The reaction of methane with oxygen from La0.8Sr0.2FeO3-δ (LSF) and several LSF-Fe2O3 configurations was studied in chemical looping mode. Shell (LSF) and core (Fe2O3) (four catalysts called CS-3, CS-4, CS-5 and CS-6, over a range of coverage), LSF mixed uniformly with Fe2O3 (UM) and Fe2O3 (front) followed by LSF (PIS) were packed in a tubular reactor. The reaction was conducted at 900 °C and weight hourly space velocity (g methane/g catalyst/h) of 3 h−1 in 20 min reduction (10 mol% methane in nitrogen) and 20 min oxidation (10 mol% oxygen in nitrogen) cycles. LSF, CS, UM and PIS configurations yielded a significantly different performance (methane conversion, CO, CO2 and H2 selectivity and coke formation) measured in 10 reproducible cycles. The reaction and XRD data indicate that CO2 and steam formed by combustion of methane on Fe2O3 modify the phase composition of LSF, inhibits the initial LSF activity and improves the performance. Feeding a mixture containing 0.4 mol% CO2, 10 mol% methane in nitrogen to LSF confirms the positive effect of CO2 on the performance of LSF.
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.
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