Catalytic hydrogenation of aromatic nitro compounds by non-noble metal complexes of chitosan

Silica-supported mono-metal (such as Ni, Cu) complexes and mixed metal (such as Cu/Zn, Cu/Cr) complexes of chitosan have been prepared. It is found that these non-noble metal complexes could be used as efficient catalysts for the hydrogenation of aromatic nitro compounds. The effects of type of metal, reaction temperature and pressure, solvent, nitrogen/metal molar ratio in the complex catalysts on the yields from nitrobenzene to aniline have been examined. It was also found that catalysts are active for the catalytic hydrogenation of other aromatic nitro compounds such as 2-nitroanisole, 2-nitroaniline, 2-nitrotoluene and 1-chloro-4-nitrobenzene.     

Effect of the Nature of Coke-Forming Species on the Crystallographic Characteristics and Catalytic Properties of Metal–Filamentous Carbon Catalysts in the Selective Hydrogenation of 1,3-Butadiene

The particle morphology and surface structure of nickel metal in metal–filamentous carbon catalysts were found to depend on the nature of coke-forming species used in the synthesis of catalysts. Metal carbonization with hydrocarbons that are characterized by high thermodynamic stability results in the formation of well-cut metal particles the surface of which is formed by (110) facets. Selective hydrogenation reactions of diene and acetylene hydrocarbons to olefins are typical of these catalysts. In the catalytic decomposition of hydrocarbons with relatively low thermodynamic stability, metal particles become irregular in shape, and their surface is formed by (111) facets. In this case, the reactions of full hydrogenation of olefin, diene, and acetylene hydrocarbons to corresponding alkanes take place. These data are consistent with the found dependence of the catalytic properties of catalysts on the character of the exterior faceting of active metal particles.     

Selective hydrogenation of aromatic compounds using modified iridium nanoparticles

Till now, Ionic liquid‐stabilized metal nanoparticles were investigated as catalytic materials, mostly in the hydrogenation of simple substrates like olefins or arenes. The adjustable hydrogenation products of aromatic compounds, including quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes, are always of special interest, since they provide more choices for additional derivatization. Iridium nanoparticles (Ir NPs) were synthesized by the H₂ reduction in imidazolium ionic liquid. TEM indicated that the Ir NPs is worm‐like shape with the diameter around 12.2 nm and IR confirmed the modification of phosphine‐functionalized ionic liquids (PFILs) to the Ir NPs. With the variation of the modifier, solvent and reaction temperature, substrate like quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes could be hydrogenated by Ir NPs with interesting adjustable catalytic activity and chemoselectivity. Ir NPs modified by PFILs are simple and efficient catalysts in challenging chemoselective hydrogenation of quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes. The activity and chemoselectivity of the Ir NPs could be obviously impacted or adjusted by altering the modifier, solvent and reaction temperature.     

Study of nickel nanoparticles supported on activated carbon prepared by aqueous hydrazine reduction

Nickel nanoparticles were obtained by the reduction in hydrazine aqueous media of nickel acetate as a precursor supported on activated carbon of high surface area. Classical catalysts using nickel acetate or nitrate were prepared for comparison. The catalysts were characterized by N(2) physisorption, H(2)-TPR, H(2)-adsorption, TPD, TEM, and XRD, and tested in the gas phase hydrogenation of benzene. Hydrazine catalysts were found much more active in benzene hydrogenation than corresponding classically prepared catalysts. Remarkably, their reactivity is comparable (turn-over frequency of 0.2001-0.2539 s(-1) at 393 K) to that of Pt classical catalysts supported on activated carbon in the same conditions. Evidence is given for the existence of the hydrogen spillover effect in benzene hydrogenation, not reported before in the literature. As a result of the hydrogen spillover effect, catalysts performances can be explained by a combination of surface metal atom reactivity, metal-support interaction strength, and specific surface area extent. Maximum effect is observed with hydrazine preparation method, for 1% Ni content and nickel acetate as a precursor. Unexpectedly, it was also found that hydrazine preparation increases the specific area of the catalysts.     

Rhodium(0) nanoparticles supported on nanocrystalline hydroxyapatite: highly effective catalytic system for the solvent-free hydrogenation of aromatics at room temperature

The hydrogenation of aromatics under mild conditions remains a challenge in the fields of synthetic and petroleum chemistry. Described herein is a new catalytic material that shows excellent catalytic performance in terms of activity, selectivity, and reusability in the hydrogenation of aromatics in solvent-free systems under mild conditions. The catalyst, consisting of rhodium nanoparticles supported on nanocrystalline hydroxyapatite, can quantitatively hydrogenate neat benzene to cyclohexane with exceptionally high rates (initial TOF > 10(3) h(-1)) at 298 K and 3 bars of initial H(2) pressure. This new material maintains its inherent catalytic activity after several reuses. Importantly, catalyst preparation does not require elaborate procedures because the active metal nanoparticles are readily formed from the in situ reduction of Rh(3+)-exchanged hydroxyapatite while submerged in the aromatic solvent at room temperature under 3 bars of H(2) pressure.     

金属有机骨架基催化剂在加氢反应中的应用

加氢是现代化工产业中的一类主干反应,广泛应用于精细化学品、药物、食品、染料、功能聚合物及香料等制造产业中.高效催化剂的引入使得加氢反应能够在相对温和的条件下还原各类不饱和化合物.金属催化剂在加氢反应中活性高,所需的反应温度较低,适用性广,但是容易和S,N,As和P等元素结合而"中毒"失去反应活性.金属氧化物催化剂和金属硫化物催化剂具有一定的抗毒性,但活性相对较差,通常需要采用高温高压的反应条件,对催化剂本身和反应器的要求较为苛刻.传统催化剂在反应中具有一定的局限性,所以亟需开发新一代高效的加氢催化剂,在保证高活性和高选择性催化效果的同时,降低对能源的消耗和对环境的负面影响.金属有机骨架(MOFs)作为一种新型的多孔材料在过去二十年中受到相当大的关注,并在催化、气体存储和分离、传感器、发光材料和药物输送等众多领域的应用中表现出卓越的性能.利用MOF材料良好的相容性,将MOF和其它功能材料结合形成新的复合材料可以在更大程度上扩大MOF材料的应用领域.与传统的催化剂相比,MOF基材料具有优异的物理化学特性和结构可调性,通过合理的设计能够满足不同的催化加氢过程:(1)MOF基催化剂具有多样且特异性的活性位点.除了组成MOF材料的金属离子/簇和功能有机配体之外,MOF材料可通过封装其他活性物质或者被活性物质包裹等方式引入其他类型的催化位点,进一步扩大MOF基催化剂在不同催化加氢中的适应性.此外,不同的活性位点之间的协同作用又能特异性地促进反应的进行,对提高反应的选择性起到重要的作用.(2)活性位点的尺寸大小和空间分布可以被有效控制.这能影响到催化剂在催化反应过程中的活性和选择性,并且通过MOF材料的限域效应,同时能增强活性位点的稳定性和耐久性.(3)高比表面积能提高MOF基催化剂的催化活性.这种结构特性不仅可以增加MOF基催化剂的活性位点,而且能够吸附反应物和还原剂达到扩大其局部浓度的效果.(4)反应分子的扩散可通过调节MOF基催化剂的结构实现控制.通过调整MOF材料的孔窗口和通道的尺寸,能够改变反应物在催化剂内部的扩散途径,影响底物和活性位点的接触,能进一步影响反应的活性和选择性.本文总结了近几年来MOF基材料在不同的催化加氢反应中的应用,其中包括烯烃、炔烃、芳硝基化合物、肉桂醛、糠醛和苯等化合物的加氢反应.首先介绍了MOF基材料中不同类型的活性位点,除了MOF材料自身的金属离子/簇和功能有机配体外,MOF基复合材料中的金属纳米颗粒?金属硫化物?金属氧化物?均相催化剂等活性位点可以通过封装或包裹的方式引入.在不同加氢反应中,着重介绍了MOF基催化剂中不同类型活性位点的加氢过程中的催化方式、催化剂本身的结构优化及催化剂与反应底物之间的相互作用,以及这些因素之间的协同作用对反应活性和选择性的影响.最后,讨论了MOF基材料在加氢反应中应用存在的问题以及未来发展展望.     

Microemulsion-templated synthesis of carbon nanotube-supported pd and rh nanoparticles for catalytic applications

Palladium, rhodium, and bimetallic Pd/Rh nanoparticles synthesized in a water-in-hexane microemulsion can be deposited directly on surfaces of functionalized multiwalled carbon nanotubes with high yields. The CNT-supported Pd nanoparticles are active catalysts for hydrogenation of olefins, for carbon-carbon bond formation, and for carbon-oxygen bond cleavage reactions. The CNT-supported Rh nanoparticles are active catalysts for hydrogenation of arenes, and the CNT-supported bimetallic Pd/Rh nanoparticles show an unusually high catalytic activity for hydrogenation of anthracene. This simple and novel synthetic technique for making CNT-supported monometallic and bimetallic nanoparticles may have a wide range of catalytic applications for chemical syntheses.     

Geometric and electronic approaches to size effects in heterogeneous catalysis

The influence of electronic and geometric factors is considered in the context of the manifestation of size effects in heterogeneous catalytic oxidation and hydrogenation reactions. Both of the factors are interdependent; however, the electronic factor predominates with regard to small metal and metal oxide particles (smaller than 10 nm), for which the energies of electron transitions in an activated complex are size-dependent. Only the geometry of active component nanoparticles exerts the main effect on the catalytic properties of coarser particles. In this case, the geometric factor depends on the accessibility of the active surface to reactants. The probability of the occurrence of complex active centers including several surface atoms increases as the active component particles of a catalyst become larger. The efficiency of the approach proposed to study the activating effect of nanophase catalysts is demonstrated using the oxidation and hydrogenation reactions of carbon oxides and the hydrogenation of acetonitrile and acetone as examples.     

Swelled plastics in supercritical CO2 as media for stabilization of metal nanoparticles and for catalytic hydrogenation

Swelled plastics in supercritical carbon dioxide provide unique environments for stabilizing palladium and rhodium nanoparticles and for catalytic hydrogenation. Complete hydrogenation of benzene to cyclohexane can be achieved in 10 minutes using the plastic stabilized Rh nanoparticles at 50 degrees C in supercritical CO(2). High efficiency, reusability, and rapid separation of products are some advantages of the plastic stabilized metal nanoparticles for catalytic hydrogenation in supercritical CO(2).     

Asymmetric synthesis of 2-methyl cyclohexane carboxylic acids by heterogeneous catalysis: mechanistic aspects

The catalytic hydrogenation of (S)-alkyl-N-(2-methylbenzoyl)pyroglutamates was studied over supported rhodium and ruthenium catalysts at room temperature and a pressure of 5 MPa. The reaction was diastereoselective with the predominant formation of (1S,2R)-2-methylcyclohexane carboxylic acid with a diastereomeric excess (de) of up to 96%. The most stable conformation was determined by means of a combination of modelling calculations, NMR spectroscopy and X-ray structural determination. In this conformation, the carbonyl group of the pyroglutamate auxiliary shields one face of the aromatic ring. The observed selectivity may thus be explained by a preferential adsorption at the unshielded face which avoids steric repulsion by the C=O group to result in a cis hydrogenation. The addition of an amine, the nature of the support (alumina or active carbon) or of the metal (Rh or Ru) were shown to give additional stabilisation of the adsorption at the unshielded face to increase the diastereoisomeric excess.     

Soluble metal–polymer catalysts in the hydrogenation of organic compounds

Literature describing the use of soluble metal–polymer catalysts in the molecular hydrogenation of alkenes, alkynes, aromatic and heterocyclic compounds has been reviewed. Special attention has been paid to coordinated metallic and organometallic catalytic systems and highly dispersed colloidal metals stabilized with polymers. The influence of metals, polymers and solvents on the structures of active sites is discussed. The prospects for the application of soluble metal–polymer catalysts in organic synthesis are also considered.     

On linear free energy correlations in liquid-phase catalytic hydrogenation of aromatic compounds

Application of linear free energy relationships (correlation between kinetics and thermodynamics) to catalytic hydrogenation of aromatic compounds in the liquidphase over supported metal catalysts is discussed.     

Transfer Hydrogenation of Nitroarenes Catalyzed by CoCu Anchored on Nitrogen-doped Porous Carbon

The non-precious metal catalysts with high catalytic activity is extremely desirable but still full of challenges. In this paper, CoCu bimetal immobilized on nitrogen-doped porous carbon (CoCu-N-C) was prepared by an effective ligand-stabilized pyrolysis strategy. CoCu-N-C exhibited excellent catalytic efficiency for the transfer hydrogenation of nitroarenes with ammonia borane as hydrogen source, which can be ascribed to the well dispersed metal nanoparticles, the synergetic interaction of CoCu bimetal and nitrogen-doped carbon. The durability and recyclability experiments of the recycled CoCu-N-C catalyst indicated that no obvious change in catalytic performance was observed after five consecutive cycles. To gain insight into the catalytic mechanism of CoCu-N-C for the hydrogenation reaction, density functional theory calculations was also conducted. This work provides an universal approach for constructing highly efficient non-precious metal heterogeneous catalysts and which may find diverse high performance applications.     

Synthesis of Ni/SiO<Subscript>2</Subscript> nanoparticles for catalytic benzene hydrogenation

Nickel nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium. The obtained solids were characterized by X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Electron Diffraction (ED), hydrogen chemisorption, and Temperature Programmed Desorption of hydrogen (H₂-TPD). The catalytic properties were evaluated for benzene hydrogenation in the temperature range 75–230 °C. XRD patterns reveal presence of the metallic nickel particles with fcc structure. Metal dispersion and hydrogen storage increase with decreasing metal particle size. The H₂-TPD profiles exhibit two domains, one due to desorption of hydrogen from Ni metal and another due to spillover from metal to the support. The catalytic activity strongly depends on the metal loading. It increases with decreasing metal loading. This is attributed to metal surface area, which also increases with decreasing metal loading. Kinetic studies of benzene hydrogenation on the Ni catalysts showed that the benzene partial order is around −2. This significant negative value is ascribed to a strong adsorption of benzene on the catalyst surface.     

Recent Advances on Confining Noble Metal Nanoparticles Inside Metal-Organic Frameworks for Hydrogenation Reactions

Hydrogenation reaction is one of the pillars of the chemical industry for the synthesis of drugs and fine chemicals. To achieve high catalytic performance, it is still highly desirable for constructing novel supported metal catalysts. Different from conventional supports like metal oxides, zeolites and carbon materials, metal-organic frameworks(MOFs) as the emerging porous materials have Hexhibited great potential to host metal nanoparticles (NPs) for achieving hydrogenation reactions with high catalytic efficiency, due to their unique porous structures. Recently, many progresses have been made, and thus, it is necessary to summarize the recent progresses on confining metal NPs inside MOFs for hydrogenation reactions. In this review, we first introduced the general synthesis methods for confining noble metal NPs inside MOFs. Then, the applications of noble metal NPs/MOFs catalysts in hydrogenation reactions were summarized, and the synergistic catalytic performances among noble metal NPs, metal nodes, functional groups, and pore channels in MOFs were illustrated. Subsequently, the hydrogen spillover effect involved in the hydrogenation reactions was discussed. Finally, we provide an outlook on the future research directions and challenges of confining noble metal NPs inside MOFs for hydrogenation reactions.     

Ultra Deep Hydrodesulfurization of Gas Oils Over Sulfide and/or Noble Metal Catalysts

Deep hydrodesulfurization (HDS) of sterically hindered sulfur compounds in gas oils will require enhanced hydrogenation activity to hydrogenate the aromatic rings of the sulfur compounds. Although H₂S is known to inhibit the direct HDS route for most of the sulfided catalysts, its promotion to the hydrogenation and subsequent HDS was newly observed for unsupported MoS₂. This promotion suggests that ultra deep HDS over sulfide catalysts can be achieved along with high metal loading, minimal support-metal interactions and optimal dependence on the Ni species. On the other hand, the strong hydrogenation activity of sulfur-tolerant noble metal catalysts suggests that ultra deep HDS as well as deep aromatics saturation can be achieved. This paper discusses recent catalytic approaches for ultra deep HDS using conventional sulfide catalysts and/or noble metal catalysts, such as the newly developed Pd-Pt/Yb-USY zeolite catalyst.     

Catalytic activity of in situ synthesized MoWNi sulfides in hydrogenation of aromatic hydrocarbons

MoWNi–sulfide catalysts were obtained in situ by thermal decomposition of metal–polymer precursors based on the copolymers of polymaleic anhydride in a hydrocarbon raw material. The activity of the synthesized catalysts in hydrogenation of bicyclic aromatic hydrocarbons was studied, and the composition and structure of active phase nanoparticles were determined.     

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Vacuum studies of metal single crystal surfaces using electron and molecular beam scattering revealed that the surface atoms relocate when the surface is clean (reconstruction) and when it is covered by adsorbates (adsorbate-induced restructuring). It was also discovered that atomic steps and other low coordination surface sites are active for breaking chemical bonds (H-H, O=O, C-H, C=O, and C-C) with high reaction probability. Investigations at high reactant pressures using sum frequency generation-vibrational spectroscopy and high pressure scanning tunneling microscopy revealed bond breaking at low reaction probability sites on the adsorbate-covered metal surface and the need for adsorbate mobility for continued turnover. Since most catalysts (heterogeneous, enzyme, and homogeneous) are nanoparticles, colloid synthesis methods were developed to produce monodispersed metal nanoparticles in the 1-10 nm range and controlled shapes to use them as new model catalyst systems in two-dimensional monolayer film or deposited in mesoporous three-dimensional oxides. Studies of reaction selectivity in multipath reactions (hydrogenation of benzene, cyclohexene, and crotonaldehyde) showed that the reaction selectivity depends on both nanoparticle size and shape. The oxide-metal nanoparticle interface was found to be an important catalytic site that is associated with the hot electron flow induced by exothermic reactions such as carbon monoxide oxidation.     

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.     

Understanding the Catalytic Sites of Metal–Nitrogen–Carbon Oxygen Reduction Electrocatalysts

The development of low-cost catalysts containing earth-abundant elements as alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) is crucial for the large-scale commercial application of proton exchange membrane fuel cells (PEMFCs). Nonprecious metal–nitrogen–carbon (M-N-C) materials represent the most promising candidates to replace Pt-based catalysts for PEMFCs applications. However, the high-temperature pyrolysis process for the preparation of M-N-C catalysts frequently leads to high structural heterogeneity, that is, the coexistence of various metal-containing sites and N-doped carbon structures. Unfortunately, this impedes the identification of the predominant catalytic active structure, and thus, the further development of highly efficient M-N-C catalysts for the ORR. This Minireview, after a brief introduction to the development of M-N-C ORR catalysts, focuses on the commonly accepted views of predominant catalytic active structures in M-N-C catalysts, including atomically dispersed metal–N_x sites, metal nanoparticles encapsulated with nitrogen-doped carbon structures, synergistic action between metal–N_x sites and encapsulated metal nanoparticles, and metal-free nitrogen-doped carbon structures.