DETERMINATION OF THERMODYNAMIC PARAMETERS FOR THE DISSOCIATIVE ADSORPTION OF DIHYDROGEN ON RH AL2O3/

High-pressure infrared spectroscopy has been used to study the interac tion of H-2 with Rh/Al2O3 catalyst films as a function of temperature and pressure. The interaction process was found to be dissociative and fit Langmuir adsorption isotherms. Two dissociative Langmuir models w ere employed in fitting the data. A model in which reversible dissocia tion of H-2 on Rh, together with reversible H spillover to react with hydroxyl groups on the Al2O3 support was included, provided a DELTAH(a ds) of -7.7 kcal mol-1 for the process. This low enthalpy of adsorptio n is indicative of weak Rh-H bonding and may explain why Rh functions well as a hydrogenation catalyst. This work demonstrates the utility o f Fourier transform infrared spectroscopy in obtaining thermodynamic d ata for supported catalysts.