INVESTIGATION OF SURFACE PHENOMENA ON SOLID CATALYSTS BY THERMOGRAVIMETRY I. METHYL ALCOHOL AND CUMENE ON THE SURFACE OF ZEOLITES AND SILICA GELS TREATED WITH SODIUM HYDROXIDE

Thermogravimetry was applied to the investigation of the phenomena of adsorption, chemisorption, desorption and surface reactions on solid catalysts. The measurements were carried out with 13 NaX and NaY type zeolites and with silica gels treated with sodium hydroxide, in the presence of cumene and methanol. On the basis of the quantitative results it is possible to give an interpretation of surface phenomena nd to establish the existence of various active centres on the surface of the catalysts. Thermogravimetric measurements have been made on solid catalysts for a number of years. "Fresh " catalysts, that have not taken part in any reaction, and catalysts after reactivation or reaction exhibit quite different characteristics as regards their weight and enthalpy changes. These differences are brought about on the whole by the loss of water and by the precipitation of polymerized, carbon-ized or irreversibly adsorbed substances on the surface. In this work, thermogravimetry was selected as the method of studying sorption and chemical processes on the surfaces of catalysts during catalytic reactions. It was assumed necessary to measure simultaneously the weight and enthalpy changes of the system under investigation and to use conditions which could reveal individual phases and elemental processes. This was found possible after changes were made in the measurement techniques. This article presents the first results obtained for reactions of cumene or methanol on zeolites of NaX and NaY type, and on silica gels treated with sodium hydroxide