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1.
Catalytic activities of supported Pd were investigated for low temperature oxidation of methane. Pd/SnO 2 catalysts demonstrated excellent activity for methane oxidation in spite of their low surface area. The catalytic activity of Pd/SnO 2 was strongly affected by the preparation procedure. Impregnation of Pd on SnO 2 using aqueous solution of Pd(CH 3COO) 2 was most effective in enhancing the catalytic activity. The catalytic activity was also improved when well-crystallized SnO 2 was employed as a support material. TEM observations revealed that catalytic activity is strongly influenced by the dispersion state of Pd. For the active catalysts, strong interaction between Pd and SnO 2 support was observed in the adsorption of oxygen. 相似文献
2.
采用等体积浸渍法和还原法结合制备了Pd/Al2 O3催化剂,通过N2吸附-脱附、SEM、TEM、X射线衍射、X射线光电子能谱和CO原位漫反射傅里叶变换红外光谱等表征手段对制备的样品微观结构进行了系统分析,考察了不同Pd负载量和测试条件下CO催化氧化性能.实验结果表明,水合肼还原法实现了Pd在Al2 O3载体上的均匀分散... 相似文献
3.
CO and CH 4 combined oxidation tests were performed over a Pd (70 g/ft 3)/Co 3O 4 monolithic catalyst in conditions of GHSV = 100,000 h −1 and feed composition close to that of emission from bi-fuel vehicles. The effect of SO 2 (5 ppm) on CO and CH 4 oxidation activity under lean condition ( λ = 2) was investigated. The presence of sulphur strongly deactivated the catalyst towards methane oxidation, while the poisoning effect was less drastic in the oxidation of CO. Saturation of the Pd/Co 3O 4 catalytic sites via chemisorbed SO 3 and/or sulphates occurred upon exposure to SO 2. A treatment of regeneration to remove sulphate species was attempted by performing a heating/cooling cycle up to 900 °C in oxidizing atmosphere. Decomposition of PdO and Co 3O 4 phases at high temperature, above 750 °C, was observed. Moreover, sintering of Pd 0 and PdO particles along with of CoO crystallites takes place. 相似文献
4.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
5.
Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO 2/Al 2O 3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO 3) 2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO 2 is highly dispersed on the surface of Al 2O 3 up to 10 wt.% ZrO 2, beyond this value tetragonal ZrO 2 is formed. The presence of a small amount of ZrO 2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO 2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO 2, but it does not accelerate the activity of 0.2% Pd/ZrO 2/Al 2O 3 for methane combustion. 0.2% Pd/ZrO 2/Al 2O 3 dried at 120 °C shows highest activity for CH 4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH 4 combustion. 相似文献
6.
Micro-channel plates with dimension of 1 mm × 0.3 mm × 48 mm were prepared by chemical etching of stainless steel plates followed by wash coating of CeO 2 and Al 2O 3 on the channels. After coating the support on the plate, Pt, Co, and Cu were added to the plate by incipient wetness method. Reaction experiments of a single reactor showed that the micro-channel reactor coated with CuO/CeO 2 catalyst was highly selective for CO oxidation while the one coated with Pt-Co/Al 2O 3 catalyst was highly active for CO oxidation. The 7-layered reactors coated with two different catalysts were prepared by laser welding and the performances of each reactor were tested in large scale of PROX conditions. The multi-layered reactor coated with Pt-Co/Al 2O 3 catalyst was highly active for PROX and the outlet concentration of CO gradually increased with the O 2/CO ratio due to the oxidation of H 2 which maintained the reactor temperature. The multi-layered reactor coated with CuO/CeO 2 showed lower catalytic activity than that coated with Pt catalyst, but its selectivity was not changed with the increase of O 2/CO ratios due to the high selectivity. In order to combine advantages (high activity and high selectivity) of the two individual catalysts (Pt-Co/Al 2O 3, CuO/CeO 2), a serial reactor was prepared by connecting the two multi-layered micro-channel reactors with different catalysts. The prepared serial reactor exhibited excellent performance for PROX. 相似文献
7.
采用柠檬酸络合法制备一系列不同铜铈比的Cu-Ce-O/γ-Al_2O_3催化剂,用XRD、H2-TPR对其进行表征,采用连续固定床微反装置对Cu-Ce-O/γ-Al_2O_3催化剂CO催化氧化活性进行评价。结果表明,Cu-Ce-O/γ-Al_2O_3催化剂的XRD图谱中除归属于γ-Al_2O_3的晶相峰外,还出现CuO和CeO_2的晶相峰。高温水热引起活性组分CeO_2的晶粒聚集、长大和尖晶石结构CuAl2O4物质的生成;CuO-CeO_2之间的共生共存与相互作用,使得Cu-Ce-O/γ-Al_2O_3催化剂中具有非完整结构的[Cu2+1-xCu+x][O1-12x12x]增多,Cu+离子和氧空位增多,有利于其H2-TPR还原峰温度向低温区偏移,有利于提高其CO的催化氧化活性,使得Cu-Ce-O/γ-Al_2O_3催化剂的TCO50和TCO90降低。Cu与Ce物质的量比为5∶5制备的Cu-Ce-O/γ-Al_2O_3-55催化剂的TCO50和TCO90分别降至最低的162℃和199℃,表明此时的Cu-Ce-O协同效应最佳;CuO-CeO_2二相的共生共存与相互作用有利于减少高温水热环境下活性组分的聚集和晶粒长大,有利于Cu-Ce-O/γ-Al_2O_3催化剂能够保持较高的CO催化氧化活性。 相似文献
8.
A new heterogeneous Fenton-like system consisting of nano-composite Mn 3O 4/SBA-15 catalyst has been developed for the complete oxidation of low concentration ethanol (100 ppm) by H 2O 2 in aqueous solution. A novel preparation method has been developed to synthesize nanoparticles of Mn 3O 4 by thermolysis of manganese (II) acetylacetonate on SBA-15. Mn 3O 4/SBA-15 was characterized by various techniques like TEM, XRD, Raman spectroscopy and N 2 adsorption isotherms. TEM images demonstrate that Mn 3O 4 nanocrystals located mainly inside the SBA-15 pores. The reaction rate for ethanol oxidation can be strongly affected by several factors, including reaction temperature, pH value, catalyst/solution ratio and concentration of ethanol. A plausible reaction mechanism has been proposed in order to explain the kinetic data. The rate for the reaction is supposed to associate with the concentration of intermediates (radicals: OH, O 2− and HO 2) that are derived from the decomposition of H 2O 2 during reaction. The complete oxidation of ethanol can be remarkably improved only under the circumstances: (i) the intermediates are stabilized, such as stronger acidic conditions and high temperature or (ii) scavenging those radicals is reduced, such as less amount of catalyst and high concentration of reactant. Nevertheless, the reactivity of the presented catalytic system is still lower comparing to the conventional homogenous Fenton process, Fe 2+/H 2O 2. A possible reason is that the concentration of intermediates in the latter is relatively high. 相似文献
9.
The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H 2, CO 2 and acetaldehyde formation was favored on Pd/CeO 2, whereas CO production was facilitated over Pd/Y 2O 3 catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y 2O 3 catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH 4 and CO at high temperatures. On Pd/CeO 2 catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H 2, CH 4 and CO. The CO formed is further oxidized to CO 2, which seems to be promoted on Pd/CeO 2 catalyst. 相似文献
10.
作为合成气制乙二醇关键步骤之一,CO与亚硝酸甲酯合成草酸二甲酯备受关注。综述了近年来CO气相偶联合成草酸二甲酯Pd/α-Al 2O 3催化剂失活与再利用研究进展,探讨催化剂再利用工艺存在的问题,指出应根据在工业应用中出现的问题对Pd/α-Al 2O 3催化剂进行失活研究,在此基础上开发针对性的再生工艺;钯催化剂回收方面萃取法和吸附法逐渐成为研究重点,高效、低耗、短流程绿色工艺的开发是失活钯催化剂再利用的发展方向。 相似文献
11.
A series of Pd/Al 2O 3 catalysts with a wide range of mean Pd particle sizes (ca. 2–30 nm in diameter) was prepared by using various precursors (H 2PdCl 4, Pd(NO 3) 2 and Pd(AcAc) 2) and pre-treatments. The mean particle size of reduced samples was determined by H 2 chemisorption. The catalytic activity in methane oxidation under lean burn conditions was measured. The oxidation of reduced samples was studied at 300 °C. The extent of oxidation was found to decrease with increasing mean particle size. While small particles (<5 nm) oxidised very rapidly, the oxidation of large particles (ca. >15 nm) proceeded via a two-step process, being first fast and then slow. The decomposition of oxide species was studied by temperature-programmed experiments under vacuum. Two distinct oxidised species with different stability were evidenced depending on the particle size. Oxidised species in larger particles were found of lower stability than in smaller ones. A correlation between the existence of distinct types of oxide species and catalytic properties in methane oxidation was discussed. 相似文献
12.
The catalytic activity of a mixed phase of copper–cobalt and copper–manganese oxides supported on magnesium fluorine or alumina has been studied in low temperature CO oxidation at 30 °C. During calcination, the oxides studied partially react to form different type spinels depending on the calcination temperature. These spinels have different effect on the catalytic activity. In low temperature CO oxidation the copper–manganese catalysts are more active than the copper–cobalt ones. 相似文献
13.
The liquid phase hydrodechlorination (HDC) of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) has been studied over 1% (w/w) Pd/C and Pd/Al 2O 3 under conditions of minimal mass transport constraints. The HDC of 2,4-DCP generated HCl and 2-CP as the only intermediate partially dechlorinated product which reacts further to yield phenol; cyclohexanone was formed over Pd/Al 2O 3, but not over Pd/C, prior to complete dechlorination. Pd/Al 2O 3 is characterized (on the basis of TEM analysis) by a narrow distribution of smaller Pd particles to give a surface area weighted mean particle DIAMETER = 2.4 nm that is appreciably lower than the value of 13.2 nm established for Pd/C, where the latter is characterized by a broader distribution of larger (spherical) particles. The addition of NaOH served to increase fractional dechlorination by suppressing HDC inhibition due to the HCl that is generated. Reuse of the catalysts revealed an appreciable deactivation of Pd/C and a limited loss of activity in the case of Pd/Al 2O 3. Deactivation of Pd/C can be linked to a decrease (up to ca. 60%) in the initial BET surface area allied to appreciable leaching (up to ca. 40%) of the starting Pd content through the corrosive action of HCl and, while the average Pd diameter is essentially unaffected, there is evidence of a preferred leaching of larger Pd particles. The stronger metal/support interactions prevalent in Pd/Al 2O 3 results in limited Pd leaching and comparable initial HDC activities during catalyst reuse with/without NaOH addition. Inclusion of HCl in the reaction mixture (pH 5–1.5) resulted in a marked decline in the initial HDC rate associated with Pd/Al 2O 3 and a lesser drop in HDC activity for Pd/C. The difference in response to bulk solution pH variations are discussed in terms of the nature of the reactive species in solution and the amphoteric behavior of the Pd supports. 相似文献
14.
The reduction of NO x by hydrogen under lean burn conditions over Pt/Al 2O 3 is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al 2O 3. In this case, although pure H 2 and pure CO are ineffective for NO x reduction under lean burn conditions, H 2/CO mixtures are very effective. With a realistic (1:3) H 2:CO ratio, typical of actual exhaust gas, Pd/Al 2O 3 is significantly more active than Pt/Al 2O 3, delivering 45% NO x conversion at 160 °C, compared to >15% for Pt/Al 2O 3 under identical conditions. The nature of the support is also critically important, with Pd/Al 2O 3 being much more active than Pd/SiO 2. Possible mechanisms for the improved performance of Pd/Al 2O 3 in the presence of H 2+CO are discussed. 相似文献
15.
Kinetic study of CO oxidation in combination with experiments of temperature-programmed oxidation (TPO) and reduction (TPR) have been performed on various unsupported crystalline manganese oxides (MnO x); while the reactivity shows an order of MnO ≤ MnO 2 < Mn 2O 3 in a mixture of unit ratio of O 2/CO at/below 523 K. We propose that under the current conditions the interaction of adsorbed CO and O is mainly responsible for CO 2 formation on Mn 2O 3 and MnO 2 catalysts, following either the Langmuir–Hinshelwood mechanism or Eley–Rideal mechanism. Meanwhile, direct evidence from transient CO oxidation suggests that the Mars-van-Krevelen mechanism may occur for all catalysts simultaneously, especially, it is predominant for the MnO catalyst. The evidence of structural modifications during reaction was confirmed by Raman spectra obtained from used MnO. 相似文献
16.
Polycylic aromatic hydrocarbons (PAHs) are listed as carcinogenic and mutagenic priority pollutants, belonging to the environmental endocrine disrupters. Most PAHs in the environment stem from the atmospheric deposition and diesel emission. Consequently, the elimination of PAHs in the off-gases is one of the priority and emerging challenges. Catalytic oxidation has been widely used in the destruction of organic compounds due to its high efficiency (or conversion of reactants), its economic benefits and good applicability. This study investigates the application of the catalytic oxidation using Pt/γ-Al2O3 catalysts to decompose PAHs and taking naphthalene (the simplest and least toxic PAH) as a target compound. It studies the relationships between conversion, operating parameters and relevant factors such as treatment temperatures, catalyst sizes and space velocities. Also, a related reaction kinetic expression is proposed to provide a simplified expression of the relevant kinetic parameters. The results indicate that the Pt/γ-Al2O3 catalyst used accelerates the reaction rate of the decomposition of naphthalene and decreases the reaction temperature. A high conversion (over 95%) can be achieved at a moderate reaction temperature of 480 K and space velocity below 35,000 h−1. Non-catalytic (thermal) oxidation achieves the same conversion at a temperature beyond 1000 K. The results also indicate that Rideal–Eley mechanism and Arrhenius equation can be reasonably applied to describe the data by using the pseudo-first-order reaction kinetic equation with activation energy of 149.97 kJ/mol and frequency factor equal to 3.26 × 1017 s−1. 相似文献
17.
对柠檬醛-乙酸乙酯溶液中柠檬醛在La 2O 3/γ-Al 2O 3催化剂上等温吸附行为进行了研究。结果表明,30 ℃柠檬醛在La 2O 3/γ-Al 2O 3催化剂上的吸附动力学符合准二阶吸附动力学模型,吸附动力学方程为:1/q t=2.350/t+0.063 3(R 2=0.998 5)。(30~65) ℃柠檬醛在La 2O 3/γ-Al 2O 3催化剂上的等温吸附符合Langmuir方程,温度升高使柠檬醛的饱和吸附量增加,吸附热为32.19 kJ·mol -1。 相似文献
18.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
19.
采用化学共沉淀方法制备了SnO2-MnO2-Sb2O3三元固溶体并对其相图进行了初步研究,绘制了固相线下SnO2-MnO2-Sb2O3三元体系相图,确定该类固溶体的类型及其形成机制。实验结果表明:该三元体系的相关系图中含有2个单相区、8个两相区和3个三相区。金红石型SnO2为主要化合物的1区和锡锑共存互溶形成的(Sn,Sb)O2ss化合物为主的2区这两个单相区中的氧化物可以作为耐腐蚀性强、导电性良好的阳极材料中间层。 相似文献
20.
Exchange and oxidation of C 16O were investigated at 450°C on 18O-predosed Rh and Pt catalysts supported on A1 2O 3, CeO 2 and CeO 2-Al 2O 3. In all cases, a rapid exchange of C 16O with the surface can be observed. CO oxidation leads to C 16O 2, C 16O 18O and C 18O 2. Significant formation of C 16O 2 is due to the relatively high 16O coverage in reaction resulting from the C 16O exchange and from an exchange between O surface species and 16O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO 2-containing catalysts than on A1 2O 3. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange. 相似文献
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