Recent studies on acid and redox catalyses of heteropoly compounds in both homogeneous and heterogeneous systems are reviewed. Acid and redox properties of heteropoly compounds are briefly summarized.
Recent applications of heteropolyacids to homogeneous acid-catalyzed reactions such as polymerization of tetrahydrofuran, glucoside synthesis, and aldehyde trimerization are interesting. In heterogeneous system, an insoluble acidic Cs salt, Cs_2.5H_0.5PW₁₂O₄₀, is much more active for liquid phase alkylation than Nafion, HY-zeolite, H-ZSM-5, and SO₄^2-/ZrO₂. Pseudoliquid phase behavior of H₃PW₁₂O₄₀ brings about a high activity for alkylation of phenol.
Homogeneous oxidation using molecular oxygen and phase-transfer catalysts for oxidation using H₂O₂ are attractive. In heterogeneous oxidations, the catalytic properties of oxidation of aldehyde and oxidative dehydrogenation has been explained by the concept of the surface-type and bulk-type (II) reactions.
Finally, catalyses of novel types of complexes with organometallics and combination system with transition metals are described with respect to oxidation of olefins, hydroformylation, and reductive carbonylation.