Structured sulphur trioxide splitting catalysts in the context of a solid sulphur-based thermochemical cycle for solar thermal energy storage

Abstract

This work is part of a wider project, aiming to demonstrate an innovative approach for the direct storage of solar energy in solid elemental sulphur. The basic idea is to use renewable heat from concentrated solar energy to cyclically drive a series of chemical reactions that interconvert sulphuric acid and sulphur. Among these reactions, the two-step sulphuric acid splitting, first to steam and sulphur trioxide and subsequently of the latter to sulphur dioxide and oxygen, is the highest-temperature (650-1000oC) endothermic step of the cycle. The heat needed can be supplied by Concentrating Solar Technologies (CST) since these tempera-tures are within the capabilities of state-of-the-art CST tower plants. The current work pre-sents an integrated approach on catalytic sulphur trioxide splitting (STS) within this perspec-tive. Iron oxide-based compositions - which are the state-of-the-art inexpensive STS catalytic materials investigated - were synthesized, shaped into spherical granules and their perfor-mance was experimentally evaluated. Shortlisted powders were subsequently shaped into larger-size honeycombs that underwent 50 h on stream catalytic testing in a suitably designed test rig and were physico-chemically characterised before and after exposure to the reaction environment. Tested honeycomb specimens demonstrated not only close-to-equilibrium con-version but also phase composition stability and remarkable corrosion resistance.