Hydrogenolysis Of Lignin Research Articles

Catalytic Hydrogenolysis of Lignin into Propenyl-monophenol over Ru Single Atoms Supported on CeO2 with Rich Oxygen Vacancies

Catalytic Hydrogenolysis of Lignin into Propenyl-monophenol over Ru Single Atoms Supported on CeO₂ with Rich Oxygen Vacancies

Solid-State Structures and Properties of Lignin Hydrogenolysis Oil Compounds: Shedding a Unique Light on Lignin Valorization

This article explores the important, and yet often overlooked, solid-state structures of selected bioaromatic compounds commonly found in lignin hydrogenolysis oil, a renewable bio-oil that holds great promise to substitute fossil-based aromatic molecules in a wide range of chemical and material industrial applications. At first, single-crystal X-ray diffraction (SCXRD) was applied to the lignin model compounds, dihydroconiferyl alcohol, propyl guaiacol, and eugenol dimers, in order to elucidate the fundamental molecular interactions present in such small lignin-derived polyols. Then, considering the potential use of these lignin-derived molecules as building blocks for polymer applications, structural analysis was also performed for two chemically modified model compounds, i.e., the methylene-bridging propyl-guaiacol dimer and propyl guaiacol and eugenol glycidyl ethers, which can be used as precursors in phenolic and epoxy resins, respectively, thus providing additional information on how the molecular packing is altered following chemical modifications. In addition to the expected H-bonding interactions, other interactions such as π–π stacking and C–H∙∙∙π were observed. This resulted in unexpected trends in the tendencies towards the crystallization of lignin compounds. This was further explored with the aid of DSC analysis and CLP intermolecular energy calculations, where the relationship between the major interactions observed in all the SCXRD solid-state structures and their physico-chemical properties were evaluated alongside other non-crystallizable lignin model compounds. Beyond lignin model compounds, our findings could also provide important insights into the solid-state structure and the molecular organization of more complex lignin fragments, paving the way to the more efficient design of lignin-based materials with improved properties for industrial applications or improving downstream processing of lignin oils in biorefining processes, such as in enhancing the separation and isolation of specific bioaromatic compounds).

Hydrogenolysis of guaiacol and lignin to phenols over Ni/Nb2O5[sbnd]HZSM-5 catalyst

Selective hydrogenolysis of CAr-O bonds in lignin to produce aromatic compounds typically necessitates severe conditions. We developed a Ni/Nb2O5HZSM-5 catalyst that facilitates direct cleavage of guaiacol's aryl ether bonds at reduced temperatures (200 °C) and pressure (0.1 MPa H2), achieving a conversion of 89.5 % with the selectivity of phenol at 81.7 %, while retaining its activity after five cycles. The Ni/Nb2O5HZSM-5 exhibits a higher yield of phenol (49.1 mmolphenol·gNi−1·h−1), currently achieving the highest phenol yield among Ni-based catalysts. The addition of Nb2O5 enhances the dispersion of Ni and augments the effective surface area. In addition, the strong interaction of Nb with the HZSM-5 changed the electronic state of Nb and enhanced the resistance of the catalyst to high temperature and mechanical stress. Employing this catalyst for lignin depolymerization in an aqueous medium led to a 17.0 wt% yield of alkyl phenolic compounds. This approach represents an advancement in biomass resource conversion, circumventing the dependency on high-pressure and precious-metal catalysts, and signaling a new trajectory for sustainable biomass utilization in scientific research.

Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent.

Lignin, a vital renewable biopolymer, serves as the Earth's primary source of aromatics and carbon. Its depolymerization presents significant potential for producing phenolic fine chemicals. This study assesses promoted Ni-based bimetallic catalysts (Ni-Co/C and Ni-Cu/C) supported on activated carbon in isopropanol for lignin depolymerization, compared to monometallic counterparts. BET, SEM, EDX, and XPS analyses highlight their physicochemical properties and promotional effects, enhancing hydrogenolysis activity and hydrogen transformation. Reaction parameter exploration elucidates the influence on lignin depolymerization, with cobalt and copper as promoters notably increasing conversion and monomer yield. Ni-Co/C exhibits the highest lignin conversion (94.2%) and maximum monomer yield (53.1 wt%) under specified conditions, with lower activation energy (36.1kJ/mol) and higher turnover frequency (31.6h-1) compared to Ni/C. FT-IR, GPC, GC-FID, and GC-MS analyses confirm effective depolymerization, identifying 20 monomer products. Proposed reaction mechanisms underscore the potential of Ni-based bimetallic catalysts for lignin valorization, offering insights into developing efficient catalytic systems for lignin hydrogenolysis. This research enhances understanding and facilitates the development of selective catalytic processes for lignin valorization.

Sustainable Production of High-Value Chemicals from Selective Hydrogenolysis of Lignin Catalyzed by Co–Pd Bimetallic Supported on Nitrogen-Doped Carbon Spheres

Sustainable Production of High-Value Chemicals from Selective Hydrogenolysis of Lignin Catalyzed by Co–Pd Bimetallic Supported on Nitrogen-Doped Carbon Spheres

Catalytic hydrogenolysis of organosolv lignin: Cleaving C–O bonds over CuMgAlOx-layered porous metal oxide catalysts for oriented monophenols production

To understand the catalytic conversion of lignin into high-value products, lignin depolymerization was performed using a layered polymetallic oxide (CuMgAlOx) catalyst. The effects of the conversion temperature, hydrogen pressure, and reaction time were studied, and the ability of CuMgAlOx to break the C–O bond was evaluated. The CuMgAlOx (Mg/Al = 3:1) catalyst contained acidic sites and had a relatively homogeneous elemental distribution with a high pore size and specific surface area. The β-O-4 was almost completely converted by disassociating the C–O bond, resulting in yields of 14.74% ethylbenzene, 47.58% α-methylphenyl ethanol, and 36.43% phenol. The highest yield of lignin-derived monophenols was 85.16% under reaction conditions of 280 °C and 3 Mpa for 4 h. As the reaction progressed, depolymerization and condensation reactions occurred simultaneously. Higher temperatures (> 280 ℃) and pressures (> 3 Mpa) tended to produce solid char. This study establishes guidelines for the high-value application of industrial lignin in the catalytic conversion of polymetallic oxides.

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.

The full utilization of bagasse via deep eutectic solvent pretreatment for low-condensed lignin and cellulose smart indicator film

Full utilization of biomass after fractionation of its components is an effective way to maximize the value of biomass. Herein, in this study, a new acetal-mediated deep eutectic solvent (DES) was explored and its excellent performance in separating lignin from biomass as well as retarding lignin condensation has been observed. Subsequently, the separated lignin and cellulose-rich residue were used to prepare sunscreen and transparent food indicator films, respectively. The results showed that the acetal-mediated DES pretreatment can reduce the recalcitrance of bagasse, stabilize lignin (β-O-4 content of 68.6% in the lignin), and retain most of the cellulose (ie. 83.43%). Besides, the pretreatment enhanced the subsequent hydrogenolysis of lignin, and the higher β-O-4 content of the lignin contributed to the high yield of aromatic monomers (40.94%). In addition, regenerated lignin was attractive for sunscreen applications due to its lighter color and excellent UV-blocking properties. Furthermore, cellulose smart indicator film was highly sensitive, biodegradable, has excellent physical properties, and allows visual real-time monitoring of seafood spoilage using smartphones. Meanwhile, the yield of the removed hemicellulose converted to xylose in the pretreatment process reached 99.24%. In general, this work proposed a sustainable bio-refinery approach for the full upgrading of biomass.

Hydrolysis-dominated catalytic system: Hydrogen-free hydrogenolysis of lignin from Pd-MoOx/TiO2

Lignin is continuously investigated by various techniques for valorization due to its high content of oxygen-containing functional groups. Catalytic systems employing hydrolysis‑hydrogenolysis, leveraging the synergistic effect of redox metal sites and acid sites, exhibit efficient degradation of lignin. The predominance of either hydrolysis or hydrogenolysis reactions hinges upon the relative activity of acid and metal sites, as well as the intensity of the reductive atmosphere. In this study, the Pd-MoOx/TiO2 catalyst was found to primarily catalyze hydrolysis in the lignin depolymerization process, attributed to the abundance of moderate acidic sites on Pd and the redox-assisted catalysis of MoOx under inert conditions. After subjecting the reaction to 240 °C for 30 h, a yield of 48.22 wt% of total phenolic monomers, with 5.90 wt% consisting of diphenols, was achieved. Investigation into the conversion of 4-propylguaiacol (4-PG), a major depolymerized monomer of corncob lignin, revealed the production of ketone intermediates, a phenomenon closely linked to the unique properties of MoOx. Dehydrogenation of the propyl is a key step in initiating the reaction, and 4-PG could be almost completely transformed, accompanied by an over 97 % of 4-propylcatechol selectivity. This distinctive system lays a new theoretical groundwork for the eco-friendly valorization of lignin.

Improved nickel nanocatalysts for selective cleavage of lignin model compounds and lignin

The selective hydrogenolysis of lignin offers a promising avenue for converting lignin into valuable chemicals and fuels. However, the development of highly active catalysts for this process remains challenging. In this study, a series of Nix/Al2O3 catalysts were synthesized by calcining and reducing layered double hydroxides (LDHs) precursors. These catalysts were evaluated for their effectiveness in catalyzing the conversion of lignin-derived model compounds (2-phenoxy-1-phenylethanol and diphenyl ether). Remarkably, the optimized Ni3/Al2O3 catalyst demonstrated exceptional performance in cleaving C–O bonds, achieving complete conversion with high selectivity for monomers product under reaction conditions of 200 °C, 1 MPa H2, and 1 h. The catalyst's outstanding performance can be attributed to its relatively large specific surface area, Ni loading exceeding 50 wt%, well-dispersed Ni metal particles, abundant surface oxygen vacancies, and a significant number of acid sites. Additionally, the hydrogenolysis of lignin using the Ni3/Al2O3 catalyst resulted in a substantial production of monophenols (15.0 wt%). This study introduces a novel approach for tailoring highly active Ni nanocatalysts and highlights the capability of Nix/Al2O3 catalysts to efficiently cleave C–O bonds in lignin under mild reaction conditions.

Boosting catalytic activity of Ni/ZrO2 by introducing MoO3 on selective hydrogenolysis of lignin

Conversion of renewable lignin to value-added aromatic chemicals presents a broad prospect to achieve the goals of “carbon neutrality”. In this work, an efficient approach is proposed for selective hydrogenolysis of lignin to valuable 4-propyl syringol in the presence of cost-effective catalyst of yNi/ZrO2-xMoO3. When the lignin hydrogenolysis is performed with 15Ni/ZrO2-10MoO3, 15.4% yield of monophenols is achieved, which is approximately twice as that from the 15Ni/ZrO2 catalytic system (7.8%). Importantly, 33.1% of these monophenols are identified as 4-propyl syringol (4-PS), a versatile fine chemical. An extensive characterization of the modified catalysts by means of XRD, nitrogen adsorption–desorption isotherm, SEM, TEM, XPS, NH3-TPD, CO2-TPD, and H2-TPR, confirms that the introduction of MoO3 changes the primary phase of ZrO2 and the acidity/basicity properties of catalyst. As a result, an enhanced cleavage of the C-O linkage between S-lignin and other units is demonstrated, which consequently contributes to the good selectivity of 4-propyl syringol. Therefore, this work provides a new insight for producing bulk aromatic chemicals via a sustainable route.

Photocatalytic Hydrogenolysis of Lignin β-O-4 Models by a Ni-Containing Polyoxometalate/CdS QDs System

Photocatalytic Hydrogenolysis of Lignin β-O-4 Models by a Ni-Containing Polyoxometalate/CdS QDs System

Catalytic hydrogenolysis of lignin over Ni/CeO2-Al2O3 catalysts with formic acid as hydrogen source

Lignin is an aromatic polymer with prospects for producing high value-added chemicals. In this study, hydrogenolysis of alkaline lignin was carried out at 240 °C for 8 h in a hydrothermal kettle using Ni/xCeO2-yAl2O3 as catalyst and formic acid as hydrogen source. Compared with Ni catalysts supported by single oxides, the results showed that Ni/xCeO2-yAl2O3 composite-supported catalysts exhibited better catalytic depolymerization performance with higher bio-oil yields. Among them, Ni/1CeO2–3Al2O3 exhibited the most outstanding catalytic activity, with a bio-oil yield of 52.77 wt% and a phenolic compound yield of 7.21 wt%.

Unraveling the mechanisms underlying lignin and xylan dissolution in recyclable biphasic catalytic systems

Despite the exceptional performance of recyclable biphasic pretreatment systems (i.e., p-toluenesulfonic acid (TsOH)/pentanol, H2SO4/butanol, and AlCl3/MTHF) in the holistic fractionation of lignocellulosic biomass (LCB), there remains a significant gap in understanding of the intricate mechanisms governing the rapid dissolution of lignin and xylan from LCB. This study conducts comparative analyses using laboratory experiments and computational simulations to gain insights into the mechanism behind removing lignin and xylan in these systems. Under identical pretreatment conditions (140 °C, 45 min), three systems exhibited distinct levels of delignification and xylan removal. TsOH/pentanol showcased the highest levels of both delignification (83.3%) and xylan removal (98.1%), followed by H2SO4/butanol (77.9% delignification and 83.0% xylan removal), and AlCl3/MTHF (73.5% delignification and 97.2% xylan removal). Lignin characterization revealed that TsOH/pentanol and AlCl3/MTHF lignin samples boasted well-preserved β-O-4 bonds (42.4/100 Ar, 40.4/100 Ar, respectively), uniform molecular weights, and <1% sugar content. This led to high yields of phenolic monomers (TsOH/pentanol, 33.9%; AlCl3/MTHF, 33.7%) after catalytic hydrogenolysis of lignin. Furthermore, mechanistic analyses revealed that the TsOH/pentanol and AlCl3/MTHF systems exhibited the most significant interaction energy formation with the lignin model (veratrylglycerol-b-guaiacyl ether) and D-xylan model due to robust hydrogen bonding interactions, yielding energy values of −2460 kJ/mol and −2385 kJ/mol, respectively. These interactions could play pivotal roles in accomplishing notable lignin and xylan extraction.

Advancing sustainable lignin valorisation: utilizing Z-scheme photocatalysts for efficient hydrogenolysis of lignin's β-O-4, α-O-4, and 4-O-5 linkages under ambient conditions

Z-Scheme photocatalysts for sustainable hydrogenolysis of β-O-4, α-O-4, and 4-O-5 linkages of lignin-derived ether in the selective production of aromatics or aliphatic hydrocarbons.

Catalytic self-transfer hydrogenolysis of lignin over Ni/C catalysts

Ni/C catalysts for the efficient self-transfer hydrogenolysis of native lignin.

Enhanced lignin hydrogenolysis through synergy-induced bimetallic NiCu catalyst for chemocatalytic production of aromatic monomers

Bimetallic catalysts are widely favored for catalytic reactions due to their superior performance and cost-effectiveness. This study delves into the utilization of a non-noble bimetallic catalyst, NiCu/C, in the hydrogenolysis of lignin to yield valuable aromatic monomers. Under optimized temperature, this catalyst achieves an impressive 92.4% conversion of lignin into liquid products, yielding 17.7 wt% of monomers. These results outperform the performance of the monometallic catalysts (Ni/C and Cu/C). To gain insight into the detailed catalytic reaction mechanism, the catalysts underwent advanced characterization techniques such as N2 physisorption, XRD, XPS, H2-TPR, and TEM, which provided information on their textural properties, structure, oxidation states, and more. The findings clearly highlight the significant role played by the synergistic interaction between Ni and Cu metallic species in bolstering the H2 adsorption capacity, thereby resulting in elevated catalytic hydrogenolysis activity. Characterization of the lignin hydrogenolysis products was also conducted to understand the effects of bimetallic and monometallic catalysts. These findings align with the catalyst characterizations and lend further support to the significant enhancement in catalytic hydrogenolysis attributed to the synergistic impact of the NiCu/C catalyst.

Relatively Electron-Rich Ni Nanoparticles Supported on α-Al2O3 for High-Efficiency Hydrogenolysis of Lignin and Its Derivatives under Mild Conditions

Relatively Electron-Rich Ni Nanoparticles Supported on α-Al₂O₃ for High-Efficiency Hydrogenolysis of Lignin and Its Derivatives under Mild Conditions

Advances in Heterogeneous Catalysts for Lignin Hydrogenolysis.

Lignin is the main component of lignocellulose and the largest source of aromatic substances on the earth. Biofuel and bio-chemicals derived from lignin can reduce the use of petroleum products. Current advances in lignin catalysis conversion have facilitated many of progress, but understanding the principles of catalyst design is critical to moving the field forward. In this review, the factors affecting the catalysts (including the type of active metal, metal particle size, acidity, pore size, the nature of the oxide supports, and the synergistic effect of the metals) are systematically reviewed based on the three most commonly used supports (carbon, oxides, and zeolites) in lignin hydrogenolysis. The catalytic performance (selectivity and yield of products) is evaluated, and the emerging catalytic mechanisms are introduced to better understand the catalyst design guidelines. Finally, based on the progress of existing studies, future directions for catalyst design in the field of lignin depolymerization are proposed.

Efficient hydrogenolysis of lignin over CeO2/AC catalyst prepared by a simple impregnation method

There are limited renewable sources of aromatic chemicals, with lignin being one of the most prominent, accounting for approximately 30% of the planet's organic carbon. Due to its intricate and irregular structure, lignin is recalcitrant to chemical conversion, often resulting in low yields of mixtures of products when it is depolymerized. This study synthesized a CeO2/AC catalyst via an impregnation technique and then explored its ability to depolymerize lignin via an oxidation-reduction strategy. The CeO2/AC catalyst efficiently depolymerized lignin by an oxidation-reduction strategy. At 200 °C, an argon pressure of 1 MPa, and a reaction time of 4 h, the conversion of the lignin model compound reached 98.5%. When using lignin derived from poplar, birch, pine, and cotton stalk, the total yields of phenolic monomers were 36.2 wt.%, 31.2 wt.%, 17.4 wt.%, and 12.1 wt.%, respectively. The CeO2/AC catalyst exhibited a higher surface oxygen vacancy concentration than CeO2, which was crucial for facilitating the hydrogenolysis of lignin.