Incorporation of Zn2+ ions into the secondary structure of heteropoly tungstate: catalytic efficiency for synthesis of glycerol carbonate from glycerol and urea

Abstract

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 Zn²⁺ 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 Zn²⁺ 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.