Mechanism of ammonia oxidation over PGM (Pt, Pd, Rh) wires by temporal analysis of products and density functional theory
authors Perez-Ramirez, J; Kondratenko, EV; Novell-Leruth, G; Ricart, JM
nationality International
journal JOURNAL OF CATALYSIS
author keywords NH(3) oxidation; Mechanism; Platinum; Palladium; Rhodium; Wires; TAP reactor; DFT
keywords SELECTIVITY-DIRECTING FACTORS; FINDING SADDLE-POINTS; NO; PLATINUM; SURFACES; NH3; KINETICS; REACTOR; ENERGY; N2O
abstract The mechanism of ammonia oxidation over Pt, Pd, and Rh wires has been investigated in the Temporal Analysis of Products (TAP) reactor at relevant temperatures in industrial ammonia burners. The results of primary (NH(3) + O(2)) and secondary (NH(3) + NO) interactions with isotopically labeled ammonia at 1073 K enable to conclude that the overall reaction pathways to NO, N(2)O, and N(2) are equivalent on the three noble metals. NO is a primary reaction product, while N(2) and N(2)O originate from consecutive NO transformations. The extent of the secondary reactions determines the net NO selectivity. Rhodium is the most active catalyst for the unwanted reduction of NO by NH(3), while platinum shows the lowest activity. This explains the superior NO selectivity attained over Pt and, therefore, its industrial application. The TAP-derived selectivity ranking was substantiated by Density Functional Theory calculations on the (100) facets of the noble metals. We proved experimentally that NO selectivity approaching 100% at complete NH(3) conversion can be equivalently attained over Pt, Pd, and Rh by increasing the oxygen content in the feed. For a feed of O(2)/NH(3) = 10, both N(2)O and N(2) production are suppressed due to the impeded NO dissociation and favored NO desorption at high oxygen coverage. (c) 2008 Elsevier Inc. All rights reserved.
publisher ACADEMIC PRESS INC ELSEVIER SCIENCE
issn 0021-9517
year published 2009
volume 261
issue 2
beginning page 217
ending page 223
digital object identifier (doi) 10.1016/j.jcat.2008.11.018
web of science category Chemistry, Physical; Engineering, Chemical
subject category Chemistry; Engineering
unique article identifier WOS:000263564900011
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journal analysis (jcr 2017):
journal impact factor 6.759
5 year journal impact factor 7.502
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