Characterisation of active phases of a copper catalyst for methanol oxidation under reaction conditions: an in situ X-ray absorption spectroscopy study in the soft energy range

The oxidation of methanol over copper is investigated by X-ray absorption spectroscopy in the soft X-ray range under reaction conditions. This in situ method allows the surface electronic structure of the catalyst to be correlated with its performance. The correlation reveals information about the catalytic function of various oxygen species on the surface. Oxide and metastable suboxide species affect in distinctly different ways the multiple action of copper as selective or unselective heterogeneous catalyst.     

Probing the electronic structure of an active catalyst surface under high-pressure reaction conditions: the oxidation of methanol over copper

The active phase of a bulk metallic copper catalyst is investigated by surface sensitive X-ray absorption spectroscopy at the oxygen K-edge and the Cu L-edges in the total electron yield mode under practical steady state flow-through conditions. The active catalyst surface contains oxygen atoms revealing significant spectral differences compared to those of known copper oxides. The partial oxidation of methanol to formaldehyde is correlated to the abundance of this copper suboxide. These oxygen atoms probe defects of the copper lattice, which represent catalytically active sites. The suboxide is undetectable under UHV conditions. The total oxidation of methanol is catalysed by a conventional copper(I) oxide species and the abundance of carbon dioxide in the gas phase is increasing with decreasing integrated intensity of the oxide species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conventional and wet proofed CuO/Al2O3 catalysts for phenol oxidation: deactivation studies in a trickle bed reactor

A large variety of catalytic systems have been studied for the catalytic wet air oxidation of phenolic solutions. Most of them show good activity, but serious stability problems. In this contribution, stability studies were performed over CuO/Al₂O₃ conventional (CNT) and polytetrafluorethylene coated (C3T) catalysts used for the oxidation of 5 g L^?1 phenol solutions in a trickle bed reactor (140 °C and 7 atm of oxygen pressure). For the hydrophilic catalyst, phenol conversion decreased with usage due to the formation of Cu₂O and copper oxalate phases. For the wet proofed catalyst, the hydrophobic layer prevented the appearence of those phases, and conversion levels remained practically constant with reaction time. After usage, both catalysts were oxidized at 400 °C and tested for reaction: in the case of the C3T catalyst, the phenol conversion was increased over its initial level; for CNT catalyst, the phenol conversion was also increased, but initial levels were not completely restored. The deactivation mechanism of the CNT catalyst is associated with the formation of the Cu₂O and copper oxalate phases during reaction. For catalyst C3T, practically no deactivation was observed. Copyright © 2007 Society of Chemical Industry     

Cu系催化剂在催化反应中的研究进展

Cu是常用的金属催化剂,具有加氢、脱氢和氧化等催化性能,铜基催化剂在化学工业中应用广泛。主要介绍了铜基催化剂在甲醇水蒸汽重整制氢、CO催化氧化消除、合成甲醇、草酸二甲酯加氢合成乙二醇、乙醇脱氢制乙酸乙酯等领域的研究进展。     

Temperature programmed oxidation of Cu/ZnO catalysts with N2O: an attempt for characterization of copper catalysts

For characterization of the surface structure of metallic copper formed on the support, temperature programmed oxidation (TPO) with N₂O was carried out over various Cu/ZnO catalysts. Four peaks of the N₂ formation (, , and ) were observed at 223, 400, 545 and 600 K in the TPO runs. The average copper crystallite size estimated from the sum of the amount of - and -peaks agreed fairly with those determined by X-ray diffraction and transmission electron microscopy. It was concluded that - and -peaks resulted from the oxidation of metallic copper atoms on the steps, corners and/ or defect sites, and on the flat sites of the surface of copper crystallites, respectively, while - and -peaks resulted from the bulk oxidation of copper.     

甲烷选择性氧化制甲醛/甲醇多相催化剂研究进展

甲烷是天然气、页岩气等化石能源的主要成分,储量十分丰富.由于甲烷分子结构高度稳定,其高效活化与选择性转化具有很大的挑战性,被认为是催化反应领域的"圣杯",因此,如何在温和条件下实现甲烷选择性氧化为高附加值的含氧化合物(如甲醇、甲醛)成为研究热点.近几十年来,研究者在甲烷选择性氧化催化剂的设计与制备方面开展了大量卓有成效...     

合成碳酸二甲酯ZnO-Al2O3催化剂研究

在Al₂O₃载体上涂覆活性组分DMC11,采用浸渍法制备负载型ZnO-Al₂O₃催化剂,采用间歇式催化剂评价装置考察催化剂活性组分涂覆量、焙烧温度、反应温度和n(甲醇)∶n(尿素)对催化剂性能的影响。在焙烧温度700 ℃和活性组分涂覆质量分数50%~60%的最佳制备条件下,制得的催化剂堆积密度1.15 g·mL^-1,比表面积85.3 m²·g^-1,孔体积0.20 m³·g^-1,孔径10 nm。在反应温度175 ℃、反应压力0.8 MPa和n(甲醇)∶n(尿素)≈35∶1条件下,碳酸二甲酯单程收率为15%。     

EELFS as a new tool of local structural characterization of solid surfaces

A new apparatus to obtain information on local structures and chemical states of solid surfaces has been constructed, with which we measure electron energy-loss fine structures (EELFS), excited by electrons of a few keV incident at a grazing angle. We describe results about O/Ni(100) and O/W(100) systems, where we extensively take advantage of anisotropy in regard to momentum transfer of the probe electron and high surface sensitivity of this technique.     

Characterization of alloy electrocatalysts for direct oxidation of methanol: new methods

The most active catalysts known for the direct electrochemical oxidation of methanol have a bimetallic or multimetallic composition, which are usually used in practice with the metals dispersed on an inert, electronically conductive support. One of the limitations to understanding the behavior of such catalysts has been the absence of methods for the systematic characterization of these complex materials, eg whether the metals are present in alloy phases, the particle size and surface area of the alloy phases, the surface composition, etc. The purpose of this paper is to review recent developments in characterization methodologies, both in situ and ex situ, and to show how these may be applied to multimetallic electrocatalysts.     

Investigation of Ammonia Oxidation over Copper with In Situ NEXAFS in the Soft X-Ray Range: Influence of Pressure on the Catalyst Performance

The oxidation of ammonia over polycrystalline copper was investigated by means of in situ NEXAFS (near-edge X-ray absorption fine structure) spectroscopy in the soft X-ray range. The reaction, carried out in a 1:12 excess of oxygen, was observed by mass spectrometry. The simultaneous detection of the surface electronic structure and its catalytic performance allows correlation of different reaction products to the current surface structure of the catalyst. It is shown that a change in total pressure from 0.4 to 1.2 mbar severely affects the reaction path. Copper(I) nitride was identified as poison and a copper oxide was found to be the active phase for the selective oxidation of ammonia to nitrogen.     

添加WO_3对铈钴催化剂CO氧化性能的影响

采用共沉淀法制备xWO_3-Ce O2-Co_3O_4复合型非贵金属CO低温催化剂,考察不同WO_3添加量和空速对催化剂催化活性的影响,并考察催化剂的抗硫性能。通过孔隙结构测试、H2-TPR、FT-IR和SEM等对催化剂进行表征。结果表明,WO_3添加质量分数1%时,催化剂具有最佳的低温活性。在CO进口体积分数0.12%、O2进口体积分数5%和空速15 000 h-1条件下,50℃时,CO转化率即可达到99.6%,60℃时,CO转化率达100%。添加WO_3,催化剂氧化能力增强,催化效率提高。随着空速升高,CO转化率下降。WO_3的加入可有效提高催化剂的比表面积,抑制硫酸盐在催化剂表面聚集,提高催化剂的抗硫性能。     

催化湿式氧化中负载型催化剂制备

采用浸渍法制备了负载型催化剂CuO/γ-Al_2O_3和Fe_2O_3/γ—Al_2O_3,以甲基橙为代表化合物,考察了制备因素对催化活性的影响,结果表明,CuO/γ-Al_2O_3的活性高于Fe_2O_3/γ-Al_2O_3,催化湿式氧化甲基橙2 h,脱色率接近100%。正交试验和稳定性研究表明,焙烧温度对催化活性影响较大,350℃焙烧,催化剂活性组分Cu溶出较少,且重复使用情况较好。采用SEM和XRD等手段对CuO/γ-Al_2O_3进行表征,发现其活性组分分散度良好。     

Hydrogen production from steam reforming of methanol over CuO/ZnO/Al2O3 catalysts: Catalytic performance and kinetic modeling

A series of CuO/ZnO/Al_2O_3, CuO/ZnO/ZrO_2/Al_2O_3 and CuO/ZnO/CeO_2/Al_2O_3 catalysts were prepared by coprecipitation and characterized by N_2 adsorption, XRD, TPR, N_2O titration and HRTEM. The catalytic performances of these catalysts for the steam reforming of methanol were evaluated in a laboratory-scale fixed-bed reactor at 0.1 MPa and temperatures between 473 and 543 K. The results showed that the catalytic activity depended greatly on the catalyst reducibility and the specific surface area of Cu. An approximate linear correlation between the catalytic activity and the Cu surface area was found for all catalysts investigated in this study.Compared to CuO/ZnO/Al_2O_3, the ZrO_2-doped CuO/ZnO/Al_2O_3 exhibited higher activity and selectivity to CO,while the CeO_2-doped catalyst displayed lower activity and selectivity. Finally, an intrinsic kinetic study was carried out over a screened CuO/ZnO/CeO_2/Al_2O_3 catalyst in the absence of internal and external mass transfer effects. A good agreement was observed between the model-derived effluent concentrations of CO(CO_2) and the experimental data. The activation energies for the reactions of methanol-steam reforming, water-gas shift and methanol decomposition over CuO/ZnO/CeO_2/Al_2O_3 were 93.1, 85.1 and 116.5 k J·mol~(-1), respectively.     

Metal sols as a useful tool for heterogeneous gold catalyst preparation: reinvestigation of a liquid phase oxidation

Differently stabilised metal sols have been used as precursors in the preparation of heterogeneous gold catalysts for liquid phase oxidation in water solution. The methodology of sols generation appears to be fundamental to obtaining nanoparticles; the support, instead, plays an important role in maintaining particle dimension and morphology.

Three different materials (γ-Al₂O₃, SiO₂ and activated carbon) have been used as the supporting agents for different gold sols that were obtained by reducing HAuCl₄ with NaBH₄ in the presence of polyvinylalcohol (PVA) or polyvinylpirrolidone (PVP) and with the tetrakis(hydroxymethyl)phosphonium chloride (THPC)/NaOH system. During the immobilisation step, the maintenance of the particle dimension observed in solution depends on both the support and the type of sol. The gold particle mean size of the colloidal suspension is more easily maintained on oxidic supports than on carbon, the latter apparently needing both steric and polar stabilisation of the gold particle.

Comparison of Au/γ-Al₂O₃ and Au/C catalyst activity in the liquid phase oxidation of ethylene glycol to glycolate highlighted the peculiarity of gold on carbon catalysts; in fact, the normally observed trend of reactivity is partially reversed, medium sized gold particle being the most active.     

载体对Au-Pd催化剂甲醇部分氧化性能的影响

采用沉积沉淀法制备了一系列Au-Pd双金属催化剂,研究了不同载体对Au-Pd双金属催化剂甲醇部分氧化性能的影响,并运用XRD、TPD和TPR等手段对催化剂进行了表征。结果表明,Au-Pd/CeO₂催化剂中形成的Au_xPd_y合金和氧空穴较多,致使Au-Pd/CeO₂催化剂的活性较高;CeO₂-TiO₂和CeO₂-ZrO₂复合载体较大的比表面积和固溶体的形成有利于H₂选择性的提高;Au-Pd/CeO₂-ZrO₂和Au-Pd/CeO₂-TiO₂催化剂有较高H₂产率的主要原因是H₂选择性的提高。     

机械研磨燃烧法制备Cu/ZnO/Al2O3甲醇合成催化剂

引言Cu/ZnO/Al2O3催化剂近年来广泛应用于低压甲醇合成、二甲醚合成和水煤气变换等领域[1-2],该催化体系具有活性高、使用寿命长、反应温度及     

甲醇直接氧化合成二甲氧基甲烷催化剂的研究

二甲氧基甲烷是重要的有机化工原料,在溶剂、化工中间体、制氢和燃料添加剂等领域应用广泛,以甲醇为原料一步合成二甲氧基甲烷是C1化工的研究新热点。以TiO₂为载体,通过负载V₂O₅并采用Ti(SO₄)₂改性制备V₂O₅/TiO₂-SO₄^2-催化剂,在温度（135～150） ℃、V（CH₃OH）∶V（O₂）∶V（N₂）=1∶（1.5～4）∶（7～20）和原料气流量(5 000～8 000) mL·(g·h)^-1条件下,将甲醇直接氧化合成二甲氧基甲烷。结果表明,甲醇转化率为48%,二甲氧基甲烷选择性为80%。     

钒铌氧化物催化剂催化氧化乙二醛制乙醛酸

对钒铌氧化物催化氧化乙二醛制乙醛酸进行研究,考察V₂O₅、Nb₂O₅及其混合物和工艺条件如乙二醛浓度、催化剂加入量、反应温度及反应时间对反应的影响。结果表明,HNO₃+NaNO₂+Nb₂O₅体系中,在乙二醛质量分数20%、催化剂用量1 g、反应温度318 K和反应时间2 h条件下,乙二醛转化率为82%,乙醛酸选择性为79%。以SiO₂为载体,采用共沉淀法制备Nb₂O₅/SiO₂催化剂,采用N₂等温吸附-脱附和XRD对催化剂进行表征,考察Nb₂O₅负载量和催化剂用量对催化氧化乙二醛合成乙醛酸的影响,并对催化剂稳定性进行研究。结果表明,Nb2O5能提高硝酸催化氧化乙二醛体系中乙二醛转化率和乙醛酸选择性,Nb₂O₅/SiO₂比纯Nb₂O₅的催化效果更好。HNO₃+NaNO₂+Nb₂O₅/SiO₂体系中,在催化剂用量5 g、活性组分Nb₂O₅负载质量分数18%和反应时间2 h条件下,乙二醛转化率为85%,乙醛酸选择性为87%,Nb₂O₅/SiO₂的稳定性和重复使用效果均良好。     

电镀法制备FeCrAl合金负载的Co_3O_4催化剂及对丙烷的电焦耳催化氧化

金属载体负载型催化剂的电焦耳催化氧化是挥发性有机物控制技术,其核心是向金属载体中通入电流,产生焦耳热来实现负载的催化剂活化。受制于催化剂涂层与金属载体之间较低的黏附力,催化剂在金属表面的负载是技术难点。将Co和Ce电镀到FeCrAl合金表面,焙烧形成氧化物催化剂,并用于丙烷的电焦耳催化氧化。结果表明,对合金载体表面进行阳极氧化预处理,可以有效促进催化剂组分的分散,而且催化剂涂层上有空穴结构,有利于反应过程的传质; CeO_2的存在显著提高Co_3O_4催化剂对丙烷的催化氧化性能。通过进一步优化,电镀法可成为制备金属负载型催化剂的有效方法。