ENTHALPY AND ENTROPY OF H2 ADSORPTION ON RH/AL2O3 MEASURED BY TEMPERATURE-PROGRAMMED DESORPTION

Temperature-programmed desorption spectroscopy under pseudo-equilibrium conditions has been used to obtain the coverage dependence of the heat and entropy of hydrogen adsorption for a 5-wt% Rh/Al2O3 catalyst. This method is considered to be more convenient than volumetric or flow methods. The latter require more effort to obtain various isotherms and isobars, from which the heat and entropy of adsorption are obtained in a manner similar to that in this study. Extrapolation of the heat and entropy of adsorption to zero coverage yields values of 24 kcal/mol and 38 cal/mol-K, respectively. For the former value, a binding energy of 64 kcal/mol is obtained, which is comparable to reported values for a polycrystalline Rh surface. © 1990.