Indium exchanged heteropoly tungstates: Efficient catalysts for the synthesis of glycerol carbonate from glycerol and urea

Abstract

In this study, heteropoly tungstate protons were exchanged with various amounts of indium to impart Lewis acidity in Keggin heteropoly acid catalysts. The synthesis of glycerol carbonate from urea and glycerol was investigated using the synthesized InxTPA catalysts. The prepared catalysts were characterized by Fourier transforms infrared (FTIR), X-ray diffraction (XRD), Laser Raman, and temperature programmed desorption of ammonia studies. The obtained characterization results confirmed that the existence of Keggin ion structure of heteropoly acid after modification with indium ions. The modification of heteropoly tungstate with transition metal ions was found to improve its acidity and the stability of heteropoly acids (HPAs). The presence of Lewis acidic sites associated with the indium ions present in the catalyst was indicated by pyridine adsorbed FT-IR spectra. The amount of indium ions in heteropoly tungstate had an impact on the catalysts acidity, which in turn affected the activity of catalyst. The partially exchanged In0.66TPA catalyst demonstrated 69.4% glycerol conversion with 98.8% selectivity to glycerol carbonate. The study also investigated the impact of various reaction parameters such as reaction time, mole ratio of glycerol to urea, reaction temperature, and catalyst concentration and established the optimum reaction conditions.