LaNixFe1−xO3 as flexible oxygen or carbon carriers for tunable syngas production and CO2 utilization

Abstract

The current study reports LaFe1−xNixO3−δ redox catalysts as flexible oxygen or carbon carriers for CO2 utilization and tunable production of syngas at relatively low temperatures (∼700 °C), in the context of a hybrid redox process. Specifically, perovskite-structured LaFe1−xNixO3−δ with seven different compositions (x = 0.4–1) were prepared and investigated. Cyclic experiments under alternating methane and CO2 flows indicated that all the samples exhibited favorable reactive performance: CH4 and CO2 conversions varied between 85% and 98% and 70–88%, respectively. While H2/CO ratio from Fe-rich redox catalysts was ~2.3:1 in the methane conversion step, Ni-rich catalysts produced a concentrated (~ 93.7 vol%) hydrogen stream via methane cracking. The flexibility of LaFe1−xNixO3−δ to produce syngas (or hydrogen) with tunable compositions was found to be governed by the iron/nickel (Fe/Ni) ratio. Redox catalysts with higher Fe contents act as a lattice oxygen carrier via chemical looping partial oxidation (CLPOx) of methane whereas those with higher Ni contents function as a carbon carrier via chemical looping methane cracking (CLMC) scheme. XRD analysis and temperature-programmed reactions revealed that both types of catalysts involve the formation of La2O3 and Ni0 /Ni-Fe phases under the methane environment. The ability to re-incorporate La2O3 and Ni/Fe into a perovskite structure gives rise to oxygen-carrying capacity whereas stable Ni0 or Ni/Fe phases would catalyze methane cracking without lattice oxygen exchange in the reaction cycles. Temperature programmed oxidation and Raman spectroscopy indicated the presence of graphitic and amorphous carbon species, which were effectively gasified by CO2 to produce concentrated CO. Stability tests over LaFe0.5Ni0.5O3 and LaNiO3 revealed that the redox performance was stable over a span of 50 cycles.