Investigation of ZIF-8/nickel loaded aerogel (silica and alumina) catalyst synthesis, characterization, and performance for use in the production of glycerol carbonate from glycerol and carbon dioxide

The synthesis of glycerol carbonate by the carbonylation reaction of glycerol with carbon dioxide is remarkable because it allows the simultaneous evaluation of biodiesel by-product glycerol and the main greenhouse gas CO2. The fact that the atom economy of the reaction is 87% and the only by-product is water (H2O) is crucial in terms of the compliance of the process with green chemistry principles. However, since carbon dioxide is an inert gas, the reaction is carried out in the presence of a co-reactant and catalyst. Within the scope of the thesis study, microporous metal-organic framework structures and mesoporous aerogels were used in synthesizing glycerol carbonate by carbonylation of glycerol in composite form for the first time in the literature. Sol-gel, wet impregnation, and in-situ methods were gradually used in the catalyst synthesis. Catalysts and supports were characterized by FTIR, DRIFTS, XRD, SEM-EDX, MAPPING, N2 physisorption, and TGA-DSC analyses. Catalysts subjected to activity testing have different support structures (alumina and silica aerogel), Nickel loading (2, 5, 8% by mass), and ZIF-8 content (Nickel loaded Aerogel/ZIF-8 mass ratio 5 or 15). The catalytic parameters tested were temperature (100, 150, 200˚C), glycerol/co-reactant ratio (0.25-2.00), co-reactant type (4 types), catalyst amount (2-10%), catalyst type (12 types), and reaction time (1-4 h). ANOVA statistical analysis were carried out with the data obtained at the end of the experimental studies. When the results are evaluated, it is seen that the silica aerogel-supported SA-5Ni-5ZIF catalyst has a quite high glycerol conversion (88%), glycerol carbonate yield (67%), and selectivity (33%) compared to the literature data under the conditions of 0.25 glycerol/Propylene oxide molar ratio, 8% catalyst loading, 7 bar CO2 initial pressure, 200˚C, 2 hours reaction time. It is thought that this success of the catalyst is due to its double active site transport (ZIF-8 and Nickel), its combination of Brönsted and Lewis acidic regions in its structure, and the use of propylene oxide co-reactant, which allows CO2 to participate more easily in the reaction. Glycerol carbonate synthesized in this study is a valuable intermediate product that has the potential to be used as a green solvent and electrolyte in lithium-ion batteries.