HYDROGENOLYSIS OF ALKANES .7. HYDROGENOLYSIS OF PROPANE AND OF NORMAL-BUTANE OVER IR/TIO2 AND OS/TIO2 CATALYSTS

The rates of hydrogenolysis of propane and of n-butane on Ir/TiO2 catalysts made by reduction at 758 K (HTR1) of IrCl3/TiO2 are much increased (by factors of up to 200 and 500, respectively) by oxidation, and a low-temperature reduction at 433 K (LTR). This procedure removes TiO(x) species from the surface of the Ir particles, but they can re-form in a second high-temperature reduction (HTR2). These large changes in rate are not, however, accompanied by any significant alteractions in product selectivities: ethane selectivities, S2, are always high (1.35-1.5), this being characteristic of well dispersed Ir and small active centres. After LTR, rates per g Ir increase with Ir concentration. With Os/TiO2 catalysts, the oxidation/LTR pretreatment does not result in an enhancement of rate; indeed, the highest rates are found after HTR1. This may be because Os experiences a strong metal-support interaction (SMSI) even during reduction at 433 K. The significance of product selectivities is obscured by the formation of carbonaceous residues.