Weng Duan

Oxygen Storage Capacity of Pt-, Pd-, Rh/CeO2-Based Oxide Catalyst

CZO (CeO2-ZrO2) and CZYO (CeO2-ZrO2-Y2O3) series of mixed oxides were prepared by coprecipitaion, and a part of these oxides were loaded with precious metals (PM). XRD, BET, and oxygen storage capacity (OSC) investigations were performed on samples aged at 750, 900, and 1050 °C. It was observed that BET surface area and OSC showed a marked decrease in CeO2 aged at high temperature, and the crystallite size showed an obvious increase. The CZO samples consist of cubic- and tetragonal crystal phases, and their crystallite size increase rapidly when aged at high temperature. The CZYO samples consist of single crystal phase when the content of Y exceeds 0.15 mol, and their crystallite size increases slowly during high-temperature aging. It is concluded that additive Y can stabilize the performance of CZYO oxides. In the aged CZO and CZYO mixed-oxide systems, addition of a small amount of precious metals (Pt, Pd, Rh) increased the rate of reduction and led to an obvious improvement in OSC. OSC of CZO and CZYO with precious metals are related to their composition and the type of precious metal.

Dynamic Oxygen Storage Capacity Measurements on Ceria-Based Material

Abstract Dynamic oxygen storage and release capability (OSC) measurement apparatus was designed to evaluate the OSC performance of ceria-based oxygen storage material. The optimum measurement condition was at a frequency of 0. 1 Hz with the inlet gas-flow sequence CO (5S)→O2(5S)→CO→O2 and a flow rate of 300 ml·min −1 . Under this condition, similar regular square wave in the inlet and outlet of the reactor was obtained to guarantee the reliability of the dynamic OSC results. The dynamic OSC performance of the CeO 2 and Ce o . 67 Zr 0.33 O 2 mixed oxide prepared using the citric sol-gel method was studied at the optimum measurement condition with focus on both quantitative and qualitative analyses. The results reveal distinctly that Ce 0.67 Zr 0.33 O 2 had better dynamic OSC performance because of its higher oxygen migration rate than CeO 2 . Under dynamic conditions, two CO 2 production peaks occurred corresponding to the CO pulse and the O 2 pulse, respectively, during the entire cycle. The intensity and ratio between the two CO 2 productions were highly influenced by temperature and frequency indicating complex surface phenomena during the oxygen storage/release process. As a result, this set-up can be applied to the evaluation of ceria-based material on the OSC performance.

Influence of Supports on Catalytic Performance and Carbon Deposition of Palladium Catalyst for Methane Partial Oxidation

Abstract The catalytic performance of methane partial oxidation was investigated on Pd/CeO 2 -ZrO 2 and Pd/α-Al 2 O 3 catalysts. The catalysts were characterized by XRD, Raman spectra, and TG-DTA techniques. The results show that CeO 2 -ZrO 2 support is more advantageous for the catalytic activity and stability of catalysts compared to α-Al 2 O 3. TG-DTA and Raman spectra results indicated that carbon deposited on the catalysts was in the form of graphite, which is the main reason for the deactivation of catalysts after a 24-hour reaction. Moreover, CeO 2 -ZrO 2 had positive effect on inhibiting carbon deposition.