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

摘要

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 H_3PO_4. Vanadium was then incorporated by chemical grafting with a VOCl_3 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 C_2H_6 oxydehydrogenation reaction. It was shown that a part of vanadium segregates as V_2O_5 in the V/TS3 sample, while Sn segregation occurs in V/TS0.5 and this system shown no formation of V_2O_5 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 V/TS0.5 system displayed the best performance. Selectivity for dehydrogenation decreased only slightly with increasing ethane conversion, whereas the selectivity to CO_2 increased to the detriment of the selectivity to C_2H_4 because CO selectivity remained close to zero. The high selectivity to C_2H_4 along the C_2H_6 interval explored appears to be related to highly dispersed vanadium species on the catalyst surface.