The Activity, Selectivity and Thermal Stability of Group VIII Metal/Al2O3Catalysts for Synthesis of Hydrocarbons from CO and H2

For hydrocarbon synthesis from mixtures of CO and H2, variation in activity and selectivity of Group VIII metals (except osmium)/Al2O3 catalysts with pretreatment temperature in flpwing H2 at 300°C∼800°C, was investigated at 300°C and 1atm using a pulse method and a circulating flow reactor. In addition, variation in the number of surface metal atoms (mS) in those catalysts with varying treatment temperature was also determined using the chemisorption technique. The activities (per unit weight of catalyst; per metal atom in the catalyst) of Pt, Ir, Pd, and Rh catalysts were maximum when they were treated at 500°C, though their mS values monotonously decreased with increasing treatment temperature due to metal sintering. The activity and the mS value of Ru(A) catalyst decreased slightly with increasing treatment temperature. On the other hand, the initial activity and the mS value of Ru(B) increased with increasing treatment temperature, but the steady-state activity decreased. The activities and mS values of Ni and Co increased with increasing treatment temperature. Fe neither adsorbed hydrogen nor showed any activity. The sequence of specific activity (per surface metal atom) was determined as follows: Ru(B), Ru(A)>Ni>Co>Rh>Pd, Pt>IrThe main reaction product was methane, but the hydrocarbon distribution of products varied over a wide range depending more on metal than on treatment temperature. The average molecular weight of product hydrocarbons changed in the following sequence: Ru(B)>Ir>Rh>Ru(A), Ni, Co>Pt>Pd.