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The selective hydrodeoxygenation (HDO) of lignin-derived bio-oil still meets the great challenges due to its complex oxygenated organic component. In this research, first time, Pd-based zeolite catalysts were prepared by the modified deposition-precipitation (DP) method for the HDO conversion of guaiacol. Notably, for the same Si/Al ratio of zeolite, Pd 2% /Hβ catalyst showed the higher catalytic activity on the HDO of guaiacol than that Pd 2% /M and Pd 2% /HZSM-5 catalyst, which mainly originated from the synergetic effect between metal nanoparticles size and acid sites of catalyst. As one of typical phenolic monomers, guaiacol can be converted into high yield of hydrocarbons under the condition of 220 °C, 3 MPa H 2 , and 4 h in n -hexane over Pd 2% /Hβ (DP) catalyst. This highly active catalyst exhibited the good recyclability in the HDO conversion of guaiacol. In addition, other typical phenolic monomers can be converted into high yield of hydrocarbons over this highly active catalyst. Considering this, after HDO upgrading, real lignin oil (RLO) can be converted into high yield of hydrocarbons with the carbon number (CN) in range of C7-C15. This work highlighted that the depolymerization monomers from lignin can be further upgraded by this high active catalyst through HDO to obtain jet hydrocarbons fuel. [Display omitted] • Compared with Pd 2% /M and Pd 2% /HZSM-5 catalyst, Pd 2% /Hβ (DP) catalyst showed higher HDO activity of guaiacol. • Pd 2% /Hβ (DP) catalyst showed more acid sites and smaller metal nanoparticles size. • Pd 2% /Hβ (DP) catalyst was also suitable for HDO of other phenolic monomers. • After upgradation, the RC of hydrocarbons in two real lignin oils significantly increased. • The upgraded lignin oils showed great potential for becoming as high-grade bio-fuel. [ABSTRACT FROM AUTHOR]

Deep insight of reaction mechanism in lignin model compounds is helpful to achieve the directed depolymerization of lignin or biomass to chemicals or fuels. In this study, the density functional theory (DFT) calculation was employed to investigate the cleavage mechanism of the C –O bonds in lignin dimers. Additionally, the intrinsic chemical reactivity of molecular in term of the Fukui function was applied to predict the most probable sites which react with hydrogen free radicals (H·). It was found that the O atoms in lignin dimers are the most reaction site involving H· because of the large f (0). By this method, the most rational path from a series of reaction paths was screen out. Apart from the Fukui function, the average local ionization energy (ALIE) was analyzed to prove the reliability of Fukui function. The kinetic analysis of the reaction path was performed to further understand the impact of temperature on the reaction rate constant (KTST). It is observed that benzyl phenyl ether (BPE) with higher KTST could be easily cleaved because of the relatively low energy barrier. Image 1 • The reaction paths of lignin dimers hydrogenolysis was simulated by DFT. • The Fukui function and average local ionization energy of molecule were calculated. • The reaction sites with H· radicals was predicted based on f (0) and ALIE. • The kinetic studies of lignin dimers hydrogenolysis were explored. [ABSTRACT FROM AUTHOR]

Controlling the C-O bond hydrogenolysis while suppressing the direct hydrogenation of aromatic rings in lignin-derived ethers is critical and challenging for the utilization of lignin. Herein, a series of metal-modified (La, Zr, Cr, Ce and Ga) α-Al 2 O 3 -supported Ru-based catalysts were synthesized for the conversion of diphenyl ether (DPE). The catalyst characterizations demonstrate that the metal modification cannot change the chemical valence of Ru but promotes the dispersion of Ru nanoparticles and adjusts the adsorption state of DPE. The results indicate that the metal modification inhibits the arenes hydrogenation at low temperatures but facilitates the C-O bond cleavage during heating (at low H 2 pressures or an inert atmosphere). Ru-Cr/α-Al 2 O 3 shows the highest reaction rate for DPE conversion at 1 MPa Ar and 200 °C. Moreover, Ru-Cr/α-Al 2 O 3 not only efficiently converts different lignin model compounds by hydrogenolysis, but also achieves the controlled depolymerization of real lignin to generate guaiacols under mild conditions. [Display omitted] • Controlling DPE hydrogenolysis is achieved over metal-modified Ru-based catalyst. • Ru-Cr/α-Al 2 O 3 shows the highest activity for DPE conversion at 1 MPa Ar and 200 °C. • The metal modification cannot change the chemical valence of Ru. • The metal doping enhances the C-O bond cleavage of lignin and its derivatives. • The routes for the conversion of DPE under different conditions are presented. [ABSTRACT FROM AUTHOR]

Guaiacol is an important raw material to produce many value-added chemicals. Here, we report a strategy for directly cleaving the C ar -C α and C β -O bonds in pine lignin over a solid acid to generate guaiacol. The guaiacol yield in 90% methanol aqueous solution is up to 18.2 wt%, which is 5.6 wt% higher than that in methanol. The reaction pathway is proposed by combining controlled experiments with density functional theory. Different from previous views, the C ar -C α bond cleavage was found to be related to deacetylation, while the formation of C α =O bond was found to change the intramolecular charge distribution and promote the C ar -C α bond cleavage through validation experiments. Adding water promotes methanol decomposition to produce more active hydrogen species and thereby promote the C ar -C α bond cleavage. This work provided a feasible pathway for obtaining guaiacol by directly cleaving the C ar -C α and C β -O bonds in lignin. [Display omitted] • The C ar -C α bond cleavage was found to be achieved by deacetylation. • The formation of C α = O bond changes the charge distribution within the molecule. • The addition of water could reduce the formation of condensation products. • The guaiacol yield in MAS enhanced by 5.6 wt% compared to methanol. [ABSTRACT FROM AUTHOR]

An eco-friendly supercritical CO 2 (scCO 2)-ethanolysis system was designed to convert Caragana korshinskii (Ck) into valuable bio-oils. Hydrocarbons and O-containing moieties (CH and O classes) in derived soluble portions (SPs) were evaluated in detail. The results show that scCO 2 -ethanol has synergistic degradation ability and strong permeability to complex structures. Optimal conditions were determined to be 10 mL g−1 ethanol/ Ck ratio, 1 MPa initial CO 2 pressure, 300 °C, and 60 min holding time based on the SP yield and the maximum yield is 38.2 wt% with high heating value of 24.06 kJ g−1. The difference of SPs between conventional ethanolysis (SP E) and scCO 2 -ethanolysis (SP SE) was compared. According to FTIR and GC/MS analyses, the distribution of functional groups and detectable group components is similar, and O-containing species are dominant. Tetrahydrofurans & furans, alkoxy-substituted benzenes & alkoxy-substituted phenols, and ketones & esters are main group components. The characteristic differences of >C-O- and >C O classes are related to the following three aspects: (1) the ring-opening, >C-O- bond cleavage, cyclization, and condensation of cellulose/hemicellulose, (2) the destruction of abundant >C ar -O- in lignin, especially guaiacyl and syringyl units, and (3) the formation of ethyl esters promoted by the nucleophilic attack of ethoxy group. Orbitrap MS analysis further confirmed that O-containing species of SP E and SP SE are mainly concentrated in O 1 - O 4 classes, and scCO 2 -ethanolysis promotes the acquisition of sugars and bioactive fragments from Ck. In addition, the characteristic distribution of O n classes in SP SE is related to the release of natural oxygenates, cleavage of weak/intermediate-strength covalent bonds, and dissociation of O-containing macromolecules. This study provides a reference perspective and a potential implementation approach for the clean and efficient utilization of Ck to produce valuable bio-oils. [Display omitted] • Supercritical CO 2 -ethanolysis has good synergistic ability and permeability. • Derived bio-oil with yield of 38.2 wt% and HHV of 24.06 kJ g−1 was obtained. • THFs & furans, ASBs & ASPs, and ketones & esters are three main components. • Aliphatics are mainly derived from the degradation of cellulose & hemicellulose. • Ck lignin contains abundant >C ar -O- moieties, especially guaiacyl & syringyl units. [ABSTRACT FROM AUTHOR]

Nickel supported on a nitrogen-doped carbon material (NDCM) was successfully prepared and used for catalyzing the hydroconversion of benzyloxybenzene (BOB) and poplar lignin (PL). Over Ni/NDCM, BOB was completely converted to toluene and phenol in the yields of 75.5 and 73.1 mol%, respectively, under initial hydrogen pressure (IHP) of 2 MPa at 240 °C for 2 h. The adsorption energies (AEs) of different systems were calculated using the density functional theory. The AEs of H 2 on Ni (111), Ni (200), and Ni (220) crystal planes are −1.26, −1.27, and − 1.28 eV, respectively, indicating that Ni (111) crystal plane is the most active for splitting H 2 to mobile H+ and immobile H−, the higher absolute value of AE (−2.5 eV) of BOB on Ni/NDCM facilitates BOB hydrocracking. Moreover, Ni/NDCM could promote the cleavage of >CH-O- bonds in PL to produce more phenols. [Display omitted] • Ni/NDCM is active for specifically cleaving the >CH-O- bonds in BOB and lignin. • Benzylium addition to phenol occurs to a small extent during BOB hydrocracking. • The RC of phenols is 73.2% in CHC lignin oil, that is higher than in NCHC. • The adsorption energy of BOB on Ni/NDCM is higher than that on NDCM. [ABSTRACT FROM AUTHOR]

Directional depolymerization of lignin represents an essential process to produce value-added aromatic compounds. The catalyst obtained by adjusting the hydrophobicity of the support can regulate the reaction pathway and products selectivity for the cleavage of lignin-related compounds. Hydrophilic modification of activated carbon (AC) using trimethylchlorosilane (TMCS) was developed to decrease the hydrophilicity of carbon-based catalyst. The contact angle of the carrier dramatically increased from 43o to 130o after modified. AC was modified with an appropriate amount of TMCS and loaded with Ni to prepare Ni/10% TMCS-AC, which could effectively inhibit the hydrolysis of diphenyl ether (DPE) and the over‑hydrogenation of products. The selectivity of monocyclic aromatics (benzene and phenol) over Ni/10% TMCS-AC increased 30% compared with the unmodified Ni/AC. TMCS occupied part of the adsorption sites, which prevented the Ni from adsorbing more active hydrogen and inhibited the hydrogenation of benzene and phenol. Meanwhile, the hydrolysis of DPE was inhibited and the hydrogenolysis reaction pathway of DPE was over 90% than Ni/AC. The construction of the hydrophobic Ni/10% TMCS-AC highlighted a promising way to convert DPE to aromatic chemicals. [Display omitted] • Adjusting the hydrophilicity of AC modulates the reaction path and product selectivity. • Using trimethylchlorosilane to decrease the hydrophilicity of carbon-based catalyst. • Ni/10% TMCS-AC inhibits hydrolysis of DPE and over‑hydrogenation of products. • The reaction route over Ni/10% TMCS-AC and Ni/AC were presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalysts of Ru supported on AC from coal tar pitch were successfully synthesized. • Ru/4-1AC exhibited the best catalytic performance for the cleavage of C-O bonds. • BPE was preferentially adsorbed on Ru metal for the C-O bond cleavage than DPE. • The reaction pathways of DPE and BPE were explored and analyzed in detail. • Oxygenated low-molecular-weight products were obtained from lignin over Ru/4-1AC. Selective hydrogenolysis of C-O bonds in lignin is regarded as the most promising strategy to produce high value-added biofuels and chemicals. Herein, Ru/AC catalysts of Ru supported on AC from coal tar pitch were successfully prepared and could effectively promote the cleavage of C-O bonds in diphenyl ether (DPE), benzyl phenyl ether (BPE) and lignin under mild conditions. In the case of an activation ratio of 4:1, the obtained Ru/4-1AC possessed the large specific surface area, more defects, small Ru metal particle size and low Ru0 bonding energy, exhibiting the high catalytic performance. The conversion investigation of the mixture of DPE and BPE revealed that BPE was preferentially adsorbed on Ru metal of the catalyst surface for the C-O bond cleavage due to the lower bond dissociation energy of C-O bonds of BPE and the stronger adsorption energy of BPE calculated by a density functional theory. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reaction mechanisms of anisole decomposition on Ni (111) were simulated by DFT. • Phenol was the major product of anisole decomposition by microkinetic analysis. • Phenol was preferred to secondary decompose due to its higher desorption energy. • H coverage enhanced reaction rate for hydrogenation of anisole on Ni (111). Anisole, as an aromatic oxygenate lignin model compound, which can be selectively cleaved into benzene over Ni/C at high temperature. On the basic of experimental results, the hydrodeoxygenation (HDO) mechanism of anisole was investigated on clean Ni (111) surface by using computational techniques. Based on static energies, the microkinetic modeling on clean Ni (111) and H-covered Ni (111) were built in which the modeling of H-covered Ni (111) approximately simulated the real catalytic system under lower temperature and higher H 2 pressure. As a result, the microkinetic analysis proved the phenol was the major product in the anisole decomposition on clean Ni (111) surface. However, the phenol was preferred to decompose rather than desorb from Ni surface because of the high desorption energy, suggesting that the benzene mainly originated from the secondary dissociation of phenol. Differently, the decreasing of energy barrier for anisole hydrogenation led to the formation of methylcyclohexane as main product on H-covered Ni (111) surface by microkinetic analysis. The differences in products distribution between Ni (111) and H-covered Ni (111) provided a mechanistic understanding for anisole conversion under different experimental conditions. [ABSTRACT FROM AUTHOR]

Conversion of lignin-derived molecules into value-added chemicals is critical for sustainable chemistry but still challenging. Herein, phosphorus-modified palladium catalyzed the degradation of lignin-derived 4-O-5 linkage to produce KA oil (cyclohexanone-cyclohexanol oil) was reported. The reaction proceeds via a restricted partial hydrogenation-hydrolysis pathway. Phosphorus-modified palladium catalyst suppressed the full hydrogenation of diary ether, which was the key point to produce KA oil selectively. Under the optimized conditions, the 4.5 nm Pd-P NPs could catalyze the conversion of 4-O-5 linkage into KA oil in 83% selectivity with a high production rate of 32.5 mmol·g−1 Pd ·min−1. This study represented an original method for KA oil production. [Display omitted] • Pd-P/C catalyzed the lignin-derived 4-O-5 linkage to produce KA oil. • Phosphorus modified Pd suppressed the full hydrogenation of diphenyl ether. • KA oil was obtained in 83% selectivity over 4.5 nm Pd-P NPs. • A partial hydrogenation-reductive hydrolysis tandem route was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective hydrogenolysis of diphenyl ether C-O bond occurred over Ni/Nb 2 O 5. • The common hydrogen supply existed between H 2 and isopropanol. • Hydrodeoxygenation reaction hardly occurred due to the weak acidity of Ni/Nb 2 O 5. • The reaction route of the hydrogenolysis in DPE was presented. Selective cleavage of stable ether C-O bonds is particularly of significance for the valorization of lignin and designing high active and cheap catalysts attracts researchers to conduct a lot of investigations. The niobium species containing both Brønsted and Lewis acid sites can be applied in hydrodeoxygenation of diphenyl ether (DPE). It is important to regulate the acidity of niobium to achieve the selective cleavage of DPE without hydrodeoxygenation. Herein, the weakly acidic Ni/Nb 2 O 5 prepared by an incipient wetness impregnation method could efficiently cleave C-O bonds of DPE without hydrodeoxygenation. DPE was completely converted and the yields of target products (cyclohexane and cyclohexanol) reached 90% under the coexistence of H 2 and isopropanol. It was ascribed to the common hydrogen supply between H 2 and isopropanol which could produce more active hydrogen. Acetone was detected in the solution after the reaction, demonstrating that a dehydrogenation reaction of isopropanol provided hydrogen. In addition, the turnover frequency (TOF) and the apparent activation energy (E a) for catalytic hydrogenolysis of DPE revealed that Ni/Nb 2 O 5 possessed higher activity than Co/Nb 2 O 5 under the same conditions. The possible reaction pathways were also summarized and analyzed. [ABSTRACT FROM AUTHOR]