Hailong Zhang

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

Abstract Fresh Pd/CeO2/Al2O3 close 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 C3H8 oxidation. XRD and XPS results indicated that well-crystallized CeO2 particles were formed during calcinations at 800 °C, which made CeO2 an effective promoter. HRTEM revealed that Pd particles found on the edge of CeO2 over the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H2-TPR and XPS results also implied that the interaction between well-crystallized CeO2 and Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.

Study on the ZrO2–Y2O3/Fe interface

XPS measurements of the electron binding energy are made for the elements Zr, Y, Fe, and O at different depths to understand the effect of oxygen ion bombardment on the interface between a ZrO2–Y2O3 film and an Fe substrate. The results show that (FeZr)O1+x (x=1–<2) is formed at the interface as a result of the bombardment and reaction of depositing atoms and ions. The AES profile shows a broad transient region about 40 nm wide. Carbon contamination, a result of residual gases in the chamber during r.f. magnetron sputter deposition, is also discussed.

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.

Promotional effect of cobalt addition on catalytic performance of Ce0.5Zr0.5O2 mixed oxide for diesel soot combustion

A series of Co-modified Ce0.5Zr0.5O2 catalysts with different concentrations of Co (mass %: 0, 2, 4, 6, 8, 10) was investigated for diesel soot combustion. Ce0.5Zr0.5O2 was prepared using the coprecipitation method and Co was loaded onto the oxide using the incipient wetness impregnation method. The activities of the catalysts were evaluated by thermogravimetric (TG) analysis and temperature-programmed oxidation (TPO) experiments. The results showed the soot combustion activities of the catalysts to be effectively improved by the addition of Co, 6 % Co/Ce0.5Zr0.5O2 and that the 8 % Co/Ce0.5Zr0.5O2 catalysts exhibited the best catalytic performance in terms of lower soot ignition temperature (Ti at 349°C) and maximal soot oxidation rate temperature (Tm at 358°C). The reasons for the improved activity were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These results revealed that the presence of Co could lower the reduction temperature due to the synergistic effect between Co and Ce, thereby improving the activity of the catalysts in soot combustion. The 6 % Co catalyst exhibited the best catalytic performance, which could be attributed to the greater amounts of Co3+ and surface oxygen species on the catalyst.