posted on 2020-03-06, 14:37authored byHui Chang, Erlend Bjørgum, Oana Mihai, Jie Yang, Hilde Lea Lein, Tor Grande, Steinar Raaen, Yi-An Zhu, Anders Holmen, De Chen
The
mechanism and structure requirements of selective and total
oxidation of methane in a chemical looping process are both experimentally
and theoretically examined on La1–xSrxFeO3−δ (x = 0, 0.2, and 0.5) and La0.5Sr0.5Fe1–xCoxO3−δ (x = 0.5 and
1) perovskites. The oxygen mobility in the perovskites described by
the formation energy of oxygen vacancy is found to have a pronounced
effect on the catalytic activity and selectivity. In particular, the
selectivity is controlled largely by the surface oxygen concentration
or the oxygen vacancy concentration on perovskites, which depends
strongly on the bulk oxygen concentration and the relative rate of
the lattice oxygen diffusion with respect to the surface reaction.
The substitution of Sr for La at the A site and the substitution of
Co for Fe at the B site of the ABO3 perovskites dramatically
increase the oxygen mobility. A higher oxygen diffusion rate, and
hence enrichment of oxygen on the surface, would improve the catalyst
selectivity toward total oxidation.