Promotional effects of Zr on K + -poisoning resistance of CeTiO x catalyst for selective catalytic reductionof NO x with NH 3

CeTiOx and CeZrTiOx catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NOx by NH3 (NH3-SCR). Various amounts of KNO3 were impregnated on the catalyst surface to investigate the effects of Zr addition on the K+-poisoning resistance of the CeTiOx catalyst. The NH3-SCR performance of the catalysts showed that the NOx removal activity of the Zr-modified catalyst after poisoning was better than that of the CeTiOx catalyst. Brunauer-Emmett-Teller data indicated that the Zr-containing catalyst had a larger specific surface area and pore volume both before and after K+ poisoning. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy showed that Zr doping inhibited anatase TiO2 crystal grain growth, i.e., the molten salt flux effect caused by the loaded KNO3 was inhibited. The Ce 3d X-ray photoelectron spectra showed that the Ce3+/Ce4+ ratio of CeZrTiOx decreased more slowly than that of CeTiOx with increasing K+ loading, indicating that Zr addition preserved more crystal defects and oxygen vacancies; this improved the catalytic performance. The acidity was a key factor in the NH3-SCR performance; the temperature-programmed desorption of NH3 results showed that Zr doping inhibited the decrease in the surface acidity. The results suggest that Zr improved the K+-poisoning resistance of the CeTiOx catalyst.