Supported Pd catalysts for solvent-free benzyl alcohol selective oxidation: Effects of calcination pretreatments and reconstruction of Pd sites

Pd catalysts supported on Al2O3 and TiO2 have been prepared by wet impregnation and studied for the solvent-free selective oxidation of benzyl alcohol by molecular oxygen. High activity as well as high selectivity to benzaldehyde can be obtained and the calcination pretreatments show distinct effects on the catalytic activities of supported Pd catalysts. Supported Pd catalysts before and after benzyl alcohol oxidation are characterized by means of XPS, FTIR spectra of CO adsorption and O2-TPD. The results clearly show that the palladium sites in supported Pd catalysts undergo reconstruction during benzyl alcohol oxidation. Based on the catalytic and characterization results, the possible benzyl alcohol oxidation reaction pathways and the active palladium sites in supported Pd catalysts for benzyl alcohol oxidation are discussed.

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► Ideal green oxidation of benzyl alcohol catalyzed by supported Pd catalysts.
► Calcination pretreatments show great effects on catalytic activity.
► Palladium sites undergo reconstruction during reaction.
► Defect sites on Pd (1 1 1) proposed to be the primary sites for benzyl alcohol oxidation.