Bimetallic Au–Ag/SiO2 catalysts: comparison in glucose, benzyl alcohol and CO oxidation reactions

Abstract

SiO2 supported Au–Ag nanoparticles prepared by the adsorption of bimetallic colloids of various Ag/Au molar ratio (0/100, 13/87, 23/77, 33/67, 51/49, 100/0) were characterized and studied in selective glucose oxidation reaction earlier (Benko et al., Applied Catalysis A 479:103–111, 2014 [32]). The same catalysts of mean metal particle size between 3 and 5 nm were applied and compared in benzyl alcohol and CO oxidation after both calcination and successive reduction treatments. In temperature programmed CO oxidation tests of the Au-containing samples, different activity zones appeared with several conversion maxima, which were affected differently by the Au/Ag ratio and pretreatment conditions. CO oxidation results suggested the coexistence of several types of active sites in various population in the different samples. In all the three reactions, the sample with Ag/Au = 23/77 composition was the most active in calcined and also in reduced state, showing synergetic effect compared to the monometallic analogous. Upon H2-treatment in benzyl alcohol oxidation, a significant, in glucose oxidation, a slight activity increase was observed for all the samples. In CO oxidation, the reduction treatment induced deactivation of sample with Ag/Au = 23/77 and 13/87 below 125 °C, while in the higher temperature region, all the samples were highly activated.