Mechanisms for Selective Catalytic Oxidation of Ammonia over Vanadium Oxides

Abstract

Selective catalytic oxidation (SCO) of ammonia to a nitrogen molecule is an important process involved in many applications such as removing NH(3) slip in selective catalytic reduction (SCR) of NO(x), reducing the NH(3) concentration from biomass-derived fuels, etc. Here we perform density functional theory calculations in conjunction with cluster models to investigate the SCO mechanisms on V(2)O(5) surfaces. Our calculations show that, at the initial stage, NH(3) can be activated by transferring an electron to the metal oxide surfaces, giving rise to an NH(3)(+) intermediate. We disclose that the subsequent pathways are strongly dependent on the availability of the gaseous species. When oxygen is limited or absent, N(2)H(4) can be produced from NH(3)(+) reacting with a second NH(3) or from two activated intermediates (e.g., NH(2) + NH(2) or ONH(2) + NH(2)), and oxidation of N(2)H(4) into N(2) by V=O is viable. On the other hand, when oxygen is abundant, NH(3)(+) will react with O(2) to make a NH(3)(+)center dot center dot center dot O(2) complex. Such a species will quiddy decompose into NO, which switches on the selective catalytic reduction (SCR) reaction, eventually leading to the formation of N(2). We propose that the combination of an efficient Ostwald reaction catalyst for NH(3) to NO transformation with a capable SCR reaction catalyst for NO reduction by NH(3) to N(2) can lead to a good candidate catalyst for SCO at the high O(2)/NH(3) ratio condition.Ministry of Science and Technology[2011CB808505, 2007CB815206]; National Natural Science Foundation of China[20973139, 20923004, 21033006, 21133004]; Program for Changjiang Scholars and Innovative Research Team in University[IRT1036]; Fundamental Research Funds for the Central Universities; Key Science and Technology Specific Projects of Fujian Province[2009HZ0002-1]; Natural Science Foundation of Fujian Province of China[2009J05035