Hydrothermal synthesis of cuV(2)O(6) supported on 3-D ordered mesoporous SiO2 (CuV/SiO2) was studied to evaluate the catalytic activity for SO3 decomposition, which is a key step in solar thermochemical hydrogen production. A composite oxide hydrate, Cu3O(V2O7)center dot H2O, and an oxide hydroxide hydrate, Cu-3(OH)(2)V2O7 center dot(H2O)(2), were formed at lower hydrothermal temperatures (<= 200 degrees C). The oxide hydrate phase mainly yielded Cu2V2O7 after calcination at 600 degrees C in air. By contrast, the hydrothermal synthesis at 250 degrees C (CuV/SiO2@250) directly crystallized cuV(2)O(6) from the oxide hydroxide hydrate, although its very large particle size (similar to 5 mu m) is not suitable for the catalytic application. The SO3 decomposition activity measured at 600 degrees C was associated with the yield as well as the dispersion of cuV(2)O(6), giving rise to the maximum for the hydrothermal synthesis at 200 degrees C. CuV/SiO2@250 achieved the highest catalytic activity at the reaction temperature of 650 degrees C, because the melting phase of cuV(2)O(6) penetrated mesoporous SiO2 and thus improved the dispersion of the active phase. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.