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Reaction Mechanism for Ammonia Activation in the Selective Ammoxidation of Propene on Bismuth Molybdates

Pudar, Sanja and Goddard, William A., III (2015) Reaction Mechanism for Ammonia Activation in the Selective Ammoxidation of Propene on Bismuth Molybdates. Journal of Physical Chemistry C, 119 (49). pp. 27370-27381. ISSN 1932-7447. https://resolver.caltech.edu/CaltechAUTHORS:20151202-075704916

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Abstract

In this paper, we report quantum mechanical studies (using the B3LYP flavor of density functional theory) for various pathways of ammonia activation on bismuth molybdates, a process required for ammoxidation of propene to acrylonitrile. Using a Mo_3O_9 cluster to model the bulk surface, we examined the activation of ammonia by both fully oxidized (MoIV) and reduced (Mo^(IV)) molybdenum sites. Our results show that ammonia activation does not take place on the fully oxidized Mo(VI) sites. Here the net barriers for the first hydrogen transfer (ΔE‡ = 44.6 kcal/mol, ΔG‡_(673K) = 44.2 kcal/mol) and the second hydrogen transfer (ΔE‡ = 54.5 kcal/mol, ΔG‡_(673K) = 51.7 kcal/mol) are prohibitively high for the reaction temperature of 400 °C. Instead, our calculations show that the reduced Mo(IV) surface sites are far more suitable for this process. Here, the calculated barrier for the first hydrogen transfer from a Mo(IV)–NH_3 to an adjacent Mo(VI)═O is 18.2 kcal/mol (ΔG‡_(673K) = 15.4 kcal/mol). For the second hydrogen transfer step, we explored three pathways, and found that the H transfer from a Mo–NH_2 to an adjacent Mo(V)–OH to form water is more favorable (ΔE‡ = 26.2 kcal/mol (ΔG‡_(673K) = 24.0 kcal/mol) than transfer to an adjacent Mo(VI)═O or Mo(V)═O group. These studies complement previous studies for activation and reaction of propene on these surfaces, completing the QM study into the fundamental mechanism.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/acs.jpcc.5b06224DOIArticle
http://pubs.acs.org/doi/10.1021/acs.jpcc.5b06224PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/acs.jpcc.5b06224PublisherSupporting Information
ORCID:
AuthorORCID
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2015 American Chemical Society. Received: June 29, 2015; Revised: October 5, 2015; Publication Date (Web): October 15, 2015. The authors thank Jonas Oxgaard for invaluable discussions. The authors declare no competing financial interest.
Other Numbering System:
Other Numbering System NameOther Numbering System ID
WAG1148
Issue or Number:49
Record Number:CaltechAUTHORS:20151202-075704916
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20151202-075704916
Official Citation:Reaction Mechanism for Ammonia Activation in the Selective Ammoxidation of Propene on Bismuth Molybdates Sanja Pudar and William A. Goddard, III The Journal of Physical Chemistry C 2015 119 (49), 27370-27381 DOI: 10.1021/acs.jpcc.5b06224
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62526
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Dec 2015 02:43
Last Modified:03 Oct 2019 09:19

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