Design and tailoring A- and B-site of Fe-based perovskites as novel oxygen carriers for Hydrogen production in chemical looping processes

Abstract

The pursuit for sustainable hydrogen (H2) production whilst minimising by-products formation has led to the development of new technologies such as chemical looping (CL). Chemical looping water-gas shift (CLWGS) allows for clean H2 production from steam whilst producing carbon dioxide (CO2) from carbon monoxide (CO) in the following gas stream, facilitating a route for CO2 capture. This process requires CO as feedstock, currently derived from methane (CH4). Chemical looping steam reforming of methane (CLSRM) generates syngas (H2 + CO), serving this CO as a reactant in the subsequent process of CLWGS, achieving up to 4 moles of H2 per mole of CH4 fed in the overall process. This thesis focuses on the design, synthesis, and characterisation of novel oxygen carrier materials (OCM) for H2 production via CLWGS and CLSRM. Initial results of this project were based on Pr0.5Ba0.5FeO3-δ and Sm0.5Ba0.5FeO3-δ as OCM. These materials exhibited higher oxygen capacity than established benchmark materials. Under CLWGS conditions, Pr0.5Ba0.5FeO3-δ showcased a sustained higher H2 production and a steam conversion rate of around 40% for 400 cycles. Further study involved the subsequent tailoring of Pr0.5Ba0.5FeO3-δ for CLSRM, consisting of Ni-doping to promote CH4 activation and A-site deficiency to facilitate exsolution of nanoparticles, yielding (Pr0.5Ba0.5)0.9Fe0.9Ni0.1O3-δ. This OCM resulted in high stability and high syngas selectivity towards syngas due to the formation of a FeNi alloy. The formation of this alloy was monitored via operando Powder X-Ray Diffraction at ESRF. OCM were tested in CLSRM over 400 cycles, underscoring their high stability and suitability for sustained H2 production. Moreover, the initially designed materials and their Ni-doped analogues were effective in the catalytic process of reverse WGS. The Ni-doped OCM displayed high CO selectivity even at low temperatures, underscoring their suitability for high-selectivity catalytic applications. The proposed materials not only are of interest for sustained clean H2 in CL process but also possess remarkable catalytic reverse Water-Gas Shift capabilities.