Effect of Acid Property Regulation on the Performance of Pd/MIL-100(Cr) Catalyzed One-step Oxidation of Benzyl Alcohol to Acetal

MIL-100(Cr) was hydrothermally synthesized and used as a solid-acid catalyst support. Pd nanoparticles were impregnated on MIL-100(Cr) by a double-solvent approach followed by hydrogen reduction to obtain Pd/MIL-100(Cr). One-step tandem conversion of benzyl alcohol to acetal was selected as a model reaction, and the influence of acid property of MIL-100 on the product distribution was investigated. The results showed that Pd/MIL-100(Cr) catalyzed tandem reaction could accelerate the benzyl alcohol oxidation, and different reduction and activation temperatures had an impact on the acid properties of MIL-100(Cr), which in turn affected the selectivity of acetal. The acid properties were characterized by pyridine adsorption infrared spectroscopy (Py-FTIR) and temperature programmed desorption of ammonia (NH3-TPD), the result showed that increasing the catalyst treatment temperature, the L acid sites increased, the B acid sites decreased, and the B acid sites was beneficial to improve the selectivity of acetal. Under optimal conditions, a benzyl alcohol conversion of 99.9% and acetal selectivity of 76.2% can be achieved at 70 degrees C in 12 h. X-ray photoelectron spectroscopy (XPS) analysis was used to characterize the electronic properties of the Pd species and the MIL-100(Cr), the cycling stability of the catalyst was investigated, and the reasons for the deactivation of the catalyst were analyzed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), N-2 adsorption-desorption isotherms and NH3-TPD.