Catalytic Activity For Hydrogenation Research Articles

Facile fabrication of TiO2 with 3D hierarchical structure and its supported Pd catalysts for high catalytic hydrogenation performance of 4-Nitrophenol to 4-Aminophenol

TiO2 with different morphology as supports can lead to different surface properties and catalytic activities of catalysts. Herein, we reported a novel facile evaporation-induced assisted hydrothermal approach to synthesize three-dimensional hierarchical structure TiO2 assembled from needle flakes by using Brij-35 as the morphology-directing agent. The morphology of the prepared TiO2 from flower-like (TiO2-FT), sea urchin-like (TiO2-SUT), to ball-like (TiO2-BT), as well as the size of needle flakes, were controlled by adjusting the amount of Brij-35. These TiO2 supported palladium catalysts were facilely prepared using a green bio-reductive method with Catalpa Fruit extract as reducing agent, where they showed remarkable catalytic activity in selective hydrogenation of 4-nitrophenol by sodium borohydride. Especially, 1 wt%Pd/TiO2-SUT with sea urchin-like exhibited higher reaction rate constant (1.44 min−1) than 1 wt%Pd/TiO2-FT (1.08 min−1) and 1 wt%Pd/TiO2-BT (0.72 min−1). Furthermore, XRD, N2 adsorption–desorption, SEM, TEM, CO-FTIR, XPS and CO chemisorption measurements were performed to study the effects of different surface morphologies on the surface properties of catalysts. It reveals that the high catalytic performance of 1 wt%Pd/TiO2-SUT can be attributed to its specific hierarchical structure and much higher surface area, improving the uniform dispersion of Pd nanoparticles on the support to expose extra active surface Pd atoms (Pd0 species) over 1 wt%Pd/TiO2-SUT.

Structural studies of ligand stabilized Ni/Ga clusters by means of vibrational spectroscopy and theoretical calculations

AbstractIn order to explain the different catalytic activity in hydrogenation of two new intermetallic Ni/Ga clusters, [Ga7](NiCp*)6 (1A) and [NiGa6](NiCp*)6 (1B) (Cp* = C5Me5), investigations of structure–function relationship have been performed based on Raman and infrared (IR) spectroscopy and theoretical (density functional theory [DFT] and normal coordinate) calculations. Full interpretation of the Raman, far‐IR, and mid‐IR spectra of these dark colored solids has been proposed. Based on the overview of metal–Cp* complexes, all the 14 characteristic Cp*− skeletal fundamental modes have been identified. By comparison of the NiCp* stretching and tilting external modes (350–380 cm−1), their force constants, and bond lengths, cluster 1B exhibited slightly stronger metal–ligand bonding. Vibrations of Ga7 and NiGa6 cluster cores showed that the stretching wavenumbers and force constants of NiGa (100–350 cm−1) and GaGa (60–250 cm−1) bonds are higher for cluster 1B, in agreement with the shorter averaged experimental and calculated bond lengths of GaGa bonds (2.873 and 2823 Å for clusters 1A and 1B, respectively). Cluster hydrogenation experiments with H2 and D2 showed strong NiH and ND stretching features (at 1750 and 1260 cm−1, respectively), and at the same time, characteristic bands of self‐hydrogenated Cp*H and remained nondegraded clusters have been detected. The extent of HD exchange in cluster deuteration was obtained about 1.5 times more effective with cluster 1B than cluster 1A. The stronger hydrogen or deuterium uptake by cluster 1B and the more intensive self‐hydrogenation of Cp* clearly support the higher hydrogenation activity of cluster 1B compared with that of 1A.

Hydrogenation of Furfural to Furfuryl Alcohol over Nickel Supported Bentonite Catalyst

AbstractIn this work, nickel‐supported bentonite catalyst was prepared by wet impregnation method followed by activation and reduction. The nickel catalyst showed excellent catalytic activity for hydrogenation of furfural with 98 % selectivity towards furfuryl alcohol. In addition, various reaction parameters such as temperature, time, catalyst loading, solvents, and catalyst recycling, were optimized to enhance furfural conversion and furfuryl alcohol selectivity.

Hg(II) and Ru(II) complexes of mono- and dichalcogenides of bis(diphenylphosphino)amine chelating ligands: Synthesis, characterization and catalytic activity in transfer hydrogenation of acetophenone derivatives

Reactions of C10H7-1-N(PPh2)2 (1) and C10H7-1-N(P(Se)Ph2)2 (2) ligands with mercury(II)iodide in equimolar ratio gave cis-[HgI2{1-κ2 P,P}] (3) and cis-[HgI2{2-κ2 Se,Se}] (4). Also, refluxing of monooxidized thioyl and selenoyl bis(phosphino)amine ligands C10H7-1-N(P(E)Ph2)(PPh2) (E = S (5), Se (6)) with [Ru(CO)3Cl2]2 dimer afforded cis-[Ru(CO)2Cl2{5-κ2 P,S}] (7) and cis-[Ru(CO)2Cl2{6-κ2 P,Se}] (8). Complexes 3, 4, 7 and 8 were identified and characterized by multinuclear NMR (1H, 13C, 31P and 77Se NMR) and IR spectroscopy. The molecular structure of 5 was determined by single X-ray crystallography. 5 is the first structurally characterized example of this kind of κ2 P,S -bidentate ligand. The novel ruthenium(II) complexes 7 and 8 show high catalytic activity in the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source.

A highly adaptable Ni catalyst for Liquid Organic Hydrogen Carriers hydrogenation

Reducing the cost of hydrogenation/dehydrogenation catalysts and improving the catalytic activity are essential steps to promote the commercial application of Liquid Organic Hydrogen Carriers (LOHCs) technology. We reported a series of highly adaptable 70 wt% Ni supported catalysts prepared by a facile co-precipitation method. The as-prepared catalysts were used in the hydrogenation of several promising LOHCs candidates, including benzene, N-propylcarbazole, N-ethylcarbazole and dibenzyltoluene. By adjusting the ratio of Al and Si, the Ni70/AlSiO-1/1 catalyst with Al and Si in a molar ratio of 1:1 presents highest catalytic activity for hydrogenation of the above LOHCs, indicating the catalyst is highly adaptable for different LOHCs. The characterization results proved that the presence of SiO2 could significantly weaken the interaction between metal and carrier and decrease the formation of NiAl2O4 species, which is beneficial to the reducibility of Ni. The introduced Al2O3 can inhibit the agglomeration of Ni and increase the dispersion of the metal. Besides, the Ni70/AlSiO-1/1 catalyst was used to hydrogenate N-propylcarbazole by 5 cycles. In the fifth cycle, the hydrogen uptake reached the theoretical hydrogenation storage within 1.5 h, which suggested the excellent stability of the catalyst. Because of its low cost, high efficiency, high adaptation and highly stable, the self-made Ni catalyst has potential prospect in large-scale LOHCs application.

Synthesis, Structure, and Catalytic Hydrogenation Activity of [NO]-Chelate Half-Sandwich Iridium Complexes with Schiff Base Ligands.

A series of N,O-coordinate iridium(III) complexes with a half-sandwich motif bearing Schiff base ligands for catalytic hydrogenation of nitro and carbonyl substrates have been synthesized. All iridium complexes showed efficient catalytic activity for the hydrogenation of ketones, aldehydes, and nitro-containing compounds using clean H2 as reducing reagent. The iridium catalyst displayed the highest TON values of 960 and 950 in the hydrogenation of carbonyl and nitro substrates, respectively. Various types of substrates with different substituted groups afforded corresponding products in excellent yields. All N,O-coordinate iridium(III) complexes 1-4 were well characterized by IR, NMR, HRMS, and elemental analysis. The molecular structure of complex 1 was further characterized by single-crystal X-ray determination.

Cationic ruthenium(II)–NHC pincer complexes: Synthesis, characterisation and catalytic activity for transfer hydrogenation of ketones

Cationic ruthenium pincer complexes, [Ru(CNC)(CO)(PPh3)Cl]X (CNC = 2,6‐bis(1‐methylimidazol‐2‐ylidene)‐pyridine, X = Cl− [1a], PF6− [1b]), [Ru(CNC)(PPh3)2Cl]X (X = Cl− [2a], PF6− [2b]) and [Ru(CNC)(PPh3)2(H)]X (X = Cl− [3a], PF6− [3b]) with triphenylphosphine, CO and halides as coligands have been synthesised and characterised by 1H, 13C, 31P NMR, mass and single‐crystal X‐ray crystallography. The application of Ru complexes in the transfer hydrogenation of a wide range of ketones with 2‐propanol as the hydrogen source is explored. The in situ transformations observed during the synthesis help understand and suggest a plausible mechanism via the hydride complex 3b. All complexes appear to be efficient catalyst precursors for transfer hydrogenation of ketones.

Ultrathin Modified Silica “Skin” for the Transfer Hydrogenation Catalyst: Improving Selectivity by Adjusting Surface Wettability

AbstractSurface wettability of heterogeneous catalysts plays a crucial role in the catalytic activity and selectivity. In this work, an ultra‐thin modified silica coating is firstly used as the “skin” to adjust the surface hydrophilicity of the catalyst, which promotes the catalytic activity and selectivity in the transfer hydrogenation of nitriles. The ultrathin‐modified silica “skin” with 2–3 nm thickness is fabricated by the consecutive hydrolysis of (3‐aminopropyl)triethoxysilane and n‐propyltriethoxysilane, and the bimetallic catalyst Fe3O4@PtCu is encapsulated in the coating. The modified catalyst demonstrated significant catalytic efficiency for hydrogenation of benzonitrile to dibenzylamine. The reaction performs 93% conversion and 99% selectivity in “green” solvent H2O. Furthermore, the modified silica “skin” encapsulates the PtCu nanoparticles to prevent the leaching of active sites, thus brings excellent catalytic recyclability. More than Fe3O4@PtCu, the modified silica “skin” is applicable to a diverse range of catalysts, that is, PtCu/SiO2, PtCu/Al2O3, and PtCu/UiO‐66, endowing them with additional catalytic activity and selectivity in the hydrogenation of nitriles.

Au/Ni/Ni(OH)2/C Nanocatalyst with High Catalytic Activity and Selectivity for m-dinitrobenzene Hydrogenation

The Au/Ni/Ni(OH)2/C bimetallic nanocatalysts with different Au loadings (Au/Ni/Ni(OH)2/C-1: 0.05 wt%Au; Au/Ni/Ni(OH)2/C-2: 0.46 wt%Au; Au/Ni/Ni(OH)2/C-3: 2.60 wt%Au) were prepared at room temperature. The characterization results proved the nanostructure of Au islands supported on the Ni/Ni(OH)2 nanoparticles (NPs) and synergy effect of Au-, Ni- and Ni(OH)2-related species in Au/Ni/Ni(OH)2/C. These are the main reasons why their catalytic performance and selectivity to m-nitroaniline in m-dinitrobenzene hydrogenation were much higher than those of monometallic catalysts (Au/C and Ni/Ni(OH)2/C). Because Au/Ni/Ni(OH)2/C-2 was with high dispersion of Au, Au(0)/Aun+ ratio≈1:1 on the surface, novel nanostructure, moderate capacity of activating and dissociating hydrogen, and synergistic effect, it had much better catalytic activity (conversion of m-dinitrobenzene-100%) and higher selectivity to m-nitroaniline (95.0%) in m-dinitrobenzene hydrogenation reaction compared to other two supported bimetallic catalysts (Au/Ni/Ni(OH)2/C-1 and Au/Ni/Ni(OH)2/C-3). Au/Ni/Ni(OH)2/C-2 also exhibited high stability.

Synthesis and Structural Characterization of Half-Sandwich Arene–Ruthenium(II) Complexes with Bis(imidazol-1-yl)methane, Imidazole and Benzimidazole

Mono- and binuclear arene–ruthenium(II) complexes with imidazole-containing ligands were prepared by the reaction of the ligands (L1 = bis(imidazole-1-yl)methane; ImH = 1H-Imidazole; BImH = 1H-Benzimidazole) with [(p-cym)Ru(µ-Cl)2]2 dimers. When bis(imidazole-1-yl)methane reacted with [(p-cym)Ru(µ-Cl)2]2 in methanol, a binuclear complex of the type [Ru2(L1)2(p-cym)2Cl2]Cl2 (2) with cyclic structure was synthesized, whereas by using acetonitrile as a solvent under the same reaction conditions, an unexpected C–N bond cleavage was observed, and a complex of formula [Ru(ImH)2(p-cym)Cl]Cl (1) with coordinated imidazole molecules was obtained. Another type of arene–ruthenium complex [Ru(BImH)(p-cym)Cl2] (3) was obtained by the reaction of benzimidazole and [(p-cym)Ru(µ-Cl)2]2. All compounds were characterized by spectral (FT-IR, NMR 1H, 13C) and single-crystal X-ray diffraction methods; their catalytic activity in transfer hydrogenation and the cytotoxicity against MCF-7 and HepG2 cells were evaluated.

Cationic Aluminium Complexes as Catalysts for Imine Hydrogenation

Strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4 − salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the R1,R2BDI ligand (R1,R2BDI=HC[C(R1)N(R2)]2) influence sterics and Lewis acidity. Ligand bulk increases along the row Me,DIPPBDI<Me,DIPePBDI≈tBu,DIPPBDI<tBu,DIPePBDI; DIPP=2,6‐C(H)Me2‐phenyl, DIPeP=2,6‐C(H)Et2‐phenyl. The Gutmann‐Beckett test showed acceptor numbers of: (tBu,DIPPBDI)AlMe+ 85.6, (tBu,DIPePBDI)AlMe+ 85.9, (Me,DIPPBDI)AlMe+ 89.7, (Me,DIPePBDI)AlMe+ 90.8, (Me,DIPPBDI)AlH+ 95.3. Steric and electronic factors need to be balanced for catalytic activity in imine hydrogenation. Open, highly Lewis acidic, cations strongly coordinate imine rendering it inactive as a Frustrated Lewis Pair (FLP). The bulkiest cations do not coordinate imine but its combination is also not an active catalyst. The cation (tBu,DIPPBDI)AlMe+ shows the best catalytic activity for various imines and is also an active catalyst for the Tishchenko reaction of benzaldehyde to benzylbenzoate. DFT calculations on the mechanism of imine hydrogenation catalysed by cationic Al complexes reveal two interconnected catalytic cycles operating in concert. Hydrogen is activated either by FLP reactivity of an Al⋅⋅⋅imine couple or, after formation of significant quantities of amine, by reaction with an Al⋅⋅⋅amine couple. The latter autocatalytic Al⋅⋅⋅amine cycle is energetically favoured.

Highly dispersed and ultra-small Ru nanoparticles deposited on silica support as highly active and stable catalyst for biphenyl hydrogenation

• Ru/SiO 2 catalysts synthesized by SEA method exhibited highly dispersed Ru nanoparticles. • Bicyclohexyl yield achieved 99.9% at 90 °C and 1.0 MPa H 2 pressure for 80 min. • 1.5 wt.% Ru/SiO 2 catalyst showed excellent stability and reusability. • The excellent catalytic activity of 1.5 wt.% Ru/SiO 2 was explained with DFT calculation results. Liquid organic hydrogen carriers have been recently developed as the promising hydrogen storage materials, which exhibit significant advantages in hydrogen storage and utilization compared with the conventional hydrogen storage systems. Highly active and sable Ru/SiO 2 catalysts for biphenyl hydrogenation to form bicyclohexyl were synthesized through the strong electrostatic adsorption (SEA) method, and the conventional dry impregnation (DI) method was also considered as comparison. X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and H 2 -temperature-programmed reduction characterization techniques were used to investigate the physicochemical properties of the representative catalysts. The results showed that the catalysts synthesized by the SEA method possessed small-sized and well-dispersed Ru nanoparticles (NPs) on the silica support. Especially, 1.5 wt.% Ru/SiO 2 catalyst exhibited excellent catalytic activity, stability and reusability, where the initial turnover frequency (TOF) was 11.9 h −1 , the conversion of biphenyl was up to 99.9%, and the yield of bicyclohexyl reached 99.9% under the mild conditions (90 °C, 1.0 MPa H 2 ). Further density functional theory (DFT) calculations elucidate that the catalyst with small Ru nanoparticle size exhibits higher catalytic activity for biphenyl hydrogenation. Ru/SiO 2 catalyst synthesized by SEA method exhibited excellent catalytic performance for biphenyl hydrogenation

Unsupported Nanoporous Palladium Catalyst for Highly Selective Hydrogenation of Carbon Dioxide and Sodium Bicarbonate into Formate

AbstractDeveloping an efficient and simple heterogeneous catalytic system for CO2 conversion into formic acid (FA) is a vibrant research area because FA is recognized as a liquid organic hydrogen carrier. On the basis of our previous work on unsupported nanoporous palladium‐catalyzed hydrogenation proceeding through a Pd‐hydride intermediate, we report herein four types of PdNPore catalysts for the CO2 hydrogenation. The PdNPore‐1 catalyst exhibited high catalytic activity for CO2 hydrogenation into formate and obtained a yield of 86 % at 80 °C under H2 (1.0 MPa) and CO2 (1.5 MPa) with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a base in acetonitrile. Moreover, the catalyst was easily recovered and reused without any loss of catalytic activity. Sodium bicarbonate could also be hydrogenated using the PdNPore‐1 catalyst.

Electron-Enriched Pd Nanoparticles for Selective Hydrogenation of Halonitrobenzenes to Haloanilines

Selective hydrogenation of halonitrobenzenes into haloanilines represents a green process to replace the environmentally unfriendly non-catalytic chemical reduction process in industry. However, this transformation often suffers from serious dehalogenation due to the easy break of carbon-halogen bonds on metal surfaces. Modulations of the electronic structure of the supported Pd nanoparticles on Lewis-basic layered double hydroxides have been demonstrated to promote catalytic activity and selectivity for hydrogenation of halonitrobenzenes into haloanilines. Mechanism studies suggest that Pd with the enhanced electron density not only improves the capability for hydrogen activation, but also generates the partially negative-charged hydrogen species to suppress the electrophilic attack on the carbon-halogen bond and avoid the dehalogenation.

Ir−Sn Tetrazole Complexes with Proton‐Responsive P−OH Groups and an Ir−Ir Tetrazole Complex for CO2 Hydrogenation

AbstractBimetallic catalytic systems, especially heterogeneous bimetallic catalytic systems, have been shown to be effective catalysts for CO2 hydrogenation as a result of synergistic effects. Here‐in we report the synthesis of bimetallic Ir−Ir, Ir−Sn and a novel five‐membered heteroatomic Ir−Sn tetrazole complex. These complexes were obtained as a result of the heterolysis of P−S bond in the ligands during complexation. These complexes were evaluated for catalytic activity in homogeneous CO2 hydrogenation where they displayed excellent catalytic activity generating formate selectively. The mechanism of action for the Ir−Sn catalysts for CO2 hydrogenation indicates metal−metal bond breakage prior to formation of catalytically active species. However, this metal−metal bond breakage did not result in the decomposition of the catalysts. In addition, these bimetallic complexes were observed to effectively hydrogenate CO2 directly, or hydrogenate bicarbonate ions formed in solution during the catalytic cycle. For Ir−Ir catalyst, only one metal center was found to be directly involved in CO2 hydrogenation with the second iridium center primarily responsible as an electron source

Hierarchical Flower-Like NiCu/SiO2 Bimetallic Catalysts with Enhanced Catalytic Activity and Stability for Petroleum Resin Hydrogenation

The catalytic hydrogenation of petroleum resin (PR) is an efficient process to produce high-value-added hydrogenated PR with improved performance and wide applications. Herein, a hierarchical flower-like NiCu/SiO₂ bimetallic catalyst has been successfully prepared by reducing the hierarchically structured NiCu silicate precursor ((Ni,Cu)₃Si₂O₅(OH)₄) and applied for PR hydrogenation. The generated bimetallic NiCu alloy nanoparticles are anchored on the surface of the intercrossed silica nanoplatelets, constructing a unique multilevel NiCu/SiO₂ superstructure. Moreover, the addition of Cu could not only lower the reduction temperature of Ni species but also provide electrons to Ni to form electron-rich active sites. The NiCu/SiO₂ bimetallic catalyst exhibited enhanced catalytic activity and stability for PR hydrogenation. The hydrogenation degrees for C₅PR and C₉PR could reach up to 94.9 and 96.3%, respectively, which are much higher than those catalyzed by the catalyst prepared via an impregnation method (85.9 and 88.7%). Such notably enhanced performances could be ascribed to the synergistic effect between Ni–Cu bimetals and the highly porous superstructure. Our findings provide guidance for the design and synthesis of efficient and stable bimetallic nanocatalysts for PR hydrogenation.

Synthesis of New Secondary Amines and Their In Situ Catalytic Activity in Transfer Hydrogenation of Ketones and Antioxidant Properties

Synthesis of New Secondary Amines and Their In Situ Catalytic Activity in Transfer Hydrogenation of Ketones and Antioxidant Properties

Postsynthetic Modification of Half-Sandwich Ruthenium Complexes by Mechanochemical Synthesis

A mild and environmentally friendly method to synthesize half-sandwich ruthenium complexes through the Wittig reaction between an aldehyde-tagged half-sandwich ruthenium complex and phosphorus ylide mechanochemically is reported herein. The mechanochemical synthesis of valuable half-sandwich ruthenium complexes resulted in a fast reaction, good yield with simple workup, and the avoidance of harsh reaction conditions and organic solvents. The synthesized half-sandwich ruthenium complexes exhibited high catalytic activity for transfer hydrogenation of ketones using 2-propanol as the hydrogen source and solvent. Density functional theory was carried out to propose a mechanism for the transfer hydrogenation process. The modeling suggests the importance of the labile p-cymene ligand in modulating the reactivity of the catalyst.

Enhanced Hydrogenation Catalytic Activity of Ruthenium Nanoparticles by Solid‐Solution Alloying with Molybdenum

AbstractWe report the hydrogenation catalytic activity application of molybdenum–ruthenium (MoRu) solid‐solution alloy nanoparticles (NPs) as catalysts for the hydrogenation of 1‐octene and 1‐octyne. The solid‐solution structure of MoRu NPs was confirmed through scanning transmission electron microscopy (STEM) coupled with energy‐dispersive X‐ray spectroscopy (EDX), and powder X‐ray diffraction (PXRD) measurement. The hydrogenation catalytic activity of these NPs toward 1‐octyne and 1‐octene in tetrahydrofuran (THF) was tested. The hydrogenation catalytic activity of Ru was enhanced by alloying with Mo at the atomic level. An electronic modification of Ru by a charge transfer from Mo to Ru, which could induce the change in the adsorption energy of reactants resulting in enhanced catalytic activity, was observed by X‐ray photoelectron spectroscopy.

Adsorption Behavior and Electron Structure Engineering of Pd-IL Catalysts for Selective Hydrogenation of Acetylene

Developing the catalytic activity and selectivity of palladium (Pd) catalysts for acetylene hydrogenation is key importance in the chemical industry and remains a challenge to this day. Here, the catalytic performance of Pd catalysts are influenced by the Pd electronic structure, in turn, controlled by different heteroatom doped support. Different catalysts are prepared by ionic liquids (ILs) with different precursors, and catalytic activity of selective hydrogenation of acetylene was investigated. The Pd/NC catalyst exhibits extraordinary conversion, selectivity and stable for the hydrogenation of acetylene (94.6% acetylene conversion with 91.3% selectivity to ethylene). This remarkable catalytic performance of Pd/NC is mainly linked to nitrogen-doped (N-doped) changes the electronic structure of Pd nanoparticles, ensures the rapid desorption of ethylene and prevents the formation of unnecessary ethane by over hydrogenation (demonstrated by XPS and DFT). Our strategy of controlling the electronic structure of Pd can be widely used in the reactions that change the micro electrochemical properties of active metals. The selective hydrogenation of acetylene to ethylene over Pd/NC with excellent conversion and selectivity is investigated. The doping of nitrogen leads to the unique electronic structure of Pd on the Pd/NC catalyst, which influences the adsorption of ethylene and acetylene, thus promoting its catalytic activity.