Synergetic role of copper-modified phosphotungstic acid supported on titania catalysts for the conversion of bio-glycerol to glycerol carbonate

Abstract

Copper-modified phosphotungstic acid (CuPW) supported on titania materials with various CuPW contents were successfully synthesized by ion exchange followed by an impregnation method. The prepared materials were characterized using XRD, Raman, ammonia TPD, pyridine FT-IR spectroscopy, and BET-surface area measurements. The XRD results revealed that the crystalites of Keggin ions of heteropolyacid were merged with the anatase support. The Raman spectroscopy results of the fresh and regenerated 30 wt% CuPW/TiO₂ clearly showed the characteristic peak of Keggin ions being intact with the support. The results from the temperature-programmed desorption (TPD) of ammonia tests revealed that a 30 wt% catalyst possessed a greater number of acidic sites than the other loadings. Pyridine-adsorbed FT-IR spectroscopy suggested that the 30 wt% catalyst calcined at 300 °C had high amount of Lewis and Brønsted acidity. The copper-modified phosphotungstic acid on the titania support significantly altered the Brønsted and Lewis acidity of the catalysts and promoted a remarkable catalytic performance during glycerol carbonylation as well as provided related structural and acidity functionalities to the CuPW/TiO₂ catalyst.