Nanodisperse gold catalysts in oxidation of benzyl alcohol: comparison of various supports under different conditions

Abstract

Monodisperse gold particles (ca. 2 nm) were prepared and deposited on various supports (SiO2, Al2O3, HAP, MgAl2O4 and MgO). The acid/base properties of supports were characterized by NH3 and CO2 sorption. The size of the gold nanoparticles spans in the 1.7–6.5 nm mean diameter range after calcination as determined from TEM measurements. The amounts of accessible surface sites were estimated by binary concentration pulse chromatography of CO with Kr adsorption. The data are in agreement with the results of CO adsorption obtained by DRIFT spectroscopy. The activities of the catalysts were compared in the oxidation of benzyl alcohol in stirred batch reactors under two different conditions: in xylene solvent with atmospheric oxygen at 60 °C (in presence and in absence of K2CO3), and in a solvent-free mixture at elevated pressure and temperature (5 bar O2, 150 °C, 5 h). The activities of catalysts in benzyl alcohol conversion are described in two variants, namely related to (i) active catalytic sites (ASNA), and (ii) number of Au atoms on the geometric surface of particles (GSNA). The activities of catalysts in xylene solvent at 60 °C were excellent, with 0.28–1.11 s−1 characteristic GSNAini values (initial reaction rates related to surface Au atoms, Ausurf) in presence of K2CO3. The observed order of activities under these conditions is Au/SiO2