Xi Feng

Cerium promotion on the hydrocarbon resistance of a Cu-SAPO-34 NH3-SCR monolith catalyst

CuCe-SAPO-34 (CuCe-x) catalysts with 3 wt% Cu and various content of Ce for selective catalytic reduction of NOx by NH3 (NH3-SCR) were prepared by a wet co-impregnation method. The activities of the CuCe-x catalysts were better than that of Cu-SAPO-34 (Cu). In addition, the hydrocarbon (HC) resistance of the CuCe-x catalysts was examined and compared to that of the Cu catalyst. The NH3-SCR performance after C3H6 poisoning of the CuCe-x catalysts was preferable to that of the Cu catalyst, since the C3H6 oxidation performance was improved by the addition of Ce. The XRD, UV-vis-DRS and H2-TPR results confirmed that the addition of Ce could inhibit the aggregation of CuO crystallites and increase the amount of isolated copper ions. Furthermore, the NH3-TPD and TGA results demonstrated that the addition of Ce decreased the amount and strength of strong acid sites, so that the amount of C3H6/O2 adsorption on the CuCe-x catalysts was lower than that on the Cu catalyst. Therefore, the activity and HC resistance of Cu-SAPO-34 was improved by the addition of Ce.

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

CeTiO x and CeZrTiO x catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NO x by NH 3 (NH 3 -SCR). Various amounts of KNO 3 were impregnated on the catalyst surface to investigate the effects of Zr addition on the K + -poisoning resistance of the CeTiO x catalyst. The NH 3 -SCR performance of the catalysts showed that the NO x removal activity of the Zr-modified catalyst after poisoning was better than that of the CeTiO x 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 TiO 2 crystal grain growth, i.e., the molten salt flux effect caused by the loaded KNO 3 was inhibited. The Ce 3 d X-ray photoelectron spectra showed that the Ce 3+ /Ce 4+ ratio of CeZrTiO x decreased more slowly than that of CeTiO x 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 NH 3 -SCR performance; the temperature-programmed desorption of NH 3 results showed that Zr doping inhibited the decrease in the surface acidity. The results suggest that Zr improved the K + -poisoning resistance of the CeTiO x catalyst.

Study on hydrothermal deactivation of Pt/MnO x -CeO 2 for NO x -assisted soot oxidation: redox property, surface nitrates, and oxygen vacancies

The study mainly focuses on surface properties to investigate the deactivation factors of Pt/MnOx-CeO2 by H2 temperature-programmed reduction, CO chemical adsorption, NOx-temperature-programmed desorption (TPD), O2-TPD, NO temperature-programmed oxidation, SEM, TEM, in situ diffuse reflectance infrared Fourier transform spectra, Raman, and thermogravimetric methods. The results show that there are three main factors to lead to hydrothermal deactivation of the catalyst: redox property, oxygen vacancy, and surface nitrates. The loss of oxygen vacancies decreases the generation and desorption of active oxygen and that of surface nitrates weakens the production of NO2 and surface peroxides (-O2−). These factors greatly result in the damage of the C-NO2-O2 cooperative reaction.