Role of the support on the behavior of Ag-based catalysts for NH3 selective catalytic oxidation (NH3-SCO)

In this work four supports with different textural properties (Al2O3, SiO2, NaY and TiO2) are used to evaluate the formation of different silver species and their effect on the NH3-SCO performance. Characterization analyses have shown that the predominant Ag-0 species and the oxidized Ag species Ag+ and Ag-n(delta+)) are located on the four catalysts with different ratio of Ag-0/oxidized Ag. Small Ag-0 particle with high dispersion which is obtained on 10 wt% Ag/Al2O3 (5 nm, Ag-0 ratio = 97.7%) shows an excellent catalytic performance for SCO reaction at low temperatures a complete NH3 conversion at 180 degrees C and a high N-2 selectivity of 89%). In addition, a certain amount of oxidized Ag species formed on the catalysts, especially for the NaY and SiO2 support, as well as the surface acidity of catalysts have also been found to play an important role in the enhanced N-2 selectivity above 140 degrees C by promoting iSCR reaction involving NO as an intermediate for N-2 formation. A model to relate the silver species with the performance of NH3-SCO is proposed, which is very significant for the further optimization of the catalyst (e.g. choosing a suitable support) for NH3-SCO reaction and its practical application in the future. (C) 2014 Elsevier B.V. All rights reserved.