Xiaoming Zheng

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.

Temperature-programmed reduction and temperature-programmed desorption studies of CuO/ZrO2 catalysts

Abstract Copper/zirconia catalysts were prepared by an impregnation method. The reducibility and characteristics of the supported copper oxide catalysts with various copper loadings were revealed and determined by H2-TPR, CO-TPR, XRD and O2-TPD, respectively. Five H2-TPR peaks could be observed. In conjunction with the observations by X-ray diffraction (XRD), three temperature-programmed reduction (TPR) peaks with lower peak temperatures (namely, α1, α2 and β) might be attributed to highly dispersed copper oxide species. These have different environment and interaction with the surface oxygen vacancies of the ZrO2 support. The other two TPR peaks of CuO/ZrO2 might be the reduction of bulk-like copper oxide. When calcination temperature was higher than 650°C, α, β-peak species were gradually transformed into the bulk CuO (γ-peak) with increasing calcination temperature. The CO-TPR curve of CuO/ZrO2 had four reduction peaks. Three peaks below 360°C on the CO-TPR curves corresponded to five peaks on the H2-TPR curves. The O2-TPD analyses showed that lattice oxygen from the highly dispersed copper oxide was desorped more easily than that from the bulk CuO. The reducibility and the desorptibility of lattice oxygen from the highly dispersed copper oxide species located on the ZrO2, which increased with CuO loading, may be related to the catalytic activity. The copper oxide species corresponding to α-peak were predominant contributors to the catalytic activity of CuO/ZrO2 catalysts, while excess copper forms bulk CuO particles contributing little to the catalytic activity.

Catalyst characterization and activity of Ag–Mn, Ag–Co and Ag–Ce composite oxides for oxidation of volatile organic compounds

Abstract Silver–manganese, silver–cobalt and silver–cerium composite oxides supported on Al 2 O 3 catalysts were prepared and used for carbon monoxide acetone, pyridine oxidation and CO–NO reaction. Results were compared to that of the individual catalysts. The catalysts were characterized by means of XRD, H 2 -TPR and O 2 -TPD. For each individual Ag/Al 2 O 3 catalyst, three O 2 desorption peaks are attributed to the decomposition of the crystalline Ag 2 O phase and the dispersed Ag 2 O phase (I) and (II). For binary oxide catalysts, the silver promotes the reduction of manganese oxide and cobalt oxide. This process is attributed to the spillover of hydrogen from silver atoms to manganese oxide or cobalt oxide. However, the manganese oxide, cobalt oxide and cerium oxide can promote the oxygen reproduction of silver oxide catalyst. The activity of binary oxide catalysts is higher than that of individual catalysts for CO, acetone, pyridine oxidation and CO–NO reaction. There is a cooperative action in binary oxide catalysts.

La-based perovskite precursors preparation and its catalytic activity for CO2 reforming of CH4

Four perovskite-type precursors (LaNiO3, La2NiO4, LaCoO3 and La2CoO4) were successfully prepared by Pechini method and were characterized by X-ray powder diffraction (XRD), temperature-programmed reduction technique (TPR) and X-ray photoelectron spectroscopy (XPS). After reduction, their catalytic activity toward CO2 reforming of CH4 was tested in a fixed-bed reactor. It was found that Ni-based La2NiO4 catalyst, after calcinations at 850 or 1100 °C, was quite active and stable with CH4 conversion of 72% and 75%, respectively. It was proposed that the well-defined structure and La2O2CO3 phase might be responsible for the unusual catalytic behavior observed over the catalyst.

Oxidation of carbon monoxide catalyzed by copper-zirconium composite oxides

Abstract CO oxidation was measured at atmospheric pressure over copper oxide catalysts supported on γ-Al 2 O 3 , 3% ZrO 2 +γ-Al 2 O 3 , ZrO 2 (UFP) and ZrO 2 , and their catalytic action was investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD). Copper oxide supported on all these catalysts existed as an excellent dispersed state; at the moment, the catalytic activity was the highest. Copper in small amounts had a strong tendency to associate with zirconium oxide and caused a large increase in activity. When the zirconium oxide surface was saturated with copper, excess copper formed bulk copper oxide particles contributing little to the catalytic activity. In the TPR experiments, three TPR peaks over CuO ZrO 2 (UFP) and CuO ZrO 2 were observed at 170–210°C (peak α and β) and above 210°C (peak β). In conjunction with the observations by XRD, it was concluded that highly dispersed copper(II) oxide and bulky copper(II) oxide were reduced to metallic copper, giving peaks α, β and γ, respectively. The TPD analyses showed CuO ZrO 2 catalysts exhibited a TPD peak of surfaces adsorbed oxygen below 350°C. Thus, not only the presence of surfaces adsorbed oxygen but also the desorptibility of α oxygen species from copper oxide located on ZrO 2 , which increased with CuO content, may also be related to the catalytic activity.

Effect of the addition of La2O3 on TPR and TPD of CuOγ-Al2O3 catalysts

Abstract In this paper, the oxidation activity of a CuO γ-Al 2 O 3 catalyst and the effects of addition of La2O3 on a CuO γ-Al 2 O 3 catalyst for the oxidation of carbon monoxide (CO) and methane (CH4) were investigated by means of a micro reactor-GC system. The crystal structure of the catalysts, reduction property and surface oxygen desorption and recovery ability of the catalysts were studied by means of XRD, TPR and TPD-MS. Experimental results show that the addition of La2O3 increases the activity of CuO γ-Al 2 O 3 for the oxidation reactions of CO and CH4; the addition of La2O3 promotes the CuO dispersion on γ-Al2O3 which was in the state of non-crystalline CuO and causes the TPR peak of the La 2 O 3 ue5f8CuO γ-Al 2 O 3 catalyst to move to a lower temperature; the addition of La2O3 has also improves surface oxygen desorption and the recovery ability of the CuO γ-Al 2 O 3 catalyst.

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.

energy-efficient coaromatization of methane and propane

Development of highly effective catalysts for one-stage conversion of methane with high selectivity to valuable products and energy efficiency will provide an efficient way to utilize natural gas and oil-associated gases and to protect environment. In recent years, there have been many efforts on direct catalytic transformations of methane into higher hydrocarbons by feeding additives together with methane under non-oxidative conditions. This paper reviewed the advances in recent research on non-oxidative aromatization of methane in the presence of propane over different modified HZSM-5 catalysts. The thermodynamic consideration, the isotope verification and the mechanism of the activation of methane in the presence of propane are discussed in the paper in detail.

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 .

Partial oxidation of p-tert butyl toluene to p-tert butyl benzaldehyde

Abstract In this paper, studies of V-Cs-Cu and V-Cs-Cu-Tl catalysts used in the partial oxidation of p -tert butyl toluene to p -tert butyl benzaldehyde are reported. The two series of catalysts are prepared by an impregnation method. The effects of temperature, space velocity, concentration, ratio of O 2 / p -tert butyl toluene and the stability of catalysts are examined. The results indicate that both the catalysts show good catalytic activity in partial oxidation of p -tert butyl toluene to p -tert butyl benzaldehyde; but the series of V-Cs-Cu-Tl catalysts exhibit more excellent catalytic activity. Under the reaction conditions of space velocity at 10,000xa0h −1 and temperature at 440xa0°C, the conversion of p -tert butyl toluene can reach 12xa0mol% and the selectivity of p -tert butyl benzaldehyde is 85xa0mol%. In addition, the good stability in the series of V-Cs-Cu-Tl catalysts is another important character: the catalytic activity still remained significant after stability test for 365xa0h.