CATALYTIC HYDRODECHLORINATION OF CHLOROCARBONS - 2 - TERNARY OXIDE SUPPORTS FOR CATALYTIC CONVERSIONS OF 1,2-DICHLOROBENZENE

Ternary oxides of Ti-Zr-Al and Ti-Zr-Si were prepared by coating comme rcial Al2O3 and SiO2 with a THF solution of Ti(OPri)(4) and Zr(OPri)(4 ) under controlled conditions. Nitrogen adsorption and X-ray powder di ffraction indicate that the structure of the base supports, Al2O3 and SiO2, were not significantly altered upon coating and that TiO2 and Zr O2 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 we re prepared to evaluate the ternary oxides relative to the component s ingle oxide supports. Palladium dispersion was determined using hydrog en chemisorption and the catalysts were evaluated for hydrodechlorinat ion 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 k inetic studies showed that the ternary oxide-based catalyst, Pd/TiZrAl Ox exhibited an improved stability and activity much higher than the a rithmetic sum of the activities of the component single oxide based pa lladium catalysts. Comparison of the specific activities of the cataly sts expressed as TOF, indicate that the observed differences in activi ty may be related to the chemical nature of the supports. The best cat alyst had an initial specific activity of 16.6 s(-1). We observed that the pretreatment of the catalyst has a profound effect on its stabili ty and activity. Also, the experimental results indicated that the maj or factors of the catalyst deactivation are agglomeration of palladium particles and HCl poisoning. Prospects for optimization of these cata lysts are discussed in light of the results of this work. (C) 1998 Aca demic Press.