Effect of Regeneration Period on the Selectivity of Synthesis Gas of Ba-Hexaaluminates in Chemical Looping Partial Oxidation of Methane

Chemical looping partial oxidation of CH 4 is a promising method for producing syngas with a suitable H 2 /CO ratio and avoiding the risk of explosion and use of an expensive air separation plant. However, regeneration of reduced oxygen carriers (OCs) by O 2 usually leads to the enrichment of surface electrophilic O 2– or O – species and thus CO 2 formation and a decrease in total CO selectivity. In this work, it was found that the CO selectivity of the BaFe 3 Al 9 O 19 hexaaluminate (BF 3 A) OC was greatly improved from 58% to 83% by tuning the regeneration period, with a CH 4 conversion of 86%, an H 2 /CO ratio of 2, and a syngas yield of 4.2 mmol/g without significant carbon deposition. This resulted from the decrease in regeneration time (from 15 to 4.2 min), leading to a decrease in Fe 3+ in Al(1), Al(2), and Al(3) sites (Fe 1, Fe 2, and Fe 3 ) active for combustion of CH 4 and an increase in reduced Fe 2+ to Fe 0 responsible for the partial oxidation of CH 4 . Consequently, the amount of CO 2 decreased while that of CO increased significantly. In addition, unoxidized surface Fe 0 resulting from shorter regeneration periods (5 and 4.2 min) acted as catalysts for dry reforming of CH 4 and CO 2 at the beginning of the reaction, which also contributed to the increase in CO formation for these two samples.