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 La_0.8Sr_0.2FeO₃ (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·g_cat. Reducing the EOR to 0.09–0.08 mmol/min·g_cat (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.