DRIFTS Study of Ammonia Activation over CaO and Sulfated CaO for NO Reduction by NH_3

摘要

CaO catalyzes NH_3 oxidation, while sulfated CaO catalyzes NO reduction by NH_3 in the presence of O_2 and the adsorption and transformation of ammonia over CaO and sulfated CaO has been investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to understand their catalytic mechanism. It has been found that ammonia is first adsorbed over Lewis or Bronsted acid sites, and later undergoes hydrogen abstraction giving rise to either NH_2 amide or NH imide intermediates. The intermediates react with NO or lattice 0 to produce N_2 or NO. Comparing the DRIFTS of NH_3 adsorption over CaO and sulfated CaO, it is obvious that ammonia adsorbed over CaO is activated mainly in NH form apt to react with surface oxygen to produce NO, while ammonia adsorbed over sulfated CaO is activated mainly in NH_2 form apt to reduce NO. The DRIFTS results agree with experimental data and explain the catalytic mechanisms of CaO and sulfated CaO.