Zhi-Qiang Zou

Synthesis and characterization of CuO/Ce1−xTixO2 catalysts used for low-temperature CO oxidation

A series of CuO/Ce(1-x)Ti(x)O(2) catalysts used for low-temperature CO oxidation were prepared by impregnation with the support derived from surfactant-assisted co-precipitation. The techniques of N(2) adsorption/desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by H(2) (H(2)-TPR) were employed for catalyst characterization. It is found that the support CeO(2) prepared by the surfactant-assisted method possesses much larger specific surface area than the one obtained from conventional precipitation. Doping Ti in the support with Ti/Ce atomic ratio of 1:9 or 3:7 can further increase the surface area of CeO(2) and decrease its crystallite size. As a result, the active Cu species possess higher dispersion on the support Ce(1-x)Ti(x)O(2) than on pure CeO(2). The strong interaction between the dispersed Cu species and the support Ce(1-x)Ti(x)O(2) makes the catalysts possess much higher oxidation activity and thermal stability. However, when the ratio of Ti/Ce reaches 5:5, opposite effect is found, due to the highest surface concentration of Ti and the lack of surface highly dispersed copper species.

Simultaneous soot combustion and nitrogen oxides storage on potassium-promoted hydrotalcite-based CoMgAlO catalysts

A series of potassium-promoted hydrotalcite-based CoMgAlO mixed oxide catalysts used for simultaneous soot combustion and nitrogen oxides storage were prepared by impregnation method. The techniques of TG/DTA, XRD, H2-TPR and in situ DRIFTS were employed for catalyst characterization. Over the catalyst containing 7.5% or 10% K, the soot ignition temperature (Ti=260 degrees C) and total removal temperature (Tf=390 degrees C) are decreased by 180 degrees C and 273 degrees C, respectively, as compared with the uncatalyzed reaction. The results of kinetic calculation show that the presence of K-promoted catalysts decreases the activation energy of soot combustion from 207kJ/mol to about 160kJ/mol. When 400ppm NO is introduced, lower characteristic temperatures or higher reaction rate for soot oxidation is achieved. Simultaneously, relatively larger nitrogen oxides storage capacity is obtained. It is revealed by H2-TPR that the addition of K increases the amount of active Co sites and the mobility of bulk lattice oxygen due to the low melting point of K-containing compounds, the low valence of K+ and the strong interaction between K and Mg(Al). For nitrogen oxides storage, different routes via chelating bidentate nitrates, monodentate nitrates and ionic nitrates are confirmed by in situ DRIFTS over the CoMgAlO catalysts with potassium loadings of 0, 1.5 and 7.5%, respectively.

Influence of Co or Ce addition on the NOx storage and sulfur-resistance performance of the lean-burn NOx trap catalyst Pt/K/TiO2-ZrO2

The Pt/K/TiO(2)-ZrO(2) catalysts promoted by Co or Ce were prepared by successive impregnation or mechanically mixing method. The influence of Co or Ce addition on the NOx storage and sulfur-resistance performance of the catalyst was investigated carefully. The techniques of XRD, FT-IR, in-situ DRIFTS, H(2)-TPR and XPS were employed for catalyst characterization. The Co or Ce addition can greatly improve the NOx storage capacity of Pt/K/TiO(2)-ZrO(2) due to the enhanced oxidation ability and the release of more K sites. Ce addition induces higher K/Ti atomic ratio and larger NOx storage capacity as compared with Co addition. After sulfation and regeneration, the promoted catalysts shows more or less decreased NSC than Pt/K/TiO(2)-ZrO(2) due to the formation of more sulfates, especially for the Co-promoted catalysts, which possess better oxidation ability and facilitate the formation of large sulfates. The effect of Ce addition on Pt/K/TiO(2)-ZrO(2) largely depends on the addition mode. The high oxidation ability and the high K/Ti ratio of the mechanically prepared Ce-promoted catalyst make it still possess considerable NOx storage capacity (NSC) of 142 micromol/g after sulfation and regeneration. With the decrease of sulfur content in fuels, the Co- and Ce-promoted catalysts possessing large NOx storage capacity, will be applicable to the purification of lean-burn NOx.