Chemical looping reaction of methane with oxygen from La0.8Sr0.2FeO3-δ and La0.8Sr0.2FeO3-δ -Fe2O3 systems to syngas

Abstract

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.

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

“…In parallel, the CO selectivity decreased, and the coke selectivity increased continuously to values of ∼30 and ∼70%, respectively, by the end of the second period. A similar behavior was reported in a recent publication, 38 and it resembles the behavior we observed above with the CO 2 -free feed (Figure 1). These findings indicate that the effect of CO 2 on LSF is reversible since its performance after the cessation of CO 2 feeding during period 2 resembled that obtained with no CO 2 in the feed.…”

“…These findings also correspond to the decrease in the content of the LSF phase in the spent catalyst (Table 2), which is associated with the lattice oxygen depletion, as described elsewhere. 29,38,51,52 The Fe2p 3/2 spectra were also measured to determine the extent to which Fe 3+ was reduced to Fe 2+ , which coincides with the formation of oxygen vacancies, as reported elsewhere. 44,52 The deconvolution of the XPS spectra recorded for the Fe2p 3/2 core after the LSF reduction step (POM) at different feed CO 2 levels (0.8−1.8%) displayed the coexistence of two main signals related to iron ions in different valence states and environments.…”

“…Tests of CO 2 and methane co-feeding (0.4 and 10 mol %, respectively) diluted in nitrogen during the reduction step demonstrated significantly improved CO selectivity, which increased from 60% at 5 min to 70% at 20 min. This finding is probably due to the oxidative regeneration of the active-selective lattice oxygen on the LSF surface by CO 2 .…”

“…A potential strategy proposed to increase the OSC of LSF involved Fe 2 O 3 @LSF core-shell materials, ,, which deliver oxygen ions from the iron oxide core (oxygen reservoir) to the surface of the LSF shell. The performance of the Fe 2 O 3 @LSF core-shell materials, however, was limited by the combustion of methane on exposed Fe 2 O 3 , even when it was almost completely covered with LSF (∼98%), which resulted in relatively low methane conversion and syngas selectivity compared with LSF.…”

Methane conversion to syngas by chemical looping on La0.8Sr0.2FexCo1-xO3 (x=0, 0.25, 0.50, 0.75) perovskites with CO2 co-feeding

“…This issue has been addressed in our recent publications. Initially, a study [19] used La 0.8 Sr 0.2 FeO 3 (LSF), a perovskite with partial La substitution by Sr in the A site, revealed the bene cial effect of its combination with Fe 2 O 3 . Signi cantly improved CO selectivity was observed when the Fe 2 O 3 was packed before the LSF in the catalytic reactor.…”