Yi-Jun Zhong

TPR and TPD studies of CuOCeO2 catalysts for low temperature CO oxidation

Abstract Copper oxide supported on cerium dioxide ( CuO CeO 2 ) catalysts were prepared and used for carbon monoxide oxidation in stoichiometric carbon monoxide and oxygen. The catalysts were characterized by means of XRD, H2-TPR and CO-TPD studies. The CuO CeO 2 catalysts exhibit high catalytic activity in CO oxidation, showing markedly enhanced catalytic activities due to the combined effect of copper oxide and cerium dioxide. The activity of the CuO CeO 2 (15%) catalyst prepared by impregnation is higher than that prepared by co-precipitation. CeO2 promotes the hydrogen reduction activity of copper, so that CuO CeO 2 catalysts show a different behavior with respect to pure CuO. Two reducible copper species were observed in all CuO CeO 2 catalysts. CO-TPD experiments revealed that CuO CeO 2 catalysts can adsorb CO, while pure CuO and CeO2 cannot. Combining the results of TPR, TPD study, and the catalytic activity measurements, it is proposed that the well dispersed CuO which can adsorb CO and which is reducible at low-temperature is responsible for low-temperature CO oxidation. The bulk CuO which cannot adsorb CO and which is reducible at high-temperature contributes little to the oxidation activity.

Comparative study of CuO/Ce0.7Sn0.3O2, CuO/CeO2 and CuO/SnO2 catalysts for low-temperature CO oxidation

Abstract CuO/Ce0.7Sn0.3O2, CuO/CeO2 and CuO/SnO2 catalysts were prepared using impregnation methods. The catalysts were characterized by means of H2-TPR, X-ray diffraction (XRD) and CO-TPD studies. CuO/Ce0.7Sn0.3O2 catalysts have three reduction peaks, α, β, and γ. The α peak is attributed to the reduction of CuO and Sn4+ species on the surface of Ce0.7Sn0.3O2, β peak to the reduction of bulk SnO2 and surface Ce4+, γ peak to the reduction of bulk CeO2. Only a small amount of CuO (6%) is needed to form the active site for CO oxidation, and the excess CuO forms bulk CuO particles which contribute little to the activity. Combining the results of CO-TPD, XRD and catalytic activity measurements, we propose that the well-dispersed CuO, which can adsorb CO, is responsible for low-temperature CO oxidation. The bulk CuO that cannot adsorb CO contributes little to the oxidation activity. Among the supported CuO catalysts, a synergistic interaction between CuO and Ce0.7Sn0.3O2 makes the reduced CuO/Ce0.7Sn0.3O2 catalyst easily oxidized, thus it can easily supply active species. This is responsible for the highest CO oxidation activity at low-temperature.

Redox Properties of CexZr1−xO2 Mixed Oxides Prepared by the Sol–gel Method

By using the citrate sol-gel method, Ce x Zr 1-x O2 mixed oxides was prepared, and the redox properties of the mixed oxides were studied.

Temperature-programmed desorption study of NO and CO2 over CeO2 and ZrO2

Abstract The adsorptive properties of CeO 2 and ZrO 2 were studied with respect to NO and CO 2 probe molecules using temperature-programmed desorption (TPD). Four species were detected during thermal desorption of NO adsorbed on CeO 2 and ZrO 2 , namely, NO ( m / e = 30), N 2 ( m / e = 28), N 2 O ( m / e = 44) and O 2 ( m / e = 32). The TPD profile suggest that there are two types of adsorbed states of NO on the CeO 2 and ZrO 2 surfaces, one is the weakly adsorbed NO which desorbs at about 170°C and the other is the more strongly adsorbed NO which desorbs at about 450°C. The adsorbed NO undergoes extensive decomposition to form N 2 , N 2 O and O 2 during thermal desorption. The TPD spectrum obtained after CO 2 adsorption on CeO 2 are composed of CO 2 desorption at 140°C and 440°C. These peaks are assigned to monodentate and bidentate carbonate species in the adsorbed states. After the successive adsorption of NO and CO 2 on the CeO 2 and ZrO 2 surfaces, the intensity of CO 2 desorption peak in TPD is weaker than that in the case of single of CO 2 . However, the intensity of NO desorption is almost the same as in the case of single NO adsorption. This indicated that the preadsorption of NO on cation sites of oxide surfaces affected the surrounding surface oxygen sites and blocked the CO 2 adsorption. Furthermore, this also indicates that the interaction of the oxide surface with NO is much stronger than that with CO 2 .

Co Oxidation Activity And Tpr Characterization Of Ag-Mn Complex Oxide Catalysts

A series of Ag-Mn complex oxides was prepared by co-precipitation method and used for carbon monoxide oxidation. The catalysts were characterized by means of XRD and H2-TPR techniques. A synergistic interaction between silver oxide and manganese oxide is responsible for the high activity of carbon monoxide oxidation at low temperature.

Study of Ce0.7Sn0.3O2 supported PdO catalysts for CO oxidation

Palladium supported by Ce0.7Sn0.3O2 has been prepared by an impregnation method, and used for low temperature carbon monoxide oxidation. They were characterized by means of XRD and H2-TPR techniques. For PdO/Ce0.7Sn0.3O2 catalyst, three reduction peaks (α, β and γ) are observed. The β peak contributes to the reduction of PdO species and Sn4+ species on the surface of Ce0.7Sn0.3O2; β peak to the reduction of bulk SnO2 and surface Ce4+and the γ peak to the reduction of bulk CeO2. The increase of Pd loading from 0 to 0.75% enhances oxidation of CO, further increase of the Pd content affects the catalytic activity but slightly. XRD and TPR results show that highly dispersed Pd on the surface of the support is the active species for CO oxidation.

Fabrication of zeolite-4A membranes on a catalyst particle level.

Zeolite-4A membranes are coated onto spherical Pt/gamma-Al2O3 particles with an average diameter of 1.5 mm, and a model oxidation reaction of a mixture of CO and n-butane (50 : 50) is used to demonstrate the concept of reactant selectivity via the coated defect-free membranes.