Influence of electronic state of rhodium in supported bimetallic catalysts on catalytic activity and selectivity in carbon monoxide hydrogenation reactions

Data on the mechanism and kinetics of the hydrogenation of carbon monoxide to saturated hydrocarbons and alcohols over supported bimetallic rhodium-containing catalysts are summarized and correlated. Rankings of specific catalytic activity and selectivity of Rh-M′/Al₂O₃ catalysts in relation to the chemical nature of M′, and hence in relation to the electronic state of the rhodium, are interpreted from a common point of view. On the basis of the interrelations that were found between the physicochemical and catalytic properties of these bimetallic systems, ground rules were formulated for selecting monotypical catalysts for the selective hydrogenation of carbon monoxide. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 199–218, July–August, 1997.     

碳纳米管负载Co-Mo催化剂在孤岛减压渣油加氢裂化反应中的应用

采用等体积浸渍法制备了一系列不同Co/Mo原子比的碳纳米管（CNT）负载Co Mo催化剂。将该系列催化剂用于孤岛减压渣油加氢裂化反应,评价其催化效果,并在相同反应条件下与 γAl2O3负载Co-Mo催化剂的催化性能进行比较。结果表明,Co-Mo/CNT催化剂的催化效果略低于Co-Mo/γAl2O3催化剂。Co/Mo原子比对Co-Mo/CNT催化剂的催化效果有较大的影响。与相同载体的催化剂相比,当Co/Mo原子比为0.50时,Co-Mo/CNT催化剂具有最佳的催化效果,而Co-Mo/γAl2O3催化剂在Co/Mo原子比为0.35时具有最佳的催化效果。     

炭材料负载金属催化剂催化硅氢加成反应进展

炭材料具有比表面积大、孔径可调、取材广泛等优点,以其为载体负载金属活性组分制备硅氢加成催化剂极具发展前景.我们详细总结了近20年不同炭材料如活性炭、石墨与石墨烯、碳纳米管、富勒烯、卡宾等在硅氢加成反应中负载金属催化剂的制备方法、催化性能以及可能的催化机理,并对有望应用到该反应的新型炭材料载体进行了对比与展望.认为未来硅氢加成炭负载型催化剂的研究可聚焦于(1)探寻新型双金属活性组分以进一步提高催化活性;(2)研发更具优势的金属配体,明晰配体与载体、配体与金属之间的相互作用关系以提高催化选择性与稳定性;(3)结合科学可靠的催化机理研究,以期研发出更符合可持续发展要求的炭负载型硅氢加成金属催化剂,可使硅氢加成反应基本实现原子经济性.     

Scientific Grounds for the Application of Mechanochemistry to Catalyst Preparation

It is shown that mechanochemical activation is efficient in creating waste-free energy-saving methods for the preparation of hydride catalysts, heteropoly acid catalysts, and catalysts for hydrocarbon decomposition into hydrogen and carbon materials, as well for the syntheses of earlier unknown catalytic systems. The capabilities of the mechanochemical methods are demonstrated on modifying the catalytic properties of catalysts and supports: an increase in the strength and catalytic activity, sorption properties, etc. Adhesion theory applied to melts helps to describe the mechanism of mechanochemical synthesis of catalytic systems.     

Effect of the functionalizing of carbon nanotubes on the electrodeposited catalysts’ structure and catalytic properties

The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation and oxygen electroreduction reactions. When minor amounts (5–10 μg cm⁻²) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst is formed, with specific surface area up to 150–300 m² g⁻¹; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers.     

Influence Type and Temperature of Activation on the Catalytic Activity of Derived Form of Au 101 Nanocatalysts

Recently, gold nanoparticles attracted an increased attention due to unusual and somewhat unexpected catalytic properties especially pronounced in the oxidation of some organic compounds. Gold nanoparticles, which was immobilized on powder Norit® activated carbon as a support (1.0 wt % Au101/AC) exhibited high activity and selectivity for benzyl alcohol oxidation particularly with the gold catalysts subjected to a specific type of activation and temperature. The interaction between Au101 particles and its support was studied by measuring the catalytic activity and selectivity as a function of activation procedure. The first method included washing with a solvent (i.e., toluene) at elevated temperature, and/or followed by heat treatments at mild temperatures (i.e., 100 and 200°C for 3 h). The highest catalytic activity of benzyl alcohol oxidation was however obtained when gold catalysts were pre-washed with hot toluene at 100°C for 2 h followed by thermal treatment under vacuum. In these cases, the gold core diameters was ∼3.5 nm. In a number of experiments, the reaction time was 3 h, whereas in other runs it was extended to 24 h. The conversion level of benzyl alcohol oxidation was affected by the type of activation and its temperature related to the gold particles size.     

Recent Progress in Application of Graphene Supported Metal Nanoparticles in C−C and C−X Coupling Reactions

The carbon‐carbon and carbon‐heteroatom bonds catalytic formation is among the most significant reactions in organic synthesis which extensively applied for synthesis of natural products, heterocycles, dendrimers, biologically active molecules and useful compounds. This review provides the latest advances in the preparation of graphene supported metal nanoparticles and their application in the catalytic formation of both carbon‐carbon (C−C) and carbon‐heteroatom (C−X) bonds including the Suzuki, Heck, Hiyama, Ullmann, Buchwald and Sonogashira coupling reactions. Numerous examples are given concerning the use of these catalysts in C−C and C−X coupling reactions along with the reliable and simple preparation methods of these catalysts, their characterization and catalytic properties and also the recycling possibilities.     

Main factors determining the catalytic properties of active carbons

The results of the authors' investigations into the catalytic properties of active carbons in acid-base and oxidation-reduction reactions, mostly obtained in recent years, are summarized. On the basis of previous and recent data the main factors affecting the course of the catalytic processes are identified, the general principles governing control of the catalytic activity of carbon catalysts are described, and new ways of using the catalytic properties of carbon sorbents from various sources are established.Institute of Sorption and Problems of Endoecology, Academy of Sciences of Ukraine, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 6, pp. 336–344, November–December, 1996. Original article submitted March 22, 1996.     

DFT Studies of Palladium Model Catalysts: Structure and Size Effects

An important task for theory is the multi-scale modeling of catalytic properties of nanocrystallites with sizes ranging from clusters of few metal atoms to particles consisting of 10³–10⁴ atoms. To explore catalytic properties of nanosized metal catalysts, we developed an approach based on three-dimensional symmetric model clusters of 1–2 nm (~100 metal atoms) with fcc structure, terminated by low-index surfaces. With this modeling technique one is able to describe at an accurate DFT level various catalytic and adsorption properties of metal nanoparticles in quantitative agreement with experimental studies of model catalysts deposited on thin oxide films. Metal nanocrystallites exhibit properties that can significantly vary with their size and shape.     

Chain Mail for Catalysts

Encapsulating transition-metal nanoparticles inside carbon nanotubes (CNTs) or spheres has emerged as a novel strategy for designing highly durable nonprecious-metal catalysts. The stable carbon layer protects the inner metal core from the destructive reaction environment and thus is described as chain mail for catalysts. Electron transfer from the active metal core to the carbon layer stimulates unique catalytic activity on the carbon surface, which has been utilized extensively in a variety of catalytic reaction systems. Here, we elaborate the underlying working principle of chain mail for catalysts as well as the key factors that determine their catalytic properties, and provide insights into the physicochemical nature of such catalyst architectures for further application of the strategy in rational catalyst design.     

Chain Mail for Catalysts

Encapsulating transition‐metal nanoparticles inside carbon nanotubes (CNTs) or spheres has emerged as a novel strategy for designing highly durable nonprecious‐metal catalysts. The stable carbon layer protects the inner metal core from the destructive reaction environment and thus is described as chain mail for catalysts. Electron transfer from the active metal core to the carbon layer stimulates unique catalytic activity on the carbon surface, which has been utilized extensively in a variety of catalytic reaction systems. Here, we elaborate the underlying working principle of chain mail for catalysts as well as the key factors that determine their catalytic properties, and provide insights into the physicochemical nature of such catalyst architectures for further application of the strategy in rational catalyst design.     

Hydrogenation of acetone on technetium catalysts

The catalytic properties of supported mono- and bimetallic catalysts of the Tc/support, M/support, and M-Tc/support types (M=Pt, Pd, Rh, Ru, Ni, Re, Co; supports are γ-Al₂O₃, MgO, SiO₂) were investigated in the acetone hydrogenation. The main products of this reaction are isopropyl alcohol and propane. The catalytic activity in the acetone hydrogenation of the metals studied decreases in the consequence Pt>Tc≈Rh>Pd>Ru >Ni≈Re>Co (with γ-Al₂O₃ as the support). The influence of support nature on the catalytic activity was investigated for the Rh−Tc system as an example. A nonadditive increase in the catalytic activity of Rh−Tc/γ-Al₂O₃ in comparison with monometallic catalysts was found. The state of the surface of the catalysts was characterized by the UV-VIS diffuse reflectance spectra. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 414–417, March, 1998.     

碳催化剂在催化反应中的应用

由于碳材料表面存在缺陷,可生成具有不同性能的活性位,因此可催化不同的热催化反应.我们首先介绍了单质碳材料的表面结构化学:其表面活性位主要为含杂原子官能团;然后对其可催化的反应进行了介绍:碳单质材料可催化选择性氧化反应、高级氧化反应、还原反应、烷烃活化反应、酸催化反应、电催化还原和氧化反应等.对碳单质催化剂的制备方法、所...     

Studies on accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt Fischer-Tropsch synthesis catalyst

Accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt (K-Ru-Co/γ-Al 2 O 3 ) Fischer-Tropsch (FT) synthesis catalyst along the catalytic bed over 120 h of time-on-stream (TOS) was investigated. Catalytic bed was divided into three parts and structural changes of the spent catalysts collected from each catalytic bed after FT synthesis were studied using different techniques. Rapid deactivation was observed during the reaction due to high reaction temperature and low feed flow rates. The physico-chemical properties of the catalyst charged in the Bed #1 of the reactor did not change significantly. Interaction of cobalt with alumina and the formation of CoAl 2 O 4 increased along the catalytic bed. Reducibility percentage decreased by 4.5%, 7.5% and 12.9% for the catalysts in the Beds #1, #2 and #3, respectively. Dispersion decreased by 8.8%, 14.4% and 26.6% for the catalysts in the Beds #1, #2 and #3, respectively. Particle diameter increased by 0.6%, 2.4% and 10.4% for the catalysts in the Beds #1, #2 and #3, respectively, suggesting higher rate of sintering at the last catalytic bed. The amount of coke at the last catalytic bed was significantly higher than those of Beds #1 and #2.     

Solid acid catalysts for synthesis of biodiesel fuel from pyrolyzed natural and synthetic polymeric materials

New heterogeneous catalysts for synthesis of a biodiesel fuel, modified with strongly acidic groups, were developed. The catalysts are produced by pyrolysis and subsequent sulfation of fruit kernels and granulated porous copolymers and resins. The structural-sorption and catalytic properties of the materials obtained were studied in the reaction of catalytic re-esterification of rapeseed oil by methanol and ethanol. The conditions in which carbon materials with high content of surface acid groups are obtained were optimized.     

Corundum impregnation conditions for preparing supported Ni catalysts for the synthesis of a uniform layer of carbon nanofibers

Impregnation techniques for corundum (S _BET = 0.5 m²/g) as a support for Ni catalysts for C₃–C₄ alkane pyrolysis into catalytic filamentous carbon (CFC) are compared. The effects of the following factors on the uniformity of the active component (Ni) deposition on the inert support and on the CFC yield (g CFC)/(g Ni) are reported: (1) pH of the nickel nitrate solution, (2) presence of aluminum(III) nitrate in the solution, (3) addition of viscosifying agents (glycerol, glucose, sucrose) to the solution, (4) catalyst calcination conditions before pyrolysis, and (5) catalyst drying technique. The surface morphology of the Ni catalysts and of the carbon deposits resulting from the catalytic pyrolysis of C₃–C₄ alkanes in the presence of hydrogen has been investigated by scanning electron microscopy. The optimum way of preparing the supported Ni catalysts is by carrying out the incipient wetness impregnation of corundum with a nickel nitrate solution (0.05–0.1 mol/l) containing glycerol (20–25 vol %), drying the product in a microwave oven, and burning away the glycerol before alkane pyrolysis.     

Pd/MWCNTs(多壁碳纳米管)催化剂的制备及其Heck反应催化活性

以浓硝酸处理后的多壁碳纳米管(MWCNTs)为载体,通过微波辅助法简单而快速地制备了高度分散、粒径均一的Pd/MWCNTs催化剂。利用XRD、HRTEM、XPS等手段对催化剂进行了表征。考察了Pd/MWCNTs催化剂对Heck反应的催化活性,并优化了反应温度、碱的种类和用量等反应条件。结果表明,Pd/MWCNTs在Heck反应中具有良好的催化活性。     

2D Graphdiyne: A Rising Star on the Horizon of Energy Conversion

Two-dimensional (2D) graphdiyne (GDY), a rapidly rising star on the horizon of carbon materials, is a new carbon allotrope featuring sp- and sp²-cohybridized carbon atoms and 2D one-atom-thick network. Since the first successful synthesis of GDY by Professor Li's group in 2010, GDY has attached great interests from both scientific and industrial viewpoints based on its unique structure and physicochemical properties, which provides a fertile ground for applications in various fields including electrocatalysis, energy conversion, energy storage and optoelectronic devices. In this work, various potential properties of the GDY-based electrocatalysts and their recent advances in energy conversion are reviewed, including atomic catalysts, heterogeneous catalysts, and metal-free catalysts. The critical role of GDY in improving catalytic activity and stability is analyzed. The perspectives of the challenges and opportunities faced by GDY-based materials for energy conversion are also outlined.     

低温催化法制备石墨化碳空心球

石墨化碳空心球因具有密度小、稳定性好和可填充中空结构等特点,受到了研究者的广泛关注。本文结合国内外的研究进展,综述了近年来发展起来的采用过渡金属如铁、钴、镍等为催化剂,低温(<1 000℃)催化法合成石墨化碳空心球的最新研究进展。介绍了低温催化法提高碳空心球石墨化程度的机理,说明了石墨化碳空心球的表征方法,展望了石墨化碳空心球的应用前景。最后指出了相关研究中有待解决的问题。     

Influence of preparation method on the performance of Mn–Ce–O catalysts

Mn–Ce–O catalysts were prepared by the sol–gel method with different citric acid amounts in preparation. The catalysts were characterized by using BET, XRD, TPR, XPS and their catalytic activities in methane combustion were also investigated. Results showed that the surface area, Mn⁴⁺ and O_latt are responsible for the high catalytic activity of Mn–Ce–O catalysts.