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1.
Ce xTi 1−xO 2 oxides have been synthesised by sol–gel method with x varying from 0 to 0.3 and characterised by XRD and TPR. The structure of oxides changes with the Ce/Ti molar ratio. The presence of ceria in Ce-Ti oxides inhibits the phase transition from anatase to rutile. When x = 0.3 (Ce 0.3Ti 0.7O 2 sample), the solid presents an amorphous state. The TPR results indicate that the presence of Ti enhances the reducibility of cerium oxide species. Catalytic oxidation of propene is investigated on Ce-Ti oxides and the better conversion is obtained with Ce 0.3Ti 0.7O 2 but the CO 2 selectivity reaches 63% at 400 °C. Gold is then deposited on theses oxides to improve the catalytic activity. On the basis of characterisation data (H 2 TPR), it has been suggested that gold influences the reduction of the Ce-Ti oxide support and the catalytic activity to the propene oxidation. Thus, Au/Ce-Ti-O system catalysts are promising catalysts for propene oxidation. 相似文献
2.
In this paper, Co 3O 4/CeO 2 catalysts for steam reforming of ethanol (SRE) were prepared by co-precipitation and impregnation methods. The catalysts prepared by co-precipitation were very active and selective for SRE. Over 10%Co 3O 4/CeO 2 catalyst, ethanol conversion was close to 100% and hydrogen selectivity was about 70% at 450 °C. The catalysts were characterized by X-ray diffraction, temperature-programmed reduction (TPR) and BET surface area measurements. The preparation method influenced the interaction between cobalt and CeO 2 evidently. The incorporation of Co ions into CeO 2 crystal lattice resulted in weaker interaction between cobalt and ceria on catalyst surface. In comparison with catalysts prepared by impregnation, more cobalt ions entered into CeO 2 lattice, and resulted in weaker interaction between active phase and ceria on surface of Co 3O 4/CeO 2 prepared by co-precipitation. Thus, cobalt oxides was easier to be reduced to metal cobalt which was the key active component for SRE. Meanwhile, the incorporation of Co ions into CeO 2 crystal lattice was beneficial for resistance to carbon deposition. 相似文献
3.
Supported base metal catalysts were tested for the preferential oxidation of CO (CO PROX). The catalysts we investigated covered a wide range of transition metals (Co, Cr, Cu, Ni, Zn) supported on oxides with very different acidic, basic and redox properties (MgO, La 2O 3, SiO 2–Al 2O 3, CeO 2, Ce 0.63Zr 0.37O 2). The influence of the metal loading (Cu), the support properties (acidity, basicity, redox, surface area) and the reaction conditions (reaction temperature, feed composition) on the catalyst activity and selectivity was evaluated. The activity of ceria and ceria–zirconia supported copper catalysts was comparable to the performances of noble metal samples classically used for the PROX reaction. In addition, Cu–CeO 2 catalysts showed a practically constant and high selectivity towards CO oxidation in the temperature range of 50–150 °C. Due to the strong synergetic effect between copper and ceria, only a small amount of copper (0.3 wt.%) was necessary to get an active catalyst. The best catalytic performances were obtained for the samples containing 1–3 wt.% copper. The presence of small copper particles in close interaction with the ceria support was shown to be responsible for the enhanced activity. Except for the hydrogen oxidation, no parallel reactions (CO or CO 2 methanation reactions, coking, RWGS) could be detected over these catalysts. Classically, an increase of the oxygen excess led to an increased CO conversion with a simultaneous loss of selectivity towards CO 2. Finally, the presence of CO 2 in the feed negatively affected the catalytic activity. This effect was attributed to the adsorption of CO 2 on the copper sites, probably as CO. 相似文献
4.
The dynamic behaviour of honeycomb type, unpromoted, and rhodium (Rh) and ceria (CeO 2) promoted palladium/alumina ( PdAl2O3) automotive catalysts has been tested under constant air/fuel ratios as well as under symmetric and asymmetric cycling of simulated exhaust feed gas. Combined use of FTIR spectroscopy and mass spectrometry allowed simultaneous monitoring of the exhaust components. Light-off tests carried out in the range 150–500°C indicated drastic differences in the conversion of the main target species NO x, CO and hydrocarbons during warm up, depending on the presence of ceria and/or Rh. Best performance with regard to NO conversion under steady feed conditions was observed with the Rh promoted Pd, whereas under cycling, addition of ceria resulted in a further improvement of NO x conversion and lowering of undesirable NH 3 formation. CO conversion was substantially enhanced by ceria addition as well as cycling operation. As concerns the behaviour in hydrocarbon conversion, Rh had a much more pronounced influence than ceria, significantly enhancing the average conversion during light-off. The benefits of λ-cycling were generally lower light-off temperatures for NO, CO and C 3H 8 conversion and an improved catalytic behaviour of the ceria-containing catalysts, especially for higher amplitudes and frequencies. 相似文献
5.
New gold catalytic system prepared on ceria-modified mesoporous titania (CeMTi) used as water-gas shift (WGS) reaction catalyst is reported. Mesoporous titania (MTi) was synthesized using surfactant templating method through a neutral [C 13(EO) 6–Ti(OC 3H 7) 4] assembly pathway. Ceria modifying additive was deposited on MTi by deposition precipitation (DP) method. Gold-based catalysts with different gold content (1–5 wt.%) were synthesized by DP of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N 2 adsorption analysis and temperature-programmed reduction (TPR). The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H 2O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new gold/ceria-modified mesoporous titania catalysts was compared with that of gold catalysts supported on simple oxides CeO 2 and mesoporous TiO 2, as well as gold/ceria-modified titania and reference catalyst Au/TiO 2 type A (World Gold Council). A high degree of synergistic interaction between ceria and mesoporous titania and a positive modification of structural and catalytic properties by ceria has been achieved. It is clearly revealed that the ceria-modified mesoporous titania is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous titania catalytic system is found to be efficient catalyst for WGSR. 相似文献
6.
采用溶胶-沉积法制备了Pt Au/ZrO_2系列催化剂,在惰性气体气氛下用于催化甘油选择性制备乳酸。研究不同反应温度下,不同单金属负载和不同比例Pt Au双金属负载催化剂的催化活性以及不同气氛下催化剂重复使用性能,对催化剂进行BET、AAS和TEM等表征。结果表明,在浓度1.1 mol·L-1甘油水溶液10 m L、(1∶1)Pt Au/ZrO_2催化剂用量0.132 g、反应温度160℃、氮气压力1.4 MPa和反应时间6 h条件下,甘油转化率90%,乳酸选择性93.7%。催化剂重复使用性能实验验证了氧气气氛下催化剂活性保持良好。 相似文献
7.
A new catalyst composed of nickel oxide and cerium oxide was studied with respect to its activity for NO reduction by CO under stoichiometric conditions in the absence as well as the presence of oxygen. Activity measurements of the NO/CO reaction were also conducted over NiO/γ-Al 2O 3, NiO/TiO 2, and NiO/CeO 2 catalysts for comparison purposes. The results showed that the conversion of NO and CO are dependent on the nature of supports, and the catalysts decreased in activity in the order of NiO/CeO 2 > NiO/γ-Al 2O 3 > NiO/TiO 2. Three kinds of CeO 2 were prepared and used as support for NiO. They are the CeO 2 prepared by (i) homogeneous precipitation (HP), (ii) precipitation (PC), and (iii) direct decomposition (DP) method. We found that the NiO/CeO 2(HP) catalyst was the most active, and complete conversion of NO and CO occurred at 210 °C at a space velocity of 120,000 h −1. Based on the results of surface analysis, a reaction model for NO/CO interaction over NiO/CeO 2 has been proposed: (i) CO reduces surface oxygen to create vacant sites; (ii) on the vacant sites, NO dissociates to produce N 2; and (iii) the oxygen originated from NO dissociation is removed by CO. 相似文献
8.
Ceria has been widely explored as an additive in alumina-supported precious metal catalysts due to a number of unique properties. The success of ceria and ceria-based materials is mainly attributed to the unique combination of an elevated oxygen transport capacity coupled with the ability to shift easily between reduced and oxidised sates. In this study the influence of CeO 2 addition to a Pt/Al 2O 3 catalyst for low temperature (<540 °C) methane oxidation in an oxidising environment has been investigated. The resistance to H 2S-poisoning and influence on catalyst regeneration by oxidation or reductive treatments has been studied. The addition of CeO 2 to the support creates an increase in the level of activity based primarily on the oxygen storage capacity offered by the cerium oxide, causing an increase in oxygen activation. The ceria–alumina-supported catalyst showed a greater shift to poorer activity upon exposure to H 2S. It appears sulphur compounds react with the oxygen storage component causing a decrease in oxygen transfer, removing any benefit offered by the ceria. However, the level of Pt-agglomeration and support changes were reduced with the incorporation of ceria, emphasising the stabilising effect and promotion of metal particle dispersion associated with ceria. In order to obtain the maximum benefit of ceria addition to the support structure in terms of activity a reductive pretreatment is required. Upon exposure to a reducing atmosphere, it appears a Pt–CeO 2 interaction generates greater levels of activity. 相似文献
9.
The present work focuses on the development of novel Cu-Pd bimetallic catalysts supported on nano-sized high-surface-area CeO 2 for the oxygen-assisted water–gas-shift (OWGS) reaction. High-surface-area CeO 2 was synthesized by urea gelation (UG) and template-assisted (TA) methods. The UG method offered CeO 2 with a BET surface area of about 215 m 2/g, significantly higher than that of commercially available CeO 2. Cu and Pd were supported on CeO 2 synthesized by the UG and TA methods and their catalytic performance in the OWGS reaction was investigated systematically. Catalysts with about 30 wt% Cu and 1 wt% Pd were found to exhibit a maximum CO conversion close to 100%. The effect of metal loading method and the influence of CeO 2 support on the catalytic performance were also investigated. The results indicated that Cu and Pd loaded by incipient wetness impregnation (IWI) exhibited better performance than that prepared by deposition–precipitation (DP) method. The difference in the catalytic activity was related to the lower Cu surface concentration, better Cu–Ce and Pd–Ce interactions and improved reducibility of Cu and Pd in the IWI catalyst as determined by the X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) studies. A direct relation between BET surface area of the CeO 2 support and CO conversion was also observed. The Cu-Pd bimetallic catalysts supported on high-surface-area CeO 2 synthesized by UG method exhibited at least two-fold higher CO conversion than the commercial CeO 2 or that obtained by TA method. The catalyst retains about 100% CO conversion even under extremely high H 2 concentration. 相似文献
10.
Combustion of CO, ethyl acetate and ethanol was studied over CuO x/Al 2O 3, CuO x–CeO 2/Al 2O 3, CuMn 2O 4/Al 2O 3 and Mn 2O 3/Al 2O 3 catalysts. It was found that modification of the alumina with ceria before subsequent copper oxide deposition increases the activity for combustion of CO substantially, but the effect of ceria was small on the combustion of ethyl acetate and ethanol. The activity increases with the CuO x loading until crystalline CuO particles are formed, which contribute little to the total active surface. The CuO x–CeO 2/Al 2O 3 catalyst is more active than the CuMn 2O 4/Al 2O 3 catalyst for the oxidation of CO but the CuMn 2O 4/Al 2O 3 catalyst is more active for the combustion of ethyl acetate and ethanol. Thermal ageing and water vapour in the feed caused a modest decrease in activity and did not affect the CuOx–CeO2/Al2O3 and CuMn2O4/Al2O3 catalysts differently. In addition, no difference in intermediates formed over the two catalysts was observed. Characterisation with XRD, FT-Raman and TPR indicates that the copper oxide is present as a copper aluminate surface phase on alumina at low loading. At high loading, bulk CuO crystallites are present as well. Modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk CuO crystallites associated to the ceria, in addition to the two copper oxide species on the bare alumina. The distribution of copper species depends on the ceria and copper oxide loading. The alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of crystalline CuMn2O4 and Mn2O3, respectively, on Al2O3. 相似文献
11.
The effect of CeO 2 loading (1–20 wt.%) on the properties and catalytic behaviors of CeO 2–Al 2O 3-supported Pt catalysts on the partial oxidation of methane was studied. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and oxygen storage capacity (OSC). XRD and TPR results showed that the pretreatment temperature of the support influences on the amount of CeO 2 with fluorite structure. The pretreatment temperature of the support and CeO 2 loading influenced the morphology of Pt. OSC analysis showed a significant increase in the oxygen storage capacity per weight of CeO 2 for samples with high CeO 2 loading (12 and 20 wt.%). TPR analyses showed that the addition of Pt promotes the reduction of CeO 2. This effect was more significant for the catalysts with high CeO 2 loading (≥12 wt.%). The dispersion of Pt, measured by the rate of cyclohexane dehydrogenation, increases with increasing of the pretreatment temperature of the support. It was shown that the kind of the support is very important for obtaining of catalysts resistant to carbon formation. The catalysts with high CeO 2 loading (≥12 wt.%) showed the highest catalytic activity and stability in the reaction of partial oxidation of methane due to a higher Pt–CeO 2 interface. 相似文献
12.
This work investigates the effects of Au 3+/Au 0 ratio or distribution of gold oxidation states in Au/ZrO 2 catalysts of different gold loadings (0.01–0.76% Au) on CO oxidation and 1,3-butadiene hydrogenation by regulating the temperature of catalyst calcination (393–673 K) and pre-reduction with hydrogen (473–523 K). The catalysts were prepared by deposition–precipitation and were characterized with elemental analysis, nitrogen adsorption/desorption, TEM, XPS and TPR. The catalytic data showed that the exposed metallic Au 0 atoms at the surface of Au particles were not the only catalytic sites for the two reactions, isolated Au 3+ ions at the surface of ZrO 2, such as those in the catalysts containing no more than 0.08% Au were more active by TOF. For 0.76% Au/ZrO 2 catalysts having coexisting Au 3+ and Au 0, the catalytic activity changed differently with varying the Au 3+/Au 0 ratio in the two reactions. The highest activity for the CO oxidation reaction was observed over the catalyst of Au 3+/Au 0 = 0.33. However, catalyst with a higher Au 3+/Au 0 ratio showed always a higher activity for the hydrogenation reaction; co-existance of Au 0 with Au 3+ ions lowered the catalyst activity. Moreover, the coexisting Au particles changed the product selectivity of 1,3-butadiene hydrogenation to favor the formation of more trans-2-butene and butane. It is thus suggested that for better control of the catalytic performance of Au catalyst the effect of Au 3+/Au 0 ratio on catalytic reactions should be investigated in combination with the particle size effect of Au. 相似文献
13.
Chromium spinels M IICr 2O 4 (M II = Co, Mn, Fe, Mg, Cu) of the same structure but different reducibility, were found new, promising supports for Au nanoparticles in oxidation of CO, including selective (preferential) oxidation in the presence of hydrogen. Oxidation of CO on Au/M IICr 2O 4 occurred already at room temperature, the activity depends on the nature of M II (100% conversion of CO at 50 °C on Au/CoCr 2O 4 was observed). The activity in CO oxidation increases with the increasing reducibility of the supports and the catalysts, measured by H 2TPR, and with the increasing potential of the M II/M III redox couple (for Co, Mn, and Fe spinels). This shows the role of the support redox properties in Au-based catalysts. In the presence of hydrogen (selective oxidation of CO), the catalysts are more active and show high (90–100%) selectivity to CO 2. 相似文献
14.
Noble metal (Rh, Pt, Pd, Ir, Ru, and Ag) and Ni catalysts supported on CeO 2–Al 2O 3 were investigated for water gas shift reaction at ultrahigh temperatures. Pt/CeO 2–Al 2O 3 and Ru/CeO 2–Al 2O 3 demonstrated as the best catalysts in terms of activity, hydrogen yield and hydrogen selectivity. At 700 °C and steam to CO ratio of 5.2:1, Pt/CeO 2–Al 2O 3 converted 76.3% of CO with 94.7% of hydrogen selectivity. At the same conditions, the activity and hydrogen selectivity for Ru/CeO 2–Al 2O 3 were 63.9% and 85.6%, respectively. Both catalysts showed a good stability over 9 h of continuous operation. However, both catalysts showed slight deactivation during the test period. The study revealed that Pt/CeO 2–Al 2O 3 and Ru/CeO 2–Al 2O 3 were excellent ultrahigh temperature water gas shift catalysts, which can be coupled with biomass gasification in a downstream reactor. 相似文献
15.
采用水热法制备CeO 2纳米颗粒(W-CeO 2)、CeO 2纳米片(S-CeO 2)、CeO 2纳米棒(B-CeO 2)及CeO 2纳米八面体(O-CeO 2),用浸渍法负载相同质量分数的铜形成CuO/CeO 2催化剂。通过扫描电镜(SEM)、高分辨透射电子显微镜(TEM)、X射线衍射(XRD)、拉曼光谱(Raman)、自动吸附分析仪(BET)、H 2程序升温还原(H 2-TPR)、N 2O滴定等表征技术对催化剂进行表征,并在可控温控压的固定床石英管反应器中对催化剂的催化性能进行评价。研究了不同形貌CuO/CeO 2催化剂对CO 2加氢制备甲醇的影响;结果表明,CuO/CeO 2催化剂的催化活性存在明显的形貌依赖性,催化剂的暴露晶面、比表面积、表面碱性位点、表面氧缺陷的差异均会对CO 2转化率、甲醇选择性和产率产生影响。其中,不同形貌CeO 2优先暴露晶面的活性顺序为S-CeO 2({100}+{110})>W-CeO 2{100}>B-CeO 2{111}≈O-CeO 2{111},暴露晶面活性越高,催化剂表面氧缺陷越多,CuO-CeO 2间相互作用越强,则催化活性越好。当为CuO/S-CeO 2时,催化剂表面中碱性位点最多,催化剂比表面积为88.8m 2/g,铜分散度为19.2%,CO 2转化率为6.56%,甲醇选择性和收率为96.3%和0.063g/(g cat·h),催化活性最好,由活性评价试验得转化率由高到低依次为S-CeO 2>B-CeO 2>W-CeO 2>O-CeO 2,可知CeO 2形貌差异会决定CuO/CeO 2催化剂的物化性能和催化活性,从而提升对不同形貌CuO/CeO 2催化剂催化CO 2加氢制甲醇的基础认识。 相似文献
16.
The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration ( λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co 3O 4/CeO 2 and Co 3O 4/CeO 2–ZrO 2 containing 30 wt.% of Co 3O 4. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples). Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g−1 h−1). The catalytic performance of Co3O4/CeO2 and Co3O4/CeO2–ZrO2 were compared with those of two pure Co3O4 oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co3O4/CeO2 and Co3O4/CeO2–ZrO2 as well as to their reducibility. Particular attention was paid to the thermal stability of the Co3O4 phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co3O4 heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co3O4 decomposition into CoO was observed. Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co3O4 and by promoting the reduction at low temperature. 相似文献
17.
Ru/C catalysts promoted, or not, by cerium were prepared by impregnation of an active carbon (961 m 2 g −1) with chlorine-free precursors of Ru and Ce. They were characterized by chemisorption of H 2 and of CO and by electron microscopy. TEM and H 2 chemisorption gives coherent results while CO chemisorption overestimates Ru dispersion. In Ru–Ce/C, Ce is in close contact with Ru and decreases Ru accessibility. Catalytic wet air oxidation (CWAO) of phenol and of acrylic acid (160°C and 20 bar of O2) was investigated over these catalysts and their performance (activity, selectivity to intermediate compounds) compared with that of a reference Ru/CeO2 catalyst. Carbon-supported catalysts were very active for the CWAO of phenol but not for acrylic acid. Although high conversions were obtained, phenol was not totally mineralized after 3 h. It was shown that acrylic acid was more strongly adsorbed than phenol. Moreover, the number of contact points between Ru particles and CeO2 crystallites constitutes a key parameter in these reactions. A high surface area of ceria is required to insure O2 activation when the organic molecule is strongly adsorbed. 相似文献
18.
The effect of tin addition on niobia supported catalysts was studied and compared to the properties of alumina supported bimetallic Pt–Sn catalysts. The catalyst surfaces were probed by methylcyclopentane conversion, showing that both the presence of Sn and the reduction of the support caused a decrease in hydrogenolysis activity, favoring the ring enlargement reaction. The thermodynamics of reduction of these systems, evaluated by following the reduction step (temperature programmed reduction — TPR) with a differential scanning calorimeter (DSC), and irreversible H 2 and CO uptakes, allowed to conclude that a Pt–Sn alloy is formed on niobia supported catalysts. 相似文献
19.
The catalytic activity of Pt on alumina catalysts, with and without MnO x incorporated to the catalyst formulation, for CO oxidation in H 2-free as well as in H 2-rich stream (PROX) has been studied in the temperature range of 25–250 °C. The effect of catalyst preparation (by successive impregnation or by co-impregnation of Mn and Pt) and Mn content in the catalyst performance has been studied. A low Mn content (2 wt.%) has been found not to improve the catalyst activity compared to the base catalyst. However, catalysts prepared by successive impregnation with 8 and 15 wt.% Mn have shown a lower operation temperature for maximum CO conversion than the base catalyst with an enhanced catalyst activity at low temperatures with respect to Pt/Al 2O 3. A maximum CO conversion of 89.8%, with selectivity of 44.9% and CO yield of 40.3% could be reached over a catalyst with 15 wt.% Mn operating at 139 °C and λ = 2. The effect of the presence of 5 vol.% CO 2 and 5 vol.% H 2O in the feedstream on catalysts performance has also been studied and discussed. The presence of CO 2 in the feedstream enhances the catalytic performance of all the studied catalysts at high temperature, whereas the presence of steam inhibits catalysts with higher MnO x content. 相似文献
20.
Steam reforming of methanol was carried out over a series of doped CuO–CeO 2 catalysts prepared via the urea–nitrate combustion method. XRD analysis showed that at least part of the dopant cations enter the ceria lattice. The addition of various metal oxide dopants in the catalyst composition affected in a different way the catalytic performance towards H 2 production. Small amounts of oxides of Sm and Zn improved the performance of CuO–CeO 2, while further addition of these oxides caused a decrease in catalyst activity. XPS analysis of Zn- and Sm-doped catalysts showed that increase of dopant loading leads to surface segregation of the dopant and decrease of copper oxide dispersion. The addition of oxides of La, Zr, Mg, Gd, Y or Ca lowered or had no effect on catalytic activity, but led to less CO in the reaction products. Noble-metal modified catalysts had slightly higher activity, but the CO selectivity was also significantly higher. 相似文献
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