Abstract

V- and/or Co-containing aluminophosphates with AEI structure (CoAPO-18, VAPO-18 and VCoAPO-18) have been prepared by hydrothermal synthesis, characterized by several physicochemical techniques ( S BET, thermogravimetric analysis, XRD, solid state MAS NMR, UV–vis, EPR, TPD), and tested in the oxidative dehydrogenation of ethane. The results obtained by the spectroscopic techniques employed here suggest that V (V 5+ and VO 2+) and Co 2+ atoms are isomorphically incorporated into the aluminophosphate framework, although some vanadium is involved in an extraframework oxide, especially at high contents. Upon calcination in air of the V, Co-containing samples with the AEI structure, most vanadium and cobalt oxidate to V 5+ and Co 3+ and present redox activity, while only Co-containing materials posses acid properties. Comparison with Co-containing AlPO-5 evidences that the strength of acid sites depends on the framework structure. VCoAPO-18 catalysts are active and selective in the oxidative dehydrogenation of ethane with selectivities to ethylene higher than the corresponding VAPO-18 or CoAPO-18. The catalytic results give evidence of the incorporation of V and Co into the AlPO-18 structure, and the segregation of an oxide phase in V-rich samples. The V- and/or Co-containing AlPO-18 are more selective in the ODH of ethane than the corresponding materials with AFI structure (i.e. VCoAPO-5, VAPO-5 or CoAPO-5).

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