Enhanced syngas selectivity and carbon utilization during chemical looping reforming of methane via a non-steady redox cycling strategy

Abstract

Solar-driven chemical looping technologies are promising pathways to convert CO₂ and other carbonaceous feedstocks such as biogas or methane to synthesis gas, a building block for renewable ‘drop-in’ fuels. Herein, a novel non-steady operating strategy, driven by computational insight, is presented to improve syngas selectivity during chemical looping reforming of methane while maintaining high conversion. We show that periodic longer reaction times enable non-steady cycling, where an optimal metal oxide oxygen deficiency at the outlet of a fixed bed reactor and lower oxygen deficiency elsewhere is key for improved performance. Using the candidate nonstoichiometric metal oxide Ni-CeO_2−δ, experiments demonstrate syngas selectivity as high as 98% and above the 95% achieved via non-steady cycling strategies, all while maintaining approximately 100% conversion of methane and 96% conversion of CO₂ at 800 °C. Advantages of this cycling strategy are projected to further increase with scale. Additionally, insights from this work can be generalized to numerous other industrially relevant chemical looping processes.