Catalytic Transfer Hydrogenolysis Research Articles

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.

Catalytic Transfer Hydrogenolysis of Glycerol over Heterogeneous Catalysts: A Short Review on Mechanistic Studies

Catalytic transfer hydrogenolysis, using liquid H-donors in the absence of pressurized H2 under mild temperatures, is regarded as the most important technology to substitute traditional hydrogenation processes in industry. Despite decade development with several breakthroughs in catalyst design, the reaction mechanism involved in H2 generation and subsequent hydrogenolysis reactions is still under debate. In this review, transfer hydrogenolysis of glycerol, as a representative example, on metallic catalysts is revised critically with respect to surface reaction mechanism and catalyst design. The detailed reaction pathways for propanol, methanol, formic acid and ethanol for H2 generation have been discussed systematically. In particular, reaction mechanism for catalytic C-H cleavage, H spillover/transfer and C-O cleavage reaction steps will be critically revised with experimental and theoretical results in literature. Insights into reaction pathways, mechanism and H2 transfer efficiency and structure-performance relation for Pd, Cu and Ni catalysts will be provided for future development of catalyst manufacture and process development. The outcome of this work is useful for successful implementation of bio-refinery.

Selective hydrodeoxygenation of lignin model compound (3,4-dimethoxybenzyl alcohol) by Pd/CNX catalyst

Upgrading of lignin derived bio-oil is an essential step for producing sustainable bio-based chemicals and fuel. Taken into account that α hydroxyl is the abundant functional group in lignin, high effective and selective catalytic alcoholysis for cleaving the Cα-OH linkages would be desirable. However, an in-depth understanding of the reaction mechanisms involved in the cleavage of Caromatic-Cα and Cα-O bonds over a novel catalyst is still needed. Herein, we report an efficient liquid-phase hydrogen transfer strategy for the selective hydrodeoxygenation of a non-phenolic lignin model compound, 3,4-dimethoxybenzyl (veratryl) alcohol, under mild conditions. By employing iso-propanol as solvent and H-donor, and palladium nanoparticles immobilized on nitrogen-doped carbon (Pd/CNX) as efficient multifunctional catalyst, veratryl alcohol dehydroxylation exhibited almost 100% conversion along with very high selectivity for 1,2-dimethoxy-benzene (46%) and 3,4-dimethoxytoluene (54%). Compared with other Pd catalysis, the Pd/CNX has excellent catalytic performances and exhibits higher selectivity for 3,4-dimethoxytoluene under incorporation with 1% HCOOH at 220 °C. The proportion of Pd (0) significantly increases in Pd/CNX catalyst when introduced into N precursor because of its highly dispersed Pd NPs and preventing the reoxidation of Pd (0). The dehydrogenation reaction occurred through the hydrogen generation of a secondary alcohol. Then, the Cα-OH and Caromatic-Cα bonds of veratryl alcohol were selectively cleaved by catalytic transfer hydrogenolysis. The alcoholysis mechanism is supported by dispersion-corrected density functional theory computations.

Antimicrobial Properties of Corn Stover Lignin Fractions Derived from Catalytic Transfer Hydrogenolysis in Supercritical Ethanol with a Ru/C Catalyst

Converting lignin to value-added products at high yields provides an avenue for making ethanol biorefineries more profitable while reducing the carbon footprint of products generally derived from petroleum. In this study, corn stover lignin was depolymerized by catalytic transfer hydrogenolysis (CTH) in supercritical ethanol with a Ru/C catalyst. The lignin-derived bio-oil was then sequentially extracted utilizing hexane, petroleum ether, chloroform, and ethyl acetate as solvents in order of less polar to polar, and the subsequent bio-oils were characterized using GPC, GC/MS, and HSQC NMR. Results show that the monomers in the bio-oil fractions contained primarily alkylated phenols, hydrogenated hydroxycinnamic acid derivatives, syringol and guaiacol-type lignins created from reductive cleavages of ether linkages, which were sequentially extracted into groups depending on the solvent polarity. The antimicrobial properties of the bio-oils were screened against Gram-positive (Bacillus subtilis, Lactobacillus amylovorus, and Staphylococcus epidermidis) and Gram-negative (Escherichia coli) bacteria and yeast (Saccharomyces cerevisiae) by examining microbial growth inhibition. Results show that CTH-derived bio-oils inhibited all tested organisms at concentrations less than 3 mg/mL. Total monomer concentration and the presence of specific monomers (i.e., syringyl propane) showed correlations to antimicrobial activity, likely due to cell death or membrane damage. This study provides insights into using sequential extraction to fractionate lignin-derived compounds and correlations between the properties of the extracted compounds and their antimicrobial activity.

An Account of the Catalytic Transfer Hydrogenation and Hydrogenolysis of Carbohydrate‐Derived Renewable Platform Chemicals over Non‐Precious Heterogeneous Metal Catalysts

AbstractSustainable and eco‐friendly catalytic processes for renewable lignocellulose biomass conversion into liquid fuels and useful chemicals offer solutions to minimize greenhouse gases emission and associated negative climate impacts. Lignocellulose derived cellulose and hemicellulose can be converted into platform chemicals including glucose, fructose, xylose, 5‐hydroxymethylfurfural, furfural, levulinic acid, levulinate esters, etc. These platform chemicals can be subsequently converted into liquid fuels and value‐added chemicals using heterogeneous catalytic processes such as; oxidation, hydrogenation, hydrogenolysis, etc. The catalytic transfer hydrogenation and hydrogenolysis (CTH) over non‐precious metal catalysts have recently drawn considerable research interest. This review summarizes recent progress on non‐precious metals catalyzed CTH processes, which also include photocatalysis and electrocatalysis, for the transformation of 5‐hydroxymethylfurfural, furfural, levulinic acid, and, levulinate esters into furfuryl alcohol, 2‐methylfuran, 2,5‐dimethylfuran, and, gamma‐valerolactone; elucidate structure‐function relationship and highlights the underlying reaction mechanisms. This review is timely and provides detailed fundamental insights about the nature of active sites and CTH processes that will be useful for the researchers willing to work in this exciting area.

Catalytic Transfer Hydrogenolysis of Native Lignin to Monomeric Phenols over a Ni–Pd Bimetallic Catalyst

Direct hydrogenolysis of native lignin in biomass into monomeric phenols has received increasing attention. In this work, catalytic transfer hydrogenolysis of native lignin from birch, pine, and co...

Catalytic Cleavage of the C-O Bond in 2,6-dimethoxyphenol Without External Hydrogen or Organic Solvent Using Catalytic Vanadium Metal.

Hydrogenolysis of the C-O bonds in lignin, which promises to be able to generate fuels and chemical feedstocks from biomass, is a particularly challenging and important area of investigation. Herein, we demonstrate a vanadium-catalyzed cleavage of a lignin model compound (2,6-dimethoxyphenol). The impact of the catalyst in the context of the temperature, reaction time, and the solvent, was examined for the cleavage of the methyl ethers in 2,6-dimethoxyphenol. In contrast to traditional catalytic transfer hydrogenolysis, which requires high pressure hydrogen gas or reductive organic molecules, such as an alcohol and formic acid, the vanadium catalyst demonstrates superior catalytic activity on the cleavage of the C-O bonds using water as a solvent. For example, the conversion of 2,6-dimethoxyphenol is 89.5% at 280°C after 48 h using distilled water. Notably, the vanadium-catalyzed cleavage of the C-O bond linkage in 2,6-dimethoxyphenol affords 3-methoxycatechol, which undergoes further cleavage to afford pyrogallol. This work is expected to provide an alternative method for the hydrogenolysis of lignin and related compounds into valuable chemicals in the absence of external hydrogen and organic solvents.

Lattice strained bimetallic PtPd nanocatalysts display multifunctional nature for transfer hydrogenolysis of sorbitol in base-free medium

Catalytic transfer hydrogenolysis (HDO) of polyols by in situ formed H2 under mild reaction conditions and displays both technological and environmental advantages over conventional HDO processes operating at elevated temperatures and pressures. Current studies on catalyst design are primarily focused on compositional features of solid catalysts to obtain superior activity and selectivity to value-added products. A major challenge is to understand the electronic nature of catalysts in C–H, C–C, and C–O cleavage of polyols. In this work, we report a design principle for modulating lattice and electronic configuration of bimetallic PtPd-N-doped mesoporous carbon (NMC) catalysts, immobilized on N-doped carbon, for highly efficient transfer HDO of sorbitol to renewable glycols and alcohols in base-free medium. The finding is that lattice strain and electronic coupling at metal-N interface induce confined growth of PtPd crystal facets, leading to strained structures with Pt lattice contraction and Pd phase segregation. While conventional PtPd nanoparticles exhibit monofunctional nature in facilitating C–H cleavage of sorbitol with poor activity, such unique PtPd-NMC catalysts display a synergistic fourfold activity enhancement (Turnover frequency (TOF): 58 h−1 at 200 °C) for tandem C–H, C–C, and C–O cleavage of polyols. Chemisoprtion and X-ray photoelectron spectroscopy spectroscopy studies reveal that N-doped carbon functions as a Lewis base and lattice modulator to manipulate electronic properties of bimetallic nanocatalysts for facile tandem C–H (H2 generation) and C–O/C–C cleavage (HDO) catalysis.

Catalytic transfer hydrogenolysis of lignin α-O-4 model compound 4-(benzyloxy)phenol and lignin over Pt/HNbWO6/CNTs catalyst

Cleavage of C–O bonds in aryl ether through the catalytic transfer hydrogenolysis (CTH) is an encouraging method for the valorization of lignin into fine chemicals and liquid fuels. In this contribution, the CTH of typical lignin α-O-4 model compound 4-(benzyloxy)phenol (BOP) and lignin extracted from ash wood have been explored over 0.45 wt% Pt/HNbWO6/CNTs catalyst. The effect of solvents was elaborated and the highest catalytic activity was achieved in the CTH of BOP using isopropanol as the solvent (98.1%). This was because isopropanol can provide more hydrogen atoms to promote CTH reaction due to the weakest interaction between isopropanol and BOP among all H-donor solvents. The favorable results obtained in the model compound study inspired us to afford Pt/HNbWO6/CNTs catalyst in the CTH of lignin. The relative oxygen content of lignin was sharply decreased after the CTH process, and the higher heating value (HHV) significantly increased from 21.4 MJ/kg to 30.8 MJ/kg. GPC, FT-IR, GC-MS, and 2D-NMR results revealed that lignin was successfully depolymerized into small molecule compounds over Pt/HNbWO6/CNTs catalyst through the CTH process. Thereinto, phenolic compounds were the major components in the liquid products in which most of them were monophenols. The results obtained in this work shed light on that Pt/HNbWO6/CNTs was a favorable catalyst in the depolymerization of lignin into valuable phenolic compounds via the CTH method.

Catalytic Transfer Hydrogenolysis of Bio-Polyols to Renewable Chemicals over Bimetallic PtPd/C Catalysts: Size-Dependent Activity and Selectivity

Most industrial hydrogenation processes are conducted under elevated temperature and pressure. Catalytic transfer hydrogenation/hydrogenolysis, in the absence of externally added hydrogen, is known...

Selective Catalytic Transfer Hydrogenolysis of Glycerol to 2-Isopropoxy-Propan-1-Ol over Noble Metal Ion-Exchanged Mordenite Zeolite

This study investigated the selective conversion of glycerol to 2-isopropoxy-propan-1-ol over noble metal ion-exchanged mordenite zeolites (RuMOR, RhMOR, and PdMOR) as heterogeneous catalysts via catalytic transfer hydrogenolysis (CTH) using propan-2-ol as the solvent, hydrogen supplier, and reactive coupling reagent with glycerol. The catalytic reactions were performed at 140 °C under inert conditions with a 0.5 MPa initial pressure of N2. A single product, 2-isopropoxy-propan-1-ol, was catalytically generated without any appreciable by-products. The catalytic results were reproducible, and the catalysts exhibited good recyclability.

Ultrasound-induced catalytic transfer hydrogenolysis of β-lactams: Facile synthesis of 2-hydroxy aromatic amide derivatives

Ultrasound-induced catalytic transfer hydrogenolysis of β-lactams: Facile synthesis of 2-hydroxy aromatic amide derivatives

Sequential Extraction and Characterization of Lignin-Derived Compounds from Thermochemically Processed Biorefinery Lignins

As the most abundant source of renewable aromatic compounds on the planet, lignin is an attractive feedstock for producing a range of chemicals and products that are currently derived from petroleum. Despite its great potential, separation of lignin depolymerization products remains one of the main obstacles toward cost-effective lignin valorization. Two lignin-rich streams, residues from enzymatic hydrolysis of the dilute acid and alkaline-pretreated corn stover, were depolymerized via pyrolysis using induction heating and catalytic transfer hydrogenolysis (CTH), respectively. Differences in phenolic compounds from gas chromatography–mass spectrometry and gel permeation chromatography analyses suggest that both pretreatment conditions and lignin depolymerization methods affected the product distribution. CTH lignin oils contain less polar compounds as compared to pyrolysis lignin oils, probably due to saturation of the derived compounds as a result of the reductive chemistry. The resulting liquid oils we...

Catalytic transfer hydrogenolysis of lignin into monophenols over platinum-rhenium supported on titanium dioxide using isopropanol as in situ hydrogen source

Using isopropanol as an in situ hydrogen donor, catalytic transfer hydrogenolysis of lignin into monomeric phenols was studied at mild conditions. The performance of catalysts and the effects of H2, temperature, and time on depolymerization of acid extracted birch lignin (ABL) were extensively examined. Platinum-rhenium supported on titanium dioxide (PtRe/TiO2) exhibited much higher activity on disrupting CO bonds than Pd/C, HZSM-5, Pt/TiO2, and Re/TiO2. 18.71 wt% monophenols was achieved for depolymerization of ABL over PtRe/TiO2 at 240 °C for 12 h with He. 4-Propylsyringol had the highest yield of 7.48 wt%. 2D HSQC NMR analysis reveals that β-O-4 bonds have been fully disrupted during depolymerization. Addition of H2 led to less monophenols, likely due to the competitive adsorption of active sites on catalysts. Structure-reactivity analysis based on six representative lignins shows that the total yields of monophenols were highly linearly correlated with the β-O-4 contents (R2 = 0.97).

Catalytic Transfer Hydrogenolysis Reactions for Lignin Valorization to Fuels and Chemicals

Lignocellulosic biomass is an abundant renewable source of chemicals and fuels. Lignin, one of biomass main structural components being widely available as by-product in the pulp and paper industry and in the process of second generation bioethanol, can provide phenolic and aromatic compounds that can be utilized for the manufacture of a wide variety of polymers, fuels, and other high added value products. The effective depolymerisation of lignin into its primary building blocks remains a challenge with regard to conversion degree and monomers selectivity and stability. This review article focuses on the state of the art in the liquid phase reductive depolymerisation of lignin under relatively mild conditions via catalytic hydrogenolysis/hydrogenation reactions, discussing the effect of lignin type/origin, hydrogen donor solvents, and related transfer hydrogenation or reforming pathways, catalysts, and reaction conditions.

Catalytic transfer hydrogenolysis as an efficient route in cleavage of lignin and model compounds

Cleavage of aromatic ether bonds through hydrogenolysis is one of the most promising routes for depolymerisation and transformation of lignin into value-added chemicals. Instead of using pressurized hydrogen gas as hydrogen source, some reductive organic molecules, such as methanol, ethanol, isopropanol as well as formates and formic acid, can serve as hydrogen donor is the process called catalytic transfer hydrogenolysis. This is an emerging and promising research field but there are very few reports. In this paper, a comprehensive review of the works is presented on catalytic transfer hydrogenolysis of lignin and lignin model compounds aiming to breakdown the aromatic ethers including α-O-4, β-O-4 and 4-O-5 linkages, with focus on reaction mechanisms. The works are organised regarding to different hydrogen donors used, to gain an in-depth understanding of the special role of various hydrogen donors in this process. Perspectives on current challenges and opportunities of future research to develop catalytic transfer hydrogenolysis as a competitive and unique strategy for lignin valorisation are also provided.

Catalytic Transfer Hydrogenolysis as an Effective Tool for the Reductive Upgrading of Cellulose, Hemicellulose, Lignin, and Their Derived Molecules

Lignocellulosic biomasses have a tremendous potential to cover the future demand of bio-based chemicals and materials, breaking down our historical dependence on petroleum resources. The development of green chemical technologies, together with the appropriate eco-politics, can make a decisive contribution to a cheap and effective conversion of lignocellulosic feedstocks into sustainable and renewable chemical building blocks. In this regard, the use of an indirect H-source for reducing the oxygen content in lignocellulosic biomasses and in their derived platform molecules is receiving increasing attention. In this contribution we highlight recent advances in the transfer hydrogenolysis of cellulose, hemicellulose, lignin, and of their derived model molecules promoted by heterogeneous catalysts for the sustainable production of biofuels and biochemicals.

Characterization and Catalytic Transfer Hydrogenolysis of Deep Eutectic Solvent Extracted Sorghum Lignin to Phenolic Compounds

Deep eutectic solvent (DES) is intrinsically cheaper than many ionic liquids (ILs) due to low precursor cost, simple synthesis, and improved recyclability. Meanwhile, DES can be as effective as ILs toward dissolving lignin from plant materials. However, the lignin depolymerization mechanism in DES, the structural and chemical properties of DES-extracted lignin (DES-EL), and the possible valorization pathways of DES-EL toward value-added products were not well understood. This study aims to characterize the lignin streams from DES (1:2 choline chloride:lactic acid) treated sorghum and further upgrade the extracted lignin to phenolic compounds. As revealed by HSQC, 13C, and 31P NMR analysis, DES cleaved nearly all ether linkages in native lignin, resulting in significant size reduction. We further catalytically upgraded DES-EL to phenolic compounds via catalytic transfer hydrogenolysis in the presence of isopropyl alcohol. Among the three tested catalysts (Ru/C, Pd/C, and Pt/C), Ru/C proved the most effecti...