STRUCTURE AND ACTIVITY OF COMPOSITE OXIDE-SUPPORTED IRIDIUM AND PLATINUM CATALYSTS

The objective of this study is to investigate the structure and activity of composite oxide (Al2O3TiO2 and TiO2Al2O3)-supported Pt and Ir catalysts. Two characterization techniques, temperature-programmed reduction/temperature-programmed desorption (TPRd/TPD) and ethane hydrogenolysis were used. TPRd/TPD provided information on the structure of the catalyst whereas ethane hydrogenolysis provided information on the structure and activity. The TPRd, TPD, and ethane hydrogenolysis results suggest that two processes, Al3+ dissolution in acidic impregnation solutions and TiOx overlayer formation occurring in reducing environments affect the structure and activity of these catalysts. Specifically, the TPRd results indicate that the readsorbed Al3+ species inhibits the amount of chloride liberated during calcination; this results in an increase in the amount of hydrogen consumed during reduction. The TPD results suggest that TiOx overlayer formation occurs in the case of composite oxides. The readsorbed Al3+ increases the hydrogenolysis activity of these catalysts. The intimate association of the noble metal and Al3+ suggests that alloys of the form Pt3Al and IrAl may exist on the surface of the Pt and Ir catalysts. These factors have been considered and models for the structures of these catalysts have been proposed. © 1991.