Dependence of n -Butane Activation on Active Site of Vanadium Phosphate Catalysts
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Dependence of n-Butane Activation on Active Site of Vanadium Phosphate Catalysts Y. H. Taufiq-Yap Æ C. K. Goh Æ G. J. Hutchings Æ N. Dummer Æ J. Bartley
Received: 6 March 2009 / Accepted: 24 April 2009 / Published online: 27 May 2009 Ó Springer Science+Business Media, LLC 2009
Abstract The nature and the role of oxygen species and vanadium oxidation states on the activation of n-butane for selective oxidation to maleic anhydride were investigated. Bi–Fe doped and undoped vanadium phosphate catalysts were used a model catalyst. XRD revealed that Bi–Fe mixture dopants led to formation of aII-VOPO4 phase together with (VO)2P2O7 as a dominant phase when the materials were heated in n-butane/air to form the final catalysts. TPR analysis showed that the reduction behaviour of Bi–Fe doped catalysts was dominated by the reduction peak assigned to the reduction of V5? species as compared to the undoped catalyst, which gave the reduction of V4? as the major feature. An excess of the oxygen species (O2-) associated with V5? in Bi–Fe doped catalysts improved the maleic anhydride selectivity but significantly lowering the rate of n-butane conversion. The reactive pairing of V4?-O- was shown to be the centre for n-butane activation. It is proposed that the availability and appearance of active oxygen species (O-) on the surface of
Y. H. Taufiq-Yap C. K. Goh Centre of Excellence for Catalysis Science and Technology, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia Y. H. Taufiq-Yap (&) C. K. Goh Department of Chemistry, Faculty of Science, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia e-mail: [email protected] G. J. Hutchings N. Dummer J. Bartley Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
vanadium phosphate catalyst is the rate determining step of the overall reaction. Keywords Vanadium phosphate n-Butane oxidation Vanadium Oxygen species Maleic anhydride Activation
1 Introduction Selective oxidation catalysis involved in many productions of important products in petrochemical industry. Among them is the manufacturing of maleic anhydride (MA) from well-known n-butane oxidation over vanadium phosphate (VPO) catalyst. The active phase claimed for this catalyst is vanadyl pyrophosphate, (VO)2P2O7. Several promoters have been incorporated in this catalyst in order to modify the catalytic performance. This reaction is the most complicated in selective oxidation process since it involved the largest amount of electrons (14 electrons). Several steps take place in the overall process where the first step, i.e. the abstraction of hydrogen from saturated hydrocarbon is the most critical. This is due to the highly stable C–H bond of light hydrocarbon. Other steps are oxidative dehydrogenation of alkene, insertion of oxygen to form oxidized products, activation of molecular oxygen, etc. [1, 2]. The aim of our present work is to identify the essential factor for butane activation which involved the nature and the specific role of different vanadiu
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