Catalytic Aluminas I. Surface Chemistry of Eta and Gamma Alumina

Abstract Surface properties of well-characterized samples of eta and gamma alumina were studied and compared by means of gas adsorption and immersion calorimetry. From the results obtained, it was concluded that the surface chemistry of an alumina sample may depend to a pronounced degree upon the structure or “type” of alumina being considered. Gamma alumina differed from eta alumina, not only in its pore-size distribution, but also in the fact that the water content of gamma alumina was much greater than that of eta alumina. This “excess” water associated with gamma alumina was regarded as consisting of molecular water strongly adsorbed on the surface of the alumina. Both types of alumina developed surface acidity as they were heated at temperatures up to 900 °C, but the strengths of the acid sites were greater in the case of eta alumina.