Polymetallic doping of Mn-based perovskite oxides for chemical looping dry reforming of methane†

Abstract

Chemical looping dry reforming of methane (CL-DRM) is an efficient pathway for the conversion of methane and CO₂ into synthesis gas ready for the Fischer–Tropsch process, which largely depends on the redox behavior of oxygen carriers. Perovskite-structured metal oxides are promising candidates for CL-DRM due to the structural diversity brought about by elemental doping. Herein, we proposed to fabricate a highly active oxygen carrier via functionally designed Mn-based perovskite oxides via polymetallic doping. Cu-doping in the B-site of SrMnO_3−δ reveals a significant anti-coking effect in the high-temperature continuous CH₄/CO₂ redox process. Ni-doping in the B-site boosts the performance of methane activation resulting in high methane conversion. Moreover, Ce-doping in the A-site elevates oxygen migration and enhances partial oxidation of methane to H₂ and CO as well as the re-oxidation of reduced perovskite oxides. Considering the roles of Cu, Ni and Ce doping of SrMnO_3−δ, a polymetallic-doped perovskite of Sr_0.8Ce_0.2Mn_0.7Cu_0.1Ni_0.2O_3−δ was synthesized and evaluated in CL-DRM. The optimized perovskite oxide demonstrated exceptional performance with a methane conversion of 85% and a CO selectivity of 93% throughout 30 redox cycles at 850 °C. In the redox reactions, the transition metals of Mn, Cu, and Ni agglomerated during the reduction but could return to a well-dispersed state after re-oxidization with CO₂. The perovskite oxide exhibits self-structural-regenerability and the nano-scale agglomeration–dispersion cycle ensures the high structural stability of the material in the successive CL-DRM cycles. This study provides an important insight into the regulation of catalytic activity, oxygen mobility and carbon-resistance via doping of perovskite oxides with various kinds of compatible elements in both A and B sites.