PALLADIUM BASED MULTICOMPONENT CATALYTIC-SYSTEMS FOR THE ALCOHOL TO CARBOXYLATE OXIDATION REACTION

Excellent palladium based multi-component catalytic systems (BiSePd/C, CeBiPd/C and CeBiSePd/C) were developed for the oxidation of primary alcohols, R-(O-CH2-CH2)n-OH (R=C10H21 to C14H29, n=3 to 6) in water to the corresponding carboxylates. The carboxylate yield, using the conventional catalyst Pd/C, ranged from 80 to 86%, based on starting alcohols, but it was impossible to complete the oxidation reaction because of catalyst deactivation by oxygen. On the other hand the newly developed multi-component catalytic systems containing both bismuth and selenium as promoters gave a 100% yield of carboxylate by the synergetic effect of both promoters. This effect completely inhibited catalyst deactivation by oxygen, especially in the last part of the oxidation reaction. This paper describes the development of the catalyst and the function of the promoters in the 5% Pd/C catalytic systems as estimated by X-ray diffraction, electron spectroscopy for chemical analysis and transmission electron microscopy. The functions of the promoters in the 5% Pd/C catalysts can be summarised as: Bi: producing a higher dispersion of the Pd metal particles (40 to 50 angstrom) by incorporation in the Pd and controlling the valency state of Pd; Se: keeping the Pd surface in the reduced state throughout the oxidation reaction; Ce: producing a much higher dispersion (20 angstrom) of the Pd over the Bi and also giving basicity, leading to a higher oxidation reaction rate. BiSe: combining the functions of Bi and Se to inhibit completely the catalyst deactivation due to oxygen and giving the optimum redox cycle which is not attainable by either presence of Bi or Se alone. Only this synergetic effect produced by the combination of Bi and Se gave the 100% yield of carboxylates. TEM observation of BiSePd/C catalyst showed that Pd particles were composed of Bi and Pd, and Se was not observed in the same particles, because the loading of Se was small (0.25%). CeBi: combining the functions of Bi and Ce to increase the reaction rate mainly by much higher dispersion of Pd. TEM observation showed that Ce was not contained in the Pd particles and that it formed separate particles apart from BiPd particles.