Investigations on the Antimony Promotional Effect on CeO2-WO3/TiO2 for Selective Catalytic Reduction of NOx with NH3

Antimony-doped CeO2-WO3/TiO2 catalysts were prepared by a conventional ultrasonic-assisted impregnation method and employed for selective catalytic reduction of NOx with NH3 at low temperature. Both experimental work and theoretical studies were employed to elucidate the effect of the antimony on promoting the CeO2-WO3/TiO2 catalyst. The catalytic activity of CeO2-WO3/TiO2 was largely improved after the addition of antimony oxide. It was found that antimony doping reduced the crystal size and strengthened the synergistic effect between the metal cations, which resulted in a favorable catalyst surface status with abundant active surface oxygen, Bronsted acid sites, and effective electron transfer. Both in situ diffuse reflectance infrared Fourier transform analysis and DFT calculation results revealed that the ammonia and NOx desorption behavior over the catalyst surface were considerably different. For the ammonia species, rather large amounts of the active NH4+ and NH3 species anchored on the surface of the Sb-doped CeO2-WO3/TiO2. In view of the NOx species, the amount of nonactive bidentate nitrate species was largely reduced and the amount of active gaseous NO2 species was clearly enhanced, which lowered the activation energy of the catalytic process and gave rise to the elevated low-temperature NH3 selective catalytic reduction activity. All these preferable properties resulted in the elevated de-NOx activity of the Sb-doped CeO2-WO3/TiO2 catalyst.