La‐hexaaluminate for synthesis gas generation by Chemical Looping Partial Oxidation of Methane Using CO₂ as Sole Oxidant

Abstract

in Wiley Online Library (wileyonlinelibrary.com)Chemical looping partial oxidation of methane using a sole CO 2 oxidant (CL-POM-CO 2 ) is an emerging technology for synthesis gas generation and CO 2 utilization, which is highly dependent on an oxygen carrier (OC). In this work, Fe-substituted La-hexaaluminate as the OC was found to exhibit good reactivity and stability during 50 periodic CH 4 / CO 2 redox cycles due to the formation of magnetoplumbite La-hexaaluminate structure with the introduction of La. Deeper reduction for synthesis gas generation did not destroy the La-hexaaluminate structure via a charge compensation mechanism, which increased CH 4 reactivity and further improved CO 2 utilization under subsequent re-oxidation. In the La-hexaaluminate structure, O 6 -Fe 31 (Oh) was highly active for the total oxidation of methane, while O 5 -Fe 31 (Tr) and O 4 -Fe 31 (Th) selectively oxidized CH 4 to synthesis gas. The sole CO 2 oxidant only selectively recovered O 5 -Fe 31 (Tr) and O 4 -Fe 31 (Th), and thus is more favorable for improving synthesis gas selectivity than O 2 /air, which offers an attractive opportunity for CO 2 utilization.

Chemical looping oxidation of CH4 with 99.5% CO selectivity over V2O3‐based redox materials using CO2 for regeneration

“…There are mainly two options: one is to enhance the reactivity of V 2 O 3 and the other is activation of CH 4 molecules. It was reported that elemental doping may result in synergetic effect on lattice oxygen mobility, melting point, and so forth . Additives such as TiO 2 , ZrO 2 , Al 2 O 3 , K 2 O, La 2 O 3 , and Ce 2 O 3 were tested, little or even negative effect was observed among these composite materials, except that SiO 2 addition showed an positive result.…”

Recent Advances of Oxygen Carriers for Chemical Looping Reforming of Methane

“…Its application for CLR of CH 4 , however, is a relatively new topic which have been studied by Wang’ research group. They firstly examined the feasibility of LaFe 3 Al 9 O 19 (LF3A) for CLDR and found that it exhibited good reactivity and stability during 50 periodic CH 4 /CO 2 redox cycles for synthesis gas formation and CO 2 conversion [59] . Interestingly, magnetoplumbite (MP) La‐hexaaluminate structure was maintained even after deeper reduction, which was quite different from the OCs reported previously where phase transformation usually occurred.…”

“…Then they further identified that oxygen coordinated with Fe 3+ in octahedral Al(3) sites (O 6 −Fe 3+ (Oh)) was highly active for the total oxidation while that in trigonal bipyramidal Al(5) sites (O 5 −Fe 3+ (Tr)) and tetrahedral Al(2) sites (O 4 −Fe 3+ (Th)) selectively oxidized CH 4 to synthesis gas. Unlike the regeneration of O 2 for O 6 −Fe 3+ (Oh), CO 2 oxidation only selectively recovered O 5 −Fe 3+ (Tr) and O 4 −Fe 3+ (Th), which indicated its more favor for improving synthesis gas selectivity as oxidants than O 2 /air [59] . Based on these results, BaFe 3 Al 9 O 19 (BF 3 A) with decreased active sites of Fe 3+ in Al(1), Al(2), and Al(3) sites (Fe 1 ,Fe 2 and Fe 3 ) for CO 2 and increased those of Fe 2+ for CO formation was designed by shortening the regeneration period, which achieved significant enhancement of CO selectivity from 58 % to 83 % [58] .…”

Chemical looping partial oxidation over FeWO /SiO2 catalysts

“…Nevertheless, the reduced Ni dramatically promotes methane decomposition, which leads to serious carbon deposition and deactivation of the redox catalysts [18][19][20]. Fe-based oxides are much cheaper than nickel oxides and nontoxic; thus, they have been studied extensively as alternative oxygen carriers [21][22][23][24]. However, owing to their lower reactivity toward methane than nickel oxides and the severe sintering under high reaction temperatures, a support material such as Al2O3 and SiO2 is required, which overcomes these drawbacks by increasing the dispersion of oxygen carriers and minimizing the crystalline size of the iron oxides [5,[25][26][27][28].…”