Being a relatively new but quite promising field in CSP, thermochemical energy storage could be the next generation solution towards the implementation of baseload cost-effective solar thermal plants. The present work, taking place within the framework of EU-funded project PEGASUS, aims at synthesizing, shaping and experimentally evaluating the catalytic activity and main physicochemical attributes of Fe2O3−based particles. These particles can be exploited as both heat transfer fluid of the CSP plant and highly active catalysts for the key step of the SO3 dissociation reaction to produce SO2 and O2 in the framework of a solid sulfur thermochemical energy storage cycle. The experimental campaign takes place in a purpose-built setup used to evaluate the materials in a fixed bed reactor formulation at a temperature of 850°C and ambient pressure while concentrated liquid sulfuric acid (H2SO4) was used as feedstock. Based on the findings, pure Fe2O3 particles sintered at 950°C offered the most promising compromise between high SO3 conversion on the one hand and crushing strength value (i.e. a preliminary measure of thermomechanical stability) and particles’ color before and after exposure at reaction conditions on the other hand.