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.

Hydrogenolysis of Poly(Ethylene-co-Vinyl Alcohol) and Related Polymer Blends over Ruthenium Heterogeneous Catalysts

The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste - poly(ethylene-co---vinyl alcohol) (EVOH) and related polymer blends - into alkane products. We report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1-C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in-situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C-C scission reveal that the hydrogenolysis of EVOH is slower than low-density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products.

Rapid Polyolefin Hydrogenolysis by a Single-Site Organo-Tantalum Catalyst on a Super-Acidic Support: Structure and Mechanism

The novel electrophilic organo-tantalum catalyst AlS/TaNpx (1) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np3 Ta=CHt Bu onto highly Brønsted acidic sulfated alumina (AlS). The proposed catalyst structure is supported by EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements and is in good agreement with DFT analysis. Catalyst 1 is highly effective for the hydrogenolysis of diverse linear and branched hydrocarbons, ranging from C2 to polyolefins. To the best of our knowledge, 1 exhibits one of the highest polyolefin hydrogenolysis activities (9,800 (CH2 units) ⋅ mol(Ta)-1  ⋅ h-1 at 200 °C/17 atm H2 ) reported to date in the peer-reviewed literature. Unlike the AlS/ZrNp2 analog, the Ta catalyst is more thermally stable and offers multiple potential C-C bond activation pathways. For hydrogenolysis, AlS/TaNpx is effective for a wide variety of pre- and post-consumer polyolefin plastics and is not significantly deactivated by standard polyolefin additives at typical industrial concentrations.

Highly Efficient Depolymerization of Waste Polyesters Enabled by Transesterification/Hydrogenation Relay Under Mild Conditions

The efficient depolymerization of polyesters under mild conditions remains a significant challenge. Herein, we demonstrate a highly efficient strategy for the degradation of a diverse array of waste polyesters as low to 80 °C, 1 bar H2 . The key to the success of this transformation relied on the initial transesterification of macromolecular polyester into more degradable oligomeric fragments in the presence of CH3 OH and the subsequent hydrogenation by the use of the rationally designed quinaldine-based Ru complex. Controlled experiments and preliminary mechanistic studies disclosed the quinaldine-based catalysts could be hydrogenated to the eventually active species, which has been confirmed by X-ray diffraction analysis and directly used as a catalyst in the hydrogenolysis of polyester. The strong viability and high activity of this new species in protic solvent were explained in detail. Besides, the crucial role of CH3 OH in promoting reaction efficiency during the whole process was also elucidated. The synthetic utility of this method was further illustrated by preparing 1,4-cyclohexanedimethanol (CHDM) from waste polyethylene terephthalate (PET).

Investigating the impact of TiO2 crystalline phases on catalytic properties of Ru/TiO2 for hydrogenolysis of polyethylene plastic waste

A series of TiO₂-supported Ru catalysts with different TiO₂ crystalline phases was synthesized and employed for the hydrogenolysis of polyethylene (PE). CO chemisorption, high-angle annular dark-field-scanning transmission electron microscopy, temperature-programmed reduction, and CO-Fourier transform infrared spectroscopy suggested that the degree of strong metal-support interactions (SMSIs) varied depending on the type of the TiO₂ phase and the reduction temperature, eventually influencing the catalysis of PE hydrogenolysis. Among the synthesized catalysts, Ru/TiO₂ with the rutile phase (Ru/TiO₂-R) exhibited the highest catalytic activity after high-temperature reduction at 500 °C, indicating that a certain degree of SMSI is necessary for ensuring high activity in PE hydrogenolysis. Ru/TiO₂-R could be successfully employed for the hydrogenolysis of post-consumer plastic wastes such as LDPE bottles to produce valuable chemicals (liquid fuel and wax) in high yields of 74.7%. This work demonstrates the possibility of harnessing the SMSIs in the design and synthesis of active catalysts for PE hydrogenolysis.

Ester Reduction with H2 on Bifunctional Metal-Acid Catalysts: Implications of Metal Identity on Rates and Selectivities

Esters reduce to form ethers and alcohols on contact with metal nanoparticles supported on Brønsted acidic faujasite (M-FAU) that cleave C-O bonds by hydrogenation and hydrogenolysis pathways. Rates and selectivities for each pathway depend on the metal identity (M=Co, Ni, Cu, Ru, Rh, Pd, and Pt). Pt-FAU gives propyl acetate consumption rates up to 100 times greater than other M-FAU catalysts and provides an ethyl propyl ether selectivity of 34 %. Measured formation rates, kinetic isotope effects, and site titrations suggest that ester reduction involves a bifunctional mechanism that implicates the stepwise addition of H* atoms to the carbonyl to form hemiacetals on the metal sites, followed by hemiacetal diffusion to a nearby Brønsted acid site to dehydrate to ethers or decompose to alcohol and aldehyde. The rates of reduction of propyl acetate appear to be determined by the H* addition to the carbonyl and by the C-O cleavage of hemiacetal.

Catalytic hydrogenolysis of plastic to liquid hydrocarbons over a nickel-based catalyst

The catalytic hydrogenolysis of a typical model compound of mulching film waste, polyethylene, was investigated as a potential way to improve economic efficiency of mulching film recycling. Nickel-based heterogeneous catalysts are proposed for polyethylene hydrogenolysis to produce liquid hydrocarbons. Among catalysts supported on various carriers, Ni/SiO₂ catalyst shows the highest activity which may due to the interactions between nickel and silica with the formation of nickel phyllosilicate. As high as 81.18% total gasoline and diesel range hydrocarbon was obtained from the polyethylene hydrogenolysis at relatively mild condition of 280 °C, and 3 MPa cold hydrogen pressure. The result is comparable to what have been reported in previous studies using noble metal catalysts. The gasoline and diesel range hydrocarbon are n-alkanes with a distribution at a range of C₄-C₂₂. The gas products are primarily CH₄ along with a small amount of C₂H₆ and C₃H₈. High yield of CH₄ as much as 9.68% was observed for the cleavage of molecule occurs along the alkane chain.

Quantum chemical hydrogenolysis strategy for elimination of heteroatoms in biomass homologous organic compounds based on oxolane and thiolane

Bio-oils obtained from biomass contain heteroatoms compounds, like oxolane and thiolane. It is quite difficult for industrialist to purify such refractory bio-oils. One of the efficient strategies for the elimination of heteroatoms is hydrogenolysis process, which results in the formation of H₂O and H₂S residues as by-products. In this work, quantum chemical studies have been used to analyse the reaction mechanism for the removal of hetero atoms (S and O) as H₂O and H₂S. We selected B3LYP functional of DFT with Pople's basis set 6-311G(d,p) for computing the hydrogenolysis steps without catalyst. LANL2DZ basis set, is used for studying hydrogenolysis steps involving AlCl₃ and WS₃H₃⁺ as catalysts. All the reactions are analysed at the temperature of 600 K and pressure of 40 bars. Structural, thermodynamic, kinetic properties have been employed to study this process. The analysis of variations parameters during the hydrogenolysis process reveals that these two organic biomass compounds undergo sequential ring opening at C-X (X = O, S) bonds. Butanol and Butanethiol are obtained as a result of first hydrogenolysis process, and these compounds are converted to butane during second catalytic process while eliminating heteroatoms.

Protecting group principles suited to late stage functionalization and global deprotection in oligosaccharide synthesis

Chemical synthesis is a powerful tool to access homogeneous complex glycans, which relies on protecting group (PG) chemistry. However, the overall efficiency of chemical glycan assembly is still low when compared to oligonucleotide or oligopeptide synthesis. There have been many contributions giving rise to collective improvement in carbohydrate synthesis that includes PG manipulation and stereoselective glycoside formation and some of this chemistry has been transferred to the solid phase or adapted for programmable one pot synthesis approaches. However, after all glycoside bond formation reactions are completed, the global deprotection (GD) required to give the desired target OS can be challenging. Difficulties observed in the removal of permanent PGs to release the desired glycans can be due to the number and diversity of PGs present in the protected OSs, nature and structural complexity of glycans, etc. Here, we have reviewed the difficulties associated with the removal of PGs from densely protected OSs to obtain their free glycans. In particularly, this review focuses on the challenges associated with hydrogenolysis of benzyl groups, saponification of esters and functional group interconversion such as oxidation/reduction that are commonly performed in GD stage. More generally, problems observed in the removal of permanent PGs is reviewed herein, including benzyl, acyl (levulinoyl, acetyl), N-trichloroacetyl, N-2,2,2-trichloroethoxycarbonyl, N-phthaloyl etc. from a number of fully protected OSs to release the free sugar, that have been previously reported in the literature.

Metal-Free Catalytic Hydrogenolysis of Silyl Triflates and Halides into Hydrosilanes

The metal-free catalytic hydrogenolysis of silyl triflates and halides (I, Br) to hydrosilanes is unlocked by using arylborane Lewis acids as catalysts. In the presence of a nitrogen base, the catalyst acts as a Frustrated Lewis Pair (FLP) able to split H₂ and generate a boron hydride intermediate capable of reducing (pseudo)halosilanes. This metal-free organocatalytic system is competitive with metal-based catalysts and enables the formation of a variety of hydrosilanes at room temperature in high yields (>85 %) under a low pressure of H₂ (≤10 bar).

Comparative study on the hydrogenolysis performance of solid residues from different bamboo pretreatments

Both alkaline organosolv and formaldehyde stabilization pretreatment can yield high-quality lignin by preventing condensation. For the hydrogenolysis of the pretreated solid residues, the highest yield of C2-C4 chemicals was 66.8% under alkaline organosolv pretreatment for 60 min. Specifically, the crimped fibers and residual lignin and hemicellulose increased the surface roughness of the residue by 40.6%, the crystallinity index decreased to 44.4%, and the crystal size was reduced to 2.15 nm, which in turn promoted hydrogenolysis of the residue. However, the increase of crystallinity and crystal size and the decrease in surface roughness of the formaldehyde stabilization pretreatment residue greatly hindered the conversion of polysaccharides. In addition, residual formaldehyde on the residue may also inhibit catalyst activity. Overall, this study provides novel perspectives on the full utilization of biomass, as well as new insights into the conversion of polysaccharides.

Insights into the interfacial effects in Cu-Co/CeOx catalysts on hydrogenolysis of 5-hydroxymethylfurfural to biofuel 2,5-dimethylfuran

The interface site between metal and support possess unique electronic and morphological structure, providing distinct active centers for favorable reaction in catalytic conversion of biomass derivatives to valuable chemicals. In this study, a series of Cu-Co/CeO_x catalysts were prepared for hydrogenolysis of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) via reduction of the corresponding layered double hydroxide precursors. The characterizations indicated the formation of CoCe-Vö interface (Vö denotes oxygen vacancy) and the effect of hydrogen spillover from Cu species to CoCe-Vö interface. Furthermore, the experiments and theoretical calculations verified that CoCe-Vö interface could activate the CO bond. The optimized catalyst showed a DMF yield of > 90% at 180 °C and 1.5 MPa H₂ with no deactivation in the cycling tests. This study reveals the interfacial effects of the nanocatalysts, including the oxygen vacancies and hydrogen spillover, on hydrogenolysis of HMF, which provided a simple and efficient approach for synthesis of high-performance non-noble metal nanocatalysts applied to the hydrogenolysis of various biomass derivatives.

On-DNA Transfer Hydrogenolysis and Hydrogenation for the Synthesis of DNA-Encoded Chemical Libraries

DNA-encoded libraries (DELs) are an increasingly popular approach to finding small molecule ligands for proteins. Many DEL synthesis protocols hinge on sequential additions of monomers using split-pool combinatorial methods. Therefore, compatible protecting group strategies that allow the unmasking of reactive functionality (e. g. amines and alcohols) prior to monomer coupling, or the removal of less desirable functionality (e. g., alkenes and alkynes) are highly desirable. Hydrogenation/hydrogenolysis procedures would achieve these ends but have not been amenable to DEL chemistry. We report a catalytic hydrogen transfer reaction using Pd/C, HCONH4 and the micelle-forming surfactant, TPGS-750-M, which gives highly efficient conversions for hydrogenolysis of Cbz-protected amines and benzyl protected alcohols and hydrogenation of nitros, halides, nitriles, aldehydes, alkenes and alkynes. Application to multicycle synthesis of an encoded compound was fully compatible with DNA-amplification and sequencing, demonstrating its applicability to DEL synthesis. This method will enable synthetic DEL sequences using orthogonal protecting groups.

On-DNA Transfer Hydrogenolysis and Hydrogenation for the Synthesis of DNA-Encoded Chemical Libraries

DNA-encoded libraries (DELs) are an increasingly popular approach to finding small molecule ligands for proteins. Many DEL synthesis protocols hinge on sequential additions of monomers using split-pool combinatorial methods. Therefore, compatible protecting group strategies that allow the unmasking of reactive functionality (e. g. amines and alcohols) prior to monomer coupling, or the removal of less desirable functionality (e. g., alkenes and alkynes) are highly desirable. Hydrogenation/hydrogenolysis procedures would achieve these ends but have not been amenable to DEL chemistry. We report a catalytic hydrogen transfer reaction using Pd/C, HCONH4 and the micelle-forming surfactant, TPGS-750-M, which gives highly efficient conversions for hydrogenolysis of Cbz-protected amines and benzyl protected alcohols and hydrogenation of nitros, halides, nitriles, aldehydes, alkenes and alkynes. Application to multicycle synthesis of an encoded compound was fully compatible with DNA-amplification and sequencing, demonstrating its applicability to DEL synthesis. This method will enable synthetic DEL sequences using orthogonal protecting groups.

Unraveling the reaction mechanism of selective C9 monomeric phenols formation from lignin using Pd-Al2O3-activated biochar catalyst

The conversion of biomass-derived lignin to valuable monomeric phenols at high selectivity is of paramount importance for sustainable biorefineries. In this study, a novel Pd-Al₂O₃ supported on activated biochar catalyst is developed for lignin hydrogenolysis. The catalyst characterization revealed that the (111) planes of both of Pd⁰ and Al₂O₃ were exposed to the surface. The maximum lignin conversion of 70.4% along with high liquid yield (∼57 wt%) was obtained at 240 °C, 3 h and 3 MPa H₂ pressure. The total monomeric phenols yield in the liquid was 51.6 wt%, out of which C9 monomeric guaiacols constituted ∼ 30.0 wt% with 38.0% selectivity to 4-propyl guaiacol. Using the reaction intermediate, coniferyl alcohol, chemoselective hydrogenation of C_α=C_β is proved to occur over the Pd site, while dehydroxylation of C_γ-OH is shown to occur over the alumina site. An impressive carbon atom economy of 60% was achieved for the production of monomeric phenols.

Lignin-to-chemicals: Application of catalytic hydrogenolysis of lignin to produce phenols and terephthalic acid via metal-based catalysts

Lignin is the only renewable aromatic material in nature and contains a large number of oxygen-containing functional groups. High-value and green utilization of "lignin-to-chemicals" can be realized via using lignin to produce fine chemicals such as phenols and carboxylic acids, which can not only reduce the waste of lignin in the process of lignocellulosic biomass treatment, but gradually make the substitution of traditional fossil fuels come true. The hydrogenolysis process under catalysis of metal catalyst has high product selectivity and less impurity, which is suitable for the production of same type or single fine chemicals. Hydrogenolysis of lignin via metal catalysts to produce lignin oil, and further modification of functional groups (e.g. methoxyl, alkyl and hydroxyl group) of depolymerized monomers in the bio-oil to yeild phenols and terephthalic acid are reviewed, and catalytic mechanisms are briefly summarized in this paper. Finally, the problems of lignin catalytic conversion existing currently are investigated, and the future development of this field is also prospected.

Molybdenum-catalyzed hydrogenolysis of herbaceous biomass: A procedure integrated lignin fragmentation and components fractionation

In this work, a low-cost MoO₂/C catalyst was prepared for the reductive catalytic fractionation (RCF) of various herbaceous biomass feedstocks (Miscanthus, Triarrhena, Floridulus, Sorghum stem and Corncob). Phenolic monomers from the hydrogenolysis of lignin component were obtained in up to 26.4 wt%, with high selectivity towards methyl coumarate (33%) and methyl ferulate (24%). The RCF left solid carbohydrate pulps with high retentions (up to 87%), which were suitable for enzymatic hydrolysis. The reaction conditions, including temperature, time, H₂ pressure, and sawdust size were examined in terms of monophenols yield, selectivity, delignification and sugar retention. This study showed that MoO₂/C could function as an excellent catalyst for lignin fragmentation as well as the fractionation of herbaceous biomass components.

Catalytic hydrogenolysis of lignin in ethanol/isopropanol over an activated carbon supported nickel-copper catalyst

Lignin is the renewable and abundant source of aromatics on earth, and the depolymerization of lignin provides significant potential for producing valuable monophenols. In this work, catalytic hydrogenolysis of organosolv poplar lignin (OPL) in ethanol/isopropanol solvent over monometallic and bimetallic nonprecious catalysts was investigated. Ni/C and a series of NiCu/C catalyst with different Cu loadings were prepared and applied for depolymerization of OPL. The highest yield of phenolic monomers was 63.4 wt% achieved over the Ni₁₀Cu₅/C catalyst at 270 °C without external H₂. The introduction of Cu in catalysts further promoted the hydrogen donor process of ethanol/isopropanol solvent and facilitated the cleavage of lignin linkages, resulting in the decreased molecular weight of bio-oil. The possible lignin dimer type structures, such as diphenylethane (β-1) type, phenylcoumaran (β-5) type, and pinoresinol (β-β) type structures, were proposed and identified by MALDI-TOF MS, giving a better understanding of the NiCu/C catalyzed lignin depolymerization.

Effect of catalyst and reaction conditions on aromatic monomer yields, product distribution, and sugar yields during lignin hydrogenolysis of silver birch wood

The impact of catalyst choice and reaction conditions during catalytic hydrogenolysis of silver birch biomass are assessed for their effect on aromatic monomer yields and selectivities, lignin removal, and sugar yields from enzymatic hydrolysis. At a reaction temperature of 220 °C with no supplemental H₂, it was demonstrated that both Co/C and Ni/C exhibited aromatic monomer yields of >50%, which were close to the theoretical maximum expected for the lignin based on total β-O-4 content and exhibited high selectivities for 4-propylguaiacol and 4-propylsyringol. Pd/C exhibited a significantly different set of products, and using a model lignin dimer, showed a product profile that shifted upon inclusion of supplemental H₂, suggesting that the generation of surface hydrogen is critical for this catalyst system. Lignin removal during hydrogenolysis could be correlated to glucose yields and inclusion of lignin depolymerizing catalysts significantly improves lignin removal and subsequent enzymatic hydrolysis yields.

A new biorefinery platform for producing (C2-5) bioalcohols through the biological/chemical hybridization process

This review presents an emerging biorefinery platform for C_2-5 bioalcohol production through chemical synthesis using the organic waste materials. Bioalcohols are the most commercialized carbon-neutral transportation fuels, compatible with existing an internal combustion (IC) engine. However, current bioalcohol fermentation processes have made from sugar-rich edible crops. Also, carbon loss from the fermentation process is substantial. To minimize carbon loss, volatile fatty acids (VFAs) can be utilized as a raw material for bioalcohol production. Thus, a two-step chemical upgrading of VFAs into C_2-5 alcohols is summarized in comparison with current challenges of biological fermentation processes for bioalcohol production. This review also provides the prospect of the hybrid biological/chemical process, presenting the technical advantages of the system. Finally, economic viability of hybridized process for bioalcohol production is compared with the current biological process.

Hydrothermal liquefaction of biogenic municipal solid waste under reduced H2 atmosphere in biorefinery format

Municipal solid waste (MSW), an inexorable by-product of anthropogenic activities composes of nearly 50% of the organic (biogenic) fraction. Hydrothermal liquefaction (HTL) was studied to facilitate thermal depolymerization of organic fraction of MSW to biocrude at sub-critical region of water (200 °C; 100 bar pressure) employing H₂ induced reducing conditions. Food, vegetable, and composite wastes were evaluated as feedstocks to produce HTL derivatives in the form of liquor (biocrude and aqueous phase), biochar and bio-gas. The biocrude (HTL_OF) showed middle oil as major fraction along with C₆-C₂₂ compounds. Composite waste resulted in relatively higher yield of biocrude fraction. The aqueous phase (HTL_AF) documented the presence of reducing sugars, sotolon and furfurals as major fraction. Biochar (HTL_BC) composition showed maximum carbon fraction followed by hydrogen and oxygen. H₂ induced reduced condition facilitated conversion of the biogenic MSW at relatively lower input conditions to various biobased fractions cohesively addressing the basic biorefinery requirement.

Microwave-assisted cleavage of cysteine perfluoroaryl thioethers

The cysteine- perfluoroarene S_NAr reaction allows for the sequence-specific attachment of dyes and affinity tags to peptides and proteins. However, while many methods exist for the desulfuration of native and functionalized cysteine residues, there are no reports of their application to perfluoroarylated cysteines. Herein we report both the hydrogenolysis of a perfluoroarylated cysteine to alanine and elimination to dehydroalanine, reactions that are both accelerated by microwave irradiation.

Catalytic hydrotreatment of kraft lignin into aromatic alcohols over nickel-rhenium supported on niobium oxide catalyst

Direct hydrogenolysis of Kraft lignin was catalyzed over a series of supported Ni or Re catalysts in ethanol solvent. The best results showed that the oil yield of 96.70 wt% was obtained with less char formation at 330 °C for 3 h over 5Ni-5Re/Nb₂O₅ catalyst. Product analysis demonstrated that the monomer yield of 35.41 wt% was given under mild condition, and low-molecular-weight aromatic alcohols were the main component in the liquid products. Ethanol was found to be more effective in H₂ production and facilitated the transformation of phenolic monomers to aromatic chemicals. The results confirmed that the optimal 5Ni-5Re/Nb₂O₅ catalyst had superior oxophilicity and appropriate acid sites, which improved the ability to directly remove the methoxyl and hydroxyl groups of lignin-derived phenolic compounds without aromatic ring hydrogenation. In addition, the temperature, time and solvent effects on the lignin depolymerization were also investigated.

High performance of Mo-promoted Ir/SiO2 catalysts combined with HZSM-5 toward the conversion of cellulose to C5/C6 alkanes

In this study, the Mo-promoted Ir/SiO₂ (Ir-MoO_x/SiO₂) catalysts combined with the zeolite HZSM-5 were used for the direct conversion of microcrystalline cellulose (MCC) to liquid fuel (C₅/C₆ alkanes) in n-dodecane/H₂O system. A synergistic effect was formed between the partially reduced MoO_x species and the Ir particles, which effectively promoted the catalytic activity of Ir/SiO₂ catalyst. When the Mo/Ir molar ratio was 0.5, a high yield of C₅/C₆ alkanes (91.7%) was achieved at 210 ℃ for 12 h. In addition, the main component of C₅/C₆ alkanes was n-hexane, which was proven to be obtained by the hydrogenolysis of the key intermediate, sorbitol, formed from the hydrolysis and hydrogenation of MCC.

Highly selective cleavage C-O ether bond of lignin model compounds over Ni/CaO-H-ZSM-5 in ethanol

Herein, 2-(2-methoxyphenoxy)-1-phenylethanol (β-O-4), 2-methoxyphenyl anisole (α-O-4) and 4-phenoxyphenol (4-O-5) were selected as typical lignin model compounds. Given the effectiveness of traditional acid-base catalysts for lignin depolymerisation, a novel Ni/CaO-H-ZSM-5(60) catalyst was prepared to investigate the difficulty level of C-O bond of three model compounds cleavage in ethanol. It was observed that Ni/CaO-H-ZSM-5(60) had prominent performance on the C-O bond cleavage at very mild conditions (140 °C, 1 MPa H₂). Among them, the C-O bond of α-O-4 and β-O-4 could be completely cleaved within 60 min. Although the C-O bond of 4-O-5 had high bond energy, 41.2% of conversion was occurred in 60 min. The introduction of CaO could regulate the acidity of H-ZSM-5 to enhance the ability to break C-O bonds. Moreover, the possible pathways of C-O ether bonds in three lignin model compounds cleavage were proposed in order to selectively obtain target products from the raw lignin degradation.

Sequential utilization of bamboo biomass through reductive catalytic fractionation of lignin

Reductive catalytic fractionation (RCF) has emerged as a new biorefinery paradigm for the fractionation and sequential utilization of entire components of biomass. Herein, we investigated the RCF of bamboo, a highly abundant herbaceous feedstock, in the presence of Pd/C catalyst. The lignin fraction in bamboo was preferentially depolymerized into well-defined low-molecular-weight phenols, with leaving carbohydrates pulp as a solid residue. In the soluble fraction, four major phenolic compounds, e.g., methyl coumarate/ferulate derived from hydroxycinnamic units and propanol guaiacol/syringol derived from β-O-4 units, were generated up to 41.7 wt% yield based on original lignin content. In the insoluble fraction, the carbohydrates of bamboo were recovered with high retentions of cellulose (68%) and hemicellulose (49%), which upon treatment with enzyme gave glucose (90%) and xylose (85%). Overall, the three major components of bamboo could efficient to be fractionated and converted into useful platform chemicals on the basis of this study.

Catalytic Conversion of Biorenewable Sugar Feedstocks into Market Chemicals

The transformation of low cost sugar feedstocks into market chemicals and monomers for existing or novel high performance polymers by chemical catalysis is reviewed. Emphasis is given to industrially relevant, continuous flow, trickle bed processes. Since long-term catalyst stability under hydrothermal conditions is an important issue to be addressed in liquid phase catalysis using carbohydrate feedstocks, we will primarily discuss the results of catalytic performance for prolonged times on stream. In particular, the selective aerobic oxidation of glucose to glucaric acid and the subsequent selective hydrogenation to adipic acid is reviewed. Hydroxymethylfurfural (HMF), which is readily available from fructose, can be upgraded by oxidation to furan dicarboxylic acid (FDCA) or by consecutive reduction and hydrogenolysis to hexanetriol (HTO) followed by hydrogenolysis to biobased hexanediol (HDO). Direct amination of HDO yields biobased hexamethylene diamine (HMDA). Aerobic oxidation of HDO represents an alternative route to biobased adipic acid. HMDA and adipic acid are the monomers required for the production of nylon- 6,6, a major polymer for engineering and fibre applications.

Quantum mechanistic study of furan and 2-methylfuran hydrodeoxygenation on molybdenum and tungsten sulfide clusters

One of the possibilities of limiting carbon dioxide emissions is to use pyrolysis oils from biomass. However, their very high oxygen content confers to these oils a chemical instability and a high viscosity. Among the oxygen-containing compounds present in bio-oils, furanic compounds derived from the decomposition of cellulosic and hemi-cellulosic biomass are the most refractory to deoxygenation. The major products of their hydrodeoxygenation are alkanes and secondly alkenes, but the intermediates are still subject to controversy. In this work, we performed a DFT simulation of the hydrodeoxygenation of furan (C₄H₄O) and 2-methylfuran in the presence of molybdenum and tungsten sulphide Mo(W)S_2. The aim of this work is to elucidate the reaction intermediates and to compare the activities of the two catalytic sites used in our reaction conditions. Our calculations show that the partial hydrogenation of the two molecules occurs preferentially in position (2,5). The hydrogenolysis reactions of the C-O bonds occur in two steps. The molybdenum sulphide exhibits higher catalytic activity.

Lignin valorization for the production of renewable chemicals: State-of-the-art review and future prospects

Lignin is an abundant biomass resource in aromatic structure with a low price in market, which can serve as renewable precursors of value-added products. However, valorization rate of annually produced lignin is less than 2%, suggesting the need for technological advancement to capitalize lignin as a versatile feedstock. In recent years, efficient utilization of lignin has attracted wide attention. This paper summarizes the research advances in the utilization of lignin resources (mainly in the last three years), with a particular emphasis on two major approaches of lignin utilization: catalytic degradation into aromatics and thermochemical treatment for carbon material production. Hydrogenolysis, direct pyrolysis, hydrothermal liquefaction, and hydrothermal carbonization of lignin are discussed in detail. Based on this critical review, future research directions and development prospects are proposed for sustainable and cost-effective lignin valorization.

Hydrogenolytic cleavage of naphthylmethyl ethers in the presence of sulfides

With the aid of a series of model thioether or thioglycoside containing polyols protected with combinations of benzyl ethers and 2-naphthylmethyl ethers it is demonstrated that the latter are readily cleaved selectively under hydrogenolytic conditions in the presence of the frequently catalyst-poisoning sulfides. These results suggest the possibility of employing 2-naphthylmethyl ethers in place of benzyl ethers in synthetic schemes when hydrogenolytic deprotection is anticipated in the presence of thioether type functionality.

Impact of lignin structure on oil production via hydroprocessing with a copper-doped porous metal oxide catalyst

A copper-catalyzed depolymerization strategy was employed to investigate the impact of lignin structure on the distribution of hydroprocessing products. Specifically, lignin was extracted from beech wood and miscanthus grass. The extracted lignins, as well as a commercial lignin (P1000), were then fractionated using ethyl acetate to provide three different portions for each source of lignin [total of 9 fractions]. Each fraction was structurally characterized and treated with a copper-doped porous metal oxide (Cu-PMO) catalyst under 4MPa H₂ and at 180°C for 12h. The reaction conditions provided notable yields of oil for each fraction of lignin. Analysis of the oils indicated phenolic monomers of commercial interest. The structure of these monomers and the yield of monomer-containing oil was dependent on the origin of the lignin. Our results indicate that hydroprocessing with a Cu-PMO catalyst can selectively provide monomers of commercial interest by careful choice of lignin starting material.

Insight into the solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin

The aim of this study is to explore the reaction mediums and conditions for producing high yield of valuable monomers from concentrated sulfuric acid hydrolyzed lignin. The solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin were investigated under the catalysis of Pd/C and CrCl₃. Supercritical methanol exhibits the best depolymerization performance, because of its unique diffusion, dissolution and acid-base properties. Afterwards, the influence of reaction temperature and time on depolymerization, repolymerization and coking during hydrogenolysis was examined in methanol. The high temperature is found to favor the depolymerization, with the β-O-4 linkages cleaved significantly. However, the repolymerization is promoted simultaneously, and a high amount of β-β groups form. These reactions are in constant competition with each other and the repolymerization is preferred at excessive high temperature, producing bulk char residues, that is coking. This study will provide a beneficial reference for the maximization of lignin waste valorization.

Investigation on the structural effect of lignin during the hydrogenolysis process

Structure has a significant effect on the lignin degradation, so the investigation of structural effect on the lignin depolymerization is important and imperative. In this study, hydrogenolysis of three typical lignins with different structures, dealkaline lignin, sodium lignosulfonate and organosolv lignin, was intensively compared over the synergistic catalyst of CrCl3 and Pd/C. The effects of reaction temperature, time, hydrogen pressure and catalyst dosage on the catalytic performance of lignin species were investigated. The structure evolution of lignins during the hydrogenolysis process was also compared. The results showed that organosolv lignin was more sensitive for hydrogenolysis than others due to its high unsaturation degree and low molecular weight. Further analysis indicated that the hydrogenolysis, hydrodeoxygenation and repolymerization reactions took place and competed intensely. Wherein, the depolymerization products with unsaturated carbonyl groups were prone to repolymerize. And the methylation was helpful to stabilize the depolymerization products and suppress the further repolymerization.

Reductive dechlorination of carbon tetrachloride using buffered alkaline ascorbic acid

Alkaline ascorbic acid (AA) was recently discovered as a novel in-situ chemical reduction (ISCR) reagent for remediating chlorinated solvents in the subsurface. For this ISCR process, the maintenance of an alkaline pH is essential. This study investigated the possibility of the reduction of carbon tetrachloride (CT) using alkaline AA solution buffered by phosphate and by NaOH. The results indicated that CT was reduced by AA, and chloroform (CF) was a major byproduct at a phosphate buffered pH of 12. However, CT was completely reduced by AA in 2M NaOH without CF formation. In the presence of iron/soil minerals, iron could be reduced by AA and Fe(2+) tends to precipitate on the mineral surface to accelerate CT degradation. A simultaneous transfer of hydrogenolysis and dichloroelimination would occur under phosphate buffered pH 12. This implies that a high alkaline environment is a crucial factor for maintaining the dominant pathway of two electron transfer from dianionic AA to dehydroascorbic acid, and to undergo dichloroelimination of CT. Moreover, threonic acid and oxalic acid were identified to be the major AA decomposition products in alkaline solutions.

Hydrogenolytic depolymerization of procyanidin polymers from hi-tannin sorghum bran

Depolymerization of procyanidin polymers into oligomers enhances their bioavailability and bioactivity because oligomers are bioavailable. Hydrogenolysis was applied in this study to depolymerize hi-tannin sorghum bran procyanidin polymers into oligomers. The yield and composition of oligomers under different hydrogenolysis conditions was investigated. Results showed that raising temperature from 50 to 100 °C significantly increased total yield of oligomers. Higher temperatures (150 and 200 °C) produced monomers with lower yield. The highest yield of oligomers (38.8%) was obtained using 1 MPa hydrogen whereas 3 MPa hydrogen in reaction vessel decreased yield. Total yield of oligomers reached the highest at 1-3 h and then decreased with prolonged reaction time. Yield increased with palladium-on-carbon (Pd/C, a catalyst) amount from 0.5 to 3 mg and plateaued with Pd/C amount from 3 to 10 mg. The maximum yield of produced oligomers was achieved under 100 °C, 1 MPa hydrogen pressure, 1-3 h, and 3-10 mg Pd/C.

Partial depolymerization of enzymolysis lignin via mild hydrogenolysis over Raney Nickel

In this work, partial depolymerization of enzymolysis lignin collected from a woody biomass-to-ethanol process was studied via mild hydrogenolysis under the catalysis of Raney Ni. The depolymerized lignin products were low molecular weight oligomers with increased hydroxyl values. The solvent selected, use of base and various reaction parameters were all found to influence yield of depolymerization, the molecular weight and hydroxyl value of the hydrogenated product. The depolymerized lignins displayed greatly enhanced solubility in organic solvents, and therefore would have great potential to be used as feedstock for many valuable thermosetting polymer applications.

Catalytic Hydrogenolysis at Low Temperature and Pressure of Polyethylene and Polypropylene to Diesels or Lower Alkanes by a Zirconium Hydride Supported on Silica-Alumina: A Step Toward Polyolefin Degradation by the Microscopic Reverse of Ziegler-Natta Polymerization

Cleavage and polymerization with the same catalyst: The catalyst system named in the title, which cleaves polyethylene and polypropylene under a hydrogen atmosphere, is also capable of polymerizing ethylene or propylene. This shows the close relationship between olefin insertion and β-alkyl elimination [Eq. (a), (P)=polymer chain(P)].