Effects of thermal treatment conditions on redox properties of ceriazirconia materials

The nanostructures and redox properties of CeO_(2)-ZrO_(2)materials can be tuned via optimized thermal treatments.In this study,the CeO_(2)-ZrO_(2)-Y_(2)O_(3)-La_(2)O_(3)(CZ) materials were prepared by co-precipitation method and submitted to different thermal treatment conditions(atmosphere:nitrogen(N) and air(A);temperature(x):700,800 and 900℃).Due to the protective effects of the "in-situ-formed" carbon powder,treating the surfactants assisted-CZ precursors under N2atmosphere can keep the pore structures and then the CZ-N700 and CZ-N800 can achieve larger surface area than CZ-A700 and CZ-A800,respectively.In comparison,with high treatment temperature(900℃),the effects of thermal atmosphere on surface area can be ignored.However,the redox properties of CZ materials correlate closely with thermal treatment atmosphere and temperature simultaneously.As demonstrated by X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) characterizations,the N_(2)atmosphere facilitates the formation of Ce^(3+)without disturbing the mixing degree of Ce and Zr.Thereby the CZ-Nx materials exhibit superior reducibility than corresponding CZ-Ax materials.In additio n,the XRD and XPS results also demonstrate the formation of a more homogeneous CZ solid solution by Zr atoms rearrangement with temperature ignoring the atmosphere.As a result,the reducibility of CZ materials increases with the treatment temperature increasing and is not affected by the worsening of the textural properties.Specially,due to the synergistic effects of N_(2)atmosphere and high treatment temperature,the CZ-N900 shows the best reducibility.This improvement also emphasizes the important role of structural properties of CZ in explaining the temperature-dependent reducibility.

Novel promoting effects of cerium on the activities of NO_x reduction by NH_3 over TiO_2-SiO_2-WO_3 monolith catalysts

A series of catalysts were prepared by doping different loadings of CeO2 over TiO2-SiO2-WO3 and used for the selective catalytic reduction of NOx by NH3. The experimental results showed that the selective catalytic reduction（SCR） performance and SO2-resistant ability of TiO2-SiO2-WO3 were greatly enhanced by the introduction of cerium. The catalyst containing 10% CeO2 showed the highest NO conversion in a wide temperature range and good N2 selectivity with broad operation temperature window at the gas hourly space velocity（GHSV） of 30000 h–1, which was a very promising catalyst for NOx abatement from diesel engine exhaust. The catalysts were characterized by X-ray diffraction（XRD）, scanning electron microscopy with energy dispersive X-ray spectroscopy（SEM-EDS）, N2 adsorption-desorption（BET） and X-ray photoelectron spectroscopy（XPS）. The characterization results showed that the bigger pore radius, higher surface atomic concentration and dispersion of Ce and the abundant adsorbed oxygen on the surface of catalyst contributed to the best NH3-SCR performance of CeO2/TiO2-SiO2-WO3 catalyst containing 10% CeO2.

Effect of high temperature pretreatment on the thermal resistance properties of Pd/CeO2/Al2O3 close-coupled catalysts

Fresh Pd/CeO/AlOclose coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for CHoxidation. XRD and XPS results indicated that well-crystallized CeOparticles were formed during calcinations at 800 °C, which made CeOan effective promoter. HRTEM revealed that Pd particles found on the edge of CeOover the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H-TPR and XPS results also implied that the interaction between well-crystallized CeOand Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.