Renxian Zhou

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.

The effect of Nd on the properties of ceria–zirconia solid solution and the catalytic performance of its supported Pd-only three-way catalyst for gasoline engine exhaust reduction

A series of ceria-zirconia-neodymia mixed oxides with different contents of neodymia and the supported Pd-only three-way catalysts before and after aging have been prepared and characterized. The influence of Nd doping on the structural/textural properties of ceria-zirconia (CZ) and the effect on the three-way catalytic performance are also investigated. The results demonstrate that the addition of neodymia results in the formation of ceria-zirconia-neodymia ternary solid solution (CZN) with better textural and structural properties as well as improved reducibility and redox behavior, leading to the promoted three-way catalytic activity and enlarged air/fuel operation window. The modified solid solution with 5 wt.% neodymia shows the preferable textural/structural properties considering that the capacity of foreign cation is limited in the crystal lattice of ceria-zirconia solid solution, and Pd/CZN5 shows the optimum three-way catalytic performance and wider air/fuel operation window, especially for the corresponding aged one.

Application of Rare Earth Modified Zr-based Ceria-Zirconia Solid Solution in Three-Way Catalyst for Automotive Emission Control

Automotive exhaust emission is a major cause of air pollution. Three-way catalyst (TWC) which can eliminate CO, HC (hydrocarbons), and NO(x) simultaneously has been used to control exhaust emissions. Ceria-zirconia is a key component in TWC and most researchers pay attention to Ceria-Zirconia (Ce-rich) solid solution. The research presented in this paper is focused on the intrinsic structure of Ceria-Zirconia (Zr-based) solid solution and its application in TWC. A series of Ce(0.2)Zr(0.8)O(2) modified with rare earths (La, Nd, Pr, Sm, and Y) have been prepared by coprecipitation method combined with supercritical drying technique. All samples showed single tetragonal solid solution, indicating that the rare earth ion inserted into the lattice structure completely, and an approximately linearly relationship between lattice parameter a and the ionic radius of doped rare earth was observed. The catalytic performances of corresponding Pd-only catalysts were investigated in simulated exhaust gas. The presence of La, Nd, and Pr was favorable to the catalytic activity and wide air/fuel operation window. The relationship between the intrinsic structure of the Zr-based ceria-zirconia solid solution and catalytic activity was discussed in detail, which has some reference value for catalyst design and application.

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 CuO 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.

Decomposition of 1,2-dichloroethane over CeO2 modified USY zeolite catalysts: Effect of acidity and redox property on the catalytic behavior

CeO(2) modified ultrastable Y zeolite (CeO(2)-USY) catalysts were prepared and were used as the catalysts for the decomposition of 1,2-dichloroethane (DCE). The catalytic behavior of these catalysts was evaluated by micro-reaction and temperature-programmed surface reaction (TPSR) technique. The results reveal that CeO(2)-USY catalysts exhibit good catalytic activity for DCE decomposition and high selectivity to the formation of CO(2) and HCl. Both acidity and redox property play important roles in the DCE decomposition, and the synergy between CeO(2) species and USY zeolite shows an enhancement in the catalytic activity for DCE decomposition. CeO(2)-USY (1:8) with high dispersion of CeO(2) species and a much more suitable combination of acidity and redox property exhibits the best catalytic activity.

Effect of iron doping into CeO2-ZrO2 on the properties and catalytic behaviour of Pd-only three-way catalyst for automotive emission control

Ce(0.67)Zr(0.33)O(2) doped with iron oxide was prepared and the corresponding Pd-only three-way catalysts were examined and characterized. Pd/CZFe(1%) catalyst exhibits the best catalytic performance for CO, HC, NO and NO(2) elimination and the widest operation window. The doping of iron oxide with 1% loading suggests the formation of more homogeneous Ce-Zr-Fe-O ternary solid solution, which seems to facilitate the reduction of Ce(4+)→Ce(3+) or the formation of oxygen vacancy and to promote the interaction between Ce-Zr and Fe. Moreover, the Ce redox behaviour for surface reduction suggests depending not only on the formation of homogeneous Ce-Zr-Fe-O but also on the surface property of the sample. The increase in the concentration of oxygen vacancies under all atmospheres for CZFe(1%) sample also results in the enhancement of oxygen storage complete capacity.

Influence of Rare Earth (Ce, Sm, Nd, La, and Pr) on the Hydrogenation Properties of Chloronitrobenzene Over Pt/ZrO2 Catalyst

The effect of rare earths (Sm, Pr, Ce, Nd, and La) on the hydrogenation properties of chloronitrobenzene (CNB) over Pt/ZrO2 catalyst was studied in ethanol at 303 K and normal pressure. The results show that the hydrogenation of CNB can be carried out over Pt/ZrO2 catalyst. The order of the hydrogenation rates of CNB is p>m>o, and the yield of chloroaniline (CAN) is p>o>m. The specific rate constant turnover frequency (TOF) expressed per surface Pt atom increases when the platinum catalyst is modified by rare earth. The conversion of CNB is >99% and CAN is the main product in the hydrogenation of CNB over PtM/ZrO2 catalysts. The PtPr/ZrO2 catalyst shows the best selectivity of CNB to CAN: 89.4 mol% for o-CAN, 94.6 mol% for m-CAN and 95.1 mol% for p-CAN.

Investigation on properties of Pd/CeO2-ZrO2-Pr2O3 catalysts with different Ce/Zr molar ratios and its application for automotive emission control.

Pd/CeO2-ZrO2-Pr2O3 (CZP) catalysts with different Ce/Zr molar ratios were synthesized and systematically investigated by XRD, N2 adsorption-desorption, XPS, H2-TPR, OSC and in situ DRIFTS techniques. The results of XPS, in situ DRIFTS, etc., show that the number of oxygen vacancies increases with the increasing Zr content and thus leads to the enhanced metal-support interaction and the accelerative formation rate of nitrate, formate, acetate and carbonate species, resulting in improving catalytic performance for HC and NO elimination, especially for Pd/CZP catalysts with Ce/Zr from 1/2 to 1/3. While Pd/CZP catalysts with higher OSC value (Ce/Zr=4/1-1/2) exhibit better catalytic activity of CO and NO2 elimination. An appropriate concentration of Zr facilitates the diffusion of Pr from the surface to the bulk of the CZP supports, thus forming more homogeneous CZP solid solution and improving the structure/textual stability, which promotes the thermal stability of catalysts. Pd/CZP catalysts with Ce/Zr from 2/1 to 1/2 exhibit good thermal stability.

Promoting effect of alkaline earth metal doping on catalytic activity of HC and NOx conversion over Pd-only three-way catalyst

The influence of alkaline earth metal (M=Mg, Ca, Sr and Ba) promoter on the structural/textural properties of Ce0.67Zr0.33O2 (designated as CZ) and the catalytic behavior of its supported Pd-only three-way catalyst (Pd/CZM) have been investigated. The results show that the modification with alkaline earth metal obviously improves the catalytic activity for hydrocarbon (HC) and nitrogen oxides (NOx) conversion, especially the introduction of Ba. Furthermore, the operation window of the promoted catalysts has also been widened. The doping of alkaline earth metal leads to the formation of more homogeneous Ce-Zr-M ternary solid solution with higher surface area and smaller crystallite size, and the corresponding Pd/CZM catalysts present improved reducibility of PdO species. The modification with Ca, Sr and Ba improves the thermal aging resistance, especially Ba. DRIFTS results reveal that the doping of alkaline earth metal enhances the oxygen and electron transfer ability and favors the dissociation of NO, which promotes the activation and storage capacity of the acidic atoms like NOx, and leads to enhanced catalytic activity performance.