Low-temperature catalytic chemical looping dry reforming of methane over Ru/La2Ce2O7

Abstract

Chemical looping dry reforming of CH₄, a promising approach to reduce fossil fuel consumption and use CO₂, hinges on designing an efficient oxygen carrier. However, high operating temperatures and unsatisfactory performance hamper its application. Loading a small amount of Ru promoter on the La₂Ce₂O₇ oxygen carrier enhances CH₄ activation considerably, lowering the onset temperature to around 545 K. The Ru/La₂Ce₂O₇ material exhibited impressive performance, achieving CH₄ conversion of around 65%, with almost negligible CO₂ produced during the reduction step and CO₂ conversion exceeding 95% during the CO₂ re-oxidation step over 10 redox cycles. Despite slight carbon deposition, the redox performance remains stable because of efficient carbon removal in the reoxidation step and the inherent structure stability of the oxygen carrier. This superior performance is attributed to the strong metal–support interaction between Ru and La₂Ce₂O₇, forming Ru–O–Ce bonds at the Ru^δ+–CeO_2−x interface. These bonds anchor active Ru onto stable La₂Ce₂O₇ with excellent oxygen-ionic conductivity, enhancing CH₄ activation by increasing surface oxygen vacancies and maintaining structural stability with well-dispersed Ru promoters during cycles. Moreover, the migration of O²⁻ in subsurface is promoted by creating an elevated oxygen chemical potential gradient induced by the oxygen-deprived surface, facilitated by the Ru promoter.