THERMODYNAMICS OF ADSORPTION OF ORGANIC VAPORS ON METAL-LOADED ACTIVE-CARBON

The influence of active carbon as support on the reducibility of supported metals (Ni, Cu, Zn, and Cd) has been studied by temperature programmed reduction (TPR). TPR profiles indicate that active carbon acts as a dispersing agent and that it enhances the reduction of the supported metals. High-temperature reduction peaks are explained on the basis of metal-surface interactions and of the porosity of the active carbon. DR analysis of nitrogen adsorption isotherms indicates that the microporosity of the active carbon decreases due to a progressive closure of micropores as the metals are supported on the surface of the carbon. The effect of doped metals on the adsorbing behavior of active carbon for different organic vapors has been studied as a function of temperature. From adsorption data, thermodynamic parameters such as free energy, enthalpy, and entropy of adsorption are computed using a virial isotherm expression and are interpreted. The results show that an increase in the adsorption affinity of organic vapors active carbon/metal dopant systems is not due to configurational factors affecting the entropy of adsorption, but to an enhanced enthalpy of adsorption.