Pd-H3PW12O40/Zr-MCM-41: An efficient catalyst for the sustainable dehydration of glycerol to acrolein

Abstract

The gas-phase dehydration of glycerol was investigated over H3PW12O40/MCM-41, H3PW12O40/Zr-MCM-41 and Pd-H3PW12O40/Zr-MCM-41 mesoporous molecular sieves catalysts. MCM-41, Zr-MCM-41 and Pt-H3PW12O40/Zr-MCM-41 were also examined for comparison. The catalysts were characterized by X-ray diffraction, nitrogen adsorption–desorption, NH3-TPD, pyridine-FTIR and thermogravimetric analysis measurements. Compared with MCM-41, Zr-MCM-41 catalyst showed higher acidity and better catalytic performance in glycerol dehydration to acrolein. Compared to Zr-MCM-41, the acidity of H3PW12O40/Zr-MCM-41 catalyst significantly increased and the catalyst showed an enhanced glycerol conversion and acrolein selectivity. In order to improve the stability of H3PW12O40/Zr-MCM-41 catalyst, a small amount of platinum group metals (Pd) was doped. The nitrogen adsorption–desorption results revealed that mesoporous structure of the Pd-H3PW12O40/Zr-MCM-41 catalyst remained almost unchanged, and the specific surface area, pore volume and pore size decreased. In comparison with H3PW12O40/Zr-MCM-41, the total acidity of Pd-H3PW12O40/Zr-MCM-41 catalyst did not show any obvious change, but the number of the Brønsted acid sites increased, the amount of the Lewis acid sites decreased. The Pd-H3PW12O40/Zr-MCM-41 catalyst exhibited significantly higher selectivity for the formation of acrolein, relatively lower coke deposition and excellent catalyst stability. After 50h of reaction, the conversion of glycerol decreased from 100% to 55% over H3PW12O40/Zr-MCM-41 catalyst, while the conversion of glycerol reduced from 97% to 87% over Pd-H3PW12O40/Zr-MCM-41 catalyst. A drastic decrease in conversion after 35h over Pt-H3PW12O40/Zr-MCM-41 catalyst was also observed. Moreover, Pd-H3PW12O40/Zr-MCM-41 catalyst was completely regenerated under the regeneration conditions and exhibited excellent reusability in the dehydration of glycerol to acrolein.