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Nitrogen activation in a Mars-van Krevelen mechanism for ammonia synthesis on Co3Mo3N

Nitrogen activation in a Mars-van Krevelen mechanism for ammonia synthesis on Co3Mo3N

Zeinalipour-Yazdi, Constantinos D. ORCID: 0000-0002-8388-1549, Hargreaves, Justin S. J. and Catlow, C. Richard A. (2015) Nitrogen activation in a Mars-van Krevelen mechanism for ammonia synthesis on Co3Mo3N. The Journal of Physical Chemistry C, 119 (51). pp. 28368-28376. ISSN 1932-7447 (Print), 1932-7455 (Online) (doi:https://doi.org/10.1021/acs.jpcc.5b06811)

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Abstract

Co3Mo3N is one of the most active catalysts for ammonia synthesis; however, little is known about the atomistic details of N2 adsorption and activation. Here we examine whether N2 can adsorb and activate at nitrogen surface vacancies. We have identified the most favorable sites for surface nitrogen vacancy formation and have calculated vacancy formation free energies (and concentrations) taking into account vacancy configurational entropy and the entropy of N2 at temperature and pressure conditions relevant to ammonia synthesis (380–550 °C, 100 atm) via a semiempirical approach. We show that 3-fold hollow bound nitrogen-containing (111)-surfaces have surprisingly high concentrations (1.6 × 1016 to 3.7 × 1016 cm–2) of nitrogen vacancies in the temperature range for ammonia synthesis. It is shown that these vacancy sites can adsorb and activate N2 demonstrating the potential of a Mars–van Krevelen type mechanism on Co3Mo3N. The catalytically active surface is one where 3f-hollow-nitrogens are bound to the molybdenum framework with a hexagonal array of embedded Co8 cobalt nanoclusters. We find that the vacancy-formation energy (VFE) combined with the adsorption energy can be used as a descriptor in the screening of materials that activate doubly and triply bonded molecules that are bound end-on at surface vacancies.

Item Type: Article
Additional Information: ACS AuthorChoice - This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Uncontrolled Keywords: Mars-van Krevelen, Ammonia synthesis, Nitrogen activation
Subjects: Q Science > QD Chemistry
Faculty / Department / Research Group: Faculty of Engineering & Science
Faculty of Engineering & Science > Department of Pharmaceutical, Chemical & Environmental Sciences
Last Modified: 04 Oct 2018 16:45
Selected for GREAT 2016: None
Selected for GREAT 2017: None
Selected for GREAT 2018: None
Selected for GREAT 2019: None
URI: http://gala.gre.ac.uk/id/eprint/21477

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