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• W2936709985 abstract "•Catalytic cleavage of both C–C and C–O bonds in lignin is achieved•The conventional theoretical limitation on lignin monomer production is broken•Excellent activity for C–C bond breakage depends on the unique property of Ru/NbOPO4•A new method for the hydrogenolysis of lignin into monocyclic hydrocarbons is proposed The conversion of lignin into monocyclic hydrocarbons as commodity chemicals and drop-in fuels is essential for the future of biorefineries. State-of-the-art lignin depolymerization is primarily achieved via cleavage of interunit C–O bonds to form low-molecular-weight feedstocks. However, these processes can hardly cleave interunit C–C bonds in lignin, and thus, the yields of lignin monomers are heavily restricted. Here, we report a multifunctional catalyst, Ru/NbOPO4, that achieves the first example of catalytic cleavage of both interunit C–C and C–O bonds in lignin in one-pot reactions to yield 153% of monocyclic C6–C9 hydrocarbons from Kraft lignin, which is 1.5 times the theoretical yield obtained from the established nitrobenzene oxidation (NBO) method. Thus, significantly, this study successfully breaks the conventional limit on lignin monomer production. Conversion of lignin into monocyclic hydrocarbons as commodity chemicals and drop-in fuels is a highly desirable target for biorefineries. However, this is severely hindered by the presence of stable interunit carbon–carbon linkages in native lignin and those formed during lignin extraction. Herein, we report a new multifunctional catalyst, Ru/NbOPO4, that achieves the first example of catalytic cleavage of both interunit C–C and C–O bonds in one-pot lignin conversions to yield 124%–153% of monocyclic hydrocarbons, which is 1.2–1.5 times the yields obtained from the established nitrobenzene oxidation method. This catalyst also exhibits high stability and selectivity (up to 68%) to monocyclic arenes over repeated cycles. The mechanism of the activation and cleavage of 5–5 C–C bonds in biphenyl, as a lignin model adopting the most robust C–C linkages, has been revealed via in situ inelastic neutron scattering coupled with modeling. This study breaks the conventional theoretical limit on lignin monomer production. Conversion of lignin into monocyclic hydrocarbons as commodity chemicals and drop-in fuels is a highly desirable target for biorefineries. However, this is severely hindered by the presence of stable interunit carbon–carbon linkages in native lignin and those formed during lignin extraction. Herein, we report a new multifunctional catalyst, Ru/NbOPO4, that achieves the first example of catalytic cleavage of both interunit C–C and C–O bonds in one-pot lignin conversions to yield 124%–153% of monocyclic hydrocarbons, which is 1.2–1.5 times the yields obtained from the established nitrobenzene oxidation method. This catalyst also exhibits high stability and selectivity (up to 68%) to monocyclic arenes over repeated cycles. The mechanism of the activation and cleavage of 5–5 C–C bonds in biphenyl, as a lignin model adopting the most robust C–C linkages, has been revealed via in situ inelastic neutron scattering coupled with modeling. This study breaks the conventional theoretical limit on lignin monomer production. Lignin, accounting for 15–40 wt % of lignocellulosic biomass, is the most abundant source of renewable aromatics on earth.1Zakzeski J. Bruijnincx P.C.A. Jongerius A.L. Weckhuysen B.M. The catalytic valorization of lignin for the production of renewable chemicals.Chem. Rev. 2010; 110: 3552-3599Crossref PubMed Scopus (3312) Google Scholar, 2Li C. Zhao X. Wang A. Huber G.W. Zhang T. Catalytic transformation of lignin for the production of chemicals and fuels.Chem. Rev. 2015; 115: 11559-11624Crossref PubMed Scopus (1791) Google Scholar, 3Ragauskas A.J. Beckham G.T. Biddy M.J. Chandra R. Chen F. Davis M.F. Davison B.H. Dixon R.A. Gilna P. Keller M. et al.Lignin valorization: improving lignin processing in the biorefinery.Science. 2014; 344: 1246843Crossref PubMed Scopus (2444) Google Scholar, 4Schutyser W. Renders T. Van den Bosch S.V. Koelewijn S.F. Beckham G.T. Sels B.F. Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading.Chem. Soc. Rev. 2018; 47: 852-908Crossref PubMed Google Scholar The heavily branched 3D network of lignin is constructed from methoxylated phenylpropanoid subunits bridged by various interunit C–O and C–C linkages (accounting for approximately 70% and 30%, respectively) in a completely random order (Figures 1 and S1).5Xu C.P. Arancon R.A.D. Labidi J. Luque R. Lignin depolymerisation strategies: towards valuable chemicals and fuels.Chem. Soc. Rev. 2014; 43: 7485-7500Crossref PubMed Google Scholar, 6Rinaldi R. Jastrzebski R. Clough M.T. Ralph J. Kennema M. Bruijnincx P.C.A. Weckhuysen B.M. Paving the way for lignin valorisation: recent advances in bioengineering, biorefining and catalysis.Angew. Chem. Int. Ed. 2016; 55: 8164-8215Crossref PubMed Scopus (1269) Google Scholar, 7Yan N. Zhao C. Dyson P.J. Wang C. Liu L.T. Kou Y. Selective degradation of wood lignin over noble-metal catalysts in a two-step process.ChemSusChem. 2008; 1: 626-629Crossref PubMed Scopus (481) Google Scholar C–C bonds have notably higher dissociation energy (226–494 kJ mol−1) than those of C–O bonds (209–348 kJ mol−1) in lignin (Table S1).6Rinaldi R. Jastrzebski R. Clough M.T. Ralph J. Kennema M. Bruijnincx P.C.A. Weckhuysen B.M. Paving the way for lignin valorisation: recent advances in bioengineering, biorefining and catalysis.Angew. Chem. Int. Ed. 2016; 55: 8164-8215Crossref PubMed Scopus (1269) Google Scholar Because of its highly robust polymeric structure, the conversion of lignin to small-molecule arenes as commodity chemicals and fuel additives represents a significant challenge for industries and biorefineries. State-of-the-art processes usually undergo lignin depolymerization via the cleavage of C–O bonds to obtain low-molecular-weight monomers, which can be sequentially upgraded to useful chemicals and fuels.1Zakzeski J. Bruijnincx P.C.A. Jongerius A.L. Weckhuysen B.M. The catalytic valorization of lignin for the production of renewable chemicals.Chem. Rev. 2010; 110: 3552-3599Crossref PubMed Scopus (3312) Google Scholar, 2Li C. Zhao X. Wang A. Huber G.W. Zhang T. Catalytic transformation of lignin for the production of chemicals and fuels.Chem. Rev. 2015; 115: 11559-11624Crossref PubMed Scopus (1791) Google Scholar A great deal of effort has been devoted to developing strategies for the depolymerization of lignin.8Rahimi A. Ulbrich A. Coon J.J. Stahl S.S. Formic-acid-induced depolymerization of oxidized lignin to aromatics.Nature. 2014; 515: 249-252Crossref PubMed Scopus (828) Google Scholar, 9Wu X. Fan X. Xie S. Lin J. Cheng J. Zhang Q. Chen L. Wang Y. Solar energy-driven lignin-first approach to full utilization of lignocellulosic biomass under mild conditions.Nat. Catal. 2018; 1: 772-780Crossref Scopus (291) Google Scholar, 10Sun Z. Bottari G. Afanasenko A. Stuart M.C.A. Deuss P.J. Fridrich B. Barta K. Complete lignocellulose conversion with integrated catalyst recycling yielding valuable aromatics and fuels.Nat. Catal. 2018; 1: 82-92Crossref Scopus (269) Google Scholar, 11Deuss P.J. Scott M. Tran F. Westwood N.J. de Vries J.G. Batra K. Aromatic monocyclics by in situ conversion of reactive intermediates in the acid-catalyzed depolymerization of lignin.J. Am. Chem. Soc. 2015; 137: 7456-7467Crossref PubMed Scopus (387) Google Scholar, 12Lahive C.W. Deuss P.J. Lancefield C.S. Sun Z. Cordes D.B. Young C.M. Tran F. Slawin A.M.Z. de Vries J.G. Kamer P.C.J. et al.Advanced model compounds for understanding acid-catalyzed lignin depolymerization: identification of renewable aromatics and a lignin-derived solvent.J. Am. Chem. Soc. 2016; 138: 8900-8911Crossref PubMed Scopus (170) Google Scholar, 13Stärk K. Taccardi N. Bösmann A. Wasserscheid P. Oxidative depolymerization of lignin in ionic liquids.ChemSusChem. 2010; 3: 719-723Crossref PubMed Scopus (192) Google Scholar, 14Li Y.D. Shuai L. Kim H. Motagamwala A.H. Mobley J.K. Yue F. Tobimatsu Y. Havkin-Frenkel D. Chen F. Dixon R.A. et al.An “ideal lignin” facilitates full biomass utilization.Sci. Adv. 2018; 4: eaau2968Crossref PubMed Scopus (138) Google Scholar, 15Rahimi A. Azarpira A. Kim H. Ralph J. Stahl S.S. Chemoselective metal-free aerobic alcohol oxidation in lignin.J. Am. Chem. Soc. 2013; 135: 6415-6418Crossref PubMed Scopus (484) Google Scholar, 16Parsell T. Yohe S. Degenstein J. Jarrell T. Klein I. Gencer E. Hewetson B. Hurt M. Kim J.I. Choudhari H. et al.A synergistic biorefinery based on catalytic conversion of lignin prior to cellulose starting from lignocellulosic biomass.Green Chem. 2015; 17: 1492-1499Crossref Google Scholar, 17Klein I. Saha B. Abu-Omar M.M. Lignin depolymerization over Ni/C catalyst in methanol, a continuation: effect of substrate and catalyst loading.Catal. Sci. Technol. 2015; 5: 3242-3245Crossref Google Scholar, 18Matson T.D. Barta K. Iretskii A.V. Ford P.C. One-pot catalytic conversion of cellulose and of woody biomass solids to liquid fuels.J. Am. Chem. Soc. 2011; 133: 14090-14097Crossref PubMed Scopus (273) Google Scholar, 19Song Q. Wang F. Cai J. Wang Y. Zhang J. Yu W. Xu J. Lignin depolymerization (LDP) in alcohol over nickel-based catalysts via a fragmentation–hydrogenolysis process.Energy Environ. Sci. 2013; 6: 994-1007Crossref Scopus (687) Google Scholar, 20Wang X. Rinaldi R. A route for lignin and bio-oil conversion: dehydroxylation of phenols into arenes by catalytic tandem reactions.Angew. Chem. Int. Ed. 2013; 52: 11499-11503Crossref PubMed Scopus (220) Google Scholar, 21Van den Bosch S. Schutyser W. Vanholme R. Driessen T. Koelewijn S.-F. Renders T. De Meester B. Huijgen W.J.J. Dehaen W. Courtin C.M. et al.Reductive lignocellulose fractionation into soluble lignin-derived phenolic monomers and dimers and processable carbohydrate pulps.Energy Environ. Sci. 2015; 8: 1748-1763Crossref Google Scholar, 22Van den Bosch S. Renders T. Kennis S. Koelewijn S.-F. Van den Bossche G. Vangeel T. Deneyer A. Depuydt D. Courtin C.M. Thevelein J.M. et al.Integrating lignin valorization and bio-ethanol production: on the role of Ni-Al2O3 catalyst pellets during lignin-first fractionation.Green Chem. 2017; 19: 3313-3326Crossref Google Scholar However, the primary products from these processes are mixtures of oxygen-containing compounds with high boiling points, which can hardly be separated by conventional distillation techniques. Moreover, the yields of lignin monomers are limited because of the presence of stable interunit C–C bonds within native lignin or those formed during lignin extraction.23Shuai L. Amiri M.T. Questell-Santiago Y.M. Héroguel F. Li Y. Kim H. Meilan R. Chapple C. Ralph J. Luterbacher J.S. Formaldehyde stabilization facilitates lignin monomer production during biomass depolymerization.Science. 2016; 354: 329-333Crossref PubMed Scopus (762) Google Scholar Importantly, adding formaldehyde during the pre-treatment of biomass can effectively improve the yield of lignin monomers by preventing the interunit C–C coupling.23Shuai L. Amiri M.T. Questell-Santiago Y.M. Héroguel F. Li Y. Kim H. Meilan R. Chapple C. Ralph J. Luterbacher J.S. Formaldehyde stabilization facilitates lignin monomer production during biomass depolymerization.Science. 2016; 354: 329-333Crossref PubMed Scopus (762) Google Scholar, 24Lan W. Amiri M.T. Hunston C.M. Luterbacher J.S. Protection group effects during α, γ-diol lignin stabilization promote high-selectivity monomer production.Angew. Chem. Int. Ed. 2018; 57: 1356-1360Crossref PubMed Scopus (144) Google Scholar More interestingly, the emerging “lignin-first” approaches have shown productions of (near)theoretical amounts of phenolic monomers via solvolytic delignification, offering great promise for high-yield lignin depolymerization.4Schutyser W. Renders T. Van den Bosch S.V. Koelewijn S.F. Beckham G.T. Sels B.F. Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading.Chem. Soc. Rev. 2018; 47: 852-908Crossref PubMed Google Scholar, 21Van den Bosch S. Schutyser W. Vanholme R. Driessen T. Koelewijn S.-F. Renders T. De Meester B. Huijgen W.J.J. Dehaen W. Courtin C.M. et al.Reductive lignocellulose fractionation into soluble lignin-derived phenolic monomers and dimers and processable carbohydrate pulps.Energy Environ. Sci. 2015; 8: 1748-1763Crossref Google Scholar, 22Van den Bosch S. Renders T. Kennis S. Koelewijn S.-F. Van den Bossche G. Vangeel T. Deneyer A. Depuydt D. Courtin C.M. Thevelein J.M. et al.Integrating lignin valorization and bio-ethanol production: on the role of Ni-Al2O3 catalyst pellets during lignin-first fractionation.Green Chem. 2017; 19: 3313-3326Crossref Google Scholar However, the cleavage of intrinsic C–C bonds within native and technical lignin remains a long-standing challenge. Very recently, a CoS2 catalyst has enabled the cleavage of C–C bonds in methylene-linked lignin models.25Shuai L. Sitison J. Sadula S. Ding J. Thies M.C. Saha B. Selective C-C bond cleavage of methylene-linked lignin models and Kraft lignin.ACS Catal. 2018; 8: 6507-6512Crossref Scopus (69) Google Scholar However, this catalyst has a limited structural stability and is inefficient to cleave the most robust 5–5 C–C linkages in lignin. Although lignin can be directly converted into volatile hydrocarbons via catalytic hydropyrolysis at typically 650°C,26Ma Z. Troussard E. van Bokhoven J.A. Controlling the selectivity to chemicals from lignin via catalytic fast pyrolysis.Appl. Catal. A Gen. 2012; 423–424: 130-136Crossref Scopus (292) Google Scholar, 27Jan O. Marchand R. Anjos L.C.A. Seufitelli G.V.S. Nikolla E. Resende F.L.P. Hydropyrolysis of lignin using Pd/HZSM-5.Energy Fuels. 2015; 29: 1793-1800Crossref Scopus (91) Google Scholar, 28Mu W. Ben H. Ragauskas A. Deng Y. Lignin pyrolysis components and upgrading—technology review.Bioenergy Res. 2013; 6: 1183-1204Crossref Scopus (242) Google Scholar these processes are very energy consuming, and deactivation of catalysts often occurs rapidly because of the coke formation (up to 40%).29Li X. Su L. Wang Y. Yu Y. Wang C. Li X. Wang Z. Catalytic fast pyrolysis of Kraft lignin with HZSM-5 zeolite for producing aromatic hydrocarbons.Front. Environ. Sci. Eng. 2012; 6: 295-303Crossref Scopus (158) Google Scholar, 30Zhao Y. Deng L. Liao B. Fu Y. Guo Q.-X. Aromatics production via catalytic pyrolysis of pyrolytic lignins from bio-oil.Energy Fuels. 2010; 24: 5735-5740Crossref Scopus (134) Google Scholar Efficient catalytic cleavage of both interunit C–C and C–O linkages in lignin can maximize the lignin monomer production and thus is highly desirable. This is, however, a very challenging task and requires solutions based upon new multifunctional catalysts. Zeolite materials incorporating Brønsted acid sites can catalyze hydrocarbon cracking in petroleum refineries.31Vermeiren W. Gilson J.-P. Impact of zeolites on the petroleum and petrochemical industry.Top. Catal. 2009; 52: 1131-1161Crossref Scopus (704) Google Scholar, 32Zhu J. Meng X. Xiao F.S. Mesoporous zeolites as efficient catalysts for oil refining and natural gas conversion.Front. Chem. Sci. Eng. 2013; 7: 233-248Crossref Scopus (67) Google Scholar Phosphate-based materials containing strong Brønsted acid sites can protonate benzene rings and thus facilitate the cleavage of C–C bonds.33Michaud P. Lemberton J.L. Pérot G. Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene: effect of an acid component on the activity of a sulfided NiMo on alumina catalyst.Appl. Catal. A Gen. 1998; 169: 343-353Crossref Scopus (164) Google Scholar, 34Zhang D. Duan A. Zhao Z. Xu C. Synthesis, characterization, and catalytic performance of NiMo catalysts supported on hierarchically porous beta-KIT-6 material in the hydrodesulfurization of dibenzothiophene.J. Catal. 2010; 274: 273-286Crossref Scopus (118) Google Scholar However, these materials alone have poor activity in cleaving C–O bonds in lignin.35Shao Y. Xia Q. Dong L. Liu X. Han X. Parker S.F. Cheng Y. Daemen L.L. Ramirez-Cuesta A.J. Yang S. et al.Selective production of arenes via direct lignin upgrading over a niobium-based catalyst.Nat. Commun. 2017; 8: 16104Crossref PubMed Scopus (277) Google Scholar Meanwhile, the emerging NbOx-supported catalysts have exhibited unique activities in cleaving C–O bonds in biomass to yield fully deoxygenated compounds.36Xia Q. Chen Z. Shao Y. Gong X. Wang H. Liu X. Parker S.F. Han X. Yang S. Wang Y. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes.Nat. Commun. 2016; 7: 11162Crossref PubMed Scopus (299) Google Scholar Here, we report a mesoporous multifunctional catalyst, Ru/NbOPO4, that combines the NbOx species and phosphates containing strong Brønsted acid sites and thus enables the efficient cleavage of both interunit C–O and C–C linkages in lignin. Significantly, the one-pot conversion of lignin over Ru/NbOPO4 integrates the depolymerization of lignin, the hydrogenolysis of depolymerized compounds, and the cleavage of interunit C–C linkages and achieves optimal production of monocyclic hydrocarbons. Theoretical yields of intrinsic lignin monomers have been determined from the established nitrobenzene oxidation (NBO) method (Note S1)23Shuai L. Amiri M.T. Questell-Santiago Y.M. Héroguel F. Li Y. Kim H. Meilan R. Chapple C. Ralph J. Luterbacher J.S. Formaldehyde stabilization facilitates lignin monomer production during biomass depolymerization.Science. 2016; 354: 329-333Crossref PubMed Scopus (762) Google Scholar, 37Li Y. Akiyama T. Yokoyama T. Matsumoto Y. NMR assignment for diaryl ether structures (4-O-5 structures) in pine wood lignin.Biomacromolecules. 2016; 17: 1921-1929Crossref PubMed Scopus (37) Google Scholar, 38Ma R. Zhang X. Wang Y. Zhang X. New insights toward quantitative relationships between lignin reactivity to monomers and their structural characteristics.ChemSusChem. 2018; 11: 2146-2155Crossref PubMed Scopus (15) Google Scholar and serve as the 100% standard in this report. Here, the ratio of molar yields (RMY) is defined as (molar yield of monocyclic compounds over Ru/NbOPO4)/(molar yield of monocyclic compounds from NBO) × 100%. When RMY above 100% is obtained, it suggests the recovery of additional monocyclic compounds from depolymerized dimer and oligomer products via the cleavage of interunit C–C linkages (Figure 1). The one-pot conversion of lignin over the Ru/NbOPO4 catalyst has produced liquid monocyclic hydrocarbons with an RMY up to 153% as well as an exceptional arene selectivity of 68%. Furthermore, the unique activity of Ru/NbOPO4 to crack the interunit C–C bonds has been confirmed in lignin dimer models (e.g., biphenyl, diphenylmethane, and diphenylethane), where high yields of monocyclic aromatics have been obtained. A combined inelastic neutron scattering (INS) and density functional theory (DFT) analysis unambiguously confirmed the strong adsorption with preferred orientation, activation, and hydrogenolysis of biphenyl on the surface of Ru/NbOPO4. To the best of our knowledge, this is the first example of using INS and DFT to study the mechanism of C–C bond activation in biomass conversions. Mesoporous NbOPO4 was prepared from a hydrothermal reaction and a loading of 5 wt % Ru conducted via wetness impregnation (Note S2). The total acid amount and Brunauer-Emmett-Teller (BET) surface area of activated Ru/NbOPO4 were determined to be 980 μmol g−1 and 235 m2 g−1, respectively, and the pore size distribution was centered at 3.5 nm (Figure S2). The mesopores and high porosity of the catalyst can promote reactions taking place at the solid-solid interface and have a positive effect on the mass transfer of substrates and reaction intermediates. Kraft lignin, typically produced from chemical pulping processes, has a highly condensed and cross-linked (via interunit C–C bonds) network. Its intrinsic monomer units were determined to be 1,040 μmol g−1 from the NBO method (Tables S2 and S3), which is widely used in the literature as a standard protocol for analyzinig lignin monomers connected by C–O bonds (including but not limited to β–O–4 linkage).23Shuai L. Amiri M.T. Questell-Santiago Y.M. Héroguel F. Li Y. Kim H. Meilan R. Chapple C. Ralph J. Luterbacher J.S. Formaldehyde stabilization facilitates lignin monomer production during biomass depolymerization.Science. 2016; 354: 329-333Crossref PubMed Scopus (762) Google Scholar, 38Ma R. Zhang X. Wang Y. Zhang X. New insights toward quantitative relationships between lignin reactivity to monomers and their structural characteristics.ChemSusChem. 2018; 11: 2146-2155Crossref PubMed Scopus (15) Google Scholar, 39Yamamura M. Hattori T. Suzuki S. Shibata D. Umezawa T. Microscale alkaline nitrobenzene oxidation method for high-throughput determination of lignin aromatic components.Plant Biotechnol. 2010; 27: 305-310Crossref Scopus (23) Google Scholar The C–C linkage in lignin cannot be cleaved in the NBO method, thus making the comparison straightforward for the present study. It has been reported that the theoretical amount of lignin monomers coincides with the square of the fraction of ether bonds in the lignin structure, and that of birch lignin varies from 45% to 58%.7Yan N. Zhao C. Dyson P.J. Wang C. Liu L.T. Kou Y. Selective degradation of wood lignin over noble-metal catalysts in a two-step process.ChemSusChem. 2008; 1: 626-629Crossref PubMed Scopus (481) Google Scholar, 22Van den Bosch S. Renders T. Kennis S. Koelewijn S.-F. Van den Bossche G. Vangeel T. Deneyer A. Depuydt D. Courtin C.M. Thevelein J.M. et al.Integrating lignin valorization and bio-ethanol production: on the role of Ni-Al2O3 catalyst pellets during lignin-first fractionation.Green Chem. 2017; 19: 3313-3326Crossref Google Scholar With the NBO method, on the basis of the molar content of S, G, and H units in birch lignin, the maximum amount of lignin monomers was found to be within the range of 52%–57% (Table S2, entry 4), highly consistent with the reported results. The one-pot conversion of Kraft lignin was first tested over the Ru/NbOPO4 catalyst in dodecane at 310°C under 0.5 MPa H2 for 40 h. Interestingly and surprisingly, a very high yield of monocyclic hydrocarbons (1,594 μmol g−1/14.5 wt %) was obtained with a C6–C9 arene selectivity of 68% (Table 1, entry 1; Table S4, entry 4; Table S5). This gives an RMY of 153%, indicating a 53% additional recovery of monocyclic hydrocarbons via the cleavage of interunit C–C linkages in Kraft lignin. Next, enzymic corncob, pine, and birch lignin (representing grasses, softwood, and hardwood lignin, respectively, Table S2 and Note S3) were employed as feedstocks (Table 1, entries 3–5; Table S6). The RMY for conversions of enzymic, pine, and birch lignin were 147%, 151%, and 124%, respectively, confirming the cleavage of interunit C–C linkages in all cases. Importantly, high selectivities to monocyclic arenes ranging from 62% to 67% were obtained throughout, demonstrating the general applicability of this multifunctional catalyst and one-pot approach to producing monocyclic arenes. In addition, the comparison of the activity and selectivity with early reported literature in the one-pot conversion of lignin is also summarized in Figure S3 and Note S4.Table 1Summary of the Products Distribution from the One-Pot Conversion of Lignin over the Ru/NbOPO4 CatalystaReaction conditions: 0.1 g lignin, 0.2 g 5% Ru/NbOPO4, 5 mL dodecane, and 0.5 MPa H2 at 310°C for 40 h.EntryLigninProduct Distribution (μmol⋅g−1)Total Amount (μmol g−1/wt %)Selectivity to Arenes (%)bSelectivity to arenes = (total amount of arenes)/(total amount of hydrocarbons) × 100%.RMY (%)cRatio of molar yields (RMY) = (molar yield of monocyclic compounds over Ru/NbOPO4)/(molar yield of monocyclic compounds from NBO) × 100% = (total amount of monocyclic hydrocarbons over Ru/NbOPO4)/(theoretical amount of monocyclic hydrocarbons from NBO) × 100%. The theoretical hydrocarbon amounts of Kraft lignin, enzymic lignin, pine lignin, and birch lignin are 1,040, 1,448, 2,162, and 2,741 μmol g−1, respectively. Theoretical hydrocarbon amounts were calculated by the NBO method as described in Table S2 and Note S1.C6–C9 ArenesC6–C9 Cycloalkanes1Kraft524389103672094216767261,594/14.5681532dReaction conditions: 0.1 g lignin, 0.2 g 5% Ru/NbOPO4, 5 mL dodecane, and 0.5 MPa H2 at 250°C for 20 h.Kraft20426214642568815088191,055/10.1621013enzymic651323387776998203266612,135/20.3671474pine1,179640177138285211448111653,254/29.3661515birch7968772511912541914871891583,394/31.962124a Reaction conditions: 0.1 g lignin, 0.2 g 5% Ru/NbOPO4, 5 mL dodecane, and 0.5 MPa H2 at 310°C for 40 h.b Selectivity to arenes = (total amount of arenes)/(total amount of hydrocarbons) × 100%.c Ratio of molar yields (RMY) = (molar yield of monocyclic compounds over Ru/NbOPO4)/(molar yield of monocyclic compounds from NBO) × 100% = (total amount of monocyclic hydrocarbons over Ru/NbOPO4)/(theoretical amount of monocyclic hydrocarbons from NBO) × 100%. The theoretical hydrocarbon amounts of Kraft lignin, enzymic lignin, pine lignin, and birch lignin are 1,040, 1,448, 2,162, and 2,741 μmol g−1, respectively. Theoretical hydrocarbon amounts were calculated by the NBO method as described in Table S2 and Note S1.d Reaction conditions: 0.1 g lignin, 0.2 g 5% Ru/NbOPO4, 5 mL dodecane, and 0.5 MPa H2 at 250°C for 20 h. Open table in a new tab To investigate the stability of Ru/NbOPO4, we conducted three consecutive conversions of Kraft lignin by using the recycled catalyst. Negligible changes in reaction yield or arene selectivity were observed (Figure 2; Table S7). For example, the yield of monocyclic hydrocarbons and arene selectivity on the third run were 1,588 μmol g−1 and 66%, comparable to those (1,594 μmol g−1 and 68%) achieved with a fresh catalyst. The stability test was also conducted with 100 wt % catalyst loading in four consecutive recycling runs (Table S8; Note S5), where the catalytic activity reduced after the first run and remained the same for the following runs. X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis further confirmed the absence of notable structural change, aggregation of Ru particles, and leaching of Ru, respectively, for the used catalyst (Figures S4 and S5; Table S9). These results demonstrate the excellent stability of Ru/NbOPO4 in this one-pot process. In addition, the effect of S element in Kraft lignin was also studied by control experiments, suggesting that the S element in Kraft lignin has little effect on the catalytic activity (Table S10; Note S6). To investigate the reaction pathways, we converted Kraft lignin at 250°C for 20 h (Table 1, entry 2; Table S4; Note S7) and isolated and analyzed reaction intermediates by 2D heteronuclear single-quantum coherence nuclear magnetic resonance (HSQC NMR). Compared with NMR signals for the raw lignin, those for A (β–O–4 linkages), B (β–5 linkages), and C (β–β linkages) decreased significantly in the side-chain regions after the reaction, and the presence of G and H subunits in the reaction residue was negligible (Figure S6). Elemental analysis shows only a minor oxygen content (<0.8 wt %) in the reaction intermediates, further suggesting the near-complete oxygen removal during the initial reaction. Meanwhile, bicyclic aromatic hydrocarbons (e.g., biphenyl and diphenylethane) were also detected (Figure S7), indicating that the activation and cleavage of interunit C–C bonds in depolymerized compounds require additional energy input, consistent with the difference in their bond dissociation energies (Table S1). The mass yield of total monocyclic compounds at 250°C for 20 h was only 10.1 wt % (Table 1, entry 2), and that can be increased to 14.5 wt % at 310°C for 40 h via further cleavage of C–C linkages in depolymerized compounds. Among all interunit C–C linkages in lignin, the 5–5 bond between two phenyl groups accounts for the highest portion in lignin (40%–50% in softwood and 25%–40% in hardwood on the basis of all C–C linkages) and has the strongest dissociation energies of 481–494 kJ mol−1. Therefore, biphenyl is selected for in-depth investigation as a model compound for C–C cleavage.7Yan N. Zhao C. Dyson P.J. Wang C. Liu L.T. Kou Y. Selective degradation of wood lignin over noble-metal catalysts in a two-step process.ChemSusChem. 2008; 1: 626-629Crossref PubMed Scopus (481) Google Scholar, 40Chui M. Metzker G. Bernt C.M. Tran A.T. Burtoloso A.C.B. Ford P.C. Probing the lignin disassembly pathways with modified catalysts based on Cu-doped porous metal oxides.ACS Sustain. Chem. Eng. 2017; 5: 3158-3169Crossref Scopus (33) Google Scholar To closely monitor the intermediates, we conducted the reaction at a reduced temperature of 280°C (Figure 3). Initially, phenylcyclohexane (1) was found to accumulate rapidly to 73% within 1 h and then gradually convert to benzene (2) and cyclohexane (3) as the reaction proceeded. This indicates that the partial hydrogenation of biphenyl occurred to activate the C5–C5 linkage from the sp2–sp2 to sp2–sp3 bond, thus effectively reducing the bond dissociation energy. Similar product distribution was obtained when 1 was used as the substrate, confirming 1 as the primary intermediate in the conversion of biphenyl (Figure S8). Interestingly, a small amount of bicyclohexyl (4) was observed after 2 h, and no further conversion of 4 occurred with prolonged reaction time. Indeed, no product was detected in the hydrogenolysis of 4 or dodecane under the same reaction conditions (Figures 4A and 4B ), indicating that Ru/NbOPO4 has a poor activity to cleave the Caliphatic–Caliphatic bonds, although they have considerably lower bond dissociation energy. Comparison of the Fourier transform infrared spectroscopy (FTIR) of adsorbed biph" @default.
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• W2936709985 date "2019-06-01" @default.
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• W2936709985 title "Breaking the Limit of Lignin Monomer Production via Cleavage of Interunit Carbon–Carbon Linkages" @default.
• W2936709985 cites W1750457094 @default.
• W2936709985 cites W1964441532 @default.
• W2936709985 cites W1971144082 @default.
• W2936709985 cites W1982267818 @default.
• W2936709985 cites W1982507628 @default.
• W2936709985 cites W1982599553 @default.
• W2936709985 cites W1989436648 @default.
• W2936709985 cites W1992994440 @default.
• W2936709985 cites W1997074991 @default.
• W2936709985 cites W2003257483 @default.
• W2936709985 cites W2023022618 @default.
• W2936709985 cites W2031293654 @default.
• W2936709985 cites W2032490349 @default.
• W2936709985 cites W2036412045 @default.
• W2936709985 cites W2038941722 @default.
• W2936709985 cites W2065970580 @default.
• W2936709985 cites W2068459118 @default.
• W2936709985 cites W2076314081 @default.
• W2936709985 cites W2077420665 @default.
• W2936709985 cites W2082607216 @default.
• W2936709985 cites W2105910874 @default.
• W2936709985 cites W2111467913 @default.
• W2936709985 cites W2136595576 @default.
• W2936709985 cites W2142591912 @default.
• W2936709985 cites W2148999761 @default.
• W2936709985 cites W2165638832 @default.
• W2936709985 cites W2169790911 @default.
• W2936709985 cites W2316355497 @default.
• W2936709985 cites W2316961324 @default.
• W2936709985 cites W2321689002 @default.
• W2936709985 cites W2322842605 @default.
• W2936709985 cites W2337798044 @default.
• W2936709985 cites W2407460809 @default.
• W2936709985 cites W2422488648 @default.
• W2936709985 cites W2441647337 @default.
• W2936709985 cites W2533242268 @default.
• W2936709985 cites W2592437515 @default.
• W2936709985 cites W2618807347 @default.
• W2936709985 cites W2624915572 @default.
• W2936709985 cites W2775620122 @default.
• W2936709985 cites W2782131232 @default.
• W2936709985 cites W2782590469 @default.
• W2936709985 cites W2802414207 @default.
• W2936709985 cites W2805771429 @default.
• W2936709985 cites W2890597636 @default.
• W2936709985 cites W2893465898 @default.
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