Vanadium oxide loaded tin-titanium phosphates Surface structures and performance for the oxidative dehydrogenation of ethane

Mixed crystalline tin-titanium phosphates with nominal Ti:Sn ratios of 0.5 and 3.0 have been prepared by precipitation of Sn(IV) and Ti(IV) soluble sa lts with H3PO4. Vanadium was then incorporated by chemical grafting with a VOCl3 precursor up to levels of 2% vanadium. Both the tin-titanium phosphat es (TS) and their V-loaded counterparts (V/TS3 and V/TS0.5) were characteri zed by X-ray diffraction, Raman spectroscopy, differential scanning calorim etry and X-ray photoelectron spectroscopy, and their reactivity was tested for the C2H6 oxydehydrogenation reaction. It was shown that a part of vanad ium segregates as V2O5 in the V/TS3 sample, while Sn segregation occurs in V/TS0.5 and this system shown no formation of V2O5 crystallites. Both the T S and V/TS systems were found to be active for this reaction, although sign ificant differences were observed depending on the crystallinity and surfac e enrichment of tin. The VITS0.5 system displayed the best performance. Sel ectivity for dehydrogenation decreased only slightly with increasing ethane conversion, whereas the selectivity to CO2 increased to the detriment of t he selectivity to C2H4 because CO selectivity remained close to zero. The h igh selectivity to C2H4 along the C2H6 interval explored appears to be rela ted to highly dispersed vanadium species on the catalyst surface. (C) 2000 Elsevier Science Ltd. All rights reserved.