Structural Rearrangement in LSM Perovskites for Enhanced Syngas Production via Solar Thermochemical Redox Cycles

Abstract

Oxygen carriers undergo many physiochemical changes such as particle growth and phase transformation during thermochemical redox reactions aimed at synthesizing solar fuels. In suitable materials, these changes favor the cyclic production of synthesis gas. Advanced study of these properties is of prime importance when strengthening the material selection criteria for thermochemical applications. Considering this, we investigate the redox behavior of LaxSr1-xMnO3 (LSM) perovskite oxide systems during dry and steam chemical looping reforming of methane. The durability and structural stability are studied for cyclic regeneration to the parent perovskite structure. It is observed that lanthanum addition suppresses the LSM structural disintegration during the reduction reaction and promotes its regeneration upon reoxidation. High syngas yields of up to 2.7 mmol g-1 are produced with 25% lanthanum content during 30 consecutive cycles of dry reforming of methane. H2 purity is also increased by up to 18% in lanthanum-rich LSM structures when compared to pure SrMnO3 with ∼74% H2 purity. It is found that despite structural disintegration, manganese plays an active role in redox activities and its oxidation state is greatly influenced by lanthanum concentration and oxidation medium. We think that this study will supplement the in-depth investigation of the material's physiochemical properties before and after the redox reactions prior to selection of a suitable oxygen carrier/catalyst.