Catalytic hydrodechlorination of chlorocarbons. 2. Ternary oxide supports for catalytic conversions of 1,2-dichlorobenzene

摘要

Ternary oxides of Ti-Zr-Al and Ti-Zr-Si were prepared by coating commercial Al2O3 and SiO2 with a THF solution of Ti(OPri)(4) and Zr(OPri)(4) under controlled conditions. Nitrogen adsorption and X-ray powder diffraction indicate that the structure of the base supports, Al2O3 and SiO2, were not significantly altered upon coating and that TiO2 and ZrO2 were quite uniformly spread on them. The acid resistance of alumina was found to be increased upon coating. Palladium supported catalysts, Pd/TiZrAlOx, Pd/TiZrSiOx, Pd/TiO2, Pd/ZrO2, Pd/SiO2, and Pd/Al2O3 were prepared to evaluate the ternary oxides relative to the component single oxide supports. Palladium dispersion was determined using hydrogen chemisorption and the catalysts were evaluated for hydrodechlorination of 1,2-dichlorobenzene. The experimental runs were carried out in a microflow reactor system at atmospheric pressure, in the gas phase. The catalysts were oxidized and then reduced, prior to reaction. The kinetic studies showed that the ternary oxide-based catalyst, Pd/TiZrAlOx exhibited an improved stability and activity much higher than the arithmetic sum of the activities of the component single oxide based palladium catalysts. Comparison of the specific activities of the catalysts expressed as TOF, indicate that the observed differences in activity may be related to the chemical nature of the supports. The best catalyst had an initial specific activity of 16.6 s(-1). We observed that the pretreatment of the catalyst has a profound effect on its stability and activity. Also, the experimental results indicated that the major factors of the catalyst deactivation are agglomeration of palladium particles and HCl poisoning. Prospects for optimization of these catalysts are discussed in light of the results of this work. (C) 1998 Academic Press. [References: 42]