Transfer Hydrogenolysis Research Articles

Tandem Methanolysis and Catalytic Transfer Hydrogenolysis of Polyethylene Terephthalate to p‐Xylene over Cu/ZnZrOx Catalysts

We demonstrate a novel approach of utilizing methanol (CH3OH) in a dual role for (1) the methanolysis of polyethylene terephthalate (PET) to form dimethyl terephthalate (DMT) at near‐quantitative yields (~97%) and (2) serving as an in‐situ H2 source for the catalytic transfer hydrogenolysis (CTH) of DMT to p‐xylene (PX, ~63% at 240 °C and 16 h) on a reducible ZnZrOx supported Cu catalyst (i.e., Cu/ZnZrOx). Pre‐ and post‐reaction surface and bulk characterization, along with density functional theory (DFT) computations, explicate the dual role of the metal‐support interface of Cu/ZnZrOx in activating both CH3OH and DMT and facilitating a lower free‐energy pathway for both CH3OH dehydrogenation and DMT hydrogenolysis, compared to Cu supported on a redox‐neutral SiO2 support. Loading studies and thermodynamic calculations showed that, under reaction conditions, CH3OH in the gas phase, rather than in the liquid phase, is critical for CTH of DMT. Interestingly, the Cu/ZnZrOx catalyst was also effective for the methanolysis and hydrogenolysis of C‐C bonds (compared to C‐O bonds for PET) of waste polycarbonate (PC), largely forming xylenol (~38%) and methyl isopropyl anisole (~42%) demonstrating the versatility of this approach toward valorizing a wide range of condensation polymers.

Tandem Methanolysis and Catalytic Transfer Hydrogenolysis of Polyethylene Terephthalate to p-Xylene Over Cu/ZnZrOx Catalysts.

We demonstrate a novel approach of utilizing methanol (CH3OH) in a dual role for (1) the methanolysis of polyethylene terephthalate (PET) to form dimethyl terephthalate (DMT) at near-quantitative yields (~97 %) and (2) serving as an in situ H2 source for the catalytic transfer hydrogenolysis (CTH) of DMT to p-xylene (PX, ~63 % at 240 °C and 16 h) on a reducible ZnZrOx supported Cu catalyst (i.e., Cu/ZnZrOx). Pre- and post-reaction surface and bulk characterization, along with density functional theory (DFT) computations, explicate the dual role of the metal-support interface of Cu/ZnZrOx in activating both CH3OH and DMT and facilitating a lower free-energy pathway for both CH3OH dehydrogenation and DMT hydrogenolysis, compared to Cu supported on a redox-neutral SiO2 support. Loading studies and thermodynamic calculations showed that, under reaction conditions, CH3OH in the gas phase, rather than in the liquid phase, is critical for CTH of DMT. Interestingly, the Cu/ZnZrOx catalyst was also effective for the methanolysis and hydrogenolysis of C-C bonds (compared to C-O bonds for PET) of waste polycarbonate (PC), largely forming xylenol (~38 %) and methyl isopropyl anisole (~42 %) demonstrating the versatility of this approach toward valorizing a wide range of condensation polymers.

Catalytic depolymerization and hydrodeoxygenation of lignin to high-density fuel precursors using Ni/Nb2O5 catalyst

Converting lignin into renewable fuels via hydrogenolysis is crucial for achieving carbon neutrality. Existing methods primarily produce monomers in the carbon range of 6–9, inadequate for sustainable aviation fuels requiring heavier components. This study introduces a Ni/Nb2O5 catalyst for catalytic transfer hydrogenolysis of organosolv birch lignin with isopropanol, predominantly resulting in dimers and trimers within carbon ranges of 8–16 and 16–30, comprising 24.7 % and 60.5 % of the lignin-oil, respectively. The catalyst's oxygen vacancies and acid sites facilitate efficient C-O and C-C bonds cleavage, preserving a highly aromatic structure with reduced O/C ratio, elevated H/C ratio, and decreased unsaturation. Characterization techniques confirm a significant 55.5 % deoxygenation degree of the lignin-oil, making it suitable for the synthesis of customized fuel across various carbon numbers. This approach offers a practical pathway for obtaining renewable heavier fuel components and precursors from lignin, significantly advancing sustainable fuel technologies.

Visible light-driven selective cleavage of Cα-Cβ or Cβ-O bond in lignin β-O-4 model into high-value aromatic chemicals over surface modified 2D g-C3N4

Selective cleavage of C–C/C–O linkages in lignin is highly pursued to obtain aromatic monomers but remains challenging due to distinct dissociation energies and steric hindrance. Herein, two photocatalysts were reported to respectively scissor the Cα-Cβ and Cβ-O in lignin β-O-4 model (2-phenoxy-1-phenylethanol) based on the reactive oxygen species control. On one hand, 2D g-C3N4 promotes protons extraction from Cβ-H and ·O2– formation, which further scissored Cα-Cβ via six-membered ring transition state produced via the coupling of ·Cβ and ·HO2, providing aromatic aldehydes and esters. When single-atomic Cu+ species were coordinated with N atoms in 2D g-C3N4 during surface modification, however, the ·O2– formation was prohibited because of the improper redox potentials. Under the catalysis of Cu/2D g-C3N4, CαO-H would be preferentially activated, causing the selective Cβ-O cleavage via self-hydrogen transfer hydrogenolysis to provide phenolics and aromatic ketones. The access and inhibition mechanism for ·O2– formation as well as the different catalytic mechanisms for two reaction pathways were discussed. Current work shows a promising way to selectively supply aromatic chemicals using the renewable biomass and photoenergy.

Self-hydrogen transfer hydrogenolysis of β-O-4 bonds in lignin model compounds over NiCu/Al2O3 catalyst

Hydrogenolysis of β-O-4 linkages in lignin to produce aromatic compounds is attractive but challenging. Currently, external hydrogen source like hydrogen gas or hydrogen-donor solvent is necessary during hydrogenolysis, leading to high cost and low selectivity of products. Herein, a NiCu/Al2O3 catalyst was prepared for self-hydrogen transfer hydrogenolysis (SHTH) of Cβ-O bond using inherent CαH-OH structure as H-source. A β-O-4 model compound, 2-phenoxy-1-phenethanol, was completely transformed into acetophenone and phenol at 220 ℃ under 1 MPa N2 for 2h. The SHTH reaction proceeded through a dehydrogenation reaction followed by a hydrogenolysis reaction. Hydrogen radicals released from CαH-OH group generated a “hydrogen pool” on the catalyst surface, which inserted into the formed β-O-4 ketone intermediate to cleave the Cβ-O bond. The catalyst presented outstanding reusability and universality during the SHTH reaction. Moreover, the methoxy groups at aryl positions impeded the SHTH process, and the steric effect was related to the amount and position of methoxy groups. This study realizes the utilization of structural hydrogen from lignin model compounds for its Cβ-O bond cleavage, providing an economical and sustainable method toward lignin valorization.

Transfer Hydrogenolysis of O‐ and N‐Benzyl Groups in Water with Tetrahydroxydiboron by Using an Amphiphilic Polymer‐Supported Nano‐Palladium Catalyst

AbstractDebenzylation of O‐ and N‐benzyl groups was achieved under safe and mild conditions by using B2(OH)4 as an alternative to gaseous hydrogen in the presence of an amphiphilic polystyrene‐poly(ethylene glycol) resin‐supported nano‐palladium catalyst (ARP−Pd) in water. Benzyl groups of a variety of benzylic ethers, esters, carbamates, and amines, including benzyl‐protected carbohydrates and amino acids, were reductively removed in high yields. ARP−Pd was recovered by simple filtration and reused seven times without a significant loss of its catalytic activity.

Double core–shell hollow nanocage CuO@Co3O4 for the selective hydrogenolysis of C–O bonds of lignin without external hydrogen

The design of a highly active Cu-Co catalyst for catalytic transfer hydrogenolysis of lignin without the use of external hydrogen remains highly challenging. In this work, Cu2O was initially encapsulated in ZIF-67, and subsequently Cu2O@ZIF-67 was utilized as a precursor and sacrificial template to prepare the unique double core–shell hollow nanocage CuO@Co3O4. Co and Cu, serving as Lewis acid sites and dehydrogenation sites for the hydrogen-donor solvent isopropanol, respectively, exhibited synergistic enhancement, further increasing the catalytic activity. Under the optimal conditions of 220 °C, 1 MPa N2, and 4 h, the catalyst achieved 100 % conversion of 2-phenoxy-1-phenylethanol and 100 % yield towards cyclohexanol and ethylbenzene. Furthermore, the catalyst remained stable and reusable after 5 cycles, providing a practicable guidance for the value-added conversion of lignin.

Ring–Opening Mechanism of O‐heterocycles into α,ω‐Diols over Ni−La(OH)3: C−O Bond Hydrogenolysis of THFA to 1,5‐Pentanediol as a Case Study

AbstractThe elucidation of the ring–opening reaction mechanism is a critical step towards improving the catalytic performance for the conversion of biomass into value–added chemicals. Herein, we focused on the stepwise C−O bond hydrogenolysis mechanism of oxygen–containing heterocycles (O‐heterocycles) into α,ω‐diols, in particular THFA to 1,5‐PeD, over selective Ni−La(OH)3 in hydrogen–donor isopropanol. A mechanistic study was carried out on a structurally well–defined Ni−La(OH)3, where the mechanism was elucidated using a combination of kinetic and 13C NMR isotope labeling experiments. It was suggested that both Ni nanoparticles and La(OH)3 support play a critical role in the reaction mechanism, where basic hydroxide species of the support initially deprotonate the CH2OH and −OH modified furan, tetrahydrofuran and tetrahydropyran rings, adsorbing them chemically on the catalyst surface. This step is followed by a direct hydride attack on the second carbon atom of these rings, which is proposed to be the key step for ring cleavage, as indicated by the increased deuteration at this position. In addition to the direct hydrogenolysis using gaseous H2, it is assumed that a catalytic transfer hydrogenolysis reaction (CTH) reaction of THFA is proposed to proceed via the dehydrogenation of isopropanol over isolated Ni species, forming hydrogen species that can be adsorbed on the Ni surface or desorb as H2 molecules.

Nitrogen-doped ordered mesoporous carbon supported ruthenium metallic nanoparticles: Opportunity for efficient hydrogenolysis of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran by catalytic transfer hydrogenation

One of the most promising solutions to the current energy crisis is an efficient catalytic transformation of abundant low-cost renewable raw biomass into high-quality biofuel. Herein, a highly effective catalyst was constructed systematically for the selective synthesis of 2,5-dimethylfuran (DMF) biofuel from biomass-derived 5-hydroxymethylfurfural (HMF) via green catalytic transfer hydrogenolysis (CTH) using a nitrogen-doped ordered mesoporous carbon (N-CMK-1) decorated ruthenium (Ru)-based catalyst in i-propanol as hydrogen source. The structures and properties of different catalysts were characterized by different characterization techniques such as FTIR, XRD, N2-sorption, CO2-sorption, TGA, TEM, ICP-AES, CHNO analysis, and acid-base back titration. A complete HMF conversion with a high DMF yield of 88% was achieved under optimized reaction conditions. Regarding substrate conversion and product yield, the influence of reaction temperature, time, and hydrogen donors was thoroughly investigated. The nitrogen-promoted carbon support enhanced the dispersion of Ru due to the formation of appropriate basic site density which could efficiently promote the activation of alcohol hydroxyl in i-propanol and subsequent release of active hydrogen species. In the meantime, highly dispersed surface Ru nanoparticles (NPs) were beneficial for hydrogen transfer and activation of both carbonyl and hydroxyl groups in HMF. Moreover, Arrhenius kinetic analysis was studied by identifying 5-methyl furfural (5-MF) and 2,5-bishydroxymethylfuran (BHMF) as two key intermediates that dominate a distinct reaction pathway during hydrogenolysis of HMF to DMF via CTH. Furthermore, high stability without obvious loss of activity after three consecutive cycles was observed in a fabricated N-CMK-1 decorated Ru-based catalyst as a result of superior metal-support interaction and the mesoporous framework nature of the catalyst. These findings would not only offer a robust catalyst synthetic approach but also open a new avenue for the exploitation of biomass to specialty chemicals and advanced biofuels.

Catalytic Transfer Hydrogenolysis of Switchgrass Lignin with Ethanol Using Spinel-Type Mixed-Metal Oxide Catalysts Affords Control of the Oxidation State of Isolated Aromatic Products

Catalytic Transfer Hydrogenolysis of Switchgrass Lignin with Ethanol Using Spinel-Type Mixed-Metal Oxide Catalysts Affords Control of the Oxidation State of Isolated Aromatic Products

Plasmonic Catalysis on Au–Pd Nanoalloy for Self-Hydrogen Transfer Hydrogenolysis of Lignin β-O-4 Models under Visible Light

Plasmonic Catalysis on Au–Pd Nanoalloy for Self-Hydrogen Transfer Hydrogenolysis of Lignin β-O-4 Models under Visible Light

Lignin Depolymerization to Guaiacol and Vanillin Derivatives via Catalytic Transfer Hydrogenolysis using Pd-Lewis Metal Oxide Supported on Activated Carbon Catalysts

Lignin valorization is the key to sustainability of second-generation bioethanol refineries. In this study, the catalytic activities of Pd-Lewis acid metal oxides (Mo, Zr) supported on commercial activated carbon (AC) and activated biochar (ABC) were evaluated for the selective production of monomeric phenols from alkali lignin through transfer hydrogenolysis. The catalysts were thoroughly characterized for phase, degree of graphitization, textural properties, and metal dispersion. The Pd crystallite size was 2.1-2.5 Å in the case of AC-supported catalysts, while it was smaller (1.4-1.5 Å) for ABC-supported catalysts. AC exhibited better degree of graphitization than ABC. 2%Pd-5%Mo supported on AC showed good catalytic activity for the production of guaiacol, alkyl guaiacols, alkene guaiacols, and vanillin derivatives, and their respective yields were 4.2, 10.3, 3.4, and 12 wt.%. Compared to other alcohols like methanol and ethanol, the use of isopropyl alcohol as solvent resulted in better yields of guaiacol, alkyl guaiacols and alkene guaiacols. Condensation reactions of the guaiacyl unit and syringyl unit were confirmed through Fourier transform infrared spectroscopic analysis of the residue. Dimerization of monomeric phenols was observed with Pd-metal oxide supported on ABC than with AC-based catalyst.

Biomethane and propylene glycol synthesis via a novel integrated catalytic transfer hydrogenolysis, carbon capture and biomethanation process

A novel conceptual design for the co-production of biomethane and propylene glycol from integrated catalytic transfer hydrogenolysis (CTH), biogenic CO2 capture and biomethanation reaction was presented in this study. Furthermore, process economics and environmental impact study was performed to appraise the feasibility of the proposed design. The minimum selling price (MSP) of propylene glycol produced considering the overall cost of biomethane as co-product is 1.41 U.S.$/kg. However, if the cost of biomethane was not considered or if the biomethane produced is not enough to yield a yearly revenue then the MSP would increase to 1.43 U.S.$/kg. The MSP of biomethane for the integrated process was 148 U.S.$/MWh. The MSPs of propylene glycol and biomethane were comparable with those of the business-as-usual technology. Factors such as hydrogen donor solvent cost, catalyst cost, electricity price and equipment purchase cost influenced the MSP. Environmental assessment studies showed that the standalone CTH had a higher overall carbon footprint (carbon emissions of 3.7 MM tonnes/yr.). This could be attributed to the consumption of CO2 derived from the process streams via biomethanation process.

Catalytic transfer hydrogenolysis mechanism of benzyl phenyl ether over NiCu/Al2O3 using isopropanol as hydrogen source

Efficient transfer hydrogenolysis of benzyl phenyl ether (BPE) was accomplished over Ni1.5Cu1.5/Al2O3 using isopropanol as hydrogen source. The characterization results demonstrated that the formation of NiCu alloy and electron transfer between Ni and Cu were responsible for the excellent catalytic performance. Isopropanol displayed better hydrogen-donating ability than other low-carbon alcohols because of its unique dehydrogenation pathway and small steric hindrance. The results of isotopic experiments elucidated that active hydrogen species for the CO bond cleavage originated from isopropanol rather than H2, while both isopropanol and H2 were responsible for hydrogenation of phenol to cyclohexanol when reaction was conducted with mixed hydrogen sources. A mechanism study illustrated that transfer hydrogenolysis of BPE proceeded through direct cleavage of CO bond followed by phenol hydrogenation, in which the active hydrogen species were in the form of H+ and H−.

Mild catalytic transfer hydrogenolysis of lignin for efficient monophenol production over lignin-coordinated N-doped ultrafine Ni nanocluster catalyst

Lignin hydrogenolysis into monophenols presents a promising route for lignin-based chemical and fuel production but still suffers from harsh reaction conditions (e.g. high temperature and high external H2 pressure). Herein, we report an ultrafine Ni nanocluster anchored on N-doped carbon nanosheets (Ni/LNC) for efficient catalytic transfer hydrogenolysis of poplar organosolv lignin. The catalyst was fabricated through a simple pyrolysis process of lignin‑nickel complex mixed with melamine, in which the lignin coordination greatly improved the Ni dispersion and the strong NiN interaction inhibited the Ni nanocluster growth, resulting in the ultrafine particle size (1–2 nm). Under mild conditions (160 °C, 1 h), 22.08% of monophenol yield was obtained over the catalyst, which was significantly higher than those over the two reference catalysts (Ni/AC and Ni/LC) as well as other previously reported Ni-based catalysts. The excellent catalytic activity can be attributed to both the substantial increase in catalytic active sites and the enhancement in H transfer from methanol resulted from the electron-rich N-doped nanosheet support. Finally, magnetically recycled Ni/LNC showed excellent recycling stability. Consequently, this work presents a facile and low-cost approach for the synthesis of N-doped carbon nanosheet supported ultrafine Ni nanocluster and further demonstrates its superior applicability in lignin hydrogenolysis.

Microwave-assisted catalytic transfer hydrogenolysis of lignin-derived aromatic ethers over Ru/C

Cleavage of aromatic ether bonds through hydrogenolysis is one of the most promising routes for depolymerisation and transformation of lignin into value-added chemicals. Herein, we investigate the catalytic transfer hydrogenolysis (CTH) of benzyl phenyl ether (BPE), as a model molecule of α-O-4 lignin linkages, over commercial Ru/C under microwave irradiation using 2-propanol as H-donor. By tuning the reaction parameters, such as time, temperature and catalyst amount, BPE was fully converted, at 150 °C in 5 min of irradiation, with a related aromatics selectivity of 92%. Phenylethylphenyl ether (PPE), and diphenyl ether (DPE), as a models of β-O-4 and 4-O-5 linkages, respectively, were also considered to this scope and under optimized reaction conditions, >99% and 72% conversion, respectively, were achieved with >89% aromatics selectivity. Remarkably, catalytic tests with moderate conversions clearly showed that the cleavage of etheric C-O bond was the primary step under CTH conditions, while the hydrogenations of the aromatic rings take place in a subsequent step. Overall, the screening of the reaction parameters was crucial to avoid the hydrogenation of aromatic rings. No less significant was the Ru/C stability, which has been recycled at least six times without any noticeable activity loss.

Functional zirconium phosphate nanosheets enabled transfer hydrogenolysis of aromatic ether bonds over a low usage of Ru nanocatalysts

Catalytic hydrogenolysis of aromatic ether bonds is a highly promising strategy for upgrading lignin into small-molecule chemicals, which relies on developing innovative heterogeneous catalysts with high activity. Herein, we designed porous zirconium phosphate nanosheet-supported Ru nanocatalysts (Ru/ZrPsheet) as the heterogeneous catalyst by a process combining ball milling and molten-salt (KNO3). Very interestingly, the fabricated Ru/ZrPsheet showed good catalytic performance on the transfer hydrogenolysis of various types of aromatic ether bonds contained in lignin, i.e., 4-O-5, α-O-4, β-O-4, and aryl-O-CH3, over a low Ru usage (<0.5 mol%) without using any acidic/basic additive. Detailed investigations indicated that the properties of Ru and the support were indispensable. The excellent activity of Ru/ZrPsheet originated from the strong acidity and basicity of ZrPsheet and the higher electron density of metallic Ru0 as well as the nanosheet structure of ZrPsheet.

Selective C–O bond cleavage in diphenyl ether via catalytic transfer hydrogenolysis over Ru-decorated nanocrystalline H-ZSM-5

Ru NPs incorporated nanocrystalline HZSM-5 selectively break C–O bonds in diphenyl ether, a lignin model compound, via a sustainable catalytic transfer hydrogenolysis pathway, transforming it into valuable fuels and fuel additives.

Photocatalytic transfer hydrogenolysis of aryl ethers

The H2-free reductive cleavage of inert aryl ethers has been achieved at room temperature via photocatalytic transfer hydrogenolysis combined with acid catalysis.

Hydrogenolysis of lignin and Lignin-based molecules catalyzed by nickel and Sc(OTf)3

Renewable aromatic carbon sources and their transformation into value-added chemicals represent one of the most promising approaches of sustainable development. Here, we prepared and characterized nickel catalysts and evaluated their activity in transfer hydrogenolysis reactions using formic acid as hydrogen donor, finding excellent activity and high selectivity to CO bond cleavage in lignin and lignin model compounds using water/ethanol or propylene carbonate as solvents. Particularly, a nickel catalyst named Ni-1, was used in the guaiacylglycerol-β-guaiacyl hydrogenolysis to selectively obtain guaiacol and isoeugenol. Thus, in the case of Ni-1 (NiIINx) we found that small clusters and nanoparticles of 3 –5 nm diameters coexist in the material. Further, the Sc(OTf)3 Lewis acid (LA) successfully promoted the CO bond cleavage of 1-(o-tolyloxy)propan-2-ol to obtain guaiacol. Additionally, we describe the synthesis of benzodioxanes catalyzed by scandium triflate from 1-(o-tolyloxy)propan-2-ol as product of the propylene carbonate decarboxylation catalyzed by ZIF-8.