Perovskite-type LaMn1−xBxO3+δ (B = Fe, CO and Ni) as oxygen carriers for chemical looping steam methane reforming

Abstract

• The doping of Fe, Co and Ni added surface active sites for methane activation. • The introduction of Fe, Co and Ni in LaMnO 3+δ accelerated migration of oxygen ion. • Fe, Co and Ni doped LaMnO 3+δ possessed higher yield of syngas and hydrogen. Chemical looping steam methane reforming (CLSMR) is capable of accomplishing both methane reforming and hydrogen generation, and the oxygen carrier is a key issue for CLSMR. In this work, LaMn 1−x B x O 3+δ (B = Fe, Co and Ni, x = 0.1, 0.2 and 0.3) perovskites were investigated as oxygen carriers for CLSMR in a fixed bed system. The test results showed that the doping of Fe, Co and Ni improved the oxygen release rate of LaMnO 3+δ and the improvement effect was in accordance with the order of Ni > Co > Fe, since the activation of methane molecule on the surface and the conduction of oxygen ion in the bulk of oxygen carrier particles were accelerated due to the evolution of perovskite structure, the addition of surface active sites and the formation of oxygen vacancies. The substitution of Fe, Co and Ni also increased the oxygen release amount, the CO selectivity and the hydrogen yield. No carbon formed on LaMnO 3+δ and LaMn 1−x Fe x O 3+δ in single tests and carbon deposition did not occur on LaMnO 3+δ , LaMn 0.7 Fe 0.3 O 3+δ and LaMn 0.8 Co 0.2 O 3+δ in the cyclic tests with short reduction stage, leading to the generation of high-quality syngas with the H 2 /CO ratio of 2 and pure hydrogen. Carbon deposition appeared on the LaMn 0.9 Ni 0.1 O 3+δ oxygen carrier in the cyclic tests due to the separation of part of Ni out of the perovskite structure. Considering the oxygen release rate, the yield of syngas and hydrogen as well as carbon deposition, it is deduced that LaMn 0.7 Fe 0.3 O 3+δ and LaMn 0.8 Co 0.2 O 3+δ could be used as desirable oxygen carriers for cyclic CLSMR.