Sulfur-Modified SBA-15 Supported Amorphous Palladium with Superior Catalytic Performance for Aerobic Oxidation of Alcohols

Abstract

A series of sulfur-modified SBA-15 supported amorphous palladium catalysts are prepared, and the effects of preparation parameters on the aerobic oxidation of benzyl alcohol are systematically investigated. The optimal catalyst exhibits remarkably enhanced catalytic activity (conversion 100 % and selectivity 99 %) and could be separated conveniently. The catalysts are characterized by X-ray diffraction patterns, BET, ICP, X-ray photoelectron spectroscopy, CO chemisorption and transmitting electron microscopy, and the results show that disulfur bond framework in the optimal catalyst act as both a stable linker and a good chelator for Pd species. Pd2+ is reduced to Pd0 with the increasement of the carbon chain lengths between sulfur bonds, which is the cause of deactivation. The mechanism is that a base abstracts a proton from the coordinated alcohol to form a Pd alcoholate species that subsequently undergo β-hydride elimination to give benzyl aldehyde, which is confirmed by the catalytic and characteristic results.