Catalytic Transfer Hydrogenolysis Research Articles

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

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.

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.

Pd nanocubes supported on SiW12 @Co-ZIF Nanosheets for High-efficiency rupture of ether bonds in model and actual lignin

A rational design of the intrinsic lattice structure of catalysts is vitally important to address catalytic performance. Herein is reported a top-down synthesis for the fabrication of a bifunctional metallic catalyst. First, palladium nanocubes with (100) lattices planes were synthesized through a shape-control strategy; next, the as-synthesized Pd/Co-ZIF was used as a template for in-situ phase reconstruction by a spontaneous phase transformation process in the presence of H4SiW under solvothermal conditions. Ultimately, formation of 3D hierarchical flower-like bimetallic nitride nanosheets (SiW12 @Pd/Co-ZIF-NS) were generated because of this process. The SiW12 @Pd/Co-ZIF-NS catalyst not only displays excellent catalytic transfer hydrogenolysis for C-O bond cleavage of lignin dimeric substrates, but also maintains superior recycling durability due to an encapsulation phenomenon preventing aggregation. Finally, the resulting nanocomposites exhibit superior activity and good size selectivity toward catalytic transfer hydrogenolysis of the actual lignin substrates to produce a significant amount of low-molecular-weight aromatic compounds.

Selective production of guaiacol from lignin via catalytic transfer hydrogenolysis using Ru-Cu/Zirconia

In this study, the effect of calcination temperature of zirconia support (400, 600, and 800 °C) and the role of bimetallic Ru-Cu over monometallic (Cu, Ru) catalysts are evaluated for catalytic transfer hydrogenolysis of alkali lignin. The prepared catalysts were characterized extensively for crystallinity, pore size distribution, acidity, thermal stability and chemical oxidation state. The transformation of zirconia from non-crystalline to crystalline phase was observed with increasing calcination temperature. The pores transformed from wide ink bottle shape into cylindrical shape with increased calcination temperature. The XPS analysis revealed the existence of Cu0 (60%) in presence of Ru with a concomitant reduction in Ru4+ on the surface of the catalyst, which is attributed to increased crystallinity of zirconia in the presence of copper. High yields of total monomers (32.4 wt.%) and guaiacol (12.7 wt.%) were obtained under the optimized condition (270 °C, 3 h) with Ru-Cu/ZrO2 when ZrO2 was calcined at 800 °C. The mesoporous nature of zirconia and the strong metal-support interaction exhibited by Ru-Cu are shown to influence the formation of monomers. Increase in temperature from 225 to 270 °C enhanced the yield of guaiacol, 4-methyl guaiacol and 4-ethyl guaiacol with a concomitant reduction in the yield of trans-isoeugenol, demonstrating the cleavage of C–C bonds. The recyclability tests of the catalyst showed that the yield of guaiacol remained stable even after two cycles of catalyst reuse without calcination.

Strong metal-support interaction of palladium carbide in PtPd/C catalysts for enhanced catalytic transfer hydrogenolysis of glycerol

Catalytic transfer hydrogenolysis of glycerol can give 1,2-propanediol under mild condition (200 °C) in the absence of external H2. Most existing studies have been focused on metallic catalysts for tandem H2 generation and hydrogenolysis. In this work, a series of bimetallic PtPd/C catalysts with PdCx as promoting role, were synthesized with different calcination temperatures (300–900 °C) and varied Pt/Pd molar ratio (Pd/Pt: 0.5–2.0), to investigate the structure-activity relationship over the in-situ transfer hydrogenation of glycerol. In particular, PtPd/C-900 catalysts showed the best performance (TOF: 37.6 h−1, 1,2-PDO selectivity: 45.3%). It is evidenced that varied metal particle sizes (2.6–7.0 nm) were obtained, and catalytic transfer hydrogenolysis of glycerol displayed size sensitivity over PtPd/C catalysts. Besides, strong metal-support interaction can promote the formation of palladium carbide (PdCx), thus changing the electronic structure of Pt atoms, and improving the activity of hydrogenation reaction and WGS + Reforming reaction. This study will provide insights for the structural design of catalyst for selective transfer hydrogenation of bio-polyols.

Enhancing α-etherification of lignin in Eucalyptus diol pretreatment to improve lignin monomer production

In this work, α-etherification of lignin in diol pretreatment was selectively enhanced at mild temperature for lignin isolation and subsequent valorisation. More than 90 % of lignin was removed from Eucalyptus at 120 °C in diol (ethylene glycol and 1,4-butanediol) pretreatment, resulting in >90 % cellulose conversion in 24 h at 7.5 FPU/g glucan cellulase loading. Subsequent catalytic transfer hydrogenolysis of the isolated lignins with Ru/C in ethanol gave 15 % monomer yield on native lignin basis, 5 times of that from the technical ethanol process (170 °C). HSQC NMR analysis revealed that diol pretreated lignin (120 °C) contained ∼23 % α-etherified β–O–4 interunit bonds, indicating that lignin degradation (i.e. cleavage of β–O–4 bonds) was suppressed via etherification by grafting a hydroxyl group at the α position of lignin. This finding was consistent with the isolated lignin (120 °C) had less number of phenolic OH and higher molecular weight via31P NMR and GPC analysis. 31P NMR analysis also revealed that diol isolated lignin contained more number of aliphatic OH than ethanol-isolated lignin, which increased lignin solubility and maintained the high yield (>80 %) of isolated lignin from Eucalyptus at 120 °C as expected. In summary, diol pretreatment of woody biomass can effectively isolate more lignin for hydrogenolysis to valued-added monomers without compromising the isolated yield of lignin and hydrolysis yield of remained cellulose.

Unraveling the Synergistic Participation of Ni–Sn in Nanostructured NiO/SnO2 for the Catalytic Transfer Hydrogenolysis of Benzyl Phenyl Ether

Unraveling the Synergistic Participation of Ni–Sn in Nanostructured NiO/SnO₂ for the Catalytic Transfer Hydrogenolysis of Benzyl Phenyl Ether

Hydrogenolysis of Glycerol to Propylene Glycol: Energy, Tech-Economic, and Environmental Studies.

Hydrogenolysis of glycerol to propylene glycol represents one of the most promising technologies for biomass conversion to chemicals. However, conventional hydrogenolysis processes are often carried out under harsh H2 pressures and temperatures, leading to intensive energy demands, fast catalyst deactivation, and potential safety risks during H2 handling. Catalytic transfer hydrogenolysis (CTH) displays high energy and atom efficiency. We have studied a series novel solid catalysts for CTH of glycerol. In this work, detailed studies have been conducted on energy optimization, tech-economic analysis, and environmental impact for both processes. The key finding is that relatively less energy demands and capital investment are required for CTH process. CO2 emission per production of propylene glycol is much lower in the case of transfer hydrogenolysis. The outcome of this study could provide useful information for process design and implementation of novel hydrogenolysis technologies for other energy and environmental applications.

Spherical NiCo-MOFs catalytic hydrogenolysis of lignin dimers and enzymatic lignin to value-added liquid fuels under nitrogen atmosphere

Ni-based MOFs catalysts are promising candidates that can be used to achieve biomass valorization following the process of selective hydrogenolysis process. Here we report a spherical NiCo-based MOFs catalyst, which provides a larger BET surface to enhance 2-phenoxy-1-phenylethan-1-ol molecules enrichment and promote the hydrogenolysis on spherical NiCo-based MOFs catalyst surface. In addition, the synergistic interaction between Ni and Co species also shows great effect on catalytic hydrogenolysis of 2-phenoxy-1-phenylethan-1-ol molecules and enzymatic lignin. The yields of ethylcyclohexane and cyclohexanol are dramatically improved to more than 90 mol% over Ni3Co1-based MOFs catalyst under nitrogen atmosphere. Various lignin dimers derivatives are investigated over Ni3Co1-based MOFs catalyst, which indicates oxygen-containing functional groups played a critical role in the hydrogenolysis process. Isopropanol is used as solvent in the hydrogenolysis of 2-phenoxy-1-phenylethan-1-ol molecules and enzymatic lignin. 21% of H2 is observed in the GC/MS, suggesting that it is a catalytic transfer hydrogenolysis process. Catalytic hydrogenolysis of enzymatic lignin is also carried out under 280 ℃ over optimal Ni3Co1-based MOFs catalyst for 6 h, giving highest lignin oil yield (75.6 wt%) and lower O/C ratio (0.17). This work can be extended to different biomass valorizations to promote the catalytic behavior of spherical MOFs catalysts.

Highly efficient catalytic transfer hydrogenolysis for the conversion of Kraft lignin into bio-oil over heteropoly acids

Herein, we have developed a heteropoly acid-catalytic transfer hydrogenolysis reaction for Kraft lignin valorization under mild conditions in the absence of H2.

Deconstruction of biomass into lignin oil and platform chemicals over heteropoly acids with carbon-supported palladium as a hybrid catalyst under mild conditions

In this work, near-complete conversion of lignocellulosic biomass and high products yields were achieved through catalytic transfer hydrogenolysis (CTH) in isopropanol using a heteropoly acid SiW12 synergistic with Pd/C catalyst at a relatively mild condition. The performances of various heteropoly acids and catalytic conditions were extensively examined. The results confirmed that SiW12 exhibited the highest activity on disrupting C–C linkages and C-O linkages than H2WO4, PW12, and PMo12. 34.91 wt% and 43.55 wt% monophenols were achieved for hydrogenolysis of bagasse and eucalyptus, respectively, at their optimal temperature for 5 h. Characterization studies on the lignin oil revealed that the notable structural changes were observed including the breaking of the side chain alkyl-aryl ether bonds and glycosidic bonds, while methoxyl groups were retained. Additionally, particle size of feedstock also has significant impact on the distribution and yields of the monophenols.

Catalytic transfer hydrogenolysis of C–O bonds in lignin model compounds without arene hydrogenation

The shortage of resources and the destruction of the environment have caused serious resource and environmental problems shared by all countries around the world. As a ubiquitous renewable resource, biomass has great prospects for replacing fossil energy and attracted attention from the society. The use of catalytic approach to transform biomass into high-value chemicals is an effective way to use biomass efficiently. In this work, Ni-supported catalysts has been developed for the selective cleavage of C–O bonds in lignin model compounds with 2-propanol as the hydrogen source solvent. Among these catalysts, it was indicated that zirconium phosphate (ZrP)-supported Ni catalysts were highly efficient and recyclable for alkyl-aryl ether (α-O-4 and β-O-4) cleavage in lignin model compounds. The further investigation demonstrated that the transfer hydrogenolysis of the C–O bond is highly selective, which afforded phenols and aromatics as dominant products without the products arising from hydrogenation of aromatic rings. Through a series of characterization of the catalyst, it was demonstrated that the medium strong acid sites of the ZrP support promoted the cleavage of alkyl-aryl ethers (α-O-4 and β-O-4), and Brønsted acid sites favored for achieving high selectivity toward C–O bond cleavage. Additionally, Ni(0) sites on the ZrP catalysts were responsible for the catalytic transfer hydrogenolysis.