A new approach to the study of the reactivity of solid-acid catalysts: Theapplication of constant rate thermal analysis to the desorption and surface reaction of isopropylamine from NaY and HY zeolites

A new and potentially valuable approach to the study of the acidity and rea ctivity of the surfaces of,solid acid materials is described. The technique uses a combination of constant rate thermal analysis (CRTA) with the rate jump technique (CRTA-RJ) for temperature programmed desorption (TPD) and re action (TPRx). CRTA, where the sample temperature is changed to force the r ate of reaction to remain constant through a process, offers a number of ad vantages over conventional linear heating thermal methods by minimizing tem perature and concentration gradients in the sample and reducing the effects of diffusion. CRTA and CRTA-RJ were applied to the TPD and TPRx of isoprop ylamine from NaY zeolite and its acidic form, HY. Activation energies of bo th the physical desorption of the amine and the surface-catalyzed Hoffman e limination reaction were calculated as a function of surface coverage and t he advantages and Limitations of the techniques are discussed. Comparisons are made with analogous TPD experiments using conventional linear heating m ethods. It is concluded that the TPR, approach reflects the reactivity of s trong acidic catalytic sites directly and so usefully complements base adso rption microcalorimetry in characterizing acid solid catalysts.