Catalytic Transfer Hydrogenation Research Articles

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge‐hosted Fe−N3 Sites

AbstractNitrogen‐doped, carbon‐supported transition metal catalysts are excellent for several reactions. Structural engineering of M−Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe−N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe−N3 sites with varying Fe−N bond lengths distinguishable by X‐ray absorption spectroscopy. We investigate the CTH activity by density‐functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe−N3 distortion, raises the Fe orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe−N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high‐performing Fe−N−C catalysts by defect engineering.

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge-hosted Fe-N3 Sites.

Nitrogen-doped, carbon-supported transition metal catalysts are excellent for several reactions. Structural engineering of M-Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe-N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe-N3 sites with varying Fe-N bond lengths distinguishable by X-ray absorption spectroscopy. We investigate the CTH activity by density-functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe-N3 distortion, raises the Fe orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe-N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high-performing Fe-N-C catalysts by defect engineering.

Efficient catalytic transfer hydrogenation of furfural and other biomass-derived compounds over sustainable magnetic catalyst

In this study, the acid-base bifunctional magnetic ZrMg@Fe3O4 metallic oxide catalysts with remarkable structural properties were synthesized by the co-precipitation method for the catalytic transfer hydrogenation (CTH) of furfural (FF), ethyl levulinate (EL), and 5-methylfurfural (5-MF) to furfuryl alcohol (FFA), gamma-valerolactone (GVL), and 5-methyl-2-furanmethanol (5-MFA). Characterization results indicated that the ZrMg@Fe3O4 (7: 1:1) catalyst possesses a substantial pore volume, large specific surface area, and mesoporous properties, which play an important role in improving catalytic activity. The leaching experiment indicated that the catalyst was not prone to leaching, proving its structural stability. The yield of FFA, GVL, and 5-MFA could be as high as 92.50%, 95.00%, and 53.95% by optimization experiments. The Py-FTIR, CO2-TPD, and poisoning experiments showed that Lewis acid-base sites significantly impact the catalytic activity. The catalyst can be readily isolated and retrieved from the liquid reaction mixture by applying the external magnetic field. The reaction mechanism and catalytic stability were also conducted by systematically studying the reaction experiments and physicochemical properties of the catalyst.

Highly selective catalytic transfer hydrogenation of biomass derived furfural to furfural alcohol over Zr/SBA-15 catalysts

The effective utilization of furfural (FU) from biomass for the production of furfuryl alcohol (FOL) is becoming increasingly important due to the versatility of FOL production of valuable chemicals. This study reports a highly efficient approach for in-situ hydrothermal methods to prepare SBA-15 (SB) and x% Zr/SBA-15 (ZSB) composite catalysts with different weight percentages (x = 1, 3, and 5 wt.%). The prepared bare and most active catalysts were analyzed by XRD, FT-IR, FE-SEM, EDS, and TEM. Characterization studies showed that Zr species were present and uniformly distributed in the SB framework. All the prepared materials were used for liquid phase catalytic transfer hydrogenation (CTH) of FU with isopropanol (2-PrOH) at atmospheric N2 pressure (1 atm) under mild reaction conditions. The 3ZSB catalyst showed excellent conversion of FU (100 %) and remarkably high selectivity for FOL (97 %). To achieve the highest possible conversion of FU with high selectivity to the desired products, the experimental parameters such as reaction temperature, hydrogen donor, time, molar ratio, and catalyst weight were optimized. The reusability of the most active 3ZSB composite catalysts was also tested for up to six sequences. Moreover, no significant change in catalytic performance was observed. In this study, a green, efficient, and sustainable process for the catalytic synthesis of FOL using biomass-derived FU is presented. This process is of great importance in promoting the sustainable use of biomass resources.

Mononuclear and dinuclear (pyridyl) dicarboxamide Ru(II) hydrido complexes: Ligand controlled coordination diversity and catalytic transfer hydrogenation of ketones

Reactions of ligand N,N-(1,4-phenylene)-dipicolinamide (H2L1), with [Ru(PPh3)3(CO)HCl] produced the dinuclear complex [Ru2(H2L1)(PPh3)4(CO)2H2]2+[2Cl−]− (Ru1). On the other hand, treatments of ligand N,N-(1,2-phenylene)-dipicolinamide (H2L2), with two and one molar equivalents of [Ru(PPh3)3(CO)HCl] afforded the dinuclear and mononuclear complexes [Ru2(HL2)(PPh3)3(CO)3HCl2] (Ru2) and [Ru(HL2)(PPh3)2(CO)H] (Ru3) respectively. The identities and structures of complexes Ru1-Ru3 were established using NMR, FT-IR spectroscopic techniques, mass spectrometry, and elemental analyses. The complexes Ru1-Ru3 displayed high catalytic activities in the transfer hydrogenation of a wide range of ketones. The hydride complex Ru1 was the most active, while the dinuclear complex Ru2 was more active than the analogous mononuclear complex Ru3. 31P NMR spectroscopic analyses of the reaction intermediates was used to propose a monohydride pathway in the transfer hydrogenation reactions involving dissociation of one PPh3 ligand.

Rigorous design, techno-economic and environmental analysis of two catalytic transfer hydrogenation (CTH) processes to produce bio-based 2-methylfuran (2-MF)

The catalytic transfer hydrogenation (CTH) reaction has emerged as a safer method for converting biomass derivatives into value-added chemicals. This study aims to comprehensively evaluate two processes for converting furfural into 2-methylfuran (2-MF) using either methanol (or MeOH, Scheme 1) or isopropyl alcohol (or IPA, Scheme 2) as hydrogen carriers. Both processes were rigorously simulated using Aspen Plus. The reaction performance was modeled using kinetic models developed from literature data. In addition, appropriate strategies are first established for separating the reactor effluents of both processes, which contain multiple azeotropes, based on the thermodynamic parameters estimated through COSMO-based calculations. From the techno-economic analysis, the minimum required selling price (MRSP) of 2-MF is 5.15 USD/kg when produced with Scheme 1, and 3.63 USD/kg when produced with Scheme 2. The MRSP in Scheme 1 becomes 4.50 USD/kg by considering the benefits of the side product, a formalin solution. Compared to various literature data, the MRSPs of these two process schemes are significantly lower than that obtained from direct hydrogenation (6.87 USD/kg). If the cost of the starting materials can be reduced by 25% or more, the MRSP becomes comparable to that obtained from an improved direct hydrogenation process (2.20–3.30 USD/kg). Furthermore, the CO2 emission analysis reveals that Scheme 2 has a lower rate of indirect CO2 emission rate (0.926 Ton-CO2/Ton-2-MF) compared to Scheme 1 (1.088 Ton-CO2/Ton-2-MF). With thorough assessment, we have concluded that the production of 2-MF through the CTH reaction in Scheme 2 is superior. This process shows promise in both economic and decarbonization aspects and could have industrial significance.

Carbon coated LaFe0.92Pd0.08O3 composites for catalytic transfer hydrogenation: Balance in the ability of substrates adsorption and conversion

Carbon coated LaFe0.92Pd0.08O3 composites for catalytic transfer hydrogenation: Balance in the ability of substrates adsorption and conversion

Ethanol as hydrogen donor: An efficient transfer hydrogenation of aldehydes, ketones, and nitroarenes with H-bonded Ru(II)-N-heterocyclic iminium complex

Isopropanol and formic acid are predominantly utilized as hydrogen sources in catalytic transfer hydrogenation reactions. However, the utilization of primary alcohols in such reactions has been sparsely documented, with only a limited number of reports available. In this article, we hereby present findings that underscore the prospective application of ecologically sustainable and economically viable ethanol, alongside a ruthenium(II) catalyst that exhibits remarkable resilience in the presence of moisture and oxygen. The air-stable Ru(II) complex (I) has been synthesized by non-covalently interacting anionic Ru(p-cymene)Cl3 and 1,3-diisopropyl-1H-perimidin-2(3H)-iminium (LH2+). The compound was subjected to experimental evaluation to conduct transfer hydrogenation reactions on aldehydes, ketones, and nitroarenes. The process entailed the utilization of ethanol, a hydrogen source that is both economically advantageous and ecologically benign. The hydrogen bond interaction existing between the Ru(p-cymene)Cl3 and LH2+ species plays a crucial in facilitating the exceptional catalytic efficiency exhibited by the Ru(II) complex (I). The reaction exhibits a wide range of substrate compatibility, enabling the hydrogenation of ketones, aldehydes, and nitroarenes. The results obtained from the control experiments have provided evidence for the formation of Ru − H species. A plausible mechanism has been hypothesized, relying on stoichiometric investigations.

Heteropolyacids promoted MOF-derived high-performance Co(H4)@C-HPW0.25 catalysts for catalytic transfer hydrogenation of vanillin in mild condition

Catalytic transfer hydrogenation (CTH) was recognized as a promising technique for converting various lignin derivatives to fuels and high-value compounds in heterogeneous systems. Herein, Co@C catalysts with diverse organic ligands, Keggin-type heteropolyacids, acid addition quantities, and metal/organic ligand molar ratios were synthesized via one-pot hydrothermal processes and carbonization methods. The optimized catalyst demonstrated highly efficient active hydrogen generation from isopropanol and the best conversion (100 %) for vanillin (VAN) hydrodeoxygenation (HDO) with 90 % 2-methoxy-4-methylphenol (MMP) yield at 180 °C for one hour under mild conditions of 0 MPa N2 (hydrogen-free circumstance), which were strongly connected to the higher specific surface area (154.45 m2/g), acidic site density (4.67 mmol/g), and stronger metal-P interactions of the Co(H4)@C-HPW0.25 catalyst. The findings in this work provided an advanced thinking for designing high-performance non-noble-metal catalysts that could be applied in the catalytic HDO transformation of various biomass derivatives into green fuel and chemicals under mild circumstances.

Exploring Hydrogen Sources in Catalytic Transfer Hydrogenation: A Review of Unsaturated Compound Reduction.

Catalytic transfer hydrogenation has emerged as a pivotal chemical process with transformative potential in various industries. This review highlights the significance of catalytic transfer hydrogenation, a reaction that facilitates the transfer of hydrogen from one molecule to another, using a distinct molecule as the hydrogen source in the presence of a catalyst. Unlike conventional direct hydrogenation, catalytic transfer hydrogenation offers numerous advantages, such as enhanced safety, cost-effective hydrogen donors, byproduct recyclability, catalyst accessibility, and the potential for catalytic asymmetric transfer hydrogenation, particularly with chiral ligands. Moreover, the diverse range of hydrogen donor molecules utilized in this reaction have been explored, shedding light on their unique properties and their impact on catalytic systems and the mechanism elucidation of some reactions. Alcohols such as methanol and isopropanol are prominent hydrogen donors, demonstrating remarkable efficacy in various reductions. Formic acid offers irreversible hydrogenation, preventing the occurrence of reverse reactions, and is extensively utilized in chiral compound synthesis. Unconventional donors such as 1,4-cyclohexadiene and glycerol have shown a good efficiency in reducing unsaturated compounds, with glycerol additionally serving as a green solvent in some transformations. The compatibility of these donors with various catalysts, substrates, and reaction conditions were all discussed. Furthermore, this paper outlines future trends which include the utilization of biomass-derived hydrogen donors, the exploration of hydrogen storage materials such as metal-organic frameworks (MOFs), catalyst development for enhanced activity and recyclability, and the utilization of eco-friendly solvents such as glycerol and ionic liquids. Innovative heating methods, diverse base materials, and continued research into catalyst-hydrogen donor interactions are aimed to shape the future of catalytic transfer hydrogenation, enhancing its selectivity and efficiency across various industries and applications.

Heterocyclic compounds: their potential application as antimicrobials of health importance and in the catalytic hydrogen transfer reaction

Heterocyclic compounds: their potential application as antimicrobials of health importance and in the catalytic hydrogen transfer reaction

Confinement effect induced Pd/UiO-66-rGO for efficient aromatic alkenes catalytic hydrogenation

A simple and adaptable synthetic method is reported here for synthesizing UiO-66-GO nanohybrid materials by modulating the growth and dispersion of UiO-66 on GO surfaces, using PdCl2 as the Pd source with thermal treatment at 120 °C without additional reduction to obtain Pd/UiO-66-rGO composite catalyst. Pd/UiO-66-rGO demonstrates excellent activity in catalytic transfer hydrogenation for C═C bond of aromatic alkenes by using HCOONH4 and water as hydrogen donor and solvent at 25 °C, with 99.6 % styrene conversion and 99.9 % selectivity to ethylbenzene. The confinement effect leads to ultra-small Pd NPs active sites evenly dispersed on Pd/UiO-66-rGO, which is the good catalytic performance of Pd/UiO-66-rGO results from. Additionally, UiO-66-rGO makes a protection effect to stabilize and prevent the Pd active sites leaching out, ensuring the cyclic stability of this catalyst.

Mechanistic Studies on the Bismuth-Catalyzed Transfer Hydrogenation of Azoarenes.

Organobismuth-catalyzed transfer hydrogenation has recently been disclosed as an example of low-valent Bi redox catalysis. However, its mechanistic details have remained speculative. Herein, we report experimental and computational studies that provide mechanistic insights into a Bi-catalyzed transfer hydrogenation of azoarenes using p-trifluoromethylphenol (4) and pinacolborane (5) as hydrogen sources. A kinetic analysis elucidated the rate orders in all components in the catalytic reaction and determined that 1 a (2,6-bis[N-(tert-butyl)iminomethyl]phenylbismuth) is the resting state. In the transfer hydrogenation of azobenzene using 1 a and 4, an equilibrium between 1 a and 1 a ⋅ [OAr]2 (Ar=p-CF3 -C6 H4 ) is observed, and its thermodynamic parameters are established through variable-temperature NMR studies. Additionally, pKa -gated reactivity is observed, validating the proton-coupled nature of the transformation. The ensuing 1 a ⋅ [OAr]2 is crystallographically characterized, and shown to be rapidly reduced to 1 a in the presence of 5. DFT calculations indicate a rate-limiting transition state in which the initial N-H bond is formed via concerted proton transfer upon nucleophilic addition of 1 a to a hydrogen-bonded adduct of azobenzene and 4. These studies guided the discovery of a second-generation Bi catalyst, the rate-limiting transition state of which is lower in energy, leading to catalytic transfer hydrogenation at lower catalyst loadings and at cryogenic temperature.

Mechanistic Studies on the Bismuth‐Catalyzed Transfer Hydrogenation of Azoarenes

AbstractOrganobismuth‐catalyzed transfer hydrogenation has recently been disclosed as an example of low‐valent Bi redox catalysis. However, its mechanistic details have remained speculative. Herein, we report experimental and computational studies that provide mechanistic insights into a Bi‐catalyzed transfer hydrogenation of azoarenes using p‐trifluoromethylphenol (4) and pinacolborane (5) as hydrogen sources. A kinetic analysis elucidated the rate orders in all components in the catalytic reaction and determined that 1 a (2,6‐bis[N‐(tert‐butyl)iminomethyl]phenylbismuth) is the resting state. In the transfer hydrogenation of azobenzene using 1 a and 4, an equilibrium between 1 a and 1 a ⋅ [OAr]2 (Ar=p‐CF3−C6H4) is observed, and its thermodynamic parameters are established through variable‐temperature NMR studies. Additionally, pKa‐gated reactivity is observed, validating the proton‐coupled nature of the transformation. The ensuing 1 a ⋅ [OAr]2 is crystallographically characterized, and shown to be rapidly reduced to 1 a in the presence of 5. DFT calculations indicate a rate‐limiting transition state in which the initial N−H bond is formed via concerted proton transfer upon nucleophilic addition of 1 a to a hydrogen‐bonded adduct of azobenzene and 4. These studies guided the discovery of a second‐generation Bi catalyst, the rate‐limiting transition state of which is lower in energy, leading to catalytic transfer hydrogenation at lower catalyst loadings and at cryogenic temperature.

Catalytic transfer hydrogenation of CO2 to formic acid with glycerol as the hydrogen donor over Ru-REUSY catalysts

In this work, a "hydrogen-free" strategy based on the ruthenium (Ru) modified REUSY molecular sieve catalysts was proposed, which can promote CO2 catalytic transfer hydrogenation using endogenous hydrogen induced by glycerol dehydrogenation. As the active component, Ru can not only act on the dehydrogenation reaction with glycerol, but also promote the hydrogenation reaction of CO2. Comparison experiments confirmed that under conditions of 200 °C, 36 h, and 7.92 g KHCO3, the reaction could obtain the highest yields over 10 wt.% Ru-deAl(5 h)-REUSY. The yields of formic acid and lactic acid were 19.81 % and 6.13 % respectively. In addition, when replacing the carbon source from KHCO3 to CO2 (dry ice), formic acid and lactic acid yields over 10 wt.% Ru-deAl(5 h)-REUSY catalysts were further improved, reaching 64.14 % and 17.13 %, respectively. This work demonstrated the feasibility of the "hydrogen-free" upgrade process realizing the catalytic transfer hydrogenation of CO2 into formic acid with glycerol as hydrogen donor.

Microwave-Induced Catalytic Transfer Hydrogenation in Different Solvents Toward Optically Active Hydroxy β-Lactams: Effects of Penetration Depth

In present work, the stereospecific synthesis of optically active cis hydroxy β-lactams by catalytic transfer hydrogenation under diversemicrowave-induced conditions is invstigated. The effects of the penetration depth of the solvents are found to be more crucial than solvents with high dipole moments and dielectric constants. Despite significant progress of microwave-induced reactions, no reports have examined the penetration depth of the solvents used in these processes

Conversion of xylose into D-xylitol using catalytic transfer hydrogenation with formic acid as H-donor

d-Xylitol, a biomass-derived sweetener, is increasingly used in cosmetics and pharmaceutical products. The raw material for d-xylitol production, d-xylose, is easily accessible from dissolving pulp production. d-xylitol production involves the heterogeneously catalyzed hydrogenation of d-xylose; this process is energy intensive, as the use of H2 requires high pressure and temperature. This work examined catalytic transfer hydrogenation for xylose conversion into xylitol. Formic acid (FA) was used to replace H2 as the H-donor, as it is easily available, inexpensive, may be obtained from renewable sources, and it avoids the risks associated with the use of high-pressure inflammable gas. A variety of commercially available catalysts were screened to reveal the one enabling the highest yield. The experiments were performed at 40, 80, and 140 °C, with pure xylose as a model compound. Triethylamine (Et3N) was added to ensure sufficient conversion rates. Based on the preliminary studies an experimental design was created (Design Expert®), including the two best performing catalysts Ru/Al2O3 and Ru/C, to investigate the influence of temperature and H-donor and base concentration on xylitol yield. Ru/C resulted in maximum d-xylitol yield of 73.2 % at 100 °C, FA to d-xylose ratio 5:1 and Et3N to FA ratio 0.4.

Enantioselective synthesis of the bioactive flavanones lonchocarpol A and 6-(1,1-dimethylallyl)naringenin by catalytic asymmetric transfer hydrogenation

Practical enantioselective syntheses of the natural products lonchocarpol A and 6-(1,1-dimethylallyl)naringenin as well as their optical antipodes are reported. A rhodium-catalyzed asymmetric transfer hydrogenation of readily available racemic substrates with virtually complete kinetic resolution served as the key step. Solvent-controlled, clay-catalyzed [1,3] or [3,3] shifts of prenyl aryl ethers were used to install the C-6 prenyl or 1,1-dimethylallyl substituent of the target flavanones.

Structure-activity relationships of ZrO2 crystalline phases in the catalytic transfer hydrogenation of methyl levulinate with ethanol

The depletion of fossil resources is driving the research towards renewable alternatives, like lignocellulosic biomass. Therefore, the development of efficient continuous-flow processes, allowing to achieve better productivity compared to batch processes, will play a crucial role in promoting a sustainable transition. In this context, we report on the continuous-flow, gas-phase, catalytic transfer hydrogenation (CTH) of methyl levulinate and ethanol over zirconia catalysts, in particular focusing on the effect of two different crystalline phases (i.e. monoclinic, m-ZrO2, and tetragonal, t-ZrO2) on catalyst performance. An in-depth catalyst characterisation was coupled with both computational and 1H NMR relaxation studies to assess the structure-activity relationship, providing fundamental insights into the catalytic process and future catalyst optimization. The results, indicate that the higher Lewis acidity and basicity along with the lower affinity with ethanol of m-ZrO2 with respect to t-ZrO2 are responsible for the promotion of undesired oligomerisation reactions of angelica lactones responsible for catalyst deactivation.

Highly active, ultra-low loading single-atom iron catalysts for catalytic transfer hydrogenation

Highly effective and selective noble metal-free catalysts attract significant attention. Here, a single-atom iron catalyst is fabricated by saturated adsorption of trace iron onto zeolitic imidazolate framework-8 (ZIF-8) followed by pyrolysis. Its performance toward catalytic transfer hydrogenation of furfural is comparable to state-of-the-art catalysts and up to four orders higher than other Fe catalysts. Isotopic labeling experiments demonstrate an intermolecular hydride transfer mechanism. First principles simulations, spectroscopic calculations and experiments, and kinetic correlations reveal that the synthesis creates pyrrolic Fe(II)-plN3 as the active center whose flexibility manifested by being pulled out of the plane, enabled by defects, is crucial for collocating the reagents and allowing the chemistry to proceed. The catalyst catalyzes chemoselectively several substrates and possesses a unique trait whereby the chemistry is hindered for more acidic substrates than the hydrogen donors. This work paves the way toward noble-metal free single-atom catalysts for important chemical reactions.