ABSTRACT
Abstract The effect of the main characteristics of vanadyl pyrophosphate, (VO)2P2O7, on catalytic performance in the gas-phase oxidation of n-pentane to maleic and phthalic anhydrides, has been investigated. A relationship was found between the distribution of products, and the oxidation state of V in catalysts. Higher concentrations of more oxidant V5+ sites in vanadyl pyrophosphate led to the preferred formation of maleic anhydride, while samples having average V valence state close to 4.0+ were the most selective to phthalic anhydride. The latter samples were also those characterized by the higher Lewis-type acid strength. In the reaction mechanism, including the competitive pathways leading either to maleic anhydride through O-insertion onto activated n-pentane, or to phthalic anhydride through the acid-assisted dehydrocyclodimerization to an intermediate C10 alkylaromatic compound, precursor of phthalic anhydride, the balance of oxidizing sites and Lewis-type acid sites controlled the selectivity to the main products. Introduction One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to
methacrylic acid, and others as well. In some cases, this activity has led to the successful development of new industrial processes.
