Study of catalytic activity at the Ag/Al-SBA-15 catalysts for CO oxidation and selective CO oxidation

Abstract

In this work, Al-SBA-15 supports and Ag catalysts were prepared by “pH-adjusting” method with Al(NO3)3·9H2O as alumina source and impregnation method, respectively. The influence of Si/Al ratio on the structure of silver catalysts and their catalytic activity for CO oxidation and selective CO oxidation are investigated. The supports and catalysts were characterized by N2 adsorption–desorption, ICP-AES, XRD, 27Al NMR, 1H NMR, TEM, H2-TPR and O2-TPD. It was found that the addition of a certain amount of Al (Al-SBA-15 (200-50)) was beneficial to the improvement of the catalytic activity. For Ag/Al-SBA-15 (25) catalyst the beneficial effect of Al3+ on metal dispersion and catalytic activity was counterbalanced by Ag2O formed. The addition of a large amount of Al was favorable for the formation of Ag2O species, the aggregation of Ag particles and caused the decrease of subsurface oxygen, leading to the decrease of catalytic activity. In addition, the effect of reaction gas on the structure and catalytic activity of Ag catalysts was systematically discussed. Reaction gas of CO oxidation is beneficial to surface restructuring of Ag/Al-SBA-15 (200) catalysts with lower Ag loading, consequently improving the catalytic activity for CO oxidation. The characterization results after reaction indicated that the in situ reduction of the Ag2O species in the reaction process should be responsible for the high activities of successive cycles of efficient catalytic reaction.