Hydrogenation of 2-ethylanthraquinone over Pd/SiO2 and Pd/Al2O3 in the fixed-bed reactor.: The effect of the type of support

The effects of the type of support and Pd concentration pro. le in alumina and silica supported egg-shell catalysts and their performance in the hydrogenation of 2-ethylanthraquinone (eAQ) were studied in 'Anthra' (AQ) and 'All-Tetra' systems. The activity and deactivation of catalysts were determined in the fixed-bed reactor. Solution saturated with hydrogen, ( concentration of active quinones 60 g/dm(3), eAQ in the AQ system, 30% of eAQ and 70% of H4eAQ-2-ethlytetrahydroanthraquinone, in the All-Tetra system) was circulated through the catalyst bed at temperature 50 degreesC and pressure 5 bar. The contents of eAQ, active quinones, H(4)eAQ and degradation products were determined in the course of hydrogenation by GC method. The egg-shell palladium catalysts (1 - 2 wt% Pd) prepared by the precipitation of palladium hydroxide onto alumina and silica supports pre-impregnated with various alkaline (NaHCO3, NaH2PO4, Na2SiO3) solutions were used in the hydrogenation experiments. Pd concentration pro. le inside the grains of catalysts was characterized by scanning electron microscopy. A difference between alumina and silica carriers with respect to the course of side reactions producing degradation products was found. Degradation of quinones in the hydrogenolytic reactions predominated on alumina supported catalysts, while the catalysts with silica favoured the hydrogenation of aromatic rings resulting in H(4)eAQ-active quinone. As a crucial factor for the decrease in the activity during the hydrogenation run, the reactivity of catalyst in the hydrogenolytic reactions was established. Alumina supported catalysts exhibited much higher deactivation than those of silica supported ones. Silica carrier as well as silica species introduced onto alumina under pre-impregnation with Na2SiO3 exhibited an advantageous role in the catalyst performance, in terms of activity and deactivation.