Selective Partial Oxidation of Methane with CO₂ Using Mobile Lattice Oxygens of LSF

Abstract

The effects of co-feeding CO2 and methane on the performance of La0.8Sr0.2FeO3 (LSF) were studied with different CO2 concentrations. The reaction was conducted in chemical looping mode at 900 °C and a weight hourly space velocity (WHSV; g methane/g catalyst/h) of 3 h–1 during 15 min reduction (10 mol % methane with 0–1.8% CO2 in nitrogen) and 10 min oxidation (10 mol % oxygen in nitrogen) cycles. Analyses of X-ray diffraction and X-ray photoelectron spectroscopy data of spent materials indicated that CO2 reacts with the oxygen vacancies on the LSF surface during methane reduction, increasing CO selectivity in POM. As the CO2 feed concentration increased to an optimal value (1.6% CO2), the CO selectivity increased to 94%. Under those conditions, the EOR (extent of reduction) of LSF, defined as the amount of oxygen depleted from the lattice, was 0.18–0.15 mmol/min·gcat. Reducing the EOR to 0.09–0.08 mmol/min·gcat (1.8% CO2) led to partial methane combustion. These results were confirmed by altering the operating conditions (WHSV = 2 and 1 h–1, T = 950 °C) and CO2 feed concentrations while extending the reduction time. Operation in an optimal EOR range (0.17–0.10 mmol/min·gcat) that enabled optimal CO selectivity (>90%) was obtained without oxidative regeneration for the 18 h reduction time.