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We report the structure–activity relationship of copper pyrovanadate (Cu2V2O7) as an efficient catalyst for SO3 decomposition in solar thermochemical water splitting cycles. Of the α, β, and γ polymorphs of Cu2V2O7, the α-phase, which has a blossite-type structure, was stable under the catalytic reaction conditions. Spontaneous oxygen desorption accompanied by charge compensation through the reduction of Cu2+ to Cu+ produced an oxygen deficiency corresponding to Cu16V16O55 at 600 °C. Density functional theory calculations based on these results showed that oxygen vacancy formation is more favorable on the Cu–O–V bridging sites than on the V–O–V site in the pyrovanadate unit. The oxygen vacancy formation energy of the (100) surface is considerably less than that of bulk Cu16V16O56. The reaction, Cu16V16O55 + SO3 → Cu16V16O56 + SO2, is exothermic, suggesting that oxygen vacancies play a key role in catalytic SO3 decomposition over a Cu2V2O7 catalyst.

SO 3 decompositionThermochemical water splitting Sulfureiodine cycle a b s t r a c t CeeV oxide catalysts supported on bimodal mesoporous SiO 2 were prepared by a wet impregnation method to study their catalytic activity for SO 3 decomposition, which is a key step in thermochemical water splitting cycles based on the sulfureiodine process. Asprepared CeeV/SiO 2 catalysts exhibited more than 50-fold higher turnover frequency at 600 C compared to unsupported CeVO 4 . This is in accordance with the smaller size (13 nm) of CeVO 4 particles highly dispersed in SiO 2 mesopores, compared to approximately 600 nm for unsupported CeVO 4 particles. The CeeV/SiO 2 catalysts exhibited a higher activity than supported V 2 O 5 or CeO 2 catalysts, which coexisted depending on the Ce/V ratio. Among the studied catalysts with different Ce/V molar ratios, the highest activity was achieved at Ce/ V ¼ 0.9, at which the greatest specific surface area of CeVO 4 was attained. The catalyst demonstrated SO 3 decomposition rates comparable to those of Pt/Al 2 O 3 in a wide range of WHSV (3.6e110 g-H 2 SO 4 g À1 h À1 ) and no indication of noticeable deactivation during 40 h of the catalytic reaction at 650 C.