Low-Temperature CH₄ Reforming and Water Splitting with Activated NiO/CeO₂ as Oxygen Carrier

Energy-efficient and selective hydrocarbon reforming techniques are crucial for a sustainable future. This study develops a highly active and selective NiO/CeO₂ oxygen carrier (OC) for low-temperature chemical looping partial oxidation of methane and water splitting. By using cubic CeO₂ (cCeO₂) as support and precisely tailoring the size and electronic structure of Ni active sites, simultaneous low-temperature CH₄ activation and high syngas selectivity (CH₄-to-syngas selectivity: > 98.5%) were achieved, effectively suppressing CH₄ cracking and complete oxidation. The as-synthesized NiO/cCeO₂ OCs operate efficiently at 600 °C, significantly lower than the conventional temperature, 800-900 °C. Nearly pure H₂ is produced in the water splitting step. High selectivity eliminates the need for additional gas separation and purification units. It is noteworthy that reaction-driven OC activation pretreatment plays a significant role in achieving the stable low-temperature activity, which leads to the moderate aggregation (10-20 nm) of Ni species and transforms Ni²⁺ from a low-spin state into a high-spin state. The OC structural evolution during reaction, key active sites responsible for water splitting, and the support effect are systematically investigated. The highly precise microstructural manipulation strategies outlined here are expected to guide further advancements in high-performance low-temperature OCs for chemical looping processes.