Acta Phys. -Chim. Sin. ›› 1995, Vol. 11 ›› Issue (10): 902-906.doi: 10.3866/PKU.WHXB19951009

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A FT-IR Study on the Interaction of CH4 and O2 with the Surface of SrO-La2O3/CaO Catalysts

Yu Lin,Xu Yi-De,Guo Xie-Xian   

  1. State Key Laboratory of Catalysis,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023
  • Received:1994-11-19 Revised:1995-03-15 Published:1995-10-15
  • Contact: Xu Yi-De

Abstract:

 SrO-La2O3/CaO(SLC) catalysts have been found to be active for the oxidative coupling of methane (OCM), but the lattice oxygen of them is only active for total oxidation as revealed by the studies of in - situ FT-IR on the interaction between CH4 and the oxide surface concerned.
The results of an in - situ FT-IR study on the interaction of the mixture of CH4 and O2 with the catalyst surface show that the oxygen in gas phase can accelerate the total oxidation of CH4 via replenishing the lattice oxygen consumed on the hand, and on the other hand, it will promote the decomposition of surface carbonates formed during the reaction. For La2O3 and LC catalysts, the decomposition of surface La2O2(CO3) carbonate results in the formation of coordination unsaturated oxygen species and oxygen vacancy, and then the oxygen in gas phase could be adsorbed on the oxygen vacancy and electron transfer from coordination unsaturated oxygen species to the oxygen adspecies takes place to produce active oxygen species, probably in the form O2-, with the characteristic IR band at 1180cm-1. Meanwhile on the surfaces of CaO, SrO and SLC catalysts, although no any active oxygen species could be detected, the formation of C2H4 product still is observed at high temperatures. Therefore, it is speculated that the decomposition of furface carbonates directly leads to the formation of active oxygen species, O22-.

Key words: SrO-La2O3/CaO, Oxidative coupling of methane, FT-IR, Lattice oxygen, Coordination unsaturated oxygen species;Surface carbonates