Catalysis by Heteropoly Compounds. III. The Structure and Properties of 12-Heteropolyacids of Molybdenum and Tungsten (H3PMo12−xWxO40) and Their Salts Pertinent to Heterogeneous Catalysis

The fundamental properties of 12-heteropolyacids of Mo and W, such as the structure, the surface area, the acidity, and the reduction-oxidation mechanism, have been studied in their solid state in relation to heterogeneous catalysis. The primary structure (heteropolyanion) was rather stable, but the secondary structure was very variable according to the interaction with various molecules, like water, alcohols, ketones, and pyridine. This structural characteristic is important for the understanding of the catalysis of these compounds; it may be called the “pseudo-liquid phase.” The heteropolyacids were all strong protonic acids, as revealed by the interaction with pyridine. The redox cycle was reversible within a limited extent of reduction. The redox mechanism is also discussed in this paper.