Dehydration of glycerin to acrolein over H3PW12O40 heteropolyacid catalyst supported on silica-alumina

• H3PW12O40/SiO2-Al2O3 (SA-X) catalysts with different SiO2 content (X) were prepared.
• Gas-phase dehydration of glycerin to acrolein was conducted.
• Brønsted acidity of the catalysts played an important role in the reaction.
• Yield for acrolein increased with increasing Brønsted acidity of the catalysts.

A series of tungstophosphoricacid (H3PW12O40) catalysts supported on silica-alumina (SA-X (X = 0, 15, 30, 50, 70, 85, and 100)) with different SiO2 content (X, mol%) were prepared, and they (H3PW12O40/SA-X) were applied to the gas-phase dehydration of glycerin to acrolein. The effect of support composition on the physicochemical properties and catalytic activities of H3PW12O40/SA-X catalysts was investigated. Total acidity and Brønsted acidity of H3PW12O40/SA-X catalysts determined from pyridine-adsorbed in situ FT-IR spectroscopy measurements showed volcano-shaped trends with respect to SiO2 content. Among the catalysts, H3PW12O40/SA-50 exhibited the largest total acidity while H3PW12O40/SA-85 showed the largest Brønsted acidity. The results of 27Al NMR spectroscopy analyses of H3PW12O40/SA-X (X = 15, 30, 50, 70, and 85) catalysts clearly demonstrated that Brønsted acidity of the catalysts was proportional to the amount of AlIV species. It was revealed that yield for acrolein increased with increasing Brønsted acidity rather than total acidity of H3PW12O40/SA-X catalysts. Among the catalysts tested, H3PW12O40/SA-85 with the largest Brønsted acidity showed the highest yield for acrolein. A synergistic effect between H3PW12O40 and SA-85 for H3PW12O40/SA-85 catalyst was also observed in the dehydration of glycerin to acrolein. Moreover, the catalytic performance of regenerated H3PW12O40/SA-85 catalyst was almost recovered compared to that of fresh H3PW12O40/SA-85 catalyst.

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