Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Abstract

•(FA)–Pd/HPC–NH2 achieves the selective HDO of benzyl ketones from mixed oxygenates•H+/H− species accelerates the selective hydrogenation of C=O bond in benzyl ketones•Formate intermediates expedite the cleavage of Cbenzyl–O bond via an EDDO pathway•Proposing a green route to produce biofuels or chemicals from only biomass Producing value-added chemicals and biofuels from renewable biomass rather than fossil fuels is reckoned as an effective recipe against global warming. However, bio-oils derived from biomass pyrolysis with high oxygen content (10–45 wt %) cannot be directly utilized. Hydrodeoxygenation (HDO) is commonly regarded as the most effective upgrading strategy. Nevertheless, traditional HDO process using H2 as hydrogen source produced by water-gas-shift reaction (WGS) is energy consuming and non-selective under harsh reaction conditions (100°C∼300°C, 1 ∼30 MPa H2, and acid sites). Instead, the current work uses biomass-derived formic acid as a reductant to in situ generate H+/H− species on Pd/HPC–NH2 catalyst, realizing the selective HDO of benzyl ketones from mixed oxygenates under ambient conditions. Therefore, an environmentally friendly route to generate valuable products from only biomass under mild conditions is proposed, which is very instructive for realizing carbon neutralization. Upgrading biomass-derived phenolic compounds provides a valuable approach for the production of higher-value-added fuels and chemicals. However, most established catalytic systems display low hydrodeoxygenation (HDO) activities even under harsh reaction conditions. Here, we found that Pd supported on –NH2-modified hierarchically porous carbon (Pd/HPC–NH2) with formic acid (FA) as hydrogen source exhibits unprecedented performance for the selective HDO of benzylic ketones from crude lignin-derived oxygenates. Designed experiments and theoretical calculations reveal that the H+/H− species generated from FA decomposition accelerates nucleophilic attack on carbonyl carbon in benzylic ketones and the formate species formed via the esterification of intermediate alcohol with FA expedites the cleavage of C–O bonds, achieving a TOF of 152.5 h−1 at 30°C for vanillin upgrading, 15 times higher than that in traditional HDO processes (∼10 h−1, 100°C–300°C). This work provides an intriguing green route to produce transportation fuels or valuable chemicals from only biomass under mild conditions. Upgrading biomass-derived phenolic compounds provides a valuable approach for the production of higher-value-added fuels and chemicals. However, most established catalytic systems display low hydrodeoxygenation (HDO) activities even under harsh reaction conditions. Here, we found that Pd supported on –NH2-modified hierarchically porous carbon (Pd/HPC–NH2) with formic acid (FA) as hydrogen source exhibits unprecedented performance for the selective HDO of benzylic ketones from crude lignin-derived oxygenates. Designed experiments and theoretical calculations reveal that the H+/H− species generated from FA decomposition accelerates nucleophilic attack on carbonyl carbon in benzylic ketones and the formate species formed via the esterification of intermediate alcohol with FA expedites the cleavage of C–O bonds, achieving a TOF of 152.5 h−1 at 30°C for vanillin upgrading, 15 times higher than that in traditional HDO processes (∼10 h−1, 100°C–300°C). This work provides an intriguing green route to produce transportation fuels or valuable chemicals from only biomass under mild conditions. IntroductionWith the fast depletion of fossil resources, renewable lignocellulosic biomass energy is increasingly becoming a well-accepted substitute for clean energy and chemicals.1Tan S. Zhang Z. Sun J. Wang Q. Recent progress of catalytic pyrolysis of biomass by HZSM-5.Chin. J. Catal. 2013; 34: 641-650Crossref Google Scholar, 2Deng W. Zhang H. Xue L. Zhang Q. Wang Y. Selective activation of the C-O bonds in lignocellulosic biomass for the efficient production of chemicals.Chin. J. Catal. 2015; 36: 1440-1460Crossref Scopus (36) Google Scholar, 3Xia 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. 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Hydrodeoxygenation of anisole over silica-supported Ni2P, MoP, and NiMoP catalysts.Energy Fuels. 2011; 25: 854-863Crossref Scopus (330) Google Scholar However, most of these catalytic systems occurred at harsh reaction conditions (100°C∼300°C, 1∼30 MPa H2, and especially acid sites), which causes the fast decay of catalysts,14Dabros T.M.H. Stummann M.Z. Høj M. Jensen P.A. Grunwaldt J.-D. Gabrielsen J. Mortensen P.M. Jensen A.D. Transportation fuels from biomass fast pyrolysis, catalytic hydrodeoxygenation, and catalytic fast hydropyrolysis.Prog. Energy Combust. Sci. 2018; 68: 268-309Crossref Scopus (134) Google Scholar,17Lin Z. Chen R. Qu Z. Chen J.G. Hydrodeoxygenation of biomass-derived oxygenates over metal carbides: from model surfaces to powder catalysts.Green Chem. 2018; 20: 2679-2696Crossref Google Scholar,21Shao Y. Xia Q. Dong L. Liu X. Han X. Parker S.F. Cheng Y. Daemen L.L. Ramirez-Cuesta A.J. Yang S. Wang Y. 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It produces heterolytic hydrogen on the dual-site of Pd/HPC–NH2, which accelerates the nucleophilic addition of polarized carbonyl carbon (+δC=Oδ−), thus promoting the selective hydrogenation. In addition, it reacts with intermediate alcohol, forming corresponding esters in which the C–O bonds are more easily to break on the Pd site. Coupling with the specific functions of FA and Pd/HPC–NH2, the efficient HDO of vanillin was achieved with a TOF and p-creosol yield as high as 152.5 h−1 and 99% at only 30°C, respectively (Scheme 1B). Notably, the combination of FA and Pd/HPC–NH2 is also effective to more challenging biomass-related substrates, such as syringaldehyde, acetosyringone, and stearic acid, indicating a broader range of subjects for this catalytic system under ambient conditions. The high HDO activities to benzyl ketones under mild conditions make the selective upgrading of benzyl ketones from a batch of mixed lignin-derived oxygenates a reality. Moreover, the Pd/HPC–NH2 catalyst also exhibited superior stability by anchoring the uniform dispersed Pd NPs with amino groups. Based on the inspiring results mentioned earlier, an environmentally friendly route to produce transportation fuels or chemicals from only biomass under mild conditions was conquered together with the work reported recently on the production of FA from biomass30Wang C. Chen X. Qi M. Wu J. Gözaydın G. Yan N. Zhong H. Jin F. Room temperature, near-quantitative conversion of glucose into formic acid.Green Chem. 2019; 21: 6089-6096Crossref Google Scholar,31Zhang P. Guo Y.-J. Chen J. Zhao Y.-R. Chang J. Junge H. Beller M. Li Y. Streamlined hydrogen production from biomass.Nat. Catal. 2018; 1: 332-338Crossref Scopus (69) Google Scholar: hydrolysis of biomass to give FA and oxygen-containing monomers, selective HDO of benzylic ketones to corresponding hydrophobic products in (FA)–Pd/HPC–NH2 system, and followed by easy separation. This work provided a feasible method to produce chemicals or fuels in the framework of carbon neutralization.Results and discussionSynthesis and characterization of amino-modified Pd catalystsHPC was prepared by a simple foaming method reported in our previous work,38Deng J. Xiong T. Xu F. Li M. Han C. Gong Y. Wang H. Wang Y. Inspired by bread leavening: one-pot synthesis of hierarchically porous carbon for supercapacitors.Green Chem. 2015; 17: 4053-4060Crossref Google Scholar, 39Li M. Deng J. Lan Y. Wang Y. Efficient catalytic hydrodeoxygenation of aromatic carbonyls over a nitrogen-doped hierarchical porous carbon supported nickel catalyst.ChemistrySelect. 2017; 2: 8486-8492Crossref Scopus (29) Google Scholar, 40Tang M. Deng J. Li M. Li X. Li H. Chen Z. 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HPC material modified with amino groups was easily prepared by a well-established hydrolysis reaction between surface -OH species and Si–O bond of (3-aminopropyl)trimethoxysilane (APTMS) (Scheme S1).37Wang Z. Wang C. Mao S. Gong Y. Chen Y. Wang Y. Pd nanoparticles anchored on amino-functionalized hierarchically porous carbon for efficient dehydrogenation of formic acid under ambient conditions.J. Mater. Chem. A. 2019; 7: 25791-25795Crossref Google Scholar,41Singh S.K. Singh M.K. Kulkarni P.P. Sonkar V.K. Grácio J.J. Dash D. Amine-modified graphene: thrombo-protective safer alternative to graphene oxide for biomedical applications.ACS Nano. 2012; 6: 2731-2740Crossref PubMed Scopus (383) Google Scholar,42Zhang F. Jiang H. Li X. Wu X. Li H. 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