Chemical Looping Co-splitting of H2O–CO2 for Efficient Generation of Syngas

Syngas generation via thermochemical H2O–CO2 splitting relies heavily on a high-temperature decomposition of metal oxides into a reduced state. Meanwhile, typical chemical looping partial oxidation of methane to syngas suffers from the carbon deposition and the low selectivity toward syngas. To overcome these drawbacks, the partial oxidation of methane and H2O–CO2 splitting are coupled to consist of an alternative chemical looping redox scheme for the generation of Fischer–Tropsch (F–T)-ready syngas. The usability of lattice oxygen in a redox catalyst is facilitated, and its redox property is also thermodynamically optimized by using H2O and CO2 as soft oxidants, guaranteeing an effective generation of syngas from both redox steps. The carbon tolerance is greatly enhanced due to H2O or CO2 gasification in the reoxidization step. Experimental studies confirm the redox scheme by using CeO2–LaFeO3 redox catalyst, demonstrating generation of syngas with an H2/CO molar ratio around 2.0 in both methane partial oxidation and H2O–CO2 splitting steps over 30 repeated cycles at 850 °C. A syngas selectivity of 95% in methane partial oxidation and nearly 100% conversion of CO2 to CO can be achieved. Synergistic effect and competing reaction between H2O and CO2 splittings over the reduced redox catalyst are the key factors for the control of syngas composition and the intensification of CO2 splitting. The proposed approach can potentially be applied for production of F–T-ready syngas with an increased yield without the need for gas separation when compared to the state-of-the-art thermochemical splitting or methane chemical looping partial oxidation processes.