Selective oxidation of hydrocarbons catalyzed by heteropoly compounds

Abstract

Publisher Summary This chapter describes selected characteristic features of heteropoly catalysts for the selective oxidation of hydrocarbons based on recent studies. A crystalline vanadium phosphorous oxide may be regarded in a broad sense to be a heteropoly compound. The chapter establishes fundamental correlations between redox properties and catalytic activity for the hydrogen form and alkali salts of 12-molybdophosphoric acid. It has also been reported that the hydrogen form of H 3 PMo 12 O 40 catalyzes the oxidation of lower alkanes to aldehydes and carboxylic acids and that the substitution of V 5+ for Mo 6+ modifies the catalytic activity and selectivity. It has been found that acidic cesium salts of Keggin-type heteropolymolybdates can efficiently catalyze the oxidation of isobutane to methacrylic acid with molecular oxygen. Various oxidants, such as dioxygen, hydrogen peroxide, and alkyl hydroperoxides, have been applied for the oxidation of hydrocarbons in the homogeneous liquid phase catalyzed by heteropoly catalysts. The chapter also discusses the results on the selective hydroxylation of benzene to phenol with H 2 O 2 catalyzed by Keggin-type heteropolyanions. It has been showed that the structures of the Keggin polyanions remained unchanged during the reaction. By choosing appropriate vanadium-substituted heteropolymolybdates and keeping the concentration of H 2 O 2 low, efficient hydroxylation of benzene to phenol has been achieved.