Active Hydrogenation Catalysts Research Articles

Ru–g-C3N4 as a highly active heterogeneous catalyst for transfer hydrogenation of α-keto amide into β-aminol or α-hydroxyl amide

This work reports a sustainable route for the catalytic transfer hydrogenation (CTH) of α-keto amide into β-aminol via an efficient heterogeneous catalyst wherein ruthenium is incorporated on an active graphite sheet of a carbon nitride support (Ru–g-C3N4).

A “competitive occupancy” strategy toward Co–N4 single-atom catalysts embedded in 2D TiN/rGO sheets for highly efficient and stable aromatic nitroreduction

Single-atom M–N-based catalysts have been synthesized based on the “competitive occupancy” of Ti species and Co2+ (Ni2+etc.) on GO, and can be used as a highly active and stable hydrogenation catalyst.

Bifunctional Synergy in CO Hydrogenation to Methanol with Supported Cu

Future energy storage could be distributed at local plants and involve production of methanol from reaction of sustainably derived hydrogen with CO or CO2 from locally available carbon sources. Such decentralized production would benefit from milder operating conditions than found in the current large-scale industrial process. We propose that a route via CO hydrogenation deserves consideration for this purpose, as it will be free of water, which is unavoidable from CO2-containing gas and strongly inhibiting to the methanol synthesis at lower temperatures. On pure Cu the rate of methanol synthesis from CO is an order of magnitude lower than the rate from CO2, but active CO hydrogenation catalysts can emerge from a bifunctional mechanism in catalysts that combine copper with a basic oxide. Mechanistic studies are consistent with the bifunctional Cu/support synergy arising from a mechanism, where basic oxide sites activate CO as formates at the metal/oxide interface followed by metal assisted hydrogenation of the interfacial formates. Active catalysts for CO hydrogenation are strongly inhibited by CO2, which forms carbonates that block the basic oxide sites and thereby prevent the synergistic pathway from CO.

Strong Synergy between Ti3C2 and N-Doped Co Nanoparticles Boosts the Selective Hydrogenation of Propyne

Two-dimensional (2D) metal carbides, carbonitrides, and nitrides (MXenes) have recently emerged as promising candidates in catalysis due to their unique properties. In this work, we composited Ti3C2 with Co-embedded N-doped carbon nanotubes (CNTs) via the pyrolysis of zeolitic imidazolate frameworks (ZIF-67) for propyne selective hydrogenation. Detailed characterizations show that strong synergistic effects are observed between the Ti3C2 and Co-embedded N-doped CNTs in the composite catalysts. This work provides an efficient strategy to achieve N-doping on Co nanoparticles, which play a vital role in the propyne selective hydrogenation. The optimized catalyst gives a high propyne conversion (∼99%) and high propene selectivity (∼96%) on propyne selective hydrogenation at 150 °C, which surpasses the reported non-noble metal catalysts in literature works. This work may not only open an avenue for obtaining active and selective catalysts for propyne selective hydrogenation but also promote research on the role of MXenes in catalysis.

Hexagonal Cu(111) Monolayers for Selective CO2 Hydrogenation to CH3OH: Insights from Density Functional Theory

Cu-based heterogeneous catalysts are the most active and promising catalysts for selective CO2 hydrogenation. Density functional theory (DFT)-based calculations have been performed to gain insight ...

Binuclear half-sandwich ruthenium(II) Schiff base complexes: Synthesis, characterization, DFT study and catalytic activity for the reduction of nitroarenes

The binuclear ruthenium(II) p-cymene complexes containing Schiff base ligands of general composition [(Ru(p-cymene)Cl)2L1-6] (1-6) have been synthesized. The complexes were characterized by analytical and spectral (FT−IR, UV–Vis &1H NMR) methods. The molecular structure of the representative complex [(Ru(p-cymene)Cl)2(L6)] (6) was determined by single-crystal X-ray diffraction and density functional theory (DFT) calculations. Further, these half-sandwich ruthenium complexes are active catalysts for the mild hydrogenation of nitroarenes to aromatic anilines in the presence of NaBH4 in ethanol. The most efficient catalyst 6, was found be compatible with nitroarenes of various functional groups.

Dehydroalkylative Activation of CNN- and PNN-Pincer Ruthenium Catalysts for Ester Hydrogenation.

Ruthenium-pincer complexes bearing CNN- and PNN-pincer ligands with diethyl- or diisopropylamino side groups, which have previously been reported to be active precatalysts for ester hydrogenation, undergo dehydroalkylation on heating in the presence of tricyclohexylphosphine to release ethane or propane, giving five-coordinate ruthenium(0) complexes containing a nascent imine functional group. Ethane or propane is also released under the conditions of catalytic ester hydrogenation, and time-course studies show that this release is concomitant with the onset of catalysis. A new PNN-pincer ruthenium(0)-imine complex is a highly active catalyst for ester hydrogenation at room temperature, giving up to 15 500 turnovers with no added base. This complex was shown to react reversibly at room temperature with two equivalents of hydrogen to give a ruthenium(II)-dihydride complex, where the imine functionality has been hydrogenated to give a protic amine side group. These observations have potentially broad implications for the identities of catalytic intermediates in ester hydrogenation and related transformations.

Highly Active CuFeAl-containing Catalysts for Selective Hydrogenation of Furfural to Furfuryl Alcohol

CuFe-containing catalysts with different copper oxide content were prepared by fusion of metal salts. The obtained catalyst showed high activity in the hydrogenation of furfural to furfuryl alcohol (FA) in the batch reactor in the presence of isopropanol as a solvent at a temperature of 100 °C and a hydrogen pressure of 6.0 MPa. The yield of FA and furfural conversion are 97% and 98%, respectively. In the solvent-free reaction in the flow-type reactor; the most active catalyst Cu20Fe66Al14 leads to the 96% formation of FA with 100% conversion of furfural at liquid hourly space velocity (LHSV) = 1 h−1; 160 °C and a hydrogen pressure of 5.0 MPa during 30 h. According to the X-ray diffraction (XRD) method, the active component of the spent and fresh Cu20Fe66Al14 catalyst is the same and is represented by metallic copper and Fe3O4-type spinel. Using different methods, the formation of active sites was investigated.

Enhanced Hydrogenation Performance over Hollow Structured Co-CoOx@N-C Capsules.

It is desirable to design nonprecious metal nanocatalysts with high stability and catalytic performance for fine chemicals production. Here, a method is reported for the preparation of cobalt metal and cobalt oxide cores confined within nanoporous nitrogen‐doped hollow carbon capsules. Core–shell structured Zn/Co‐ZIF@polymer materials are fabricated through a facile coating polymer strategy on the surface of zeolitic imidazolate frameworks (ZIF). A series of hollow carbon capsules with cobalt metal and cobalt oxide are derived from a facile confined pyrolysis of Zn/Co‐ZIF@polymer. The hollow Co‐CoOx@N‐C capsules can prevent sintering and agglomeration of the cobalt nanoparticles and the nanoporous shell allows for efficient mass transport. The specific surface area and Co particle size are optimized through finely tuning the original Zn content in ZIF particles, thus enhancing overall catalytic activity. The yolk–shell structured Zn4Co1Ox@carbon hollow capsules are shown to be a highly active and selective catalyst (selectivity >99%) for hydrogenation of nitrobenzene to aniline. Furthermore, Zn4Co1Ox@carbon hollow particles show superior catalytic stability, and no deactivation after 8 cycles of reaction. The hollow Co‐CoOx@N‐C capsules may shed light on a green and sustainable catalytic process for fine chemicals production.

Nitrogen-doped carbon nanotubes as a highly active metal-free catalyst for nitrobenzene hydrogenation

A series of metal-free N-doped carbon nanotubes (CNTs) are fabricated using an in-situ synthesis and post nitridation treatment. N-doped carbon nanotubes with various defects, nitrogen contents, and nitrogen species are employed as the catalysts for nitrobenzene hydrogenation. The potential active sites of N-doped carbon nanotubes are explored in terms of catalytic performance in nitrobenzene hydrogenation as well as DFT calculations of hydrogen adsorption on carbon nanotubes and nitrogen species. Active and selective hydrogenation of nitrobenzene is achieved over N-doped carbon nanotubes prepared by post nitridation. Pyrrolic-N in the N-doped carbon nanotubes is found to play an active site for nitrobenzene hydrogenation, which is greatly in favor of the chemisorption and dissociation of hydrogen molecules. N-doped carbon nanotubes with pyrrolic-N show an encouraging catalytic hydrogenation activity in nitrobenzene reduction. These findings provide a promising route for the rational design of the metal-free hydrogenation catalysts and the development of carbon nanotube-based materials.

Ru nanoparticles deposited on ultrathin TiO2 nanosheets as highly active catalyst for levulinic acid hydrogenation to γ-valerolactone

Highly efficient synthesis of valuable γ-valerolactone (GVL) by levulinic acid (LA) hydrogenation is still a challenge for Ru-based catalysts under mild condition. In this work, we have reported that ultrathin TiO2 nanosheets supported Ru nanoparticles showed extraordinarily high catalytic activity, GVL yield (99.1%) and reusability owing to the formation of RuOTi interfacial structure. The turnover frequency (TOF) reached as high as 19,045 h−1 at 100 °C, much higher than those of Ru/SiO2, Ru/GO, Ru/MoS2, and commercial Ru/C. DFT calculation elucidates that the dominant reaction pathway of LA hydrogenation to GVL is preferentially hydrogenated to CH3CHOCH2CH2COOH*, followed by cyclization to CH3(OH)C4OH4OH* (GVL − OH) and final dehydroxylation, irrespective of surface structure. Compared to Ru (0 0 2) facet, Ru/TiO2 interfacial structure changes the rate-determining step from initial hydrogenation to cyclization, which greatly declines the activation barrier from 0.81 eV to 0.48 eV.

Resurgence of Organomanganese(I) Chemistry. Bidentate Manganese(I) Phosphine-Phenol(ate) Complexes.

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese(I) complexes has recently emerged as an important area with the discovery that pincer manganese(I) complexes that can activate substrates through metal-ligand cooperative mechanisms are active (de)hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn(CO)5Br to prepare manganese(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine-phenol ligand along with its corresponding coordination chemistry of five new manganese(I) complexes is described. The complexes having two phenol-phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese(I) dicarbonyl centers.

Unsupported Nanoporous Gold‐Catalyzed Chemoselective Reduction of Quinolines Using Formic Acid as a Hydrogen Source

AbstractThe unsupported nanoporous gold (AuNPore) is demonstrated to be an active and stable heterogeneous catalyst for chemoselective transfer hydrogenation of quinolines using bio‐renewable formic acid (HCO2H) as hydrogen source. The AuNPore‐catalyzed transfer hydrogenation of quinolines proceeded smoothly in the presence of low amounts of HCO2H at a relatively low temperature to produce the desired 1,2,3,4‐tetrahydroquinolines (py‐THQs) in good to excellent yields. Mechanistic studies revealed that the AuNPore‐catalyzed transfer hydrogenation of quinolines proceeded through a sequence of 1,4‐hydride addition, isomerization, and 1,2‐hydride addition. This operationally simple protocol offers a practical alternative to the currently known methods for chemoselective quinoline reduction.

Pd-Supported N/S-Codoped Graphene-Like Carbons Boost Quinoline Hydrogenation Activity

Pd nanoparticles (∼2.1 nm) supported on biomolecule-derived graphene-like carbons have been studied as highly active and stable catalysts for the selective hydrogenation of quinolines. A novel stra...

N-doped carbon spheres impregnated with highly monodispersed ruthenium nanoparticles as a hydrogenation catalyst

Ru/carbon catalyst has been considered as a very active catalyst in aqueous-phase hydrogenation of bio-resourced carbonyl compounds. High dispersion of Ru NPs on a carbon support could enhance catalytic performance. In this work, well dispersed Ru nanoparticles on the surface of carbon spheres have been developed by the introduction of nitrogen-doping. Compared with carbon spheres without N-doping, the incorporation of the N-dopant with in the carbon matrix effectively improved the dispersion of Ru nanoparticles, which was confirmed by X-ray photoelectron spectroscopy (XPS) and CO chemisorption characterizations, finding that the presence of quaternary N was responsible for the high dispersion of Ru nanoparticles. Through adjusting the carbonization temperature from 400 to 850 °C, we have shown that the absolute content of quaternary N can be modulated from 3.2 to 22.4 mg g−1. As a result, the dispersion of Ru nanoparticles was improved from 29.8% to 70.9%. The Ru/N-CS-850 catalyst revealed excellent catalytic performance (9858 h−1 turnover frequency) for the hydrogenation of levulinic acid to γ-valerolactone, also demonstrated very high catalytic activity for other hydrogenation reactions.

Catalytic Transfer Hydrogenation of Biomass-Derived Ethyl Levulinate into Gamma-Valerolactone Over Graphene Oxide-Supported Zirconia Catalysts

The transformation of biomass-derived intermediates into value-added chemicals and liquid fuels is of great importance in sustainable chemistry. In this study, graphene oxide supported ZrO2 (ZrO2/GO) was found to be an active heterogeneous catalyst for the transfer hydrogenation of ethyl levulinate to γ-valerolactone (GVL) with iso-propanol as the hydrogen donor. Several important reaction parameters such as the hydrogen donor, the reaction temperature and the catalyst loading were studied in detail with the aim to get a high yield of GVL. It was found that the structure of alcohols had a great effect towards the activity of the ZrO2/GO catalyst and the selectivity of GVL. Iso-propanol was the best hydrogen donor for the transfer hydrogenation of ethyl levulinate to GVL. The highest GVL yield reached 91.7% with an ethyl levulinate conversion of 96.2% under optimal reaction conditions. More importantly, the ZrO2/GO catalyst demonstrated a high stability without the loss of its catalytic activity during the recycling experiments, which should be due to the strong interaction between GO and ZrO2. The graphene oxide supported ZrO2 (ZrO2/GO) catalyst showed high activity for the transfer hydrogenation of ethyl levulinate to GVL with a high yield up to 91.7%.

Tuning Selectivity of Maleic Anhydride Hydrogenation Reaction over Ni/Sc-Doped ZrO2 Catalysts

A series of Sc-doped ZrO2 supports, with Sc2O3 content in the range of 0 to 7.5% (mol/mol), were prepared using the hydrothermal method. Ni/Sc-doped ZrO2 catalysts with nickel loading of 10% (w/w) were prepared using impregnation method, and characterized with the use of XRD, Raman, H2 temperature-programmed reduction (H2-TPR), H2 temperature-programmed desorption (H2-TPD), XPS, and in situ FT-IR techniques. The catalytic performances of Ni/Sc-doped ZrO2 catalysts in maleic anhydride hydrogenation were tested. The results showed that the introduction of Sc3+ into ZrO2 support could effectively manipulate the distribution of maleic anhydride hydrogenation products. γ-butyrolactone was the major hydrogenation product over Sc-free Ni/ZrO2 catalyst with selectivity as high as 65.8% at 210 °C and 5 MPa of H2 pressure. The Ni/Sc-doped ZrO2 catalyst, with 7.5 mol% of Sc2O3 content, selectively catalyzed maleic anhydride hydrogenation to succinic anhydride, the selectivity towards succinic anhydride was up to 97.6% under the same reaction condition. The results of the catalysts’ structure–activity relationships revealed that there was an interdependence between the surface structure of ZrO2-based support and the C=O hydrogenation performance of the ZrO2-based supported nickel catalysts. By controlling the Sc2O3 content, the surface structure of ZrO2-based support could be regulated effectively. The different surface structure of ZrO2-based supports, resulted in the different degree of interaction between the nickel species and ZrO2-based supports; furthermore, the different interaction led to the different surface oxygen vacancies electron properties of ZrO2-based supported nickel catalysts and the C=O hydrogenation activity of the catalyst. This result provides new insight into the effect of ZrO2 support on the selective hydrogenation activity of ZrO2-supported metal catalysts and contributes to the design of selective hydrogenation catalysts for other unsaturated carbonyl compounds.

Transfer Hydrogenation of Carbonyl Groups, Imines andN‐Heterocycles Catalyzed by Simple, Bipyridine‐Based MnIComplexes

AbstractUtilization of hydroxy‐substituted bipyridine ligands in transition metal catalysis mimicking [Fe]‐hydrogenase has been shown to be a promising approach in developing new catalysts for hydrogenation. For example, MnIcomplexes with 6,6′‐dihydroxy‐2,2′‐bipyridine ligand have been previously shown to be active catalysts for CO2hydrogenation. In this work, simple bipyridine‐based Mn catalysts were developed that act as active catalysts for transfer hydrogenation of ketones, aldehydes and imines. For the first time, Mn‐catalyzed transfer hydrogenation ofN‐heterocycles was reported. The highest catalytic activity among complexes with variously substituted ligands was observed for the complex bearing two OH groups in bipyridine. Deuterium labeling experiments suggest a monohydride pathway.

Structural and Electron Properties of High-Disperse Particles of the Active Component of Pd/Al2O3 Catalysts for Hydrogenation of Butadiene-1,3

Studies of the influence of acidity of alumina supports on properties of supported palladium particles were aimed at improving the activity of catalysts for hydrogenation of unsaturated hydrocarbons of pyrolysis gasoline fraction. High-disperse palladium particles demonstrate the high catalytic activity but their electron deficiency make them suffering from blocking with unsaturated hydrocarbons. NH3 TPR, TEM and XPS techniques were used for studying aluminopalladium catalysts; different acidities of the catalyst supports resulted from their chemical modification with various agents. The catalysts were tested for lab-scale hydrogenation of butadiene-1,3. Against the non-modified samples, the catalysts supported on modified alumina provided a lower conversion of butadiene-1,3 but a higher selectivity to butene-1. A higher conversion of butadiene-1,3 at the preserved selectivity to butene-1 and butane was observed in the presence of the catalyst supported on base-modified alumina.

Monodisperse CuPt alloy nanoparticles assembled on reduced graphene oxide as catalysts in the transfer hydrogenation of various functional organic groups

We present herein a new nanocatalyst, namely binary CuPt alloy nanoparticles (NPs) supported on reduced graphene oxide (CuPt‐rGO), as a highly active heterogeneous catalyst for the transfer hydrogenation (TH) protocol that is demonstrated to be applicable over the reduction of various unsaturated organic compounds (olefins, aldehydes/ketones and nitroarenes) in aqueous solutions at room temperature. CuPt alloy NPs were synthesized by the co‐reduction of metal (II) acetylacetonates by borane‐tert‐butylamine (BTB) complex in hot oleylamine (OAm) solution and then assembled on reduced graphene oxide (rGO) via ultrasonic‐assisted liquid phase self‐assembly method. The structure of yielded CuPt NPs and CuPt‐rGO nanocatalyst were characterized by TEM, XRD and ICP‐MS. The activity of Cu7Pt3‐rGO nanocatalysts were then tested for the THs that were conducted in a commercially available high‐pressure tube using water as sole solvent and ammonia borane as a hydrogen donor at room temperature. The presented catalytic TH protocol was successfully applied over nitroarenes, olefines and aldehydes/ketones, and all the tested compounds were converted to corresponding reduction products with the yields reaching up to 99% under ambient conditions. Moreover, the Cu7Pt3‐rGO nanocatalyst was also reusable in the TH by providing 99% yield after five consecutive runs in TH of nitrobenzene as an example.