Investigation of factors influencing the catalytic performance of CO oxidation over Au–Ag/SBA-15 catalyst

Abstract

Au–Ag bimetallic nanoparticles (NPs) supported on SBA-15 have been prepared by a two-step method and characterized by ICP-AES, XRD, UV–vis, TG-DTG, XPS and TEM. Au–Ag/SBA-15 bimetallic catalyst with a low metal loading of 1.26wt.% exhibited high catalytic performance for low temperature CO oxidation, which was governed by Au/Ag molar ratio and the pretreatment conditions (calcination and reduction). The Au–Ag/SBA-15 with an actual Au/Ag molar ratio of 5.4/1 showed the highest catalytic activity for CO oxidation (T100=20°C), and it has also been found that catalytic activity was strongly related with the calcination and reduction temperature of the bimetallic catalyst. The initial CO conversion was increased with the calcination temperature and then decreased above 500°C. It was necessary to activate the bimetallic catalyst and completely remove the amine groups in the catalyst at 500°C for the high activity of CO oxidation. The severe sintering of Au–Ag bimetallic NPs at 700°C resulted in an obvious loss of activity. H2 reduction following the calcination played an important role in the enhancement of catalytic activity for CO oxidation. The best catalytic performance was obtained in the activation temperature range of 500–600°C, and then decreased with a further increase of reduction temperature to 700°C. The reduction treatment induced the surface redistribution of gold and silver. The formation of a closer bulk value of the surface Au/Ag molar ratio after reduction at 500–600°C and a more random alloy resulted in the improvement in activity. However, the surface enrichment of Ag NPs and the severe aggregation of particles after high temperature reduction (>600°C) caused the activity decrease.