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Mechanism of Selective Oxidation of Propene to Acrolein on Bismuth Molybdates from Quantum Mechanical Calculations

Pudar, Sanja and Oxgaard, Jonas and Chenoweth, Kimberly and van Duin, Adri C. T. and Goddard, William A., III (2007) Mechanism of Selective Oxidation of Propene to Acrolein on Bismuth Molybdates from Quantum Mechanical Calculations. Journal of Physical Chemistry C, 111 (44). pp. 16405-16415. ISSN 1932-7447. doi:10.1021/jp074452a.

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In order to provide a basis for understanding the fundamental chemical mechanisms underlying the selective oxidation of propene to acrolein by bismuth molybdates, we report quantum mechanical studies (at the DFT/B3LYP/LACVP^(**) level) of various reaction steps on bismuth oxide (Bi_4O_6/Bi_4O_7) and molybdenum oxide (Mo_3O_9) cluster models. For CH activation, we find a low-energy pathway on a Bi^V site with a calculated barrier of ΔH^⧧ = 11.0 kcal/mol (ΔG^⧧ = 30.4 kcal/mol), which is ∼3 kcal/mol lower than the experimentally measured barrier on a pure Bi_2O_3 condensed phase. We find this process to be not feasible on Bi^(III) (it is highly endothermic, ΔE = 50.9 kcal/mol, ΔG = 41.6 kcal/mol) or on pure molybdenum oxide (prohibitively high barriers, ΔE^⧧ = 32.5 kcal/mol, ΔG^⧧ = 48.1 kcal/mol), suggesting that the CH activation event occurs on (rare) Bi^V sites on the Bi_2O_3 surface. The expected low concentration of Bi^V could explain the 3 kcal/mol discrepancy between our calculated barrier and experiment. We present in detail the allyl oxidation mechanism over Mo_3O_9, which includes the adsorption of allyl to form the π-allyl and σ-allyl species, the second hydrogen abstraction to form acrolein, and acrolein desorption. The formation of σ-allyl intermediate is reversible, with forward ΔE^⧧ (ΔG^⧧) barriers of 2.7 (9.0 with respect to the π-allyl intermediate) kcal/mol and reverse barriers of 21.6 (23.7) kcal/mol. The second hydrogen abstraction is the rate-determining step for allyl conversion, with a calculated ΔE^⧧ = 35.6 kcal/mol (ΔG^⧧ = 37.5 kcal/mol). Finally, studies of acrolein desorption in presence of gaseous O_2 suggest that the reoxidation significantly weakens the coordination of acrolein to the reduced MoIV site, helping drive desorption of acrolein from the surface.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
van Duin, Adri C. T.0000-0002-3478-4945
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2007 American Chemical Society. Received 8 June 2007. Published online 11 October 2007. Published in print 1 November 2007. The personnel involved in this research were partially supported by DOE (DE-PS36-03GO93015), ONR (N00014-06-1-0938), and Chevron. The facilities were supported by ARO-DURIP and ONR-DURIP funds.
Funding AgencyGrant Number
Department of Energy (DOE)DE-PS36-03GO93015
Office of Naval Research (ONR)N00014-06-1-0938
Army Research Office (ARO)UNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Issue or Number:44
Record Number:CaltechAUTHORS:20170614-082600265
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Official Citation:Mechanism of Selective Oxidation of Propene to Acrolein on Bismuth Molybdates from Quantum Mechanical Calculations Sanja Pudar, Jonas Oxgaard, Kimberly Chenoweth, Adri C. T. van Duin, and William A. Goddard, III The Journal of Physical Chemistry C 2007 111 (44), 16405-16415 DOI: 10.1021/jp074452a
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78189
Deposited By: Ruth Sustaita
Deposited On:14 Jun 2017 16:06
Last Modified:15 Nov 2021 17:37

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