Nickel-catalyzed simultaneous iron and cerium redox reactions for durable chemical looping dry reforming of methane†

This study investigates the synergistic interaction among elements in nickel–(iron and cerium oxide) for chemical looping dry reforming of methane (CLDRM) at 700 °C to 900 °C. Nickel catalyzes methane conversion to enable simultaneous reduction of iron and cerium. We quantified methane conversion by two co-existing mechanisms: partial oxidation to syngas and pyrolysis to solid carbon and H₂. In the CO₂ step, the bulk interaction between Fe and Ce forms cerium orthoferrite (CeFeO₃) that enhances methane conversion, despite the anomalously reduced Ce³⁺ in the oxidation product, CeFeO₃. An optimal nickel loading enhances methane conversion and CeFeO₃ formation while limiting solid carbon accumulation, and it decreases with increasing CLDRM temperature, because high temperature also facilitates the reactions. The optimal nickel loading in Ni_0.34–(Fe_0.67Ce_0.50O_x)-900 maintained 76% conversion rates for methane and CO₂ over 100 CLDRM cycles at 900 °C, with only 0.26% of the carbon in methane accumulated as solid carbon across the cycles. Highly adjustable syngas ratio is achieved, because methane step generates mostly H₂ while CO is mostly from CO₂ step. Our findings illustrate the mechanisms of the nickel–(iron and cerium oxide) materials for efficient and durable CLDRM, offering valuable insights about mixed catalyst and oxygen carrier material design.