Research on properties and catalytic behaviour in CO hydrogenation at atmospheric and high pressure of bimetallic systems (10%Co + 0.5%Pd)/TiO 2 (Al 2 O 3 )

The properties of prereduced (10%Co + 0.5%Pd)/Al 2 O 3 (TiO 2 ) systems in the CO hydrogenation reaction at atmospheric and high pressure were studied. At atmospheric pressure, alumina-supported catalysts were more selective toward methane but those using titania were more active. Alumina containing samples demonstrated high temperature H 2 desorption, firmly held surface carbonate species, high tendency to agglomeration. During the reaction metal surface reconstruction and increased formation of CH 2 groups occurred being more pronounced with titania-supported catalysts. Stability tests at 250 °C showed opposite behaviour of both systems. Monodentate carbonate intermediates adsorbed on sites of moderate strength prevailed on titania samples, while formate species predominated on high strength sites of alumina-supported catalysts. High pressure catalytic tests revealed dependence of activity on T red , synthesis of C 2+ hydrocarbons, decreased CO 2 production, a higher CH 4 /CO 2 ratio for alumina containing system. Due to SMSI, increased CO 2 production on titania samples was preserved. Titania-supported catalysts revealed a stronger decrease of CO conversion rising T red while alumina catalysts had almost unchanged activity. CO conversion decreased with time due to difficulties in surface diffusion of reagents/intermediates/products and metal particle agglomeration. Concerning T red comparison of product distribution showed a steady trend. Because of stable CO and CH x surface species, titania containing catalysts produced lower content of C 5+ compounds. Alumina-supported samples showed a higher selectivity to C 5+ compounds at the expense of methane. A higher selectivity ratio for CH 4 and CO 2 determined in catalytic CO hydrogenation over a certain catalyst at atmospheric pressure could indicate that a given sample is predisposed to form C 2+ hydrocarbons at a higher pressure.