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 H-2 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 (similar to 600 degrees 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 degrees C) of the present system. (C) 2014 Elsevier B.V. All rights reserved.