SUPPORTED PALLADIUM CATALYSTS FOR ALCOHOLS OXIDATION BASEDON CHEMICALLY MODIFIED BOEHMITE

Abstract

New palladium catalysts based on Pd(II) coordination heterogenization on the surface of synthetic boehmite chemically modified with nitrilotris(methylenephosphonic) acid (NTP) were ob-tained. The catalysts were prepared by impregnating the carrier (boehmite (γ-AlOOH), NTP-boehmite (NTP-γ-AlOOH)) with a PdCl2solution followed by the reduction of Pd(II) to metallic palladium with potassium formate. The resulting samples were characterized by XPA, SEM, XPS, BET, and IR spectroscopy. The carriers have a high specific surface area (100–250 m2/g) and a mesoporous structure. The content of palladium in the obtained metal catalysts is 2–4 wt%, with an average particle size of 10–50 μm. An analysis of the XPS spectra of the catalysts (Pd3d, N1s, P2p) shows that they contain metallic palladium Pd(0) and ionic forms of Pd(II) bonded to the oxygen and nitrogen atoms of the support.The possible composition of Pd(II) surface complexes on boehmite and NTP-boehmite was established by modeling the sorption vs. pH curve according to the theory of surface complexation. The reaction of the selective oxidation of benzyl alcohol to benzaldehyde in an aqueous solution (4 vol.% alcohol, 60°C, 1 h) using atmospheric oxygen was chosen as a model reaction for evaluating the catalytic activity, which corresponds to the principles of "green chemistry": 2C6H5CH2OH+O2= 2C6H5COH+ 2H2O. The oxidation processwas moni-tored by measuring the IR spectra of the chloroform extractof the reaction mixture using the in-tensities of the absorption bands of alcohol (3100–3600 см-1(νO-H)) and aldehyde (1700 см-1(νC=O)). The following series of catalyst activity was established: Pd(II) > Pd(0)/NTP-γ-AlOOH > Pd(0)/ γ-AlOOH > Pd(II)/ γ-AlOOH >> Pd(II)/NTP-γ-AlOOH. The metallic form of palladium is required for the catalytic activity. The coordination fixation of palladium on NTP-boehmite due to chelate binding by an aminophosphonic group increases catalyst activity compared to monodentate binding by hydroxo groups of unmodified boehmite.