Liu-Bin" }, { "family_name": "Cao", "given_name": "Zhi", "clpid": "Cao-Zhi" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Liu", "given_name": "Wei", "orcid": "0000-0001-6249-3179", "clpid": "Liu-Wei-Chemistry" } ], "abstract": "Carbon\u2013carbon bond-forming reductive elimination from elusive organocopper(III) complexes has been considered the key step in many copper-catalyzed and organocuprate reactions. However, organocopper(III) complexes with well-defined structures that can undergo reductive elimination are extremely rare, especially for the formation of Csp^3\u2013Csp^3 bonds. We report herein a general method for the synthesis of a series of [alkyl-Cu^(III)-(CF_3)_3]^\u2212 complexes, the structures of which have been unequivocally characterized by NMR spectroscopy, mass spectrometry, and X-ray crystal diffraction. At elevated temperature, these complexes undergo reductive elimination following first-order kinetics, forming alkyl-CF3 products with good yields (up to 91%). Both kinetic studies and DFT calculations indicate that the reductive elimination to form Csp^3\u2013CF^3 bonds proceeds through a concerted transition state, with a \u0394H\u29e7 = 20 kcal/mol barrier.", "doi": "10.1021/jacs.8b12632", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2019-02-20", "series_number": "7", "volume": "141", "issue": "7", "pages": "3153-3159" }, { "id": "authors:24dz6-kt634", "collection": "authors", "collection_id": "24dz6-kt634", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180110-102226313", "type": "article", "title": "The importance of grand-canonical quantum mechanical methods to describe the effect of electrode potential on the stability of intermediates involved in both electrochemical CO_2 reduction and hydrogen evolution", "author": [ { "family_name": "Zhang", "given_name": "Haochen", "orcid": "0000-0002-2774-5868", "clpid": "Zhang-Haochen" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Lu", "given_name": "Qi", "orcid": "0000-0002-0380-2629", "clpid": "Lu-Qi" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" } ], "abstract": "The rational design of electrocatalysts to convert CO_2 to fuel requires predicting the effect of the electrode potential (U) on the binding and structures of the intermediates involved in CO_2 electrochemical reduction (CO2ER). In this study, we used grand-canonical quantum mechanics (GC-QM) to keep the potential constant during the reactions (rather than keeping the charge constant as in standard QM) to investigate the effect of Uon adsorption free energies (\u0394Gs) of 14 CO_2ER intermediates on Cu(111) as well as the intermediates involved in the competitive hydrogen evolution reaction (HER). In contrast to most previous theoretical studies where \u0394Gs were calculated under constant charge (= 0, neutral), we calculated \u0394Gs under constant potential (U = 0.0, \u22120.5, \u22121.0, and \u22121.5 V_(SHE)). By comparing the \u0394Gs calculated under constant U (= 0.0 V_(SHE)) to those calculated under constant charge, we found differences up to 0.22 eV which would change the rates at 298 K by a factor of about 5300. In particular we found that the adsorption of species with a C O functional group (i.e., *COOH, *CO, and *CHO) strengthened by up to 0.16 eV as U became more negative by 1 V, whereas the adsorption of \u2013O\u2013 species (i.e., *OH, *OCH3, *COH, and *CHOH) weakened by up to 0.20 eV. For the (111) index surfaces of Cu, Au, Ag, Ir, Ni, Pd, Pt and Rh, we investigated the effect of U on the reaction free energy (\u0394G) at pH = 0 for the crucial elementary steps for CO_2ER (*CO + (H+/e\u2212) \u2192 *CHO, \u0394G = (\u0394G_(*CHO) \u2013 \u0394G_(*CO)) + eU) and HER (* + (H+/e\u2212) \u2192 *H, \u0394G = \u0394G_(*H) + eU. Our results indicated that the influence of U on (\u0394G_(*CHO) \u2013 \u0394G_(*CO)) was metal dependent. In contrast, the energy for converting a proton in solution to H* on the surface, \u0394G_(*H), was barely affected by U(for the studied metals). Overall we found substantial differences (MAD > 0.18 eV) between the \u0394Gs calculated under U = \u22121.0 V_(SHE) (relevant to experiments) and those calculated under constant charge (= 0, neutral) common to most theoretical investigations. Therefore, we strongly recommend application GC-QM to obtain accurate energetics for CO_2ER.", "doi": "10.1039/c7cp08153g", "issn": "1463-9076", "publisher": "Royal Society of Chemistry", "publication": "Physical Chemistry Chemical Physics", "publication_date": "2018-01-28", "series_number": "4", "volume": "20", "issue": "4", "pages": "2549-2557" }, { "id": "authors:63at1-67620", "collection": "authors", "collection_id": "63at1-67620", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170919-081753764", "type": "article", "title": "The Dual-Phase Mechanism for the Catalytic Conversion of n-Butane to Maleic Anhydride by the Vanadyl Pyrophosphate Heterogeneous Catalyst", "author": [ { "family_name": "O'Leary", "given_name": "Willis C.", "clpid": "O'Leary-W-C" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" } ], "abstract": "Industrial production of maleic anhydride (MA) from n-butane relies on the vanadyl pyrophosphate (VPO) catalyst. Improving VPO's selectivity and activity could have enormous economic and environmental impact, but efforts have been impeded by uncertainties regarding the active phases and atomistic mechanism of the VPO catalyst. We report here a plausible 15-step mechanism taking n-butane to MA with energetics computed using hybrid density functional theory calculations on periodic models of the surface layers. We find that the P\u2550O group on the X1 phase is solely responsible for butane activation. The P\u2550O group is made active by the reduction of a nearby vanadium atom, a so-called reduction-coupled oxo-activation. However, we show that a catalyst consisting only of the X1 phase would not be selective because of several highly exothermic steps. Instead, we show that the more stable \u03b11 phase can catalyze the formation of MA after initial activation, thus proposing and validating a dual-phase mechanism that takes butane to MA. Our new mechanism inspires the development of a more selective VPO catalyst containing small X1 regions highly separated by \u03b1_1 surfaces.", "doi": "10.1021/acs.jpcc.7b07881", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2017-11-02", "series_number": "43", "volume": "121", "issue": "43", "pages": "24069-24076" }, { "id": "authors:5k2jc-kzn70", "collection": "authors", "collection_id": "5k2jc-kzn70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170515-132737377", "type": "article", "title": "Probing the C-O bond-formation step in metalloporphyrin catalyzed C-H oxygenation reactions", "author": [ { "family_name": "Liu", "given_name": "Wei", "orcid": "0000-0001-6249-3179", "clpid": "Liu-Wei-Chemistry" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Groves", "given_name": "John T.", "orcid": "0000-0002-9944-5899", "clpid": "Groves-J-T" } ], "abstract": "The oxygen rebound mechanism, proposed four decades ago, is invoked in a wide range of oxygen and hetero-atom transfer reactions. In this process, a high-valent metal-oxo species abstracts a hydrogen atom from the substrate to generate a carbon-centered radical, which immediately recombines with the hydroxometal intermediate with very fast rate constants that can be in the ns to ps regime. In addition to catalyzing C-O bond formation, we found that manganese porphyrins can also directly catalyze C-H halogenations and pseudohalogenations, including chlorination, bromination and fluorination as well as C-H azidation. For these cases, we showed that long-lived substrate radicals are involved, indicating that radical rebound may involve a barrier in some cases. In this study, we show that axial ligands significantly affect the oxygen rebound rate. Fluoride, hydroxide and oxo ligands all slow down the oxygen rebound rate by factors of 10-40 fold. The oxidation of norcarane by a manganese porphyrin coordinated with fluoride or hydroxide leads to the formation of significant amounts of radical rearranged products. Cis-decalin oxidation afforded both cis- and trans-decalol. Xanthene afforded dioxygen trapped products and the radical dimer product, bixanthene, under aerobic and anaerobic conditions, respectively. DFT calculations probing the rebound step show that the rebound barrier increases significantly (by 3.3, 5.4 and 6.0 kcal/mol, respectively) with fluoride, hydroxide and oxo as axial ligands.", "doi": "10.1021/acscatal.7b00655", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2017-06", "series_number": "6", "volume": "7", "issue": "6", "pages": "4182-4188" }, { "id": "authors:m04nr-z7s05", "collection": "authors", "collection_id": "m04nr-z7s05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161129-090636992", "type": "article", "title": "Computational design of a pincer phosphinito vanadium ((OPO)V) propane monoxygenation homogeneous catalyst based on the reduction-coupled oxo activation (ROA) mechanism", "author": [ { "family_name": "Fu", "given_name": "Ross", "clpid": "Fu-Ross" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" } ], "abstract": "We propose the vanadium bis(2-phenoxyl)phosphinite pincer complex, denoted (OPO)V, as a low temperature water-soluble catalyst for monoxygenation of propane to isopropanol with functionalization and catalyst regeneration using molecular oxygen. We use DFT study to predict that the barrier for (OPO)V to activate the secondary hydrogen of propane is \u0394G\u2021 = 25.2 kcal/mol at 298K, leading to isopropanol via the new reduction-coupled oxo activation (ROA) mechanism. We then show that reoxidation by dioxygen to complete the cycle is also favorable with \u0394G\u2021 = 6.2 kcal/mol at 298K. We conclude that (OPO)V represents a promising homogeneous catalyst for the monoxygenation of propane and other alkanes (including ethane), warranting experimental validation.", "doi": "10.1021/acscatal.6b02781", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2017-01-06", "series_number": "1", "volume": "7", "issue": "1", "pages": "356-364" }, { "id": "authors:ngawq-83b37", "collection": "authors", "collection_id": "ngawq-83b37", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160805-154511939", "type": "article", "title": "The Mechanism of Alkane Selective Oxidation by the M1 Phase of Mo\u2013V\u2013Nb\u2013Te Mixed Metal Oxides: Suggestions for Improved Catalysts", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "We report here first principles predictions (density functional theory with periodic boundary conditions) of the structures, mechanisms, and activation barriers for the catalytic activation and functionalization of propane by the M1 phase of the Mitsubishi-BP America generation of Mo\u2013V\u2013Nb\u2013Te\u2013O mixed metal oxide (MMO) catalysts. Our calculations show that the reduction-coupled oxo activation (ROA) principle, which we reported at Irsee VI to play the critical role for the selective oxidation of n-butane to maleic anhydride by vanadium phosphorous oxide, also plays the critical role for the MMO activation of propane, as speculated during Irsee VI. However for MMO, this ROA principle involves Te=O and V rather than P=O and V. The ability of the Te=O bond to activate the propane CH bond depends sensitively upon the number of V atoms that are coupled through a bridging O to the Te=O center. Based on this ROA mechanism, we suggest synthetic procedures aimed at developing a single phase MMO catalyst with dramatically improved selectivity for ammoxidation. We also suggest a modified single phase composition suitable for simultaneous oxidative dehydrogenation of ethane and propane to ethene and propene, respectively, which is becoming more important with the increase in petroleum fracking. Moreover, we also suggest some organometallic molecules that activate alkane CH bonds through the ROA principle.", "doi": "10.1007/s11244-016-0669-9", "issn": "1022-5528", "publisher": "Springer", "publication": "Topics in Catalysis", "publication_date": "2016-10", "series_number": "17", "volume": "59", "issue": "17", "pages": "1506-1517" }, { "id": "authors:mtkn3-s6e10", "collection": "authors", "collection_id": "mtkn3-s6e10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160413-130958292", "type": "conference_item", "title": "Metal-carbon bond functionalization in the context of methane oxidation", "author": [ { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Cheng", "given_name": "Mujeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A.", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "Metal-mediated alkane functionalization requires catalyzing C-H cleavage and carbon- heteroatom bond formation, each of\nwhich pose high, potentially rate- limiting barriers. To complement the traditional nucleophilic attack mechanism for\nfunctionalizing M-CH_3 bonds, we have used computed free energy surfaces to develop the attack of electrophiles on metalcarbon\nbonds. Recently we described the conversion of a vanadium- Ph bond to phenoxide via migration of the Ph group to a\nsep. vanadate oxo group. This formally homolytic M-C bond cleavage results in the one- electron redn. of both vanadium\ncenters. We predict that some one-electron oxidants will allow this mechanism to be transferred to late transition metals\ncompatible with non- radical methane oxidn. Iridium- Me bonds, however, are less polar than those of Group 10 metals and\nstronger than those of 1st and 2nd row metals. We find their functionalization is likely to begin with attack at the C-H\nbonds.", "publisher": "Caltech Library", "publication_date": "2016-03" }, { "id": "authors:aw8qs-a9n70", "collection": "authors", "collection_id": "aw8qs-a9n70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160331-155552955", "type": "conference_item", "title": "Detailed reaction mechanisms for heterogeneous catalysis", "author": [ { "family_name": "Goddard", "given_name": "William", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "An", "given_name": "Qi", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Cheng", "given_name": "Mujeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Qian", "given_name": "Jin", "orcid": "0000-0002-0162-0477", "clpid": "Qian-Jin" } ], "abstract": "We will report here first principles predictions (d. functional theory with periodic boundary conditions) of the structures,\nmechanisms, and acivation barriers for heterogeneous eactions selected from The selective oxidn. and ammoxidn. by\nMoVNbTeOx catalysts The Haber Bosch process on Fe.", "publisher": "Caltech Library", "publication_date": "2016-03" }, { "id": "authors:18qnw-6s343", "collection": "authors", "collection_id": "18qnw-6s343", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151019-111246285", "type": "article", "title": "In Silico Design of Highly Selective Mo-V-Te-Nb-O Mixed Metal Oxide Catalysts for Ammoxidation and Oxidative Dehydrogenation of Propane and Ethane", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "We used density functional theory quantum mechanics with periodic boundary conditions to determine the atomistic mechanism underlying catalytic activation of propane by the M1 phase of Mo-V-Nb-Te-O mixed metal oxides. We find that propane is activated by Te\u2550O through our recently established reduction-coupled oxo activation mechanism. More importantly, we find that the C\u2013H activation activity of Te\u2550O is controlled by the distribution of nearby V atoms, leading to a range of activation barriers from 34 to 23 kcal/mol. On the basis of the new insight into this mechanism, we propose a synthesis strategy that we expect to form a much more selective single-phase Mo-V-Nb-Te-O catalyst.", "doi": "10.1021/jacs.5b07073", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2015-10-21", "series_number": "41", "volume": "137", "issue": "41", "pages": "13224-13227" }, { "id": "authors:15d2w-zh647", "collection": "authors", "collection_id": "15d2w-zh647", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140808-083238459", "type": "article", "title": "A homolytic oxy-functionalization mechanism: intermolecular hydrocarbyl migration from M\u2013R to vanadate oxo", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "A new mechanism for generating C\u2013O bonds from metal-hydrocarbyls involving homolytic, intermolecular migration of the hydrocarbyl group to a vanadium oxo is reported. Responsible for the C\u2013O bond in phenol formed by the reaction of OVCl_3 with HgPh_2, it may provide air-regenerable metal oxos a role in aerobic alkane oxidations.", "doi": "10.1039/c4cc03067b", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2014-09-28", "series_number": "75", "volume": "50", "issue": "75", "pages": "10994-10996" }, { "id": "authors:2b9sd-0a943", "collection": "authors", "collection_id": "2b9sd-0a943", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140729-083058804", "type": "article", "title": "The Reduction-Coupled Oxo Activation (ROA) Mechanism Responsible for the Catalytic Selective Activation and Functionalization of n-Butane to Maleic Anhydride by Vanadium Phosphate Oxide", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Fu", "given_name": "Ross", "clpid": "Fu-Ross" } ], "abstract": "We report here the results of density functional theory quantum mechanical (QM) studies of the detailed chemical mechanism underlying the n-butane selective oxidation to form maleic anhydride (MA) on vanadyl pyrophosphate [(VO)_(2)P_(2)O_(7)] and vanadyl phosphate [VOPO_(4)] surfaces. This QM-derived mechanism differs substantially from previous suggestions but is in excellent agreement with key experimental observations. We find that the O(1)=P bond of the oxidized X1 phase of the VOPO_(4) surface is the active site for initiating the VPO chemistry, by extracting the H from the n-butane C\u2013H bond. This contrasts sharply with previous suggestions, all of which involved the V=O bonds. The ability of O(1)=P to cleave alkane C\u2013H bonds arises from a new unique mechanism that decouples the proton transfer and electron transfer components of this H atom transfer reaction. We find that the juxtaposition of a highly reducible V^(+5) next to the P=O bond but coupled via a bridging oxygen dramatically enhances the activity of the P=O bond to extract the proton from an alkane, while simultaneously transferring the electron to the V to form V^(+4). This Reduction-Coupled Oxo Activation (ROA) mechanism had not been known prior to these QM studies, but we believe that it may lead to a new strategy in designing selective catalysts for alkane activation and functionalization, and indeed it may be responsible for the selective oxidation by a number of known mixed metal oxide catalysts. To demonstrate the viability of this new ROA mechanism, we examine step by step the full sequence of reactions from n-butane to MA via two independent pathways. We that find that every step is plausible, with a highest reaction barrier of 21.7 kcal/mol.", "doi": "10.1007/s11244-014-0284-6", "issn": "1022-5528", "publisher": "Springer", "publication": "Topics in Catalysis", "publication_date": "2014-09", "series_number": "14-16", "volume": "57", "issue": "14-16", "pages": "1171-1187" }, { "id": "authors:j7r37-9sg53", "collection": "authors", "collection_id": "j7r37-9sg53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140129-133221585", "type": "article", "title": "CCI Radicals As a Carbon Source for Diamond Thin Film Deposition", "author": [ { "family_name": "An", "given_name": "Qi", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Jaramillo-Botero", "given_name": "Andres", "orcid": "0000-0003-2844-0756", "clpid": "Jaramillo-Botero-A" } ], "abstract": "We use first-principles quantum mechanical calculations to study diamond thin film growth on the (100) surface using CCI radicals as the carbon source. Our results show that CCI inserts into the surface dimer C\u2013C bonds with a barrier of 10.5 kcal/mol, roughly half of the energy required for traditional CH_2 insertion (22.0 kcal/mol). In addition to this, CCI has improved surface mobility (~30.0 kcal/mol barrier, versus 35 kcal/mol for CH_2, along the C\u2013C dimer chain direction), and hydrogen abstraction from the surface is also favored via atomic CI in the vapor phase. These results explain the lower substrate temperatures achieved in crystal diamond growth from the use of chlorinated sources in CVD processes, as opposed to the more traditional CH_4/H_2 derived species. Our results also suggest that further reductions in substrate temperatures are possible from using CCI as the only carbon source.", "doi": "10.1021/jz402527y", "issn": "1948-7185", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry Letters", "publication_date": "2014-01-13", "series_number": "5", "volume": "2014", "issue": "5", "pages": "481-484" }, { "id": "authors:xc1wm-7hh57", "collection": "authors", "collection_id": "xc1wm-7hh57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140109-120001059", "type": "article", "title": "Design and validation of non-metal oxo complexes for C\u2013H activation", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Fu", "given_name": "Ross", "clpid": "Fu-Ross" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "We use our recent discovery of the reduction-coupled oxo activation (ROA) principle to design a series of organometallic molecules that activate C\u2013H bonds through this unique proton/electron-decoupled hydrogen abstraction mechanism, in which the main group oxo moiety binds to the proton while the electron is transferred to the transition metal. Here we illustrate this general class of catalyst clusters with several examples that are validated through quantum mechanics calculations.", "doi": "10.1039/c3cc47502f", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2013-12-18", "series_number": "14", "volume": "50", "issue": "14", "pages": "1748-1750" }, { "id": "authors:ptwvt-n1397", "collection": "authors", "collection_id": "ptwvt-n1397", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130729-104103263", "type": "conference_item", "title": "First principles based theory and applications to understanding and developing new catalysts for energy and fuels", "author": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Merinov", "given_name": "Boris", "orcid": "0000-0002-2783-4262", "clpid": "Merinov-B-V" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Cortez", "given_name": "Mendoza", "clpid": "Cortez-M" } ], "abstract": "We will summarize recent advances in First-principles based methods for catalysis and surface reactions and the application of\nthese methods for predicting catalytic processes on surfaces with a focus on the Oxygen Redn. Reaction (ORR) The\nOxygen Evolution Reaction (OER), and Selective activation and functionalization for various metallic and oxide electrodes\nand catalysts.", "publisher": "Caltech Library", "publication_date": "2013-04" }, { "id": "authors:7tmac-rmw17", "collection": "authors", "collection_id": "7tmac-rmw17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130502-132101627", "type": "article", "title": "The Critical Role of Phosphate in Vanadium Phosphate Oxide for the Catalytic Activation and Functionalization of n-Butane to Maleic Anhydride", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "We used density functional theory to study the mechanism of n-butane oxidation to maleic anhydride on the vanadium phosphorus oxide (VPO) surface. We found that O(1)\u2550P on the V^(V)OPO_4 surface is the active center for initiating the VPO chemistry through extraction of H from alkane C\u2013H bonds. This contrasts sharply with previous suggestions that the active center is either the V\u2013O bonds or else a chemisorbed O_2 on the (V^(IV)O)_(2)P_(2)O_7 surface. The ability of O(1)\u2550P to cleave alkane C\u2013H bonds is due to its strong basicity coupled with large reduction potentials of nearby V^V ions. We examined several pathways for the subsequent functionalization of n-butane to maleic anhydride and found that the overall barrier does not exceed 21.7 kcal/mol.", "doi": "10.1021/ja3115746", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2013-03-27", "series_number": "12", "volume": "135", "issue": "12", "pages": "4600-4603" }, { "id": "authors:b3xax-9aw95", "collection": "authors", "collection_id": "b3xax-9aw95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130103-093549050", "type": "article", "title": "Hypervelocity Impact Effect of Molecules from Enceladus' Plume and Titan's Upper Atmosphere on NASA's Cassini Spectrometer from Reactive Dynamics Simulation", "author": [ { "family_name": "Jaramillo-Botero", "given_name": "Andres", "orcid": "0000-0003-2844-0756", "clpid": "Jaramillo-Botero-A" }, { "family_name": "An", "given_name": "Qi", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Beegle", "given_name": "Luther W.", "orcid": "0000-0002-4944-4353", "clpid": "Beegle-L-W" }, { "family_name": "Hodyss", "given_name": "Robert", "orcid": "0000-0002-6523-3660", "clpid": "Hodyss-R-P" } ], "abstract": "The NASA/ESA Cassini probe of Saturn analyzed the molecular composition of plumes emanating from one of its moons, Enceladus, and the upper atmosphere of another, Titan. However, interpretation of this data is complicated by the hypervelocity (HV) flybys of up to \u223c18\u2009\u2009km/sec that cause substantial molecular fragmentation. To interpret this data we use quantum mechanical based reactive force fields to simulate the HV impact of various molecular species and ice clathrates on oxidized titanium surfaces mimicking those in Cassini's neutral and ion mass spectrometer (INMS). The predicted velocity dependent fragmentation patterns and composition mixing ratios agree with INMS data providing the means for identifying the molecules in the plume. We used our simulations to predict the surface damage from the HV impacts on the INMS interior walls, which we suggest acts as a titanium sublimation pump that could alter the instrument's readings. These results show how the theory can identify chemical events from hypervelocity impacts in space plumes and atmospheres, providing in turn clues to the internal structure of the corresponding sources (e.g., Enceladus). This may be valuable in steering modifications in future missions.", "doi": "10.1103/PhysRevLett.109.213201", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2012-11-21", "series_number": "21", "volume": "109", "issue": "21", "pages": "Art. No. 213201" }, { "id": "authors:tnkq0-ptk26", "collection": "authors", "collection_id": "tnkq0-ptk26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121127-142950090", "type": "article", "title": "Oxidative Aliphatic C-H Fluorination with Fluoride Ion Catalyzed by a Manganese Porphyrin", "author": [ { "family_name": "Liu", "given_name": "Wei", "orcid": "0000-0001-6249-3179", "clpid": "Liu-Wei-Chemistry" }, { "family_name": "Huang", "given_name": "Xiongyi", "orcid": "0000-0001-7156-8881", "clpid": "Huang-Xiongyi" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Groves", "given_name": "John T.", "orcid": "0000-0002-9944-5899", "clpid": "Groves-J-T" } ], "abstract": "Despite the growing importance of fluorinated organic compounds in drug development, there are no direct protocols for the fluorination of aliphatic C-H bonds using conveniently handled fluoride salts. We have discovered that a manganese porphyrin complex catalyzes alkyl fluorination by fluoride ion under mild conditions in conjunction with stoichiometric oxidation by iodosylbenzene. Simple alkanes, terpenoids, and even steroids were selectively fluorinated at otherwise inaccessible sites in 50 to 60% yield. Decalin was fluorinated predominantly at the C2 and C3 methylene positions. Bornyl acetate was converted to exo-5-fluoro-bornyl acetate, and 5\u03b1-androstan-17-one was fluorinated selectively in the A ring. Mechanistic analysis suggests that the regioselectivity for C-H bond cleavage is directed by an oxomanganese(V) catalytic intermediate followed by F delivery via an unusual manganese(IV) fluoride that has been isolated and structurally characterized.", "doi": "10.1126/science.1222327", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2012-09-14", "series_number": "6100", "volume": "337", "issue": "6100", "pages": "1322-1325" }, { "id": "authors:pyb18-x3623", "collection": "authors", "collection_id": "pyb18-x3623", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120822-105841903", "type": "conference_item", "title": "Structures, mechanisms, and spectroscopic signatures of catalytic reactions on surfaces", "author": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Liu", "given_name": "Liangchi", "clpid": "Liu-Liangchi" }, { "family_name": "Mueller", "given_name": "Jonathan E.", "orcid": "0000-0001-8811-8799", "clpid": "Mueller-J-E" }, { "family_name": "Nielsen", "given_name": "Robert", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" } ], "abstract": "We use a combination of new qunatum mechanics (QM) methods (XYGJ-OS and PBE-ulg) and ReaxFF reactive force fields trained using such QM to predict the atomistic structures and reaction mechanisms for metal oxide catalysts capable of selecitve oxidn. and functionalization. These reaction mechanisms involve metal oxo bonds with unique spectroscopic signitures that provide the basis for exptl. validation of the detailed mechanisms.", "publisher": "Caltech Library", "publication_date": "2012-08" }, { "id": "authors:j132v-9bg53", "collection": "authors", "collection_id": "j132v-9bg53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120410-080644226", "type": "article", "title": "The para-substituent effect and pH-dependence of the organometallic Baeyer\u2013Villiger oxidation of rhenium\u2013carbon bonds", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Bischof", "given_name": "Steven M.", "clpid": "Bischof-S-M" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Gunnoe", "given_name": "T. Brent", "orcid": "0000-0001-5714-3887", "clpid": "Gunnoe-T-B" }, { "family_name": "Periana", "given_name": "Roy A.", "orcid": "0000-0001-7838-257X", "clpid": "Periana-R-A" } ], "abstract": "We studied the Baeyer\u2013Villiger (BV) type oxidation of phenylrhenium trioxide (PTO) by H2O2 in the aqueous phase using Quantum Mechanics (density functional theory with the M06 functional) focusing on how the solution pH and the para-substituent affect the Gibbs free energy surfaces. For both PTO and MTO (methylrhenium trioxide) cases, we find that for pH > 1 the BV pathway having OH\u2212 as the leaving group is lower in energy than the one involving simultaneous protonation of hydroxide. We also find that during this organometallic BV oxidation, the migrating phenyl is a nucleophile so that substituting functional groups in the para-position of phenyl with increased electron-donating character lowers the migration barrier, just as in organic BV reactions. However, this substituent effect also pushes electron density to Re, impeding HOO\u2212 coordination and slowing down the reaction. This is in direct contrast to the organic analog, in which para-substitution has an insignificant influence on 1,2-addition of peracids. Due to the competition of the two opposing effects and the dependence of the resting state on pH and concentration, the reaction rate of the organometallic BV oxidation is surprisingly unaffected by para-substitution.", "doi": "10.1039/c2dt11984f", "issn": "1477-9226", "publisher": "Royal Society of Chemistry", "publication": "Dalton Transactions", "publication_date": "2012-04-07", "series_number": "13", "volume": "41", "issue": "13", "pages": "3758-3763" }, { "id": "authors:3qt1y-55x47", "collection": "authors", "collection_id": "3qt1y-55x47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111025-104606894", "type": "article", "title": "Synthesis and Characterization of the k^2-acac-O,O Complex\n Os_(IV)(acac)_2PhCl and Study of CH Activation with Benzene", "author": [ { "family_name": "Young", "given_name": "Kenneth J. H.", "clpid": "Young-K-J-H" }, { "family_name": "Mironov", "given_name": "Oleg A.", "orcid": "0000-0002-9787-944X", "clpid": "Mironov-O-A" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Stewart", "given_name": "Timothy", "clpid": "Stewart-T" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Periana", "given_name": "Roy A.", "orcid": "0000-0001-7838-257X", "clpid": "Periana-R-A" } ], "abstract": "We have synthesized and fully characterized the air-stable complex (\u03ba^2-acac-O,O)2Os^(IV)(Ph)Cl (Cl-1-Ph; acac-O,O = acetylacetonate), which reacts with C_6D_6 to generate Cl-1-Ph-d_5 in high yield and catalyzes the H/D exchange reaction between benzene and toluene-d_8 upon heating to 140 \u00b0C. To our knowledge, this is the first example of stoichiometric and catalytic, homogeneous, intermolecular CH activation of arenes by a discrete Os complex. The reactions show extended induction periods. DFT studies of Cl-1-Ph and cis-(\u03ba^2-acac-O,O)_2Os^(III)(C_6H_5)(C_6D_6) (cis-(C_6D_6)-2-Ph) found a mechanism involving CH activation by traces of Os(III) and Cl atom transfer between Cl-1-Ph and cis-(C_6D_6)-2-Ph. Experimental data showing that addition of reductants eliminates the induction periods suggest that CH activation occurs from an oxidation state lower than Os^(IV), consistent with the DFT predictions. Consistent with a Cl atom transfer mechanism, the triflate analogue of Cl-1-Ph, OTf-1-Ph, does not undergo a stoichiometric or catalytic reaction with C_6D_6.", "doi": "10.1021/om1010512", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2011-10-10", "series_number": "19", "volume": "30", "issue": "19", "pages": "5088-5094" }, { "id": "authors:6b2tk-66654", "collection": "authors", "collection_id": "6b2tk-66654", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110512-100508849", "type": "article", "title": "The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Tahir-Kheli", "given_name": "Jamil", "clpid": "Tahir-Kheli-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "We have studied the magnetic structure of the high \nsymmetry vanadyl pyrophosphate ((VO)_(2)P_(2)O)7, VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, J_(OPO) = \u2212156.8 K and J_O = \u221268.6 K, and two weaker couplings appear along the c (between two layers) and b directions (between two chains in the same layer), which we calculate to be ferromagnetic, J_layer = 19.2 K and J_chain = 2.8 K. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that J_(OPO) originates from a super-exchange interaction through the bridging \u2013O\u2013P\u2013O\u2013 unit. In contrast, J_O results from a direct overlap of 3d_(x^2 \u2212 y^2) orbitals on two vanadium atoms in the same V_(2)O_8 motif, making it very sensitive to structural fluctuations. Based on the variations in V\u2013O bond length as a function of strain along a, we found that the V\u2013O bonds of V\u2013(OPO)_(2)\u2013V are covalent and rigid, whereas the bonds of V\u2013(O)_(2)\u2013V are fragile and dative. These distinctions suggest that compression along the a-axis would have a dramatic impact on J_O, changing the magnetic structure and spin gap of VOPO. This result also suggests that assuming J_O to be a constant over the range of 2\u2013300 K whilst fitting couplings to the experimental magnetic susceptibility is an invalid method. Regarding its role as a catalyst, the bonding pattern suggests that O_2 can penetrate beyond the top layers of the VOPO surface, converting multiple V atoms from the +4 to +5 oxidation state, which seems crucial to explain the deep oxidation of n-butane to maleic anhydride.", "doi": "10.1039/C0CP02777D", "issn": "1463-9076", "publisher": "Royal Society of Chemistry", "publication": "Physical Chemistry Chemical Physics", "publication_date": "2011-05-28", "series_number": "20", "volume": "13", "issue": "20", "pages": "9831-9838" }, { "id": "authors:tmawn-v8247", "collection": "authors", "collection_id": "tmawn-v8247", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110504-073755259", "type": "article", "title": "Functionalization of Rhenium Aryl Bonds by O-Atom Transfer", "author": [ { "family_name": "Bischof", "given_name": "Steven M.", "clpid": "Bischof-S-M" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Gunnoe", "given_name": "T. Brent", "orcid": "0000-0001-5714-3887", "clpid": "Gunnoe-T-B" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Periana", "given_name": "Roy A.", "orcid": "0000-0001-7838-257X", "clpid": "Periana-R-A" } ], "abstract": "Aryltrioxorhenium (ArReO_3) has been demonstrated to show rapid oxy-functionalization upon reaction with O-atom donors, YO, to selectively generate the corresponding phenols in near quantitative yields. (18)^O-Labeling experiments show that the oxygen in the products is exclusively from YO. DFT studies reveal a 10.7 kcal/mol barrier (Ar = Ph) for oxy-functionalization with H_2O_2 via a Baeyer-Villiger type mechanism involving nudeophilic attack of the aryl group on an electrophilic oxygen of YO coordinated to rhenium.", "doi": "10.1021/om2002365", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2011-04-25", "series_number": "8", "volume": "30", "issue": "8", "pages": "2079-2082" }, { "id": "authors:4f9ea-esa15", "collection": "authors", "collection_id": "4f9ea-esa15", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110601-092305453", "type": "article", "title": "Synthesis of osmium and ruthenium complexes bearing dimethyl (S,S)-2,2\u2032-(pyridine-2,6-diyl)-bis-(4,5-dihydrooxazol-4-carboxylate) ligand and application to catalytic H/D exchange", "author": [ { "family_name": "Young", "given_name": "Kenneth J. H.", "clpid": "Young-K-J-H" }, { "family_name": "Lokare", "given_name": "Kapil S.", "clpid": "Lokare-K-S" }, { "family_name": "Leung", "given_name": "Chin Hin", "clpid": "Leung-Chih-Hin" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Petasis", "given_name": "Nicos A.", "clpid": "Petasis-N-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Periana", "given_name": "Roy A.", "orcid": "0000-0001-7838-257X", "clpid": "Periana-R-A" } ], "abstract": "Using tridentate, neutral PyBox ligands, several new osmium and ruthenium complexes [M(PyBox)Cl_(2)(C_(2)H_(4)), where M = Ru, Os] have been prepared, all thermally stable. Some of these PyBox compounds are active for C\u2013H activation of benzene. The Os(PyBox)Cl_(2)(C_(2)H_(4) complex was characterized by X-ray diffraction. DFT calculations (B3LYP and M06 including Poisson\u2013Boltzmann solvation) corroborate that the Os/PyBox complex in acetic acid (\u0394G\u2021 = 32.0 kcal/mol) is more reactive for benzene C\u2013H activation than Ru/PyBox in basic conditions (\u0394G\u2021 = 34.8 kcal/mol at pH = 13). The stability of hydroxide- and chloride-bridged dinuclear resting states determines calculated barriers.", "doi": "10.1016/j.molcata.2011.01.029", "issn": "1381-1169", "publisher": "Elsevier", "publication": "Journal of Molecular Catalysis A: Chemical", "publication_date": "2011-04-01", "series_number": "1-2", "volume": "339", "issue": "1-2", "pages": "17-23" }, { "id": "authors:5326b-33854", "collection": "authors", "collection_id": "5326b-33854", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100524-150452201", "type": "article", "title": "Carbon\u2212Oxygen Bond Forming Mechanisms in Rhenium Oxo-Alkyl Complexes", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" }, { "family_name": "Ahlquist", "given_name": "M\u00e5rten", "clpid": "Ahlquist-M" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "Three C\u2212X bond formation mechanisms observed in the oxidation of (HBpz_3)ReO(R)(OTf) [HBpz_3 = hydrotris(1-pyrazolyl)borate; R = Me, Et, and iPr; OTf = OSO_2CF_3] by dimethyl sulfoxide (DMSO) were investigated using quantum mechanics (M06//B3LYP DFT) combined with solvation (using the PBF Poisson\u2212Boltzmann polarizable continuum solvent model). For R = Et we find the alkyl group is activated through \u03b1-hydrogen abstraction by external base OTf^\u2212 with a free energy barrier of only 12.0 kcal/mol, leading to formation of acetaldehyde. Alternatively, ethyl migration across the M\u2550O bond (leading to the formation of acetaldehyde and ethanol) poses a free energy barrier of 22.1 kcal/mol, and the previously proposed \u03b1-hydrogen transfer to oxo (a 2+2 forbidden reaction) poses a barrier of 44.9 kcal/mol. The rate-determining step to formation of the final product acetaldehyde is an oxygen atom transfer from DMSO to the ethylidene, with a free energy barrier of 15.3 kcal/mol. When R = iPr, the alkyl 1,2-migration pathway becomes the more favorable pathway (both kinetically and thermodynamically), with a free energy barrier (\u0394G^\u2021 = 11.8 kcal/mol) lower than \u03b1-hydrogen abstraction by OTf^\u2212 (\u0394G^\u2021 = 13.5 kcal/mol). This suggests the feasibility of utilizing this type of migration to functionalize M\u2212R to M\u2212OR. We also considered the nucleophilic attack of water and ammonia on the Re-ethylidene \u03b1-carbon as a means of recovering two-electron-oxidized products from an alkane oxidation. Nucleophilic attack (with internal deprotonation of the nucleophile) is exothermic. However, the subsequent protonolysis of the Re\u2212alkyl bond (to liberate an alcohol or amine) poses a barrier of 37.0 or 42.4 kcal/mol, respectively. Where comparisons are possible, calculated free energies agree very well with experimental measurements.", "doi": "10.1021/om900881x", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2010-05-10", "series_number": "9", "volume": "29", "issue": "9", "pages": "2026-2033" }, { "id": "authors:0989y-y7807", "collection": "authors", "collection_id": "0989y-y7807", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GODtic08", "type": "article", "title": "Structures, mechanisms, and kinetics of selective ammoxidation and oxidation of propane over multi-metal oxide catalysts", "author": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Chenoweth", "given_name": "Kimberley", "clpid": "Chenoweth-K" }, { "family_name": "Pudar", "given_name": "Sanja", "clpid": "Pudar-S" }, { "family_name": "van Duin", "given_name": "Adri C. T.", "orcid": "0000-0002-3478-4945", "clpid": "van-Duin-A-C-T" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" } ], "abstract": "In order to determine the chemical mechanism for the (amm)oxidation of propane and propene on multimetal oxide (MMO) catalysts, we have carried out quantum mechanical (QM) calculations for model reactions on small clusters that we have used to train the parameters for the ReaxFF reactive force field, which enables molecular dynamics (MD) simulations for reactions on the complex reconstructed surfaces of MMO. We report here insights from the QM on the reaction mechanisms of selective(amm)oxidation of propene on bismuth molybdate catalysts and the oxidative dehydrogenation of propane on vanadium oxide catalysts. We also report the application of ReaxFF to predict the stable surfaces of the M1 phases of the MoVTeNbO catalysts.", "doi": "10.1007/s11244-008-9096-x", "issn": "1022-5528", "publisher": "Springer Verlag", "publication": "Topics in catalysis", "publication_date": "2008-11", "series_number": "1-4", "volume": "50", "issue": "1-4", "pages": "2-18" }, { "id": "authors:jb1a6-qfm56", "collection": "authors", "collection_id": "jb1a6-qfm56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170719-093305273", "type": "article", "title": "Development and Application of a ReaxFF Reactive Force Field for Oxidative Dehydrogenation on Vanadium Oxide Catalysts", "author": [ { "family_name": "Chenoweth", "given_name": "Kimberly", "clpid": "Chenoweth-K" }, { "family_name": "van Duin", "given_name": "Adri C. T.", "orcid": "0000-0002-3478-4945", "clpid": "van-Duin-A-C-T" }, { "family_name": "Persson", "given_name": "Petter", "orcid": "0000-0001-7600-3230", "clpid": "Persson-P" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Oxgaard", "given_name": "Jonas", "clpid": "Oxgaard-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "We have developed a new ReaxFF reactive force field to describe accurately reactions of hydrocarbons with vanadium oxide catalysts. The ReaxFF force field parameters have been fit to a large quantum mechanics (QM) training set containing over 700 structures and energetics related to bond dissociations, angle and dihedral distortions, and reactions between hydrocarbons and vanadium oxide clusters. In addition, the training set contains charge distributions for small vanadium oxide clusters and the stabilities of condensed-phase systems. We find that ReaxFF reproduces accurately the QM training set for structures and energetics of small clusters. Most important is that ReaxFF describes accurately the energetics for various oxidation states of the condensed phases, including V_2O_5, VO_2, and V_2O_3 in addition to metallic V(V^0). To demonstrate the capability of the ReaxFF force field for describing catalytic processes involving vanadium oxides, we performed molecular dynamics (MD) simulation for reactions of a gas of methanol exposed to the (001) surface of V_2O_5. We find that formaldehyde is the major product, in agreement with experiment. These studies find that water desorption from surface VIII sites is facilitated by interlayer bonding.", "doi": "10.1021/jp802134x", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2008-09-18", "series_number": "37", "volume": "112", "issue": "37", "pages": "14645-14654" }, { "id": "authors:99186-84t66", "collection": "authors", "collection_id": "99186-84t66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170712-070026084", "type": "article", "title": "Single-Site Vanadyl Activation, Functionalization, and Reoxidation Reaction Mechanism for Propane Oxidative Dehydrogenation on the Cubic V_4O_(10)Cluster", "author": [ { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Chenoweth", "given_name": "Kimberly", "clpid": "Chenoweth-K" }, { "family_name": "Oxgaard", "given_name": "Jonas", "clpid": "Oxgaard-J" }, { "family_name": "van Duin", "given_name": "Adri", "orcid": "0000-0002-3478-4945", "clpid": "van-Duin-A-C-T" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "abstract": "Vanadyl oxide (V\u2550O) sites are thought to play a role in a number of industrially important catalysts for activating saturated alkanes, but in no system is the mechanism for the activation, product formation, and reoxidation steps established. In this paper, we use quantum mechanical methods (B3LYP flavor of density functional theory) to examine the detailed mechanism for propane reacting with a V_4O_(10) cluster to model the catalytic oxidative dehydrogenation (ODH) of propane on the V_2O_5(001) surface. We here report the mechanism of the complete catalytic cycle, including the regeneration of the reduced catalyst using gaseous O_2. The rate-determining step is hydrogen abstraction by the vanadyl (V\u2550O) group (in agreement with experiment) to form an iso-propyl radical that binds to an adjacent V\u2212O\u2212V site. Subsequently, this bound iso-propyl forms propene product by \u03b2-hydride elimination to form bound H_2O. We find that this H_2O (bound to a V^(III) site) is too stable to desorb unimolecularly. Instead, the desorption is induced by binding of gaseous O_2 to the V^(III) site, which dramatically decreases the coordination energy of H_2O from 37.8 to 12.9 kcal/mol. Further rearrangement of the O_2 molecule leads to formation of a cyclic VO_2 peroxide, which activates the C\u2212H bond of a second propane to form a second propene (with a lower reaction barrier). Desorption of this propene regenerates the original V_4O_(10) cluster. We find that all reactions involve the single vanadyl oxygen (V\u2550O), with the bridging oxygens (V\u2212O\u2212V) serving to stabilize the iso-propyl radical intermediate. We refer to this mechanism as the single-site vanadyl activation, functionalization, and reoxidation mechanism (SS-VAFR). This SS-VAFR mechanism should be applicable to propane ODH on the supported vanadium oxide catalysts where only monovanadate (VO_4) species are present.", "doi": "10.1021/jp0663917", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2007-04-05", "series_number": "13", "volume": "111", "issue": "13", "pages": "5115-5127" }, { "id": "authors:2fv6f-wg552", "collection": "authors", "collection_id": "2fv6f-wg552", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110601-142550273", "type": "article", "title": "Development of the ReaxFF reactive force field for mechanistic studies of catalytic selective oxidation processes on BiMoO_x", "author": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "van Duin", "given_name": "Adri", "orcid": "0000-0002-3478-4945", "clpid": "van-Duin-A-C-T" }, { "family_name": "Chenoweth", "given_name": "Kimberly", "clpid": "Chenoweth-Kimberly" }, { "family_name": "Cheng", "given_name": "Mu-Jeng", "orcid": "0000-0002-8121-0485", "clpid": "Cheng-Mu-Jeng" }, { "family_name": "Pudar", "given_name": "Sanja", "clpid": "Pudar-Sanja" }, { "family_name": "Oxgaard", "given_name": "Jonas", "clpid": "Oxgaard-J" }, { "family_name": "Merinov", "given_name": "Boris", "orcid": "0000-0002-2783-4262", "clpid": "Merinov-B-V" }, { "family_name": "Jang", "given_name": "Yun Hee", "orcid": "0000-0002-6604-5813", "clpid": "Jang-Yun-Hee" }, { "family_name": "Persson", "given_name": "Petter", "orcid": "0000-0001-7600-3230", "clpid": "Persson-P" } ], "abstract": "We have developed a new reactive force field, ReaxFF, for use in molecular dynamics (MD) simulations to investigate the structures and reactive dynamics of complex metal oxide catalysts. The parameters in ReaxFF are derived directly from QM and have been validated to provide reasonable accuracy for a wide variety of reactions. We report the use of ReaxFF to study the activation and conversion of propene to acrolein by various metal oxide surfaces. Using high-remperature MD-simulations on metal oxides slabs exposed to a propene gas phase we find that (1) Propene is not activated by MoO_3 but it is activated by amorphous Bi_2O_3 to form allyl which does not get oxidized by the surface; (2) Propene is activated by Bi_2Mo_3O_(12) to form an allyl-radical and the hydrogen gets abstracted by a Mo=O bond, which is bridged via an O to a Bi-site; (3) Propene is activated over V_2O_5 to form an allyl, which is then selectively oxidized on the surface to form acrolein. The propene reations on V_2O_5 occur at lower temperatures than on Bi_2O_3 or Bi_2Mo_3O_(12). The results are all consistent with experimental observations, encouraging us that such investigations will enhance our mechanistic understanding of catalytic hydrocarbon oxidation sufficiently to suggest modifications for improving efficiency and/or selectivity.", "doi": "10.1007/s11244-006-0074-x", "issn": "1022-5528", "publisher": "Springer", "publication": "Topics in Catalysis", "publication_date": "2006-07", "series_number": "1-3", "volume": "38", "issue": "1-3", "pages": "93-103" } ]