Catalytic Transfer Hydrogenation Research Articles

Polymeric organophosphate-hafnium unconventional MOFs nanohybrids enable high-efficiency upgrading of biomass feedstocks via cascade catalytic transfer hydrogenation-dehydration

Efficiently selective catalytic conversion of biomass into biofuels and high-value chemicals using robust and porous catalysts is of great significance for valorization of renewable carbon resources. With respect to this, to reduce the supply dependence on natural oils, heterogeneous catalysis provides the opportunity for versatile anethole (AN) synthesis from bio-derived 4′-methoxypropiophenone (4-MOPP) via the one-pot cascade reactions of catalytic transfer hydrogenation (CTH) followed by dehydration, using an alcohol hydrogen donor and a Lewis/Brønsted acid catalyst. Herein, a sustainable and green strategy for catalytic upgrading of 4-MOPP to AN was developed via the cascade CTH-dehydration process, which was remarkably promoted by polymeric organophosphate unconventional MOFs-hafnium nanohybrids (PDVP-Hf) prepared via a simple solvothermal method. Interestingly, Brønsted/Lewis acidity, Lewis basicity, and hydrophobicity of PDVP-Hf could be effectively regulated by simply adjusting the composite components, among which PDVP-Hf-3 having an amorphous and porous inorganic-organic framework structure (with mesopores centered at 6.52 nm), an enhanced acidity of a suitable B/L molar ratio with lower basicity, and a strong hydrophobicity (water contact angle of 113°), was demonstrated to be efficient for selective conversion of 4-MOPP to AN with a maximum yield of 98.9% using 2-pentanol as hydrogen donor. Moreover, this developed catalytic system exhibited broad substrate generality, and could be employed for reductive upgrading of various carbonyl compounds to alcohols, or further coupled with dehydration to afford olefins. The catalyst synergistic roles of L acid-base couple sites (Hf 4+ -O 2− ) and B acid species (-OH) contributed to its pronounced performance, while high thermostability and robust hydrophobicity of PDVP-Hf-3 endowed its superior reusability, with no significant decline in reactivity for five consecutive recycles. The involved catalytic mechanisms and reaction pathways were explicitly elucidated by control experiments and theoretical calculations. This work sheds light on the appropriate design of unconventional MOF-polymer nanohybrids by combining both advantages for enhanced biomass upgrading via tough cascade reactions. • Hf-containing UMOFs-polymer hybrids were prepared via a simple solvothermal method. • PDVP-Hf-3 enabled biomass transformation of cascade CTH-dehydration. • Synergy of acid-base sites in PDVP-Hf-3 contributed up to 99.7% conversion. • PDVP-Hf-3 was highly reusable due to robust UMOFs-polymer and strong hydrophobicity. • DFT calculations and GC-MS revealed the reaction mechanism and pathways.

Fabrication of Zirconium-Doped Activated Carbon by Chemical Activation for Catalytic Transfer Hydrogenation of 5-Hydroxymethylfurfural into 2,5-Dihydroxymethylfuran

Fabrication of Zirconium-Doped Activated Carbon by Chemical Activation for Catalytic Transfer Hydrogenation of 5-Hydroxymethylfurfural into 2,5-Dihydroxymethylfuran

Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol over Magnetic Fe–Fe3O4/UiO-66

Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol over Magnetic Fe–Fe3O4/UiO-66

Elucidating the role of amine donors in manganese catalyzed transfer hydrogenation

Catalysts for transfer hydrogenation (TH) reactions based on the earth abundant transition metal manganese are an emerging field of research. A common moiety found in most reported phosphine-free catalysts is a primary or secondary amine donor, which is generally considered to be crucial within an outer-sphere mechanism. Here, we investigated the role of the NH-motif in the mechanism in catalytic transfer hydrogenation of ketones. Therefore, we synthesized Mn(I) complexes with a pyridyl-pyrazole or a pyridyl-imidazole ligand, which carry an NH-motif at different positions. Subsequent investigation of their catalytic activity points towards an inner-spere mechanism in which the NH-motif of the amino ligand is deprotonated throughout the catalytic cycle. The resulting amido ligand increases the electron density at the metal which facilitates the hydride transfer to the substrate. The presented alternative inner-sphere mechanism may aid in the future development of manganese-based catalysts for hydrogen transfer reactions.

Catalytic transfer hydrogenation of N2 to NH3 via a photoredox catalysis strategy.

Inspired by momentum in applications of reductive photoredox catalysis to organic synthesis, photodriven transfer hydrogenations toward deep (>2 e-) reductions of small molecules are attractive compared to using harsh chemical reagents. Noteworthy in this context is the nitrogen reduction reaction (N2RR), where a synthetic photocatalyst system had yet to be developed. Noting that a reduced Hantzsch ester (HEH2) and related organic structures can behave as 2 e-/2 H+ photoreductants, we show here that, when partnered with a suitable catalyst (Mo) under blue light irradiation, HEH2 facilitates delivery of successive H2 equivalents for the 6 e-/6 H+ catalytic reduction of N2 to NH3; this catalysis is enhanced by addition of a photoredox catalyst (Ir). Reductions of additional substrates (nitrate and acetylene) are also described.

Tilting the Balance: London Dispersion Systematically Enhances Enantioselectivities in Brønsted Acid Catalyzed Transfer Hydrogenation of Imines.

London dispersion (LD) is attracting more and more attention in catalysis since LD is ubiquitously present and cumulative. Since dispersion is hard to grasp, recent research has concentrated mainly on the effect of LD in individual catalytic complexes or on the impact of dispersion energy donors (DEDs) on balance systems. The systematic transfer of LD effects onto confined and more complex systems in catalysis is still in its infancy, and no general approach for using DED residues in catalysis has emerged so far. Thus, on the example of asymmetric Brønsted acid catalyzed transfer hydrogenation of imines, we translated the findings of previously isolated balance systems onto confined catalytic intermediates, resulting in a systematic enhancement of stereoselectivity when employing DED-substituted substrates. As the imine substrate is present as Z- and E-isomers, which can, respectively, be converted to R- and S-product enantiomers, implementing tert-butyl groups as DED residues led to an additional stabilization of the Z-imine by up to 4.5 kJ/mol. NMR studies revealed that this effect is transferred onto catalyst/imine and catalyst/imine/nucleophile intermediates and that the underlying reaction mechanism is not affected. A clear correlation between ee and LD stabilization was demonstrated for 3 substrates and 10 catalysts, allowing to convert moderate-good to good-excellent enantioselectivities. Our findings conceptualize a general approach on how to beneficially employ DED residues in catalysis: they clearly showcase that bulky alkyl residues such as tert-butyl groups must be considered regarding not only their repulsive steric bulk but also their attractive properties even in catalytic complexes.

Two-dimensional MXenes as catalytic “flying carpets” to transport biomass valorization towards new horizons: The case of furfural catalytic transfer hydrogenation over noble-metal free niobium-based carbides

The reductive conversion of biomass-derived furfural through catalytic transfer hydrogenation (CTH) over non-precious metal catalysts is regarded as a promising strategy to successfully implement the biorefinery concept. Here, we show that two-dimensional niobium carbides (MXenes) efficiently catalyze the liquid-phase CTH of furfural in the presence of 2-propanol as hydrogen donor. At 160 °C Nb2CTx and Nb4C3Tx showed remarkable initial activity values (130 and 73 h−1, respectively), exceeding the one of pure Nb2O5 (21 h−1) by factor of 6.2 and 3.5. A targeted surface characterization by acid site titrations and X-ray photoelectron spectroscopy allowed to correlate the catalytic behavior with the acidic features and the peculiar surface chemistry of Nb-MXenes species. The presence of strong acid sites in Nb2CTx was associated to high initial activity, but also to a pronounced tendency to undergo deactivation. Differently, Nb4C3Tx, despite the lower initial activity, assured 70 % of furfural conversion after 8 h and it showed good stability over six runs. This study could bring new opportunities for the rational design of advanced noble metal-free catalysts with enhanced activity for biomass valorization.

Production of γ-valerolactone from ethyl levulinate over hydrothermally synthesized Sn-Beta under mild conditions

Production of γ-valerolactone (GVL) from ethyl levulinate (EL) was studied by catalytic transfer hydrogenation (CTH) strategy under mild conditions. Hydrothermally synthesized Sn-Beta zeolites with high crystallinity show high catalytic activity and selectivity. With isopropanol as hydrogen source, 97.1 % GVL yield with 100 % selectivity was given under 110 °C. Crystallization time for synthesis of Sn-Beta showed great effect on the catalytic performance. Sn-Beta-xd catalysts with longer crystallization time (≥7 days) have high crystallinity and better catalytic performance. Firstly, longer crystallization time is necessary for the formation of large amount of Lewis acid sites which catalyze the conversion of EL to GVL. Secondly, high level of silanol groups in Sn-Beta has negative effect on the catalytic performance. High crystallinity means the amount of silanol groups in Sn-Beta-xd at a low level which is favorable for this CTH reaction. Meanwhile, this is why hydrothermally synthesized Sn-Beta shows higher catalytic activity than post-synthesized Sn-Beta in the conversion of EL to GVL. Furthermore, the catalyst was reusable.

Bimetallic CoNi Nanoflowers for Catalytic Transfer Hydrogenation of Terminal Alkynes

AbstractThe development of bimetallic and magnetic nanomaterials as a catalyst is highly desirable for organic transformations due to their recyclability for the sustainable future of chemical industries. Bimetallic CoNi nanoflowers were developed via the facile liquid‐phase reduction method and were employed for the hydrogenation of terminal alkynes. The structural and morphological studies were analyzed by X‐ray diffraction, Field‐Emission Scanning Electron Microscopy, and High Resolution Transmission Electron Microscopy. The bimetallic CoNi nanoflower exhibited 100 % conversion with ∼100 % selectivity towards alkane products with recyclability up to six cycles. The transfer hydrogenation mechanism was proposed via diimide formation with Co(0)/Ni(0) state, confirmed by X‐ray Photoemission Spectroscopy analysis.

Acceptorless Dehydrogenation of Alcohols and Transfer Hydrogenation of Aldehydes in Water Using a Single Bifunctional, Bistate, Water-soluble Ruthenium Catalyst.

A water-soluble bifunctional, bistate ruthenium catalyst has been developed using the 8-aminoquinoline ligand which responds to an acid-base stimuli and is catalytically active for two complementary reactions. The "Ru-amino state" is highly active for catalytic transfer hydrogenation of various aldehydes using formic acid as the hydrogen source resulting in a range of primary alcohols. On the other hand, the "Ru-amido state" is active for the acceptorless dehydrogenation of alcohols to yield carboxylate salts or ketones. The reactions can be carried out in air without an inert atmosphere and the products can be purified by simple extraction without the use of any chromatographic techniques. A range of functional groups which include electron-rich and deficient (hetero)arenes and alkenes, alkynes, halides, esters, cyano, and nitro groups, are all well tolerated, indicating excellent chemoselectivity for transfer hydrogenation.

Tea polyphenol and HfCl4 Co-doped polyacrylonitrile nanofiber for highly efficient transformation of levulinic acid to γ-valerolactone

Design catalytic materials with high Lewis acid/base sites for catalytic transfer hydrogenation (CTH) of levulinic acid (LvA) to γ-valerolactone (GVL) is highly demanded but challenging. Herein, we report a concept of metal ion-polymer hybridization to design a tea polyphenol (TP) and HfCl4 co-doped polyacrylonitrile (PAN) nanofiber (Hf@PAN-TP) via electrospinning technique. Comprehensive characterization revealed the well coordination between hafnium ions and phenolic hydroxyl groups of TP on PAN fiber, which promoted the formation of Lewis acid and Lewis base sites. As expected, a satisfactory GVL yield of 99.1% with 100% of LvA conversion was obtained using isopropanol as a hydrogen donor at 170 °C in 5 h, and the catalytic activity remained unchanged for five cycles. The kinetic study revealed the lower activation energy for CTH of LvA to GVL (33.5 kJ/mol), demonstrating the outstanding GVL formation rate of 3383.9 μmol/g.h. Based on the systematical combine of catalyst characterization and catalytic behavior, the structure-function relationship and reaction mechanism were proposed. More gratifyingly, Hf@PAN-TP was applicable for catalytic reduction of various carbonyl compounds, demonstrating a great potential for upgrading biomass-derived aldehydes/ketones.

Magnetic graphene oxide-anchored Ni/Cu nanoparticles with a Cu-rich surface for transfer hydrogenation of nitroaromatics

• The Ni/Cu NPs with a Cu-rich surface were prepared by thermal decomposition. • Graphene oxide anchored Ni/Cu NPs to prepare magnetic Ni/Cu-GO catalyst. • Ni/Cu-GO with different composition for CTH of 2-methyl-5-nitrophenol were studied. • Ni 7 /Cu 3 -GO did not dehalogenate for CTH of halogen-containing nitroaromatics. The bimetallic nanoparticles compositing of Ni-rich core and Cu-rich shell (Ni/Cu NPs) were successfully synthesized by a liquid-phase thermal decomposition method. The content of copper and nickel in Ni/Cu NPs was controllable by adjusting the ratio of two metal precursors, copper formate (Cuf) and nickel acetate tetrahydrate (Ni(OAc) 2 ∙4H 2 O). Ni/Cu NPs were further anchored on graphene oxide (GO) to prepare a magnetic composite catalyst, called Ni/Cu-GO. The dispersibility of Ni/Cu NPs in solution was enhanced by GO anchoring to prevent the sintering and aggregation during the reaction process, thereby ensuring the catalytic and cycling performance of the catalyst. The catalytic transfer hydrogenation (CTH) reaction of nitroaromatics was investigated when ammonia borane was used as the hydrogen source. Cu dominated the main catalytic role in the reaction, while Ni played a synergistic role of catalysis and providing magnetic properties for separation. The Ni 7 /Cu 3 -GO catalyst exhibited the best catalytic performance with the conversion and yield of 99% and 96%, respectively, when 2-methyl-5-nitrophenol was used as the substrate. The Ni 7 /Cu 3 -GO catalyst also exhibited excellent cyclic catalytic performance with the 5-amino-2-methylphenol yield of above 90% after 6 cycles. In addition, the Ni 7 /Cu 3 -GO catalyst could be quickly recycled by magnetic separation. Moreover, the Ni 7 /Cu 3 -GO catalyst showed good catalytic performance for halogen-containing nitroaromatics without dehalogenation.

1,4-Reduction of α,β-Unsaturated Ketones through Rhodium(III)-Catalyzed Transfer Hydrogenation

AbstractA rhodium(III)-catalyzed transfer hydrogenation of unsaturated ketones was developed. The simple catalytic system could be used for the 1,4-reduction of unsaturated cyclic, acyclic ketones, diketones, as well as β-ketoester, and a variety of functional groups were well-tolerated, affording products in moderate to excellent yields.

Micro/mesoporous LTL derived materials for catalytic transfer hydrogenation and acid reactions of bio-based levulinic acid and furanics.

The biomass-derived platform chemicals furfural and 5-(hydroxymethyl)furfural (HMF) may be converted to α-angelica lactone (AnL) and levulinic acid (LA). Presently, LA (synthesized from carbohydrates) has several multinational market players. Attractive biobased oxygenated fuel additives, solvents, etc., may be produced from AnL and LA via acid and reduction chemistry, namely alkyl levulinates and γ-valerolactone (GVL). In this work, hierarchical hafnium-containing multifunctional Linde type L (LTL) related zeotypes were prepared via top-down strategies, for the chemical valorization of LA, AnL and HMF via integrated catalytic transfer hydrogenation (CTH) and acid reactions in alcohol medium. This is the first report of CTH applications (in general) of LTL related materials. The influence of the post-synthesis treatments/conditions (desilication, dealumination, solid-state impregnation of Hf or Zr) on the material properties and catalytic performances was studied. AnL and LA were converted to 2-butyl levulinate (2BL) and GVL in high total yields of up to ca. 100%, at 200°C, and GVL/2BL molar ratios up to 10. HMF conversion gave mainly the furanic ethers 5-(sec-butoxymethyl)furfural and 2,5-bis(sec-butoxymethyl)furan (up to 63% total yield, in 2-butanol at 200°C/24 h). Mechanistic, reaction kinetics and material characterization studies indicated that the catalytic results depend on a complex interplay of different factors (material properties, type of substrate). The recovered-reused solids performed steadily.

Selectivity catalytic transfer hydrogenation of biomass-based furfural to cyclopentanone

Because of furfural’s diverse unsaturated groups and the rearrangement of oxygen atoms, the production of cyclopentanone (CPO) from furfural (FF) can be challenging. Herein, a novel nitrogen-doped encapsulated catalyst (Co@NC) was synthesized to catalyze the selective hydrogenation of FF in an aqueous phase to CPO. A CPO yield of 86.5 % was obtained at 200 °C and 3 MPa H2. Meanwhile, furfuryl alcohol (FA) was inferred to be the primary intermediate in the formation of CPO and cyclopentanol (CPL). CPL originated from the further hydrogenation of CPO that was produced via FF selective hydrogenation to FA, followed by FA hydrodeoxgenation to CPO. The main presence of CPO illustrated that it avoided overhydrogenation, which contributed to the tailored hydrogenation ability of Co@NC and facilitated the selective preservation of CO bonds. The N atoms acting as electronegative heteroatoms can not only enhance the adsorption of FF but also provide weak Lewis acid sites for CPO production.

Conversion of biomass to γ-valerolactone by efficient transfer hydrogenation of ethyl levulinate over Al-SPAN nanosheets

It is a green and environment-friendly strategy to use biomass to assist the synthesis of catalysts and use the prepared catalysts for biomass utilization. In this study, aluminum-rich silicon-phosphorus-aluminum nanosheet (Al-SPAN) was synthesized with biomass amino acids as additives for catalytic transfer hydrogenation of ethyl levulinate to γ-valerolactone. Compared with commercial Al2O3, Al-SPAN showed greatly improved catalytic performance for the reaction. The conversion of ethyl levulinate was increased by 47 % and the yield of γ-valerolactone was increased by 52 %. The effects of different alcohol on the reaction properties were investigated, with isopropanol used as a safe and efficient hydrogen source. The catalyst has good stability with little change in reaction performance after five cycles.

Trimeric Ruthenium Cluster-Derived Ru Nanoparticles Dispersed in MIL-101(Cr) for Catalytic Transfer Hydrogenation

The synthesis of highly dispersed metal nanoparticles supported on metal–organic frameworks has been widely studied as a means to provide high-performance heterogeneous catalysts. Here, a Ru-nanoparticles-supported MIL-101(Cr) catalyst was prepared via a diamine and oxo-centered trimeric ruthenium cluster ([Ru3(μ3-O)(μ-CH3COO)6(H2O)3]CH3COO), Ru3 cluster sequential grafting, followed by alcohol reduction. Ethylenediamine (ED) acted as the linker, coordinating with unsaturated sites on both MIL-101(Cr) and the Ru3 cluster to produce Ru3-ED-MIL-101(Cr), after which selective alcohol reduction process provided the Ru/ED-MIL-101(Cr) catalyst. The synthesized Ru/ED-MIL-101(Cr) catalyst contained small, finely dispersed Ru nanoparticles, and the structural integrity of ED-MIL-101(Cr) was maintained. The Ru/ED-MIL-101(Cr) catalyst was tested for the transfer hydrogenation of benzene using isopropanol as the hydrogen source, where it was shown to outperform other Ru-based catalysts.

Efficient catalytic transfer hydrogenation of furfural to furfuryl alcohol over Zr-doped ordered mesoporous carbon synthesized by Zr-arbutin coordinated self-assembly

The green synthesis of ordered mesoporous carbons (OMCs) with sustainable biomass resources as carbon precursors has attracted widespread interest in various applications. In this work, Zr-doped ordered mesoporous carbon (Zr@OMC) with an environmentally friendly process was synthesized with arbutin (a kind of polyphenol extracted from plants) as the carbon precursor, F127 as the soft template, and Zr4+ as the cross-linker through the solvent evaporation-induced self-assembly method. The obtained Zr@OMC exhibited highly ordered mesoporous structures with a BET surface area of 375–427 m2/g and an average pore size of 3.9–4.6 nm, which exhibited excellent catalytic performance for the conversion of furfural (FF) to furfuryl alcohol (FA) through Meerwein-Ponnodorf-Verley (MPV) reaction with isopropanol as hydrogen donor, and a maximum FA yield of 93.2 % with FF conversion of 100 % could be achieved at 180 °C. Meanwhile, Zr@OMCs could be easily regenerated by heating at 400 °C for 2 h under nitrogen flux to recover its high catalytic activity in FF conversion.

Highly Active Large Au Clusters and Even More Active Ag Nanoparticles Supported on Ceria-Zirconia: Impact of Particle Size and Potassium Ion Loading on Activity in Catalytic Transfer Hydrogenation

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, i.e., over 30 nm in diameter, than of smaller particles of average 4 nm in size was observed. Moreover, this effect was contradictory to that observed for supported monometallic silver catalysts in which the interaction with the support and hence particle size was shown to cause drastic changes in the activity in this reaction, with the large particles being completely inactive and tiny ones being the most active system studied. In this reaction, the ceria-zirconia solid solutions were used as the supports for the catalysts and both zirconium doped ceria, as well as cerium doped zirconia carriers were tested. The supports themselves exhibited little activity in this reaction. It was shown that the activity of the supports and catalysts depends on the Ce/Zr ratio and potassium content. Both types of catalysts showed excellent selectivity to 1-phenylethanol and conversion of acetophenone, although it was noted that a high loading of potassium carbonate in the gold catalysts propelled undesired reactions, thereby reducing the selectivity to 1-phenylethanol.

Promoted catalytic vapor phase transfer hydrogenation of levulinic acid to γ‐valerolactone by coordinated size effect and acid property of bimetallic Ni/ CeO 2 catalyst

Promoted catalytic vapor phase transfer hydrogenation of levulinic acid to γ‐valerolactone by coordinated size effect and acid property of bimetallic Ni/ <scp> CeO ₂ </scp> catalyst