A fixed-bed reactor for methane dry reforming via a ceria-based redox cycle – modeling and experimental validation

This study explores the production of sustainable aviation fuels through the sun-to-liquid pathway, focusing on the thermochemical production of syngas–a mixture of H 2 and CO–using concentrated solar energy. One promising route, termed dry redox reforming, involves the dry reforming of CH 4 via a two-step redox cyclic process using non-stoichiometric ceria (CeO 2 ). This process consists of: (1) the methanothermal reduction of ceria to form syngas; and (2) the oxidation of reduced ceria with CO 2 to form CO. Thermodynamic modeling and fixed-bed tubular reactor simulations of dry redox reforming are presented. Ellingham diagrams and species-temperature diagrams illustrate reaction favourability and equilibrium compositions, detailing how elevated non-stoichiometries improve syngas selectivity. The thermodynamic relations are incorporated into a computational fluid dynamic solver developed within OpenFOAM. The transient solver models a system of reversible heterogeneous reactions and fluid flow over a non-stoichiometric solid oxide as a fixed-bed, accounting for the governing conservation equations in both fluid and solid phases. The model is validated with experiments conducted in a lab-scale tubular reactor ( D fxb = 19 mm, l fxb = 30 cm, 5% educts, V ˙ in = 1 L n ·min −1 , T sp = 936 °C–1,016 °C, ambient pressure, ceria pellet morphology), showing relative errors within 7% for key metrics such as cumulative and instantaneous conversion and selectivity. The validated model is applied as a design tool. A geometric case study considering 100% CH 4 educt, ambient pressure, l fxb = 2 m, and temperatures at around 990 °C, suggests optimal operation of a reactor tube at V ˙ in = 10 L n ·min −1 , with tube diameters of 7–10 cm. A novel operating strategy is introduced, priming and cycling, that leverages the δ -gradient in the fixed-bed to enhance syngas selectivity and conversion, indicating the potential production of a high-purity syngas stream.