Highly selective CO removal by sorption enhanced Boudouard reaction for hydrogen production

Abstract

The development of an energy-efficient and cost-effective technology for the purification of a hydrogen rich stream to achieve a CO concentration below 10 ppm, suitable for low temperature fuel cell applications, is one of the major objectives of energy research. Here we report the sorption enhanced Boudouard (SEB) reaction as an effective route for pure hydrogen production on metal-free catalysts by the highly selective removal of CO and CO₂ from a hydrogen rich stream, where CaO serves as both a catalyst and a CO₂ sorbent. We reveal that the in situ generated oxygen vacancy by CO adsorption on CaO catalyzes the sorption enhanced Boudouard reaction, hence the Boudouard reaction and CO₂ removal occur simultaneously in a single step. The capture of CO₂ in the presence of H₂ by the solid sorbent shifts the chemical equilibrium towards complete CO conversion. The results demonstrate a remarkable decrease in the CO concentration from 0.5% in a hydrogen rich stream to less than 5 ppm, suitable for low temperature fuel cells. It avoids a subsequent preferential oxidation process or methanation reaction, as well as an additional CO₂ capture process. The feasibility of applying the sorption enhanced Boudouard reaction in the production of highly pure hydrogen (CO content less than 10 ppm) was demonstrated by multicycle tests of Boudouard-carbonation/regeneration on Ca-based oxides with stable cyclic operation.