NATURE OF THE ACTIVE AND SELECTIVE SITES IN VANADYL PYROPHOSPHATE, CATALYST OF OXIDATION OF N-BUTANE, BUTENE AND PENTANE TO MALEIC-ANHYDRIDE

VPO catalysts are able to yield maleic anhydride from n-butenes, n-butane and n-pentane, and even phthalic anhydride in the last case. The active and selective phase was identified as (VO)2P2O7 in the case of butane and pentane. The main results and correlations found in the literature and in our own work provide information on the nature of the active sites. and on the way they act selectively. The structural properties required to oxidize butene (olefin) and butane (alkane) are compared. The main conclusions obtained by application of the Crystallochemical Model of Active Sites to the oxidation of n-butane, account for the specificity of the surface structure which influences the development of the selective reaction.