Hydrodeoxygenation Of Lignin-derived Phenols Research Articles

Hydrodeoxygenation of lignin-derived phenols into cycloalkanes by atomically dispersed Pt-polyoxometalate catalysts

We report atomically dispersed Pt sites anchored on polyoxometalate cesium salts as robust and durable catalysts for upgrading lignin into hydrocarbons at relatively mild conditions. Experimental results and DFT calculations cross-validate the catalytic performance, considering the porosity, acidity, H2 storage capacity, and HOMO-LUMO energy gap of these catalysts. The optimal Pt0.4/CsPW-H2 catalyst enables the hydrodeoxygenation (HDO) of a diverse range of lignin-derived phenolics into hydrocarbons with up to 97% yield at the conditions of 150 °C and 0.1–2 MPa H2. A lignin oil from the reductive catalytic fractionation (RCF) of Eucalyptus wood can be transformed into cyclohexanes with a 32.7 wt% yield under a solvent-free condition. This catalyst demonstrates excellent reusability in the HDO of 4-propyl guaiacol for 20 cycles, achieving a 15095 molpropylcyclohexane molPt−1 total turnover number (TON). This work broadens the horizons of designing highly efficient catalytic systems aimed at sustainably producing liquid fuels from lignin.

Hydrodeoxygenation of lignin biophenolics to cyclohexanes over sub-nanometric Ru multifunctional catalyst

Hydrodeoxygenation of lignin-derived phenolics into cyclohexanes is recognized as an attractive philosophy for producing high energy density fuels in a sustainable manner. Here, we report a catalyst made of low-loading, sub-nanoscaled Ru species and multifarious acidic centers on amorphous-silica-alumina, which shows excellent activity, selectivity, and stability in hydrodeoxygenation of 4-propylguaiacol to propylcyclohexane. Catalytic performance exhibits a linear relationship to the total acidities of this family catalysts, demonstrating a synergistic interaction between the metallic and acidic components. The superior performance of this catalyst allows the conversion of various lignin-derived monophenols, dimers, more significantly, a biophenolic stream from miscanthus lignin into cyclohexanes with high efficiency and yield. This work highlights the importance of the sub-nanometric size of Ru species in the advancement of efficient and affordable approaches towards lignin-based fuel production.

Selective Hydrodeoxygenation of Lignin-Derived Phenols to Aromatics Catalyzed by Nb2O5-Supported Iridium.

The dominating catalytic approach to aromatic hydrocarbons from renewables, deoxygenation of phenol-rich depolymerized lignin bio-oils, is hard to achieve: hydrodeoxygenation (HDO) of phenols typically leads to the loss of aromaticity and to non-negligible fractions of cyclohexanones and cyclohexanols. Here, we report a catalyst, niobia-supported iridium nanoparticles (Ir@Nb2O5), which combines full conversion in the HDO of lignin-derived phenols with appreciable and tunable selectivity for aromatics (25–95%) under mild conditions (200–300 °C, 2.5–10 bar of H2). A simple approach to the removal of Brønsted-acidic sites via Hünig’s base prevents coking and allows reaction conditions (T > 225 °C, 2.5 bar of H2), promoting high yields of aromatic hydrocarbons.

Hydrodeoxygenation of lignin-derived phenolics over facile prepared bimetallic RuCoNx/NC

Cyclohexanols, promising oxygenated fuel additives and value-added chemicals, can be obtained by hydrodeoxygenation (HDO) of lignin-derived phenolics. Here, an N-doped bimetallic RuCoNx/NC catalyst was facilely prepared for HDO by direct pyrolysis of chitin impregnated with precursors of Ru and Co. Characterization of RuCoNx/NC with N2 sorption, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and NH3 temperature-programmed desorption (NH3-TPD) reveal that the metallic particles of electron-deficient Ru species and electron-enriched Co species were uniformly anchored on the micro-mesoporous N-doped carbon matrix with high dispersion and nano-scale size. The abundant accessible active sites and continuous spillover of H from Ru to Co make RuCoNx/NC an excellent HDO catalyst. 4-Propylguaiacol, a typical phenolic compound from lignin degradation, was hydrodeoxygenated into 92% 4-propylcyclohexanol over RuCoNx/NC at 210 ℃. With temperature increasing, propylcyclohexane became the major product, possessing 95% selectivity at 280 °C after 6 h. Reusability tests show that RuCoNx/NC can be recycled four times without the loss of conversion and initial selectivity. HDO of other phenolic compounds confirms the general applicability of RuCoNx/NC.

Catalytic Hydrotreatment of β-O-4 Ether in Lignin: Cleavage of the C–O Bond and Hydrodeoxygenation of Lignin-Derived Phenols in One Pot

Selective hydrotreatment of β-O-4 ether bonds in lignin is a key strategy for the lignin valorization. The current catalytic strategy can only transfer β-O-4 model compounds to aromatics. Also, fur...

Hydrodeoxygenation of Lignin-Derived Aromatic Oxygenates Over Pd-Fe Bimetallic Catalyst: A Mechanistic Study of Direct C–O Bond Cleavage and Direct Ring Hydrogenation

Hydrodeoxygenation of lignin-derived phenols could be achieved generally with three reaction pathways: tautomerization, direct ring hydrogenation and direct C–O bond cleavage. The former pathway has been extensively studied over Pd/Fe catalyst in liquid-phase reaction, however, the contribution of the latter two is yet subject to further investigations. In this report, a comparative study of direct C–O bond cleavage and direct ring hydrogenation reaction pathways is presented on Pd/Fe, Fe and Pd/C catalysts using diphenyl ether as modelling compound. Despite its much higher activation energy than direct ring hydrogenation, direct C–O bond cleavage is dominant over Pd/Fe with much higher rates than the monometallic analogues due to the synergic catalysis of Pd–Fe. Based on this study and our previous results, the detailed reaction network for HDO of diphenyl ether is proposed.

Hydrodeoxygenation of lignin-derived phenolics – a review on the active sites of supported metal catalysts

This article mainly reviews the state-of-the-art achievements of supported metal catalysts and the characteristics and actions of their active sites, working in the reactions involved in HDO of lignin-derived phenolic compounds.

The synergistic effect between Ni sites and Ni-Fe alloy sites on hydrodeoxygenation of lignin-derived phenols

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is a critical step in the upgrading of bio-oil. Here, bimetallic Ni-Fe nanoparticles supported on mesoporous carbon spheres (MCSs) were fabricated and applied in HDO of phenol. In comparison with monometallic Ni and Fe catalysts, the bimetallic Ni-Fe catalyst exhibited better performance for phenol HDO due to the formation of Ni-Fe alloy phase identified by X-ray powder diffraction (XRD) and Mössbauer spectroscopy techniques. Among several explored ratios, the catalysts with Ni/Fe ratio of 3/1 presented the highest cyclohexane yield. The reaction occurred in two consecutive steps: the hydrogenation of phenol to cyclohexanol and the further hydrogenolysis of cyclohexanol to cyclohexane. Kinetic studies showed that the hydrogenolysis of cyclohexanol controlled the overall reaction rate of phenol HDO due to the lower reaction rate of this step. Indeed, the turnover frequency (TOF) values of cyclohexanol normalized by surface metallic Ni sites exhibited a linear correlation with Ni-Fe alloy sites. The alloying of iron in the bimetallic Ni-Fe catalysts significantly enhanced the adsorption strength of cyclohexanol, which is the reason of the high activity of the Ni-Fe alloy particles. Thus, Fe-containing sites adsorb the hydroxyl species while Ni sites perform the H2 activation, their synergistic effect plays a key role in phenol HDO process.

Hydrodeoxygenation of Lignin-Derived Phenols: From Fundamental Studies towards Industrial Applications

Hydrodeoxygenation (HDO) of bio-oils, lignin and their model compounds is summarized in this review. The main emphasis is put on elucidating the reaction network, catalyst stability and time-on-stream behavior, in order to better understand the prerequisite for industrial utilization of biomass in HDO to produce fuels and chemicals. The results have shown that more oxygenated feedstock, selection of temperature and pressure as well as presence of certain catalyst poisons or co-feed have a prominent role in the HDO of real biomass. Theoretical considerations, such as density function theory (DFT) calculations, were also considered, giving scientific background for the further development of HDO of real biomass.

Hydrodeoxygenation of lignin-derived phenols into alkanes over carbon nanotube supported Ru catalysts in biphasic systems

Lignin derived phenols and dimers were converted into alkanes through the HDO process over Ru/CNT catalysts in biphasic solvents.