自组装型Pt/γ-Al2O3催化剂用于低温去除挥发性有机物

分别通过自组装法(AS)和浸渍法(WI)制备得到纳米催化剂Pt/γ-Al₂O₃-AS和Pt/γ-Al₂O₃-WI, 并用于评价甲苯、异丙醇、丙酮、乙酸乙酯等易挥发性有机物(VOCs)的氧化性能. 通过各种表征手段探究了催化剂形态、结构及表面性质与催化剂氧化活性的关系. 结果表明, Pt/γ-Al₂O₃-AS在低温下即可实现VOCs的完全氧化. 在气体浓度(体积分数)为1000×10^-6, 空速为18000 mL·g^-1·h^-1的条件下, 甲苯、异丙醇、丙酮、乙酸乙酯被Pt/γ-Al₂O₃-AS催化剂完全氧化的温度分别为130、135、145、215℃, 展现出了优异的氧化性能, 且具有很好的稳定性. 该催化剂较高的比表面积、较小的Pt纳米粒径、较好的Pt纳米颗粒分散度、更好的低温还原效果及丰富的表面羟基是具有较高催化活性的重要因素.     

A study of Pt–Pd/γ-Al2O3 catalysts for methane oxidation resistant to deactivation by sulfur poisoning

The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al₂O₃ catalysts, in the presence and the absence of SO₂ in the CH₄–O₂ reaction feed. The effect of sulfation (SO₂ + O₂ for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al₂O₃ catalysts resulted in a strong deactivation for the CH₄–O₂ reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al₂O₃ catalyst for CH₄–O₂ reaction remained rather unaffected in the presence and in the absence of SO₂ in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al₂O₃ catalysts, the presence of Pt(0) metallic surface species on which SO₂ interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO₂ and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al₂O₃ catalysts for CH₄–O₂ reactions remained rather unaffected despite the presence of SO₂ in the reaction feed.     

荧光XAFS表征Pt/BaAl2O4-Al2O3催化剂中的微量铂物种

随着稀薄燃烧(lean-burn)发动机的推广使用和环保法规的日趋严格,消除稀燃尾气中的氮氧化物(N O x)已刻不容缓。N O x储存还原技术被认为是最具应用前景的方法之一[1,2]。目前,对Pt/BaA l2O4-A l2O3体系中N O x储存与还原机制的研究较多[1￣4],但对该体系中微量铂物种微观结构及其与性能的关系研究较少,这主要是由于Pt含量(0.1w t%￣0.5wt%)太低,分散度较高,使表征方法受到很大限制。本文采用共沉淀-浸渍法制得具有较高比表面积和热稳定性的N O x储存还原催化剂Pt/BaA l2O4-A l2O3,应用荧光X-射线吸收精细结构方法(Fluores-cence-…     

Distinctive features of supported catalysts prepared from platinum carbonyl clusters

The formation of Pt/γ-Al₂O₃ and Pt/C catalysts from platinum carbonyl clusters H₂[Pt₃(CO)₆]_n (n = 2, 5) is studied. The strength of interaction between clusters (strong Lewis bases) and the support and the state of platinum in catalysts are governed by the acceptor strength of the support. The formation of a stable platinum compound with a surface of γ-Al₂O₃ (strong Lewis acid) is shown for a Pt/γ-Al₂O₃ catalyst by the method of radial distribution functions. In a Pt/C catalyst containing the same amount of Pt supported on a carbon material known to be a weaker acceptor, metallic platinum is formed along with surface-bonded platinum. Proceeding from the existence of the active phase of catalysts in the form of a surface platinum complex and platinum crystallites, the properties of catalysts are discussed in the complete oxidation of methane and the dehydrogenation of cyclohexane, as well as the high dispersity of platinum and its thermal stability     

Partial Oxidation of Ethane to Syngas over Supported Metal Catalysts

The reaction performance for C₂H₆-O₂ to syngas over different supported metal catalysts was investigated in a flow-reactor. The activated behavior of ethane is different from that of methane over the supported nickel catalysts. Although there may exist a gas phase reaction at high temperatures, over a Ni (or Rh)/-Al₂O₃ catalyst, the partial oxidation of ethane to syngas is a heterogeneous process, while over a Pt (or Pd)/-Al₂O₃ catalyst, it may be a homo-heterogeneous process. The Ni/-Al₂O₃ and Rh/-Al₂O₃ catalysts are suitable for partial oxidation of ethane to syngas at high temperatures.     

Hydroisomerization of <Emphasis Type="Italic">cis</Emphasis>-Stilbene into <Emphasis Type="Italic">trans</Emphasis>-Stilbene on Supported Heterogeneous Metal Catalysts (Rh,Pd, Pt,Ru, Ir/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)

The hydroisomerization of a cis-isomer to produce a trans-isomer on Rh, Pd, Pt, Ru, and Ir/α-Al₂O₃ catalysts is studied. It is shown that Rh and Ru catalysts on which the hydroisomerization reaction mostly takes place exhibit the most favorable characteristics, whereas on the other metals, the main route is the hydrogenation reaction. Rh/α-Al₂O₃ is the optimum catalyst, since it has much higher activity than Ru/α-Al₂O₃. It is found that the increased selectivity of the trans-isomer formation is facilitated by a decrease in the hydrogen pressure and by an increase in the substrate concentration. The maximum selectivity is achieved when the reaction is carried out in nonpolar n-hexane and toluene, whereas in the case of the more polar tetrahydrofuran (THF), dimethylformamide (DMFA), and methanol both the reaction rate and the selectivity of the trans-isomer formation decline.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Studies of the roles of Sn or Fe on γ-Al2O3-supported Pt catalysts by CO adsorption microcalorimetry and dehydrogenation reaction of C4 alkanes

CO adsorption microcalorimetry was employed in the study of γ-Al₂O₃-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/γ-Al₂O₃ catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-N₂O₃ catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and Fe to the Pt/γ-Al₂O₃ catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential heat of 60–110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was changed by adding Sn or Fe to Pt/γ-N₂O₃. The distribution of differential heat of CO adsorption on the Pt-Sn(C)/γ-Al₂O₃ catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C₄ alkanes with the number of CO adsorption sites with differential heat of 60–110 kJ/mol showed a good correlation. These results indicate that the surface Pt centers with differential heats of 60–110 kJ/mol for CO adsorption possess superior activity for the dehydrogenation of alkanes. Project supported by FORD and the National Natural Science Foundation of China (Grant No. 09412302) and the Transcentury Training Program Foundation for the Talents by The State Education Commission of China.     

Zur Kenntnis der μ-Peroxo-bis(pentacyanokobaltate(III)). Neuartige Darstellung,Beschreibung eines μ-Hydroperoxo-komplexes K5[Co2OOH(CN)10] · 2 H2O und eines μ-Peroxo-Carbonato-Komplexes K6[Co2CO4(CN)10] · 2 H2O

Investigations on Metal Catalysts. XXII. Chemisorption of Hydrogen on Pt? Ru and η-Al₂O₃ Supported Pt? Ru Catalysts Measurements of the H₂ chemisorption by volumetric method were carried out on several series of Pt? Ru and η-Al₂O₃ supported Pt? Ru catalysts. Addition of Ru to Pt and vice versa effects a remarkable influence on the sorption behaviour of the starting samples. For mixtures of carrier-free catalysts and η-Al₂O₃ as well as Pt? Ru/η-Al₂O₃ catalysts a hydrogen-spillover effect was found.     

The role of doped Fe on the activity of alumina-supported Pt and Pd diesel exhaust catalysts

Supported Pt and Pd are most commonly used for oxidation catalysts. They have similar and different characteristics for deactivation factors. The catalytic activity of Pt and Pd catalysts supported on ??-Al₂O₃ was studied in the presence and absence of H₂O and SO₂ during CO oxidation under simulated conditions of diesel exhaust gas. Without the addition of H₂O and SO₂ to the feed gas, Pd/Al₂O₃ had a superior catalytic activity compared to Pt/Al₂O₃. The addition of H₂O to the feed gas strongly and negligibly affected the activity of Pd and Pt, respectively, while the addition of SO₂ to the feed gas had a strong poisoning effect on the catalytic activity of both Pt and Pd catalysts. Although being the most active, Pd catalysts exhibited a strong sensitivity to water and sulfur-containing compounds. Fe was added to the Pt and Pd catalysts to introduce sulfur resistance. The addition of Fe enhanced the activity of the catalysts by suppressing the phase transition of Al₂O₃ to Al₂(SO₄)₃ and by hindering metal sintering.     

Intermetallic Pd<Subscript>1</Subscript>–Zn<Subscript>1</Subscript> nanoparticles in the selective liquid-phase hydrogenation of substituted alkynes

A comparative study of the catalytic characteristics of monometallic Pd/α-Al₂O₃ and bimetallic Pd–Zn/α-Al₂O₃catalysts in the liquid-phase hydrogenation of structurally different substituted alkynes (terminal and internal, symmetrical and asymmetrical) was carried out. It was established that an increase in the reduction temperature from 200 to 400 and 600°C led to a primary decrease in the activity of Pd–Zn/α-Al₂O₃ due to the formation and agglomeration of Pd1–Zn1 intermetallic nanoparticles. The Pd–Zn/α-Al₂O₃ catalyst containing Pd1–Zn1 nanoparticles exhibited increased selectivity to the target alkene formation, as compared with that of Pd/α-Al₂O₃. Furthermore, the use of the Pd–Zn/α-Al₂O₃ catalyst made it possible to more effectively perform the kinetic process control of hydrogenation because the rate of an undesirable complete hydrogenation stage decreased on this catalyst.     

An <Emphasis Type="Italic">in situ</Emphasis> cell for investigation of the catalyst structure using synchrotron radiation

Design of a cell for in situ characterization of heterogeneous catalysts by X-ray absorption spectroscopy EXAFS/XANES and X-ray diffraction on synchrotron radiation at high temperatures in a controllable gas medium, which was implemented at the Structural Materials Science end-station installed at KCSRNT, is presented. First results on nanostructural evolution of Pt/γ-Al₂O₃, Pd/γ-Al₂O₃ and other catalysts during various treatments — oxidation in oxygen, reduction in H₂/N₂, and annealing in vacuum — are reported.     

Ce改性的Pt/γ-AlO3催化剂用于富氢气氛下CO选择氧化

研究了Ce改性的Pt/γ-AlO3对于富氢气氛下CO选择氧化反应的催化行为考察了制备条件（共沉积沉淀法、分步沉积沉淀法以及沉积沉淀温度）对催化活性的影响．结果表明，在80℃时用共沉积沉淀方法制备的催化剂Pt/γ-AlO3-CP-80对CO氧化反应表现出良好的活性和选择性，CO转化率在120℃时可以达到85％．利用氢气程序升温还原和原位漫反射红外光谱对不同条件下制备的催化剂进行了表征，分析了Cc的促进作用．     

Novel cobalt nitride-induced oxygen activation on Pt-based catalyst for catalytic oxidation

Abstract

Cobalt nitride as a new type of O₂ activator was used to modify Pt-based catalyst for catalytic oxidation. The nitrided Co/Pt/γ-Al₂O₃ catalyst system was highly efficient for preferential CO oxidation in excess H₂ at low temperatures, which was attributed to a noncompetitive dual-site reaction pathway.     

Pt LIII-edge XANES and EXAFS studies on γ-Al2O3 supported Pt catalysts

Pt L_III-edge XANES and EXAFS were employed to investigate the nature of Pt/γ-Al₂O₃, Pt−Sn/γ-Al₂O₃ and Pt−Fe/γ-Al₂O₃ catalysts. The results indicated that Pt species on these catalysts were all in the oxidized states before reduction, and in the metallic states after reduction. The dispersity of the Pt species on the catalysts was very high after reduction. The electronic properties of the highly dispersed Pt species were different from that of the bulk Pt in large crystallites. An interaction between Pt and the metal-oxide modified γ-Al₂O₃ support is proposed. The interaction improved the dispersity of the Pt species on the catalysts and is thought to be the reason for the enhanced activity and selectivity for dehydrogenation reactions over these catalysts.     

Fe- and Cu-oxides supported on γ-Al2O3 as catalysts for the selective catalytic reduction of NO with ethanol. Part I: catalyst preparation,characterization, and activity

Fe- and Cu-oxides supported on γ-alumina (γ-Al₂O₃; metal loading of 3 mass %) were investigated as alternative catalysts to the conventional Ag-based system in the selective catalytic reduction of NO with ethanol (EtOH-SCR). The catalysts were characterized by elemental analysis, N₂ sorption, X-ray diffraction, temperature-prgrammed desorption of NH₃, temperature-programmed reduction with H2, diffuse reflectance UV-VIS (DR-UV-VIS) spectroscopy, and compared with 3 mass % Ag/γ-Al₂O₃ as a reference catalyst. Catalytic experiments were carried out between 423 K and 773 K in the steady state and by temperature-programmed surface reaction (TPSR) experiments. For all catalysts, the highest NO conversion (900 ppm (ppm = parts of the mixture component per million parts of all mixture components) NO, 900 ppm EtOH, 0.5 vol. % H₂O, 4 vol. % O₂ in He) was found at 573 K. While 84 % of NO were converted over the Ag-based catalysts, only 20–60 % NO conversion was observed for the Fe- and Cu-containing catalysts. Total oxidation of ethanol as an unwanted side reaction occurs over 3 mass % Cu on γ-Al₂O₃ already at 573 K, whereas the highest activity of 3 mass % Fe on γ-Al₂O₃ for this conversion was reached at 743 K. For lower temperatures, partial oxidation of ethanol leads to organic by-products which can act as active intermediates in EtOH-SCR. TPSR experiments show that ethanol reacts over both the Fe- and the Cu-based catalysts to organic by-products, such as ethene or acetaldehyde, which affect the EtOH-SCR reaction.     

Untersuchungen an Metallkatalysatoren. XI. Untersuchungen an eisen-, kobalt- und nickelmodifizierten Pt-η-Al2O3-Katalysatoren

Investigations on Metal Catalysts. XI. Investigations on Pt? η-Al₂O₃ Catalysts Modifieded by Iron, Cobalt, and Nickel Pt? Me? η-Al₂O₃ catalysts (M: Fe, Co, Ni) were characterized by magnetic investigations, reflectance spectra and determination of dispersity (chemisorption of CO, oxygen-hydrogen titration), respectively. The phase structure of platinum-rich catalysts is composed of a high degree by Pt₃Fe super-structure. All the Pt? Fe? η-Al₂O₃ catalysts contained Fe^III ions in octahedral symmetry. The dispersity of the metallic components is determined essentially by their phase structure.     

Preparation of Highly Active Pt-K/γ-Al2O3 Catalyst for o-Phenylphenol Synthesis from o-Cyclohexenyl-cyclohexanone Dehydrogenation

0.5%Pt-K/γ-Al2O3 catalysts for the synthesis of o-phenylphenol（OPP） from o-cyclohexenyl-cyclohexanone （dimer） dehydrogenation were prepared by means of a two subsequent impregnation method. The effects of catalyst preparation parameters, such as K promoters, calcination, and reduction conditions, were investigated. The results showed that the addition of K2SO4 to Pt/γ-Al2O3 catalyst notably promoted the selectivity of OPP, and its optimum content was found to be 6% in mass fraction. The higher activity was obtained when Pt/γ-Al2O3 catalyst was calcined in nitrogen atmosphere at 400--500 ℃ and then reduced at the same temperature for 3 h in hydrogen atmosphere. The conversion of the dimer and the selectivity of OPP were always above 99% and 90%, respectively, over 0.5%Pt-6% K2SO4/γ-Al2O3 catalyst during the pilot scale test of 8000 h.     

Heterogeneous bimetallic Pt-Sn/γ-Al2O3 catalyzed direct synthesis of diamines from N-alkylation of amines with diols through a borrowing hydrogen strategy

Direct synthesis of diamines has been efficiently realized from the N-alkylation of amines with diols by means of heterogeneous bimetallic Pt-Sn/γ-Al₂O₃ catalyst (0.5 wt % Pt, molar ratio Pt:Sn = 1:3) through a ‘Borrowing Hydrogen’ strategy under ligand-free conditions. The present methodology provides an environmentally benign route to diamines.     

Hydrodeoxygenation of Anisole over Ni/α-Al2O3 Catalyst

Ni-based catalysts supported on di erent supports (α-Al₂O₃,γ-Al₂O₃, SiO2, TiO₂, and ZrO₂) were prepared by impregnation. Effects of supports on catalytic performance were tested using hydrodeoxygenation reaction (HDO) of anisole as model reaction. Ni/α-Al₂O₃ was found to be the highest active catalyst for HDO of anisole. Under the optimal conditions, the anisole conversion is 93.25% and the hydrocarbon yield is 90.47%. Catalyst characteriza-tion using H₂-TPD method demonstrates that Ni/α-Al₂O₃ catalyst possesses more amount of active metal Ni than those of other investigated catalysts, which can enhance the cat-alytic activity for hydrogenation. Furthermore, it is found that the Ni/α-Al₂O₃ catalyst has excellent repeatability, and the carbon deposited on the surface of catalyst is negligible.