Catalysis by heteropoly compounds: IX. Role of water in catalytic dehydration of 2-propanol over copper salts of H 3PW 12O 40

Abstract

The catalytic and acidic properties of copper salts of 12-tungstophosphoric acid have been studied. An induction period was observed in the dehydration of 2-propanol and it became longer as the water content decreased. In addition the catalytic activity was enhanced by the addition of water to the feed gas. This catalytic behavior has been explained on the basis of the “pseudo-liquid phase” model as follows. The absorption of 2-propanol into the bulk of the copper salts was accelerated by the presence of water. Thus, the increase of the rate is ascribed to the expansion of the effective reaction zone caused by water-promoted absorption of 2-propanol. Infrared spectroscopy of adsorbed pyridine revealed that the copper salts were strong protonic acids, and the amounts of proton were about one-third that of the acid form. Based on the infrared data of absorbed pyridine and electron spin resonance of Cu 2+, the mechanism for the generation of acidity is discussed.