Catalysis of Organic..

Bacchini et al . 10914. The Transformation of Light Alkanes toChemicals: Mechanistic Aspects of the Gas-phaseOxidation of n-Pentane to Maleic Anhydride andPhthalic AnhydrideMirko Bacchini 1 , Nicola Ballarini 1 , Fabrizio Cavani 1 , Carlotta Cortelli 1 ,Stefano Cortesi 1 , Carlo Fumagalli 2 , Gianluca Mazzoni 2 , Tiziana Monti 2 ,Francesca Pierelli 1 , Ferruccio Trifirò 11 Dipartimento di Chimica Industriale e dei Materiali, Viale Risorgimento 4, 40136Bologna, Italy. INSTM, Research Unit of Bologna.A member of the Concorde CA and Idecat NoE (6FP of the EU)2 Lonza SpA, Via E. Fermi 51, 24020 Scanzorosciate (BG), ItalyAbstractfabrizio.cavani@unibo.itThe effect of the main characteristics of vanadyl pyrophosphate, (VO) 2 P 2 O 7 , oncatalytic performance in the gas-phase oxidation of n-pentane to maleic and phthalicanhydrides, has been investigated. A relationship was found between the distributionof products, and the oxidation state of V in catalysts. Higher concentrations of moreoxidant V 5+ sites in vanadyl pyrophosphate led to the preferred formation of maleicanhydride, while samples having average V valence state close to 4.0+ were the mostselective to phthalic anhydride. The latter samples were also those characterized bythe higher Lewis-type acid strength. In the reaction mechanism, including thecompetitive pathways leading either to maleic anhydride through O-insertion ontoactivated n-pentane, or to phthalic anhydride through the acid-assisteddehydrocyclodimerization to an intermediate C 10 alkylaromatic compound, precursorof phthalic anhydride, the balance of oxidizing sites and Lewis-type acid sitescontrolled the selectivity to the main products.IntroductionOne of the most important challenges in the modern chemical industry is representedby the development of new processes aimed at the exploitation of alternative rawmaterials, in replacement of technologies that make use of building blocks derivedfrom oil (olefins and aromatics). This has led to a scientific activity devoted to thevalorization of natural gas components, through catalytic, environmentally benignprocesses of transformation (1). Examples include the direct exoenthalpictransformation of methane to methanol, DME or formaldehyde, the oxidation ofethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propaneto acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to