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Title: Partial Oxidation of Methanol on MoO 3 (010): A DFT and Microkinetic Study

Abstract

Methanol oxidation is employed as a probe reaction to evaluate the catalytic properties of the (010) facets of molybdenum trioxide (MoO 3), a reducible oxide that exhibits a rich interplay of catalytic chemistry and structural transformations. The reaction mechanism is investigated with a combination of electronic structure calculations, using the BEEF-vdW and HSE06 functionals, and mean-field microkinetic modeling. Considered pathways include vacancy formation and oxidation, monomolecular dehydrogenation of methanol on reduced and nonreduced surfaces, bimolecular reactions between dehydrogenated intermediates, and precursor steps for hydrogen molybdenum phase (H yMoO 3–x) formation. Methanol dissociation begins with C–H or O–H scission, with the O–H route found to be kinetically and thermodynamically preferred. Dehydrogenation of CH 2O* to CHO* is slow in comparison to desorption, leading to complete selectivity toward CH 2O. C–H scission of CH 3O* and recombination of dissociated OH* to form H 2O* are kinetically significant steps exhibiting positive degrees of rate control, while oxidation of the reduced surface through adsorbed O 2 has a negative degree of rate control. The energetics of the latter elementary step are somewhat sensitive to the choice of density functional, and although this does not affect the predicted reaction orders, the overall rate may change.more » To estimate the impact of the surface oxidation state on the kinetics, the external pressure of oxygen is varied in the microkinetic model, and the reaction rate is found to follow a volcano-like dependency, with the optimum rate located where surface oxidation neither promotes nor inhibits the overall rate. In conclusion, the methodology demonstrated in this study should be more broadly applicable to modeling catalytic kinetics on reducible oxide single-crystal surfaces.« less

Authors:
 [1];  [1]
  1. Purdue Univ., West Lafayette, IN (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1542659
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 6; Journal Issue: 11; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; methanol oxidation; MoO3; reducible oxide; DFT; microkinetic modeling; adsorption; oxygen; defects in solids; oxidation; kinetics

Citation Formats

Choksi, Tej, and Greeley, Jeffrey. Partial Oxidation of Methanol on MoO3 (010): A DFT and Microkinetic Study. United States: N. p., 2016. Web. doi:10.1021/acscatal.6b01633.
Choksi, Tej, & Greeley, Jeffrey. Partial Oxidation of Methanol on MoO3 (010): A DFT and Microkinetic Study. United States. doi:10.1021/acscatal.6b01633.
Choksi, Tej, and Greeley, Jeffrey. Fri . "Partial Oxidation of Methanol on MoO3 (010): A DFT and Microkinetic Study". United States. doi:10.1021/acscatal.6b01633. https://www.osti.gov/servlets/purl/1542659.
@article{osti_1542659,
title = {Partial Oxidation of Methanol on MoO3 (010): A DFT and Microkinetic Study},
author = {Choksi, Tej and Greeley, Jeffrey},
abstractNote = {Methanol oxidation is employed as a probe reaction to evaluate the catalytic properties of the (010) facets of molybdenum trioxide (MoO3), a reducible oxide that exhibits a rich interplay of catalytic chemistry and structural transformations. The reaction mechanism is investigated with a combination of electronic structure calculations, using the BEEF-vdW and HSE06 functionals, and mean-field microkinetic modeling. Considered pathways include vacancy formation and oxidation, monomolecular dehydrogenation of methanol on reduced and nonreduced surfaces, bimolecular reactions between dehydrogenated intermediates, and precursor steps for hydrogen molybdenum phase (HyMoO3–x) formation. Methanol dissociation begins with C–H or O–H scission, with the O–H route found to be kinetically and thermodynamically preferred. Dehydrogenation of CH2O* to CHO* is slow in comparison to desorption, leading to complete selectivity toward CH2O. C–H scission of CH3O* and recombination of dissociated OH* to form H2O* are kinetically significant steps exhibiting positive degrees of rate control, while oxidation of the reduced surface through adsorbed O2 has a negative degree of rate control. The energetics of the latter elementary step are somewhat sensitive to the choice of density functional, and although this does not affect the predicted reaction orders, the overall rate may change. To estimate the impact of the surface oxidation state on the kinetics, the external pressure of oxygen is varied in the microkinetic model, and the reaction rate is found to follow a volcano-like dependency, with the optimum rate located where surface oxidation neither promotes nor inhibits the overall rate. In conclusion, the methodology demonstrated in this study should be more broadly applicable to modeling catalytic kinetics on reducible oxide single-crystal surfaces.},
doi = {10.1021/acscatal.6b01633},
journal = {ACS Catalysis},
issn = {2155-5435},
number = 11,
volume = 6,
place = {United States},
year = {2016},
month = {9}
}

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