Aluminum sulfate salt hydrate was dispersed on two different porous supports (MCM-41 and SBA-15) presenting a hydrophobic behavior at low relative humidity (P/P-0 <= 0.3) with the objective to increase the energy density of the formed composites compared to pure host materials. Two different series of composite materials (MCM-41(Al-2)(x) and SBA-15(Al-2)(x)) with 3, 5 and 7 wt% of aluminum sulfate were prepared by wetness impregnation method and tested for thermochemical heat storage at low temperature. The dehydration heats, the water sorption capacities and the physicochemical characteristics have been determined for both series of composites. MCM-41(Al-2)(x) and SBA-15(Al-2)(x) composites exhibit much higher sorption capacities (up to 0.17 and 0.09 kg(H2O) kg(-1) respectively) than those observed for pure host materials, 0.04 and 0.02 kg(H2O) kg(-1) respectively for MCM-41 and SBA-15 at P/P-0=0.3. These improved results were clearly linked to the interaction of water vapor with the confined salt. Water was found to be sorbed by the impregnated salt rather than by the host matrix. The textural properties such as specific surface area, pore size distributions and pore volumes are the most relevant properties of these materials in relation with their potential use. The best performance was observed for MCM-41(Al-2)(7) composite with 612 kJ kg(sample)(-1). This encouraging result indicates that it is possible to use MCM-41(Al-2)(x) and SBA-15(Al-2) composites at low water vapor pressure for thermochemical heat storage purposes. (C) 2016 Elsevier B.V. All rights reserved.