Structure and SO3 decomposition activity of nCuO–V2O5/SiO2 (n = 0, 1, 2, 3 and 5) catalysts for solar thermochemical water splitting cycles

• SiO2-supported nCuO–V2O5 catalysts with different ratios (n) were prepared.
• The catalytic activity for SO3 decomposition was strongly dependent on n.
• The highest activity was achieved for n = 1, the phase with the lowest melting point.
• Melting copper vanadate achieves a high surface coverage of SiO2 porous cavity wall.

SiO2-supported nCuO–V2O5 catalysts with different ratios (n = 0, 1, 2, 3 and 5) were prepared to study their catalytic activity for SO3 decomposition, which is a key reaction necessary for solar thermochemical H2 production. Although four binary compounds, CuV2O6, Cu2V2O7, Cu3V2O8 and Cu5V2O10, were formed on three-dimensional (3-D) mesoporous SiO2 depending on the ratio (n), the thermal ageing caused their incongruent melting and precipitation of Cu2V2O7. The highly corrosive molten vanadate phase resulted in mesopore-to-macropore conversion of SiO2, which was accompanied by significant decrease of BET surface area and pore volume. Nevertheless, the structural conversion yielded copper vanadate with a high surface coverage of SiO2 cavity walls enabling efficient catalytic SO3 decomposition at moderated reaction temperatures (∼600 °C). Among nCuO–V2O5/SiO2 catalysts, the highest catalytic activity was achieved for n = 1, which corresponds to the phase with the lowest melting point (630 °C) of the present system.

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