Catalytic activity of gold-silver nanoalloys for HCHO oxidation: Effect of hydroxyl and particle size

Supported AuAg bimetallic nanoalloys were synthesized by post-grafting strategy on mesoporous silica materials, and the effect of particle size and hydroxyl number of support were tuned and investigated for HCHO oxidation. The particle size of 3.1 nm and less hydroxyl was prepared via methyl-modified SBA-15 (CH3-SBA-15) supporting Au-Ag bimetallic nanoalloys. The size of 5.3 nm and 6.4 nm for Au-Ag bimetallic nanoalloys was respectively obtained using calcined conventional SBA-15 (SBA-15) and uncalcined SBA-15 (as-SBA-15) as the support, both of them had large amount hydroxyls. The results indicated that AuAg/SBA-15 with 5.3 nm and large density of hydroxyls exhibited the best HCHO catalytic behavior and had the lowest activation energy of 73.9 kJ/mol. It was found that hydroxyl group on AuAg/SBA-15 effectively facilitated HCHO adsorption and transformation into intermediate species (DOM, formate and CO(a). The further facile decomposition of intermediates was correlated with the higher ability of O-2 activation that was strongly related with the smaller size of Au-Ag nanoalloys. It was revealed that the process of intermediates formation on the catalyst was very essential for HCHO oxidation, and the high activity for HCHO oxidation depended upon the combining action of metal particle size and hydroxyl group on the catalyst.