Page 47 - חוברת תזות הנדסה ירוקה 2023

Recyclable Pd-Based Polysaccharide Catalyst for Aerobic Oxidation of Benzyl Alcohol
Eliraz stamker1; elirazst@sviva.gov.il
Prof. Adi Wolfson1, Dr. Oshrat Levy-Ontman1, 1Sami Shamoon College of Engineering
The aerobic oxidation of alcohols, in the presence of air or oxygen, may proceed with many catalysts, among which are the catalysts of palladium. To that end, using heterogeneous catalysts has drawn much attention in the last decade, whereas supports that originate from a biological and renewable source that is also nontoxic and biodegradable, like polysaccharides, were found to be superior.
In the present research, we were immobilizing palladium complexes with the TPPTS ligand, e.g., Pd)OAc(2)TPPTS(2 and PdCl2)TPPTS(2, in the xerogels and hydrogels of various polysaccharides, and that have generated two types of heterogeneous catalysts. The new heterogenic systems were tested in the aerobic oxidation of benzyl alcohol, as a test reaction, in different solvents: ethanol, ethyl acetate, and hexane, and their performances were compared to those of the analogous homogeneous reactions. In regard to hydrogels that were prepared with either chitosan or calcium chloride solution, it was found that the most resistant polysaccharide that produced the best results was the iota in hexane, apparently because the beads contained a larger quantity of water that did not flow into the solution. In addition, the hydrogels that were prepared in the calcium chloride solution were less dense and less hard than those prepared with the chitosan; therefore, they yielded higher conversions in all the solvents. Also during the heterogenization of the complexes in the various polysaccharide xerogels, iota yielded the most stable system, and the performances in ethanol were the best. Raising the pressure or transitioning from air to oxygen altered the solubility of both the oxygen and the nitrogen in the solvent, and accordingly influenced the catalytic performance. In general, as the oxygen concentration increased in the solution, the degree of conversion also grew. Nevertheless, in the reactions with air, the rise in pressure also caused increased solubility of the nitrogen, that may be absorbed into the palladium, thus reducing the conversion. Likewise, the oxidation of additional aromatic alcohols produced conversions fairly similar to those observed with benzyl alcohol. In all the new heterogeneous systems no leaching of the metal was detected.
The new heterogeneous catalysts were also characterized by FTIR, SEM-EDS, XPS, DLS, TEM and zeta potential analyses, raveling the formation of new bond between the polysaccharide and TPPTS and dispersion of the palladium in the support, whereas in alcohols the palladium was reduced and nanoparticles were formed during the reaction. At last, for the xerogel- based catalyst, it was found that mixing the catalyst in ethanol for up to 24 hours before
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