III International Conference

PP-II-76THE ROLE OF SURFACE VANADIA SPECIES IN BUTANE DEHYDROGENATIONOVER VO X /Al 2 O 3McGregor J., Huang Z., Gladden L.F., Wu Z. 1 , Stair P.C. 1 , Rugmini S. 2 , Jackson S.D. 2University of Cambridge, Dept. of Chemical Engineering, New Museums Site, PembrokeStreet, Cambridge CB2 3RA, UK1 Department of Chemistry, Northwestern University, IL 60208, USA2 WestCHEM, Dept. of Chemistry, University of Glasgow, Glasgow G12 8QQ, UKE-mail: jm405@cam.ac.ukThe dehydrogenation of butane has been studied over a series of VO x /Al 2 O 3 catalysts.Through the use of a broad range of techniques the activity and selectivity of the catalysts hasbeen related to vanadium and aluminium species present on the catalyst surface. The catalystshave been investigated throughout the reaction cycle: fresh catalyst, calcination, reaction andregeneration. It is shown that isolated VO x species are highly efficient with respect to cokeformation. An understanding of the role played by different surface species will facilitate thedevelopment of catalysts of higher activity and selectivity.Vanadium catalysts are an important class of industrial materials, showing highselectivity in a number of reactions including the selective dehydrogenation of butane tobutenes and butadienes [1, 2]. This reaction is of key industrial importance in, e.g. producingthe precursors for synthetic rubber manufacturing. Accordingly a large number of studieshave been conducted on this, and related systems. Despite this there remains significantdebate and controversy in the literature as to the basis of this selectivity. Our work aims tounderstand the origin of catalyst activity and selectivity, to both molecular species and to cokeformation. In particular the role played by different surface vanadium species and the reactionconditions which result in their formation has been investigated, with the ultimate aim oftailoring catalysts to achieve high activity and 100 % selectivity.A number of different techniques have been employed through the collaborative effort ofthree institutions. These include catalytic reactor studies, TEOM, TPO, TGA, TPR and XRDin addition to UV-vis, 13 C-, 51 V- and 27 Al-MAS NMR and Raman spectroscopies, see e.g. [3].Raman spectroscopy has been used, for the first time, to quantify the vanadium speciespresent in a number of VO x /Al 2 O 3 catalysts differing only by their vanadium loading. In thiswork catalysts with loadings of 1, 3.5 and 8 wt.% vanadium (1V, 3.5V and 8V respectively)have been studied. Additionally, the Al sites present have been characterised by 27 Al MASand 27 Al MQMAS NMR.302