助剂对VPO 催化剂物性的影响

以V₂O₅ 和浓硫酸为原料, 浓盐酸和柠檬酸作还原剂, 分别加入一定含量的不同金属离子作助剂, 采用超临界流体干燥法制备了VPO 催化剂, 并在不同气氛下进行活化。应用BET、XRD 和XPS 等表征手段, 考察了各种VPO 催化剂粒子的比表面积、晶相结构及表面V 离子价态等物性。实验表明, 采用超临界流体干燥法可使催化剂比表面显著增大。助剂的种类和添加量不同, 活化气氛不同, 对催化剂比表面积的影响也不同; 助剂的种类对催化剂的晶相结构亦有一定的影响, 但对催化剂表面V 离子价态影响不大。     

Preparation of Novel Composite VPO/Fumed Silica Catalyst for Partial Oxidation of n-Butane

By applying fumed SiO₂ and the deposition–precipitation method based on organic medium, the composite VPO/fumed SiO₂ catalysts were first prepared and tried for partial oxidation of n-butane to maleic anhydride. In the temperature range of 653–693 K the fumed SiO₂-based catalysts not only showed good activity but also maintained sufficiently high MA selectivity in comparison to some conventional supported VPO catalysts. As an example, the catalyst with 30% VPO content showed butane conversion of 60% and MA selectivity of 58 mol% at 673 K. The turnover rates of low loading samples are found to be higher than that of high loading sample as well as unsupported catalyst. Besides the unique interaction which may exist between VPO component and the fumed SiO₂ material, co-existence of dominant (VO)₂P₂O₇ and minor VOPO₄ in these non-equilibrated catalysts may be favorable for MA formation. Moreover, introducing the additive of polyethylene glycol (PEG) in the preparation medium can obviously enhance the dispersion of VPO component and hence lead to a more selective catalyst.     

A Study on VPO Specimen Supported on Aluminum-Containing MCM-41 for Partial Oxidation of n-Butane to MA

Dispersed vanadium–phosphorus oxide species supported on Al-MCM-41 with different vanadium loadings have been synthesized for the first time for partial oxidation of butane to MA. It was found that the VPO species was dispersed over the Al-MCM-41 support material, both in the internal channel and on the external surface. With increasing vanadium loading, n-butane conversion increased but MA selectivity decreased considerably under the same reaction conditions. At lower conversions (<30%), rather high MA selectivity (ca. 70%) can be achieved on the low loading sample. Compared with the amorphous structure of large pore SiO₂ support, the unique structure of the MCM-41 and the incorporated Al³⁺ in the framework do have an impact on the reaction behavior of the supported VPO specimen. The chemical nature of the supported VPO species and the interaction between the applied VPO species and the support was found to vary notably with the content of vanadium in the sample and likewise affected the related physico-chemical characteristics and their reaction behaviors.     

丁烷氧化制顺酐VPO催化剂的制备研究

重点介绍了丁烷氧化制顺酐流化床催化剂的制备工艺：以及催化剂的流化床活性评价装置,还考察了对催化剂的催化性能有重要影响的酸浓度对催化剂催化活性的影响。     

Influence of the Ethylene Glycol, Water Treatment and Microwave Irradiation on the Characteristics and Performance of VPO Catalysts for n-Butane Oxidation to Maleic Anhydride

In this paper, the preparation of vanadium phosphate catalysts was shown to be improved by (1) using V₂O₅ and ethylene glycol as starting and reducing agent material, respectively for VOPO₄ · 2H₂O, (2) subsequent water treatment and (3) microwave irradiation. In particular, the preparation route, based on the reduction of VOPO₄ · 2H₂O with various alcohols, is described in detail and contrasted with other three established methods performed by using ethylene glycol and isobutyl alcohol as reductant and solvent for V₂O₅ or distilled water as a solvent material. The preparation of catalyst precursor is carried out by two different methods, namely conventional heating and microwave irradiation. With this new technique, catalysts derived from the reduction of VOPO₄ · 2H₂O by ethylene glycol exhibit substantially higher surface area (typically >40 m² g^?1) and activity. In fact, the surface area of the catalyst is significantly enhanced when the precursor is refluxed by distilled water and dried by microwave heating. The characterization of catalysts was carried out using X-ray diffraction (XRD), Brunauer–Emmer–Teller (BET) surface area measurement, temperature programmed reduction (H₂-TPR), temperature-programmed reaction (TPRn) and scanning electron microscopy (SEM). This study shows that employing ethylene glycol as reducing agent, followed by adding the water treatment step to catalyst synthesis procedure, and using microwave irradiation would give rise to enhanced surface area, activity and selectivity of the catalyst. Moreover, it introduces a more energy efficient procedure for preparation of vanadium phosphate catalyst used in selective oxidation of n-butane process.     

How the Yield of Maleic Anhydride in n-Butane Oxidation,Using VPO Catalysts,was Improved Over the Years

Key patents for the oxidation of n-butane to maleic anhydride (MA) using V/P mixed metal oxides (VPO) have been analyzed to evidence the important parameters needed to optimize the catalytic behaviour. The important aspects for the optimization of the catalyst performance are the preparation of the precursor (VO)HPO₄·0.5H₂0, its activation to form the active catalyst VO₂P₂O₇ and a small amount of VOPO₄, the methodology of the addition of promoters, and the shaping of the catalyst. Even small, sustainable improvements in the MA yield (>1 %) achieved by improved, modified or optimized catalysts are significant on an industrial scale with the world production of MA being a respectable 2.7 Million tons/year. Although substantial improvements in MA yield have been achieved industrially over the past 40 years by improving the VPO catalyst composition and by optimizing process operations; the MA process remains, as practiced today, one of the least efficient industrial selective oxidation processes. Therefore, a huge incentive exists in the field to improve the MA catalyst and process, which led us to search for clues towards this end by analyzing the pertinent patent literature, as reported here.     

Ordered Mesostructured Mixed Metal Oxides: Microporous VPO Phases for n-Butane Oxidation to Maleic Anhydride

High surface area (～250 m²/g) microporous VPO phases were prepared from the VPO/surfactant mesophases by a two-step postsynthesis treatment, consisting of a Soxhlet extraction and thermal activation in reducing atmosphere at 400 °C. The resultant microporous VPO phases were studied in the partial oxidation of n-butane to maleic anhydride.     

活化条件对碳四烃氧化制顺酐VPO催化剂的影响

以V2O5和磷酸为原料,异丁醇为还原剂,合成催化剂前体VOHPO4·0.5H2O,分别在正丁烷/空气、混合碳四/空气气氛中活化得催化剂VPDB和VPDC.采用X射线衍射(XRD)、氢气-程序升温还原实验(H2-TPR)和等离子发射光谱(ICP)等对催化剂进行表征,并考察其分别在正丁烷和混合碳四氧化制顺酐反应中的催化性能.结果表明,催化剂VPDB与VPDC的主要括性相均是(VO)2P2O7相,后者晶格氧的活性较高,比表面积相对较小,两者的钒平均价态分别为4.28和4.12.在相同反应条件下分别进行正丁烷和混合碳四催化氧化反应,VPDC的催化活性均高于VPDB,前者的顺酐选择性低于后者.在相同反应温度下,混合碳四的转化率远大于正丁烷,但混合碳四氧化产物顺酐的选择性较差,故混合碳四催化氧化的适宜反应温度低于正丁烷催化氧化.     

Pd-Decorated Tungsten as Pt-Free Bimetallic Catalysts for Hydrogen Oxidation Reaction in Alkaline Electrolyte

Developing Pt-free catalysts for hydrogen oxidation reaction (HOR) in alkaline solution is becoming a key challenge in the development of anion exchange membrane fuel cells and electrochemical reactors. Herein, we present the preparation, HOR activity, and stability of Pd-decorated tungsten (Pd-d-W) catalysts. The Pd-d-W catalysts were prepared by the chemically activated surface of tungsten nanoparticles by Pd ions. The resultant bimetallic catalysts consisted of crystalline phases of both Pd and W nanoparticles. The CO stripping voltammograms and H-desorption (H_des) peak potential of hydrogen desorption in Pd suggests that the enhancement of HOR catalytic activity observed in Pd-d-W catalyst can be ascribed to the modification of electronic property of Pd and availability of OH_ad near-surface Pd atoms.     

正丁烷异构化的研究进展

正丁烷异构化产物异丁烷是烷基化反应的主要原料和合成MTBE、ETBE等汽油添加剂的重要前躯体。从烷烃异构化反应机理、影响因素、工艺进展、催化剂研究进展等几个方面,论述了烷烃异构化催化剂的发展概况。催化剂研究新进展主要包括：贵金属改性、非贵金属改性、Mo（W）体系、硫酸锆、杂多酸等,并展望了新型催化剂的应用前景。     

甲苯氨氧化合成苯甲腈VPO催化剂研究

用浸渍法制备了不同磷钒比（P／V）的VPO和VPO／硅胶催化剂，并用XRD、FTIR、TPR进行了表征，在思苯氨氧化制苯甲腈反应中考察了其催化性能，发现P的引入破坏了V2O5的晶态结构，有效阻止活性晶粒生长。V＝O与V－O－V键在P作用下向催化剂内层移动，并被高层扭曲，催化剂表面生成磷酸盐物质，晶格氧数量明显减少，钒平均氧化态下降，催化剂供氧能力减弱。活性测试表明，催化剂P／V越高，它对苯甲腈选择性也越好，其中V^3 离子和O^2-空位扮演了重要的角色。认为VPO催化剂中内层V＝O氧化－还原中心与P－OH的B酸中心共同形成了一个复合活性中心，P／V比在1到2之间的VPO／硅胶催化剂都具有较好催化性能。在440℃时甲苯转化率达到97％，对苯甲腈的选择性达到94％，故在此温度时苯甲腈产率约为91．2％。     

载体对Au-Pd催化剂甲醇部分氧化制氢性能的影响

用PVP保护乙醇还原法制备了一系列Au-Pd/MOx(M=Zn、Ce、Fe、Ti、Cr和Al)双金属催化剂,考察了不同载体对Au-Pd催化剂甲醇部分氧化制氢性能的影响,用XRD、TG、TPD、TPR和TPH等对催化剂进行了表征。结果表明,载体对催化剂性能有较大影响,与钛、铬和铝氧化物载体相比,448K时偏碱性的锌、铈和铁氧化物载体负载的Au-Pd催化剂的甲醇转化率均在80.0%以上,催化剂积碳量降低。其中以Au-Pd/ZnO催化剂的效果最好,523K时甲醇转化率和氢气选择性分别为99.0%和45.6%,反应20h后积碳量仅为0.0232g/gcat.。     

Support Effect in Supported Ni Catalysts on Their Performance for Methane Partial Oxidation

Supported nickel catalysts were prepared by impregnation of La₂O₃, MgO and ZrO₂ substrates and tested in the partial oxidation of methane to synthesis gas at atmospheric pressure. Nickel interacted strongly with La₂O₃ forming a deficient LaNiO_3- perovskite structure upon calcination. Upon reduction at 973 K, the Ni/La₂O₃ catalysts that resulted were highly active and selective for syngas production. By contrast, a separate and readily reducible NiO phase was formed on the ZrO₂ support. Because the interaction of metallic nickel particles on ZrO₂ is weak, the catalysts underwent deactivation by sintering of metal particles during on-stream operation as confirmed by photoelectron spectroscopy. The relatively high activity of the Ni/MgO systems was associated with the formation of a highly stable cubic Ni-Mg-O solid solution, in which nickel remains highly dispersed during the methane partial oxidation reaction.     

国内外甲烷催化部分氧化催化剂研究

主要讨论国内外甲烷催化部分氧化催化剂在载体、助剂、活性组分及制备方法等方面的研究进展,对改善催化剂的抗积炭性、提高催化剂的稳定性和选择性提供了建议及参考。     

Reaction Kinetics of C3H6 Oxidation for Various Reaction Pathways Over Diesel Oxidation Catalysts

Reaction kinetics studies of C₃H₆ oxidation over Pt/Al₂O₃ and Pt/SiO₂ catalysts were characterized using temperature-programmed oxidation with different oxidants: O₂, NO₂ and surface nitrates. Activation energies and conversion performance were compared in order to determine which hydrocarbon oxidation reaction pathway(s) is relevant in diesel exhaust gas aftertreatment applications. NO _x adsorption did not occur on the SiO₂ surface so the reaction between C₃H₆ and NO₂ could be isolated, i.e. no nitrate effect would complicate the analysis and their significance could be decoupled. These results were then compared with Pt/Al₂O₃ where surface nitrates did form upon exposure to NO _x . The onset of C₃H₆ oxidation was observed at a lower temperature with O₂ than with NO₂, but the activation energy was lower with NO₂. This apparent discrepancy is related to the different oxidant concentrations used and the different adsorption pathways. The results indicate that hydrocarbons must be activated first for oxidation to begin, for either NO₂ or O₂. In analyzing the reaction between C₃H₆ and nitrates, the reaction did not occur until NO _x started to desorb from the catalyst at higher temperatures, i.e. when nitrates became unstable and decomposed, thus providing a readily available oxidant source. However, when O₂ was added to the nitrate/C₃H₆ system, the reaction began at even lower temperature than with just C₃H₆ and O₂. Nitrate consumption was also observed once oxidation began. The presence of the combination of nitrates and O₂ resulted in a lower C₃H₆ oxidation activation energy.     

Role of Promoters on Tungstated Zirconia Catalysts

The isomerization of straight-chain alkanes is effectively catalyzed by tungstated zirconia promoted by Pt or Pt and Fe. In the present paper, it is attempted to better understand the role of these promoters. The materials were characterized by CO chemisorption and by transmission electron microscopy (TEM) in combination with EDX, and their catalytic performance was tested by the isomerization of n-pentane to isopentane in the presence of H₂. At low calcination temperature, very high Pt dispersion is observed with Pt atoms/clusters being embedded in or decorated by oxide material. The highly dispersed Pt moieties appear to catalyze the hydrogenolysis reaction, thus leading to low isoalkane selectivities. Higher calcination temperatures yield larger Pt particles (lower dispersion), which results in high catalytic activity and selectivity toward the isoalkane target product. It is inferred that the dissociative H₂ chemisorption occurs on the Pt particles and facilitates the reduction of the surface tungstate, which is responsible for the dehydrogenation and isomerization of n-alkane. The role of the additional promoter iron oxide still remains unresolved.