Gas phase dehydration of glycerol to acrolein over Cs2.5H0.5PW12O40/Zr-MCM-41 catalysts prepared by supercritical impregnation

Abstract

The Cs2.5H0.5PW12O40/Zr-MCM-41 samples were synthesized by supercritical impregnation and investigated in gas phase dehydration of glycerol to acrolein. The Cs2.5H0.5PW12O40/Zr-MCM-41 sample prepared by conventional wet impregnation was also examined for comparison. The catalysts were studied using X-ray diffraction, N2 adsorption, the temperature-programmed desorption of ammonia, infrared spectroscopy after pyridine adsorption, thermogravimetric analysis, 31P MAS NMR, inductively coupled plasma-atomic emission spectrometry and CHNS analysis. According to the results of characterization, the preparation condition of supercritical carbon dioxide facilitated the improvement of the Cs2.5H0.5PW12O40 dispersion on Zr-MCM-41. The specific surface area, pore volume and pore size were increased, and the total amount of surface acid sites and the ratio of Brønsted acid sites to total acidity were increased. The strong acid sites were transformed into the weak and medium acid sites. The formation of coke was retarded. Therefore, the glycerol conversion, acrolein selectivity and yield, and the catalytic stability were obviously improved.