2-Ethylanthraquinone hydrogenation on Pd/Al2O3 -: The effect of water and NaOH on the degradation process

The effect of water and NaOH was studied on the hydrogenation of 2-ethylanthraquinone (eAQ) over alumina supported 2% Pd/Al2O3-A and 1.2% Pd/Al2O3-B catalysts. The hydrogenation was performed in a fixed-bed reactor by circulating the eAQ solution (the concentration of eAQ was 60 g/dm(3)) at 50 degrees C and 5 bar hydrogen pressure. The egg-shell catalysts were prepared by the precipitation of palladium hydroxide onto the support A (activated alumina, preimpregnated with NaH2PO4) or support B (alumina containing 10% SiO2, and preimpregnated with Na2SiO3). Prior to the hydrogenation, the catalysts were dried and pre-treated with water vapour or NaOH solution. The effect of water and NaOH on the amount of active quinones (eAQ and 2-ethyl-5,6,7,8-tetrahydroanthraquinone, H(4)eAQ) and in particular the role of such reagents in the consumption of aromatic hydroquinone eAQH(2), the primary product of the quinone system of eAQ reduction was examined. The saturation of the phenyl rings in eAQH(2) produces H(4)eAQH(2), which is a reactive compound and the hydrogenolysis of the C-O bond in the tautomerized eAQH(2) leads to other degradation products. Water and NaOH influence the hydrogenation of C=O and the hydrogenolysis of C-O bond but have no effect on the hydrogenation of the aromatic rings. The increase in activity in the former C=O to C-OH reduction did not depend of alumina A and B as well as the type of reagent (NaH2PO4 or Na2SiO3) introduced to alumina during the catalyst preparation. These reagents however, influenced the course of degradation processes. Water when introduced to the catalyst exhibited unprofitable effect on maintenance the activity of catalyst during the hydrogenation run. Such an unprofitable role is related to influence of water on the course of reactions yielding degradation products. (c) 2004 Elsevier B.V. All rights reserved.