Pilot-scale evaluation of Fe₂O₃-MgAl₂O₄ extrudates for chemical looping reverse water-gas shift reaction: performance and mechanical integrity

Tackling industrial CO₂ emissions demands advanced technologies that enable the scalable conversion of CO₂ into value-added products, thereby mitigating climate impacts and supporting sustainable chemical production. This study presents a detailed pilot-scale experimental assessment of the chemical looping reverse water-gas shift (CL-rWGS) process, employing up to 3.5 kg of 50 wt% Fe₂O₃-MgAl₂O₄ oxygen carrier in a packed-bed reactor. Three different reactor beds were operated under cyclic redox conditions to evaluate CO₂ conversion, productivity, and long-term material performance across a range of temperatures, reduction durations, and bed dilutions. Countercurrent operation mode consistently outperformed cocurrent mode, achieving CO₂ conversions up to 73%, well above the gas-phase equilibrium, which limits catalytic rWGS, while meeting industrial productivity benchmarks (> 100 kg CO m⁻³ h⁻¹). Nevertheless, undiluted oxygen carrier beds experienced rising pressure drops up to 8.4 bar observed after 85 h, linked to carbon accumulation, sintering, and redox-induced stresses, whereas diluted bed configurations maintained mechanical stability while avoiding pressure build-up. In contrast, catalytic rWGS tests showed lower activity (23% CO₂ conversion) and CO selectivity, along with trace CH₄ formation. Temperature-programmed analyses revealed incomplete reduction and potential sintering at lower temperatures, whereas higher temperatures improved redox kinetics. Mechanical testing and micro-computed tomography showed that prolonged CL-rWGS operation caused irreversible mechanical weakening of the oxygen carrier, including substantial strength loss, and pronounced pore restructuring with surface cracking and reduced internal porosity driven by sintering and outward cation diffusion. Overall, the findings demonstrate that Fe-based CL-rWGS enables efficient and stable CO₂ conversion at scale, provided that carbon formation and the mechanical integrity of the oxygen carrier bed are effectively controlled.