Shining a light on methane dry reforming – exploring the impact of visible light on carbon formation over Co/xCeO2–Al2O3†

Abstract

Introducing light to thermal DRM may be an effective strategy to improve catalyst stability, but light's role in the stability mechanism is not well understood. This study systematically moderated the support's basicity and oxygen release capacity by synthesising several cobalt-impregnated (10 wt% Co) xCeO₂–Al₂O₃ supports (xCe–Al, x = 0, 5, 10 and 20 mol%) to investigate light's impact on carbon formation and the CH_x oxidation and dehydrogenation rates (x = 0–3). The support's reducibility and CO₂ uptake increased with Ce content, arising from oxygen vacancies created upon surface reduction. Co/Al was the most active (29% CO₂ and 18% CH₄ conversion at 650 °C), and the activity and selectivity (H₂/CO) decreased with Ce concentration due to ceria's propensity for RWGS and/or the Co size increase upon Ce incorporation (after reduction, from 13 nm for Co/Al to 36 nm for Co/20Ce–Al). Co/Al deactivated the most by carbon accumulation (4.6 wt%, 7 h stability test, 650 °C), as the support provided no O for CH_x oxidation (x = 0–3). Introducing Ce improved the carbon content and stability under thermal conditions due to ceria's oxygen release capacity from oxygen vacancies (0.78 wt% for Co/5Ce–Al). Visible light (2.0 W cm⁻²) improved CH₄ conversion of Co/xCe–Al, but the increased CH_x dehydrogenation rate accelerated carbon deposition for all catalysts, harming the stability. In situ DRIFTS identified no CH_xO intermediate, suggesting poor CH_x oxidation rates relative to CH_x dehydrogenation. These findings highlight that sufficient support oxygen release is necessary to facilitate CH_x oxidation, achieving light-facilitated stability improvements.