Experimental and theoretical insights into sulfur resistance of transition metal-doped Cu–Fe spinel during chemical looping combustion

Abstract

A series of transition-metal doped Cu–Fe spinel oxygen carriers (M-CuFe2O4, M = Mn, Cr, Co and Ni) were synthesized and examined for their sulfur resistance by 500 ppm H2S in N2 atmosphere. The results showed that H2S vulcanized the M-CuFe2O4 surfaces and led to the generation of metal sulfide. The gaseous sulfur product was mainly SO2. The interaction between sulfur and CuFe2O4 was weakened when doping transition-metal into Fe site of CuFe2O4, especially Cr as dopant. The increase of temperature had an obvious impact on the reaction between H2S and the adsorbed oxygen species. Cr dopant reduced the enrichment of sulfur element on the surface, and it showed the weakest affinity towards sulfur because of the lowest orbital hybridization between S and Cr atom below the Fermi level. Moreover, the energies barriers of H2S dissociation over Cr–CuFe2O4 surface were obviously higher than those over CuFe2O4.