Nowadays, thermochemical storage systems show high theoretical energy performances and are even considered as more appropriated than sensible or latent storage systems, especially for long-term thermal storage. Nevertheless, in thermochemical reactor, agglomeration phenomenon caused by the formation of hydrates on the surface layer of the bulk salt usually occurs. To counteract this negative effect, composite materials composed by a porous matrix with impregnated salts are under investigation. The present contribution focuses on the LaCl3 , which is one of the most promising salts, in order to provide a better understanding of its energetic properties. First studies were carried out at the salt crystal scale and then at larger scale of the thermochemical reactor with impregnated matrix. Studies of LaCl3 crystal provide the thermodynamic equilibrium and the reactor scale highlights temperature distribution and humidity variations during storage/release of heat.