Understanding the Role of Tantalum in Heteropoly Tungstate Catalysts for the Synthesis of Glycerol Carbonate from Glycerol and Urea

Abstract

Tantalum exchanged tungstophosphoric acid (Ta x TPA) catalysts were prepared and studied for the synthesis of glycerol carbonate from glycerol and urea. These catalysts were characterized by FT-IR, X-ray diffraction, Laser Raman, pyridine adsorbed FT-IR and temperature programmed desorption of ammonia. The characterization results indicate that the Keggin ion structure of tungstophosphoric acid (TPA) is intact. The activity towards the synthesis of GC over the Ta x TPA catalysts depended on the number of Ta 5? ions exchanged in the secondary structure of heteropoly tungstate. Presence of Ta in TPA leads to the generation of Lewis acidic sites. Catalysts with partially exchanged Ta with the protons of TPA showed high activity due to the presence of both Brønsted and Lewis acidic sites. Different reaction parameters such as reaction temperature, glycerol to urea molar ratio and catalyst loading were studied and optimum conditions were established. These catalysts exhibited reusability. Graphical Abstract1 2 3 4 5 0 10 20 30 40 50 60 70 80 90 100 Selectivity (%) Conversin (%) Reaction time (h) 0 10 20 30 40 50 60 70 80 90 100

Incorporation of CO2 into carbonates through carboxylation/hydration reaction

“…After optimizing the reaction conditions, the catalyst Sm 0.66 TPA, with the most acidic sites, was proved to be the best catalyst with the highest activity . Similarly, in another report, a tantalum‐exchanged tungstophosphoric acid (TaxTPA) catalyst was prepared and its reaction activity was demonstrated to depend on the overall acidity of the catalyst, which could be controlled by exchangeable Ta content …”

Bifunctional molybdenum phosphate catalyst with tunable acidity–basicity for the sustainable synthesis of glycerol carbonate via solvent‐free carbonylation of glycerol with urea

“…The selectivity towards glycerol carbonate decreases because of by-product formation as the free hydroxyl group of glycerol carbonate reacts with extra urea. [11,29,31] To produce a high output of glycerol carbonate, a mole ratio of 1:1 for glycerol and urea is sufficient. The effect of catalyst weight percentage for the synthesis of glycerol carbonate was investigated and shown in Figure 10a.…”

“…Apart from that, ammonia, which is formed as a by‐product, can be used for the production of urea again, thus making the process efficient. The carbonylation reaction of glycerol has been investigated with various heterogeneous catalysts such as Zn–Sn mixed oxide, [ 20 ] ZnO, [ 21 ] γ‐Zirconium phosphate, [ 22 ] Co 3 O 4 /ZnO, [ 23 ] Sn‐W mixed oxide, [ 24 ] ZnSn (OH) 6 , [ 25 ] La 2 O 3 , [ 26 ] Zn 1 TPA, [ 11 ] Sm 0.6 TPA, [ 27 ] Zn/MCM‐41, [ 28 ] Zn‐exchanged zeolites, [ 6 ] HTc‐Zn derived from HT, [ 12 ] Au‐supported ZSM‐5, [ 1 ] Ta‐HPA, [ 29 ] Sn (OH) 2 , [ 30 ] and Cu‐Mn mixed oxide, [ 31 ] which resulted in good production of glycerol carbonate. Noticeably the catalysts having both acidic and basic sites showed good catalytic activity.…”