SBA-15-supported Pd catalysts: The effect of pretreatment conditions on particle size and its application to benzyl alcohol oxidation

SBA-15-supported Pd catalysts were prepared by impregnation, thermal pretreatment, and H-2 reduction. The pretreatment conditions have an important influence on the resulting size (from 1.3 to 10.3 nm) of the Pd particles; the catalyst prepared under vacuum conditions possessed the smallest particles (size 1.3 nm). X-ray absorption spectra were used to analyze the transformation of the Pd precursor in each step of the preparation. These catalysts were applied to the oxidation of benzyl alcohol by molecular oxygen; the catalyst with the smallest Pd particles exhibited the highest turnover frequency (9684 h(-1)). The catalyst was reusable three times without loss of activity (with conversion >96%). X-ray absorption spectra were recorded ex situ to monitor the oxidation and the coordination structure of Pd at varied temperatures of reaction; when the reaction temperature was above 100 degrees C, the Pd species were in the metallic state. This result indicates that metallic Pd might be the active phase in the oxidation of benzyl alcohol by molecular oxygen. (C) 2017 Elsevier Inc. All rights reserved.