Incorporation of Zn~(2+) ions into the secondary structure of heteropoly tungstate: catalytic efficiency for synthesis of glycerol carbonate from glycerol and urea

摘要

Zinc exchanged heteropoly tungstate (Zn_xTPA) catalysts were prepared and characterized by FT-IR, X-ray diffraction. Laser Raman spectroscopy, temperature programmed desorption of ammonia and pyridine adsorbed FT-IR spectroscopy. The activity of the catalysts was evaluated for the carbonylation of glycerol using urea as a carbonylating agent. Zn_xTPA catalysts showed high activity for glycerol carbonate synthesis compared to the parent TPA. The activity of Zn_xTPA catalysts depended on the number of Zn~(2+) ions in the secondary structure of heteropoly tungstate. Catalysts with partial exchange of Zn with the protons of TPA (Zn1TPA) exhibited high activity towards glycerol carbonate synthesis. Exchange of protons of TPA with Zn~(2+) ions resulted in generation of Lewis acidic sites. The changes in surface and structural properties of Zn1TPA catalysts with change in calcination temperature were also evaluated. The catalytic activities of Zn_xTPA catalysts were explained based on the variation in their properties. Reaction conditions such as reaction temperature, catalyst weight and glycerol to urea ratio were also optimized.