Hydrodeoxygenation Of Lignin Model Compound Research Articles

Selective catalytic hydrodeoxygenation of vanillin to 2-Methoxy-4-methyl phenol and 4-Methyl cyclohexanol over Pd/CuFe2O4 and PdNi/CuFe2O4 catalysts

The development of a sustainable catalytic process for the hydrodeoxygenation of lignin model compounds to renewable fuels and chemicals is essential to meet the requirement of a fossil-fuel-free modern society. Herein a Pd/CuFe2O4 and bimetallic PdNi/CuFe2O4 catalysts were developed for the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol (MMP) and 4-methyl cyclohexanol (4-MC), respectively. The Pd/CuFe2O4 provided selective catalytic transfer hydrodeoxygenation of vanillin to MMP with isopropanol (IPA). The synergistic participation of Pd NPs and CuFe2O4 (1Pd/CuFe2O4) afforded 99.4% vanillin conversion and 99.2% MMP selectivity at 150 °C. The acidity of the catalyst facilitated the efficient adsorption of vanillin and IPA, and the high dispersion of Pd NPs lowered the hydrogen abstraction barrier of IPA to facilitate the transformation. Then Ni was incorporated into Pd/CuFe2O4 to produce 4-methyl cyclohexanol from vanillin. The interfacial interaction between Pd and Ni over CuFe2O4 (1Pd7Ni/CuFe2O4) provided 95.8% 4-methyl cyclohexanol (4-MC) in H2 (20 bar) at 180 °C. The acidity of the catalyst, formation of Pd-Ni alloys, and efficient adsorption of vanillin and MMP were responsible for the high activity of the catalyst towards 4-methyl cyclohexanol (4-MC) production. Density functional theory (DFT) calculations were also performed to elucidate the reaction mechanism for vanillin transformation to MMP and 4-MC on the Pd/CuFe2O4 and bimetallic PdNi/CuFe2O4 catalysts.

A unique Co@CoO catalyst for hydrogenolysis of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran

The development of precious-metal-free catalysts to promote the sustainable production of fuels and chemicals from biomass remains an important and challenging target. Here, we report the efficient hydrogenolysis of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran over a unique core-shell structured catalyst, Co@CoO that affords the highest productivity among all catalysts, including noble-metal-based catalysts, reported to date. Surprisingly, we find that the catalytically active sites reside on the shell of CoO with oxygen vacancies rather than the metallic Co. The combination of various spectroscopic experiments and computational modelling reveals that the CoO shell incorporating oxygen vacancies not only drives the heterolytic cleavage, but also the homolytic cleavage of H2 to yield more active Hδ− species, resulting in the exceptional catalytic activity. Co@CoO also exhibits excellent activity toward the direct hydrodeoxygenation of lignin model compounds. This study unlocks, for the first time, the potential of simple metal-oxide-based catalysts for the hydrodeoxygenation of renewable biomass to chemical feedstocks.

Selective hydrodeoxygenation of lignin model compound to renewable fuel precursors using two-dimensional nanosheet Ni/HZ5-NS catalyst

The catalytic upgrading of renewable lignin to value-added transportation fuels and chemicals is considered as the best solution to environmental and energy-related issues, however, such conversions are challenging. In this study, a new type of two-dimensional (2D) nanosheet catalyst, Ni/HZ5-NS (50 nm), was synthesized and used to catalyze the selective hydrodeoxygenation of a lignin model compound, 4-ethylguaiacol, to prepare renewable fuel precursors (C8–C16 alkanes). The Ni/HZ5-NS catalyzed conversion of 4-ethylguaiacol to ethyl-cycloalkane reached 100%, and the product selectivity was greater than 95%. The microenvironment of the Ni species in Ni/HZ5-NS was regulated by HZ5-NS. The catalytic activity of Ni/HZ5-NS was twice than that of the traditional Ni/HZ5 catalyst. The high catalytic activity of Ni/HZ5-NS can be attributed to the synergy between the electron-rich Ni and the acidic sites on HZ5-NS but more importantly to the 2D nanosheet structure, which reduces the mass transfer resistance of the system and facilitates molecular diffusion. The application of Ni/HZ5-NS to catalyze C–O bond cleavage was extended to other lignin-derived aromatic ring compounds, and the conversion was found to reach 100%. Importantly cycloalkanes could be obtained with high selectivity. Therefore, this study will be useful for extracting alternative sources of valuable fuel precursors from biomass.

Mordenite-supported ruthenium catalyst for selective hydrodeoxygenation of lignin model compounds and lignin-derived bio-oil to produce cycloalkanes

Recently high yield of cycloalkanes originates from selective hydrodeoxygenation (HDO) of lignin-derived bio-oil under mild conditions, which still encounters the great challenges. Herein, mordenite-supported ruthenium bifunctional catalyst (Ru3%/M) was prepared by using the deposition-precipitation (DP) method for the HDO reaction of the petroleum ether-extractable portions (PEEP) from alkali catalytic ethanolysis of lignin (CEOL). Ru3%/M catalyst was characterized systematically by XRD, XPS, FTIRS, NH3-TPD, N2-adsorption, SEM, and TEM, indicating that it had the moderate acid sites and uniform Ru nanoparticles dispersion. The synthesized catalyst was further tested for the HDO performance of diphenyl ether, oxybis(methylene)dibenzene, and anisole, respectively. Results showed that three lignin model compounds can be converted to high yield of cycloalkanes under 160 °C and 3 MPa H2 in n-hexane. This catalyst showed the high catalytic activity for diphenyl ether HDO reaction, the conversion decreased slightly to 87.6% after five recycle times. Furthermore, catalyst feed mass was the key factor for HDO reaction of raw PEEP from CEOL, promoting the HDO reaction process to produce high yield of cycloalkanes. Interestingly, the mass ratio between catalyst feed and raw PEEP was 1, thus 74.36% relative content (RC) of cycloalkanes can be obtained. The upgraded PEEP from CEOL has potential to be used as clean liquid fuels.

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.

Hydrodeoxygenation of lignin model compounds to alkanes over Pd–Ni/HZSM-5 catalysts

In this work, a bimetallic catalyst of Pd and Ni supported on HZSM-5 was designed and evaluated in the hydrodeoxygenation of model compounds representing various C–O bonds in lignin. The effects of temperature, holding time, and initial H2 pressure on the catalytic performance of the Pd–Ni/HZSM-5 catalyst were investigated. The results indicated that the Pd–Ni/HZSM-5 catalyst exhibited superior catalytic activity towards the conversion of the model compounds to alkanes compared to its monometallic counterparts. Direct cleavage of the C–O bond in DPE was achieved under low H2 pressure, mainly producing benzene and minor amounts of phenol and cyclohexane, while at high H2 pressure, the reaction pathway was altered towards hydrogenation of the benzene ring, followed by then cleavage of the C–O bond to afford only cyclohexane. Moreover, the Pd–Ni/HZSM-5 catalyst showed high activities when applying other substrates including anisole, veratrole, guaiacol, benzyloxybenzene, phenethyl phenyl ether, and dibenzyl ether.

Correlation of the catalytic performance with Nb2O5 surface properties in the hydrodeoxygenation of lignin model compound

Production of aromatic hydrocarbons through lignin hydrodeoxygenation (HDO) is of significant importance. Previously, we found that Ru/Nb2O5 was an excellent catalyst for the conversion of lignin to arenes with relatively high selectivity (71%). Herein, we aim to clarify which properties of Nb2O5 influence the activity and selectivity. Four Ru/Nb2O5 catalysts with different Nb2O5 morphologies were used in the HDO of 4-methylphenol. Intensive studies show that layered Nb2O5 supported Ru has more NbO groups (unsaturated NbOx sites) and highest Ru dispersion, which led to the highest activity and toluene selectivity, this was further confirmed by loading pre-synthesized Ru colloids in various Nb2O5. Finally, a Ru/Nb2O5 catalyst with more unsaturated NbO groups was designed and it was found that even with enzymatic lignin as the feedstock, the selectivity to arenes can reach up to 94.8% with the yield of hydrocarbons of 99.6%. This study provides a promising strategy for catalyst design towards the selective production of aromatic hydrocarbons from lignin.

Bimetallic Cu-Ni catalysts supported on MCM-41 and Ti-MCM-41 porous materials for hydrodeoxygenation of lignin model compound into transportation fuels

The design of novel, efficient supported bimetallic catalysts for the transformation of renewable lignin model compounds into valuable products is currently an emerging research topic. This study investigates the synthesis, characterization and the catalytic application of bimetallic Cu-Ni catalysts supported on pure MCM-41 and Ti incorporated MCM-41 porous materials for the valorization of a lignin model compound (i.e. guaiacol) into the transportation fuels via hydrodeoxygenation route (HDO). The investigated characterization results revealed that the Ti species are well-dispersed within the MCM-41 framework by a tetrahedral coordination. NH3-TPD studies show that the incorporation of Ti into the MCM-41 framework generates large amounts of acidic sites. It was also found that, the coordinated Ti species enhance the dispersion of CuO and NiO species on the surface of Ti-MCM-41 support. The CuNi/Ti-MCM-41 catalyst shows excellent reducible properties due to the co-operative effects of CuO and NiO with the Ti-MCM-41 support. The catalytic experiments revealed that the CuNi/Ti-MCM-41 catalyst exhibits a higher guaiacol conversion (~90.49%) and superior selectivity to cyclohexane (~50.09%) than the CuNi/MCM-41 catalyst which exhibits only ~10.57% cyclohexane selectivity with a guaiacol conversion of ~37.03%. The guaiacol conversion and cyclohexane selectivity were found to increase with the increase of reaction pressure from 40 to 100bar for CuNi/Ti-MCM-41 catalyst. It has been demonstrated that the HDO of guaiacol proceeds via demethoxylation (CAR-OCH3 cleavage) over the CuNi/Ti-MCM-41 catalyst and both demethylation (CARO-CH3 cleavage) and demethoxylation (CAR-OCH3 cleavage) pathways are possible over the CuNi/MCM-41 catalyst in HDO of guaiacol.

Layered MWW zeolite-supported Rh catalysts for the hydrodeoxygenation of lignin model compounds

The improved catalytic activity of Rh nanoparticles deposited on the swollen and pillared zeolites was observed in the hydrodeoxygenation (HDO) reactions of 1,3,5-trimethoxybenzene (1,3,5-TMB), a bulky lignin model compound, and guaiacol, one of the most frequently used lignin model compounds. As the high dispersion of metal nanoparticles increases HDO activity, the swelling/calcination and pillaring of crystalline MCM-22 zeolites increased the dispersion of Rh metal nanoparticles on the external surface area, and thus the corresponding HDO activity with respect to 1,3,5-TMB. On the contrary, although the mesopores in the amorphous MCM-41 and silica-alumina aerogel (SAA) supports accommodated higher Rh dispersion, overall, the resulting catalysts suffered from mass transfer limitation, and thus showed poor HDO reaction activity for 1,3,5-TMB. Finally, the Rh nanoparticles supported on the pillared zeolite showed the highest HDO activity for guaiacol, mainly due to the higher Rh dispersion and acid sites on the external surface among the zeolite-supported Rh catalysts.

Hydrodeoxygenation of lignin model compounds over a copper chromite catalyst

The hydrodeoxygenation of benzyl alcohol, phenol, anisole, o-cresol, catechol, guaiacol, and vanillyl alcohol were carried out from 150 to 275°C at 50bar H2 with a CuCr2O4·CuO catalyst in a decalin solvent. The hydroxymethyl group of benzyl alcohol was found to be highly reactive towards hydrogenolysis to form toluene. Demethoxylation of anisole to form benzene was found to be the primary reaction pathway in contrast to demethylation and transalkylation reactions, which are more prevalent for conventional hydrotreating catalysts. The hydroxyl group of phenol strongly activated the aromatic ring towards hydrogenation forming cyclohexanol which was subsequently dehydrated and hydrogenated to form cyclohexane. Reaction networks of increasing complexity were devised for the major functional groups and integrated to describe the most complex molecule studied, vanillyl alcohol.

CoMo sulfide-catalyzed hydrodeoxygenation of lignin model compounds: An extended reaction network for the conversion of monomeric and dimeric substrates

In the present work, extensive hydrodeoxygenation (HDO) studies with a commercial sulfided CoMo/Al2O3 catalyst were performed on a library of lignin model compounds at 50bar hydrogen pressure and 300°C in dodecane, using a batch autoclave system. The catalyst was activated under hydrogen atmosphere prior to the reaction, and the spent catalyst was analyzed using thermogravimetric analysis. An extended reaction network is proposed, showing that HDO, demethylation, and hydrogenation reactions take place simultaneously. HDO of mono-oxygenated substrates proved to be difficult at the applied conditions. Starting from most positions in the network, phenol, and cresols are therefore the main final products, suggesting the possibility of convergence on a limited number of products from a mixture of substrates. HDO of dimeric model compounds mimicking typical lignin linkages revealed that coumaran alkyl ethers and β-O-4 bonds can be broken, but 5–5′ linkages not.