Role of Zirconium Counter ions Content in the Secondary Structure of Keggin-type Heteropoly Tungstate for the Solvent-free Glycerol Carbonate Synthesis

Zirconium ions incorporated into the secondary structure of the Keggin type heteropoly tungstate by titration method by varying the zirconium content. The FT-IR, Laser Raman, and XRD analysis of the synthesized catalysts revealed that the incorporation of the zirconium does not affect the primary structure of the Keggin ion. The quantitative acid measurement of the catalysts was done by TPD-NH₃ technique. The type of acid site was identified by adsorbing pyridine on the catalyst and qualitative analysis was carried out by DRIFTS. The activity of the catalysts was tested for the glycerol carbonylation using urea as a CO source. The catalyst with moderate content of Zr⁴⁺ ions in the secondary structure presented high activity. Catalysts acidity and activity depend on the intact primary Keggin heteropoly tungstate together with the counter ions type and its size in the secondary structure and catalyst calcination temperature.