STUDIES ON RUTHENIUM CATALYSTS .4. HYDROGENOLYSIS OF N-BUTANE ON RU/AL2O3 CATALYST-DEPENDENCE OF REACTION-KINETICS ON PARTICLE-SIZE AND ON PRETREATMENT

Turnover frequencies (TOF) for hydrogenolysis of n-butane on Ru/Al2O3 catalysts, measured with a 10-fold excess of H-2, depend on dispersion and on pretreatment. After a first high-temperature reduction at 753 K (HTR1), 1% Ru/Al2O3 showed high dispersion and moderate activity; oxidation at 623 K followed by reduction at 433 K caused dispersion to decrease, and rates and TOFs to increase. However, the magnitude and even the sign of the effects depended on the H-2 Pressure used, because the form of the rate dependence on H-2 PreSSUre changed significantly. Many of the discrepancies in the literature concerning particle size effects may originate in the use of different conditions for measuring rates and of different pretreatments. Alterations in the form of the dependence of rates and of product selectivities on H-2 pressure suggest that ''structure sensitivity'' in these systems may in fact be due to variations in the strength of H-2 chemisorption.