Bi添加对MoVO/AlPO4催化剂异丁烯选择氧化反应性能的影响

采用溶胶-凝胶法制备了MoVO/AIPO4和MoVBiO/AIPO4催化剂,运用X射线衍射、激光拉曼光谱、X光电子能谱、程序升温还原对催化剂进行了表征,考察了Bi的添加对催化剂结构及其催化异丁烯选择氧化制甲基丙烯醛(MAL)反应性能的影响.结果表明,适量Bi的引入可显著提高MoVO-AIPO4上异丁烯选择氧化反应性能,...     

Effect of Bi promoter on the performances of selective oxidation of isobutane to methacrolein over MoVO/AlPO4 catalysts

The effects of Bi on the catalytic performance of selective oxidation of isobutane to methacrolein over MoVO/AlPO4 catalyst were investigated by XRD, FT-Raman, XPS, UV-vis DRS techniques. The results show that the addition of Bi component into the MoVO/AlPO4 catalyst obviously improves the catalytic performance, and the selectivity to methacrolein can increase from 14.2% to 45.1% with the increase of Bi/V molar ratio from 0 to 1. Combining the characterization results with the reaction evaluation, it is concluded that the catalytic activities of the MoV0.3Bix/AlPO4 catalysts are related to the crystalline phase composition and the dispersion of molybdenum and vanadium oxides species in general, and also to the V5+/V4+ molar ratio on the surface in particular.     

Hydroxyl‐Mediated Non‐oxidative Propane Dehydrogenation over VOx/γ‐Al2O3 Catalysts with Improved Stability

Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VO_x / γ‐Al₂O₃ catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VO_x /Al₂O₃ catalyst (V?OH) are produced under H₂ pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V?OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.     

Exploring catalytic solid/liquid interfaces by in situ attenuated total reflection infrared spectroscopy

In situ attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy has gained considerable attention as a powerful tool for exploring processes occurring at solid/liquid and solid/liquid/gas interfaces as encountered in heterogeneous catalysis and electrochemistry. Understanding of the molecular interactions occurring at the surface of a catalyst is not only of fundamental interest but constitutes the basis for a rational design of heterogeneous catalytic systems. Infrared spectroscopy has the exceptional advantage to provide information about structure and environment of molecules. In the last decade, in situ ATR-FT-IR has been developed rapidly and successfully applied for unraveling processes occurring at solid/liquid interfaces. Additionally, the kinetics of complex reactions can be followed by quantifying the concentration of products and reactants simultaneously in a non-destructive way. In this tutorial review we discuss some key aspects which have to be taken into account for successful application of in situ ATR-FT-IR to examine solid/liquid catalytic interfaces, including different experimental aspects concerned with the internal reflection element, catalyst deposition, cell design, and advanced experimental methods and spectrum analysis. Some of these aspects are illustrated using recent examples from our research. Finally, the potential and some limitations of ATR will be elucidated.     

Adaptive Bifunctional Electrocatalyst of Amorphous CoFe Oxide @ 2D Black Phosphorus for Overall Water Splitting

Water electrolysis offers a promising green technology to tackle the global energy and environmental crisis, but its efficiency is greatly limited by the sluggish reaction kinetics of both the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). In this work, by growing amorphous multi-transition-metal (cobalt and iron) oxide on two-dimensional (2D) black phosphorus (BP), we develop a bifunctional electrocatalyst (CoFeO@BP), which is able to efficiently catalyze both HER and OER. The overpotentials for the hybrid CoFeO@BP catalyst to reach a current density of 10 mA cm⁻² in 1 m KOH are 88 and 266 mV for HER and OER, respectively. Based on a series of ex-situ and in situ investigations, the excellent catalytic performance of CoFeO@BP is found to result from the adaptive surface structure under reduction and oxidation potentials. CoFeO@BP can be transformed to CoFe phosphide under reduction potential, in situ generating the real active catalyst for HER.     

Reshaping of Metal Nanoparticles Under Reaction Conditions

The shape of metal nanoparticles (NPs) is one of the key factors determining their catalytic reactivity. Recent in situ TEM observations show that dynamic reshaping of metal NPs occurs under the reaction conditions, which becomes a major hurdle for fully understanding catalytic mechanisms at the molecular level. This Minireview provides a summary of the latest progress in characterizing and modeling the equilibrium shape of metal NPs in various reactive environments through the joint effort of state‐of‐the‐art in situ environmental transmission electron microscopy experiments and a newly developed multiscale structure reconstruction model. The quantitative agreement between the experimental observations and theoretical modeling demonstrate that the fundamental mechanism of the reshaping phenomenon is driven by anisotropically changed surface energies under gas adsorption. The predictable reshaping of metal NPs paves the way for the rational design of truly efficient nanocatalysts in real reactions.     

烷基化催化剂表面酸性及催化性能的动力学研究

在确定关联升温速率、脱附峰温和脱附峰覆盖率的程序升温脱附动力学模型的基础上，通过TPD实验和模型参数估值，建立了表征催化剂酸密度、酸强度及强度分布情况的方法。研究表明，随着活化温度的提高，固体酸催化剂表面酸中心强度分布先变宽后趋于均匀，350?℃活化催化剂的强度分布最宽；催化剂表面酸强度和酸密度随活化温度提高均呈先增大后降低、分别在350 ℃和250 ℃活化温度达到极大值的变化规律。催化剂酸性与催化性能关联的结果表明，随着活化温度的提高，烷基化反应速率常数与总脱附量的变化趋势相同，而催化剂失活速率常数与脱附活化能变化趋势相同；催化剂活性稳定性随其酸强度的增大而变差，催化剂活性与催化剂酸量和酸强度有关。     

Galactose Grafted Two-Dimensional Nanosheets as a Scaffold for the In Situ Synthesis of Silver Nanoparticles: A Potential Catalyst for the Reduction of Nitroaromatics

Two major hurdles in NP-based catalysis are the aggregation of the NPs and their recycling. Immobilization of NPs onto a 2D support is the most promising strategy to overcome these difficulties. Herein, amphiphilicity-driven self-assembly of galactose-hexaphenylbenzene-based amphiphiles into galactose-decorated 2D nanosheet is reported. The extremely dense decoration of reducing sugar on the surface of the sheets is used for the in situ synthesis and immobilization of ultrafine catalytically active AgNPs by using Tollens’ reaction. The potential of the system as a catalyst for the reduction of various nitroaromatics is demonstrated. Enhanced catalytic activity is observed for the immobilized AgNPs when compared to the corresponding discrete AgNPs. Recovery of the catalytic system from the reaction mixture by ultrafiltration and its subsequent recycling for several cycles without dropping its activity is shown. This is the first report demonstrating the in situ synthesis and immobilization of ultrafine AgNPs onto a 2D nanosheet that exhibits excellent catalytic performance for the reduction of nitroaromatics.     

Infrared and Raman imaging of heterogeneous catalysts

The miniaturization of in situ spectroscopic tools has been recognized as a forefront instrumental development for the characterization of heterogeneous catalysts. With the multitude of micro-spectroscopic methods available fundamental insight into the structure-function relationships of catalytic processes can be obtained. Among these techniques vibrational spectroscopy is one of the most versatile methods and capable to shed insight into the molecular structure of reaction intermediates and products, the chemical state of catalyst materials during reaction as well as the nature of interactions between reactants/intermediates/products and the catalyst surface. In this tutorial review we discuss the recent developments in the field of infrared (IR) and Raman micro-spectroscopy and illustrate their potential. Showcase examples include (1) chemical imaging of spatial heterogeneities during catalyst preparation, (2) high-throughput catalyst screening, (3) transport and adsorption phenomena within catalytic solids and (4) reactivity studies of porous oxides, such as zeolites. Finally, new in situ spectroscopy tools based on vibrational spectroscopy and their potential in the catalysis domain are discussed.     

CoPt纳米空心球甲醇电催化氧化和原位电化学傅里叶变换红外光谱研究

采用化学还原和电位置换法制备了CoPt 纳米空心球, 该催化剂对甲醇氧化表现出较好的电催化活性.透射电镜(TEM)、能量散射光谱(EDS)和电化学循环伏安实验结果表明, 在0.1 mol·L^-1 H₂SO₄+0.1 mol·L^-1CH₃OH中进行测试时, CoPt 纳米空心球发生了去合金化过程, 催化剂表面Co元素溶解, 形成了富Pt 表面, 表现出更好的电催化活性, 同时表现出较好的结构稳定性. 采用原位电化学红外光谱在分子水平研究了CoPt 纳米空心球上甲醇氧化过程, 发现甲醇在CoPt 纳米空心球氧化中间产物主要为CO, 且CO表现出异常红外效应, 与CO为探针分子在CoPt纳米空心球上得到的红外光谱结果一致. 研究结果表明, 去合金化方法是一种有效调节催化剂表面组成和性能的手段, 原位电化学红外光谱是潜在的原位研究有机小分子氧化机理的方法, 在燃料电池中将得到广泛的应用.     

Ti-MCM-41催化环氧化合物与胺的开环反应

以十六烷基三甲基溴化铵(CTAB)为模板剂, 钛酸异丙酯为钛源, 通过水热法合成了Ti-MCM-41分子筛催化剂并对其进行了表征, 结果表明, Ti-MCM-41催化剂具有介孔结构, 其孔径约2.0~4.0 nm. 考察了无溶剂条件下Ti-MCM-41对环氧化合物与胺的开环反应的催化性能. 结果表明, 当反应温度和压力分别为145 ℃和2.5 MPa时, Ti-MCM-41(5)对环氧乙烷(EO)与二甲胺(DMA)的反应具有良好的催化性能, 环氧乙烷的转化率和N,N-二甲基乙醇胺的选择性分别为98.37%和86.68%. 表征结果表明, 催化剂骨架中四配位结构的Ti使其表面具有丰富的路易斯酸性位, 该酸性位对环氧化合物与胺的开环反应具有重要促进作用. 此外, 还对Ti-MCM-41催化环氧乙烷与二甲胺开环反应的机理进行了初步探讨.     

微波辅助催化氧化苯高性能催化剂实验研究

采用传统浸渍法制备分子筛负载过渡金属和稀土元素催化剂,通过微波辅助催化氧化苯性能实验考察其催化活性。研究表明,天津科密欧的5A分子筛为优良的催化剂载体,分子筛负载铜-锰-铈催化剂对苯的完全燃烧温度为230℃,铜(Cu)锰(Mn)双金属催化剂中晶相与非晶相Cu_1.5Mn_1.5O₄尖晶石提高了催化剂的催化活性,稀土铈(Ce)的助催化效果显著;30 h的连续性实验表明,Cu-Mn-Ce/分子筛催化剂具有良好的稳定性和高的催化活性。催化剂的比表面积和表面形貌表征表明,催化剂比表面积和孔径受高温煅烧和氧化反应而增大,从而有助于苯的吸附与氧化降解;X射线衍射表明,实验前后分子筛结构未发生明显变化,铜锰主要以二价和三价的氧化物形态分布于催化剂表面。     

Nanostructure Engineering of Metal–Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient ORR Catalyst

Heteroatom doping is considered an efficient strategy when tuning the electronic and structural modulation of catalysts to achieve improved performance towards renewable energy applications. Herein, we synthesized a series of carbon-based hierarchical nanostructures through the controlled pyrolysis of Co-MOF (metal organic framework) precursors followed by in situ phosphidation. Two kinds of catalysts were prepared: metal nanoparticles embedded in carbon nanotubes, and metal nanoparticles dispersed on the carbon surface. The results proved that the metal nanoparticles embedded in carbon nanotubes exhibit enhanced ORR electrocatalytic performance, owed to the enriched catalytic sites and the mass transfer facilitating channels provided by the hierarchical porous structure of the carbon nanotubes. Furthermore, the phosphidation of the metal nanoparticles embedded in carbon nanotubes (P-Co-CNTs) increases the surface area and porosity, resulting in faster electron transfer, greater conductivity, and lower charge transfer resistance towards ORR pathways. The P-Co-CNT catalyst shows a half-wave potential of 0.887 V, a Tafel slope of 67 mV dec⁻¹, and robust stability, which are comparatively better than the precious metal catalyst (Pt/C). Conclusively, this study delivers a novel path for designing multiple crystal phases with improved catalytic performance for energy devices.     

In Situ Formation of Au–Pd Bimetallic Active Sites Promoting the Physically Mixed Monometallic Catalysts in the Liquid‐Phase Oxidation of Alcohols

The catalytic oxidation of alcohols with molecular oxygen on supported nanometallic catalysts represents one of the green methods in a crucial process for the synthesis of fine chemicals. We have designed an experiment using physically mixed Au/AC and Pd/AC (AC=activated carbon) as the catalyst in the liquid‐phase oxidation of benzyl alcohol by aerobic oxygen. The evolution of the physically mixed catalyst structures at different stages in the catalytic reaction was investigated by aberration‐corrected high‐resolution transmission electron microscopy and spatially resolved element mapping techniques at the nanometre scale, and they were also compared with the structure of the bimetallic alloy. For the first time we show the formation of surface Au–Pd bimetallic sites by reprecipitation of Pd onto Au nanoparticles. Negligible Au leaching was observed. The in situ structural evolution can be directly correlated to the great enhancement of the catalyst activity. Moreover, we distinguish the different behaviours of Au and Pd, thus suggesting an oxygen differentiating mechanism for Au and Pd sites. The findings are of great importance to both the understanding of the structure–activity correlation and the design of highly active catalysts in green chemistry.     

表面活性剂对完全液相法制Cu-Zn-Al浆状催化剂结构和性能的影响

采用完全液相法制备了Cu-Zn-Al双功能浆状催化剂, 利用不同类型表面活性剂对其进行了修饰和改性. 通过N2气吸附、XRD和XPS等方法考察了表面活性剂类型对催化剂织构、物相以及表面性质的影响, 采用浆态床反应装置对其合成气一步法制备二甲醚的催化活性进行了评价, 讨论了催化剂结构与性能的关系. 结果表明, 表面活性剂主要是通过与活性金属的作用调节催化剂的表面性质、孔结构、相结构以及晶粒大小, 进而影响催化剂的催化活性; 非离子表面活性剂总体上对催化剂的性能有促进作用, 阳离子表面活性剂和阴离子表面活性剂对催化剂性能存在不利影响; 表面活性剂与活性金属作用的强弱是影响性能的关键.     

Liquid-Phase Hydrogenation of Chloronitrobenzene Over Pt-Sn-B Amorphous Catalyst Supported by Carbon Nanotubes

The Pt-Sn-B/carbon nanotubes (CNTs) catalyst was prepared by impregnation-chemical reduction method. Its catalytic performance was evaluated by liquid-phase hydrogenation of chloronitrobenzene (CNB). The results showed that the catalyst had higher catalytic performance than common hydrogenation catalysts. The conversion of CNB could reach 99.9%, and the dechlorination of chloroaniline (CAN) was less than 1.9% when catalyzed by Pt-Sn-B/CNTs and more than 8.0% when catalyzed by common hydrogenation catalysts. X-ray diffraction and selected area electron diffraction analysis showed that Pt-Sn-B/CNTs had an amorphous alloy structure that can improve catalytic performance. Transmission electron micrograph image showed that the catalyst particles were highly distributed on the surface of CNTs. The hydrodechlorination of CNB was mainly affected by the unique structure of CNTs and the nature of the amorphous metals on the surface of CNTs. The relationship between the interaction of CNTs and amorphous metals and the catalytic performance of the catalyst is also discussed. Translated from the Chinese Journal of Catalysis, 2005, 26(3) (in Chinese)     

用于乙炔氢氯化反应的活性炭负载铋无汞催化剂

采用浸渍法制备了活性炭负载铋无汞催化剂,并通过X射线衍射、氮气物理吸附、透射电镜、扫描电镜和X射线电子能谱等方法对催化剂进行了表征。对催化剂进行了催化乙炔氢氯化反应性能的研究,结果表明,催化剂对乙炔氢氯化反应具有良好的催化性能,活性组分主要以BiOCl的形式存在于催化剂表面。反应过程中积碳的产生使得催化剂活性有所降低。     

原位反应法制备CpTi(dbm)Cl2/MgCl2载体型催化剂及其催化乙烯聚合的研究

非茂催化剂对烯烃聚合显示出优异的催化特性,是继ziegler—Natta催化剂及茂金属催化剂之后的新一代烯烃聚合催化剂^[1],其中非环戊二烯基配体有含氮化合物[2-8]和含氧化合物^[9-15]等,这些非茂配合物可催化乙烯或丙烯聚合．将金属中心与一个环戊二烯基和一个非环戊二烯基配体而     

碳纳米管负载Pt-Sn-B非晶态催化剂催化氯代硝基苯

 用浸渍-化学还原法制备了碳纳米管负载的Pt-Sn-B非晶态催化剂,并采用透射电子显微镜、X射线衍射、选区电子衍射、X射线能谱等表征手段研究了催化剂在碳纳米管表面的存在状态、组成及其非晶性质. 将此催化剂用于三种氯代硝基苯的液相催化加氢反应,结果表明该催化剂具有较好的加氢性能和较高的抑制脱卤性能. 在不添加脱卤抑制剂的情况下,三种氯代硝基苯的转化率均高于99.8%,脱卤率小于1.9%. 而将通用加氢催化剂用于相同的反应时,产物的脱卤率均高于8%. 碳纳米管的特殊结构与表面金属的非晶性质是影响氯代硝基苯加氢性能的主要因素. 讨论了碳纳米管与表面非晶态金属的作用规律及其与催化加氢性能的关系.     

碱 性 载 体 对 负 载 型ＣｏＯ 催 化 剂 催 化 性 能 的 影 响

采用XRD、TPR、TPD、XPS和催化活性评价等技术,考察了负载型CoO催化剂的表面性质和其对CH4与CO2重整制合成气反应的催化性能.实验结果表明,碱性载体或助剂MgO和La2O3的添加能有效地改善CoO催化剂的表面结构、抗积炭能力和还原性能,CoO/MgO催化剂显示出最佳的催化反应稳定性,在750℃、GHSV=2500h-1、CH4/CO2原料比为1:1下,连续反应100h内催化剂活性较为稳定,CoO/MgO和CoO/γ-Al2O3催化剂的表面性质本质上是不相同的.