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 salts with H3PO4. Vanadium was then incorporated by chemical grafting with a VOCl3 precursor up to levels of 2% vanadium. Both the tin-titanium phosphates (TS) and their V-loaded counterparts (V/TS3 and V/TS0.5) were characterized by X-ray diffraction, Raman spectroscopy, differential scanning calorimetry and X-ray photoelectron spectroscopy, and their reactivity was tested for the C2H6 oxydehydrogenation reaction. It was shown that a part of vanadium 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 TS and V/TS systems were found to be active for this reaction, although significant differences were observed depending on the crystallinity and surface enrichment of tin. The VITS0.5 system displayed the best performance. Selectivity for dehydrogenation decreased only slightly with increasing ethane conversion, whereas the selectivity to CO2 increased to the detriment of the selectivity to C2H4 because CO selectivity remained close to zero. The high selectivity to C2H4 along the C2H6 interval explored appears to be related to highly dispersed vanadium species on the catalyst surface. (C) 2000 Elsevier Science Ltd. All rights reserved.