Acid-base properties of Al2O3: Effects of morphology, crystalline phase, and additives

Abstract

The acid-base properties of Al2O3 with various surface characteristics were studied by XRD, HR-TEM, ethanol TPD, and ethanol dehydration reaction rate measurements. Ethanol TPD showed that the desorption temperature (at maximum rate of ethylene desorption, Td) of dissociative ethanol was significantly dependent on morphology, crystalline phase, and additives. Ethylene formation rates, normalized with respect to the amount of dissociative ethanol (quantified by ethanol TPD), exhibited an inverse correlation with Td on Al2O3 with various morphologies, crystalline phases, and additives, which suggests that Td can be used as a descriptor for acid-base properties of Al2O3, irrespective of modification origins. This also indicates that the dissociative ethanol (ethoxide) is the key intermediate of ethylene formation during ethanol dehydration on Al2O3. The activities and activation barriers of commercial Al2O3 were consistent with our empirical model. This fundamental understanding of the acid-base properties of alumina is helpful for the further development of new catalysts with better activity and selectivity.