Dynamically Crystalline/Amorphous Structure Transitions of Metal–Organic Frameworks with Switchable Catalytic Selectivity

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLES2 Jul 2024Dynamically Crystalline/Amorphous Structure Transitions of Metal–Organic Frameworks with Switchable Catalytic Selectivity Meina Song†, Yue Wan†, Chuanqi Cheng†, Jing Du, Yutian Qin, Zhixi Li, Shuyue Kong, Bingqing Yao, Shaopeng Li, Jun Guo, Zhiyong Tang and Meiting Zhao Meina Song† Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Yue Wan† Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Chuanqi Cheng† Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Jing Du Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Yutian Qin Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Zhixi Li Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Shuyue Kong State Key Laboratory of Separation Membranes and Membrane Processes, School of Chemistry, Tiangong University, Tianjin 300387 , Bingqing Yao *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Department of Materials Science and Engineering, National University of Singapore, Singapore 117575 , Shaopeng Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 , Jun Guo *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Separation Membranes and Membrane Processes, School of Chemistry, Tiangong University, Tianjin 300387 , Zhiyong Tang CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190 and Meiting Zhao *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin 300072 Cite this: CCS Chemistry. 2024;0:1–14https://doi.org/10.31635/ccschem.024.202404172 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Distinct from molecular machines with frustrated dynamics, infinite framework assemblies are anticipated to behave with amplified and even synergistic performances in versatile application fields by performing their functionalities in a coherent fashion. This work reports an interconverted crystalline Pd/Zr-SDC and amorphous Pd/Zr-SDC-Br metal–organic framework (MOF) system through dynamic bromination/debromination processes. In the upgrading of biomass-derived vanillin, Pd/Zr-SDC produces vanillyl alcohol intermediate via the hydrogenation route while Pd/Zr-SDC-Br switches to 2-methoxy-4-methylphenol via an alternative hydrodeoxygenation route. More significantly, quasi-crystalline Pd/Zr-SDC-Br50% intermediate through controlled debromination is further optimized for vanillin catalysis with an excellent turnover frequency of 717 h−1 and a high 2-methoxy-4-methylphenol selectivity up to 99.2% under very mild conditions. Both experiments and density functional theory calculation results jointly reveal that the remarkably boosted catalytic performances are attributed to the appropriate coverage of PdBr2 onto Pd nanoparticles during the dynamic debromination transitions. This work inspires guidance in designing and developing excellent MOF catalysts via dynamical structure intertransitions. Download figure Download PowerPoint Introduction Dynamic responses and transitions are famous as pivotal characteristics of smart materials for stimuli-responsive applications.1–5 The well-known dynamics in living systems such as biomolecular machines,6,7 enzyme-powered pumps,8,9 and genetic storage systems10,11 are essential in transporting bio-signals, converting energies, and conducting basic biological processes. Via lessons from nature, a series of molecular machines have been inspired in the application fields of chirality recognitions,12–14 controlled drug deliveries,15,16 precise molecule separation,17,18 high-performance devices,19–22 and so on.23,24 Nevertheless, constrained to their random and unsystematic arrangements and movements,24,25 molecular dynamics and machines conventionally give frustrated responses in a single-molecule way. Similarly, when studying the collective and amplified synergies requiring the precise operation of entire molecules in a controlled and cooperated dynamic might only be realizable within an infinite molecular framework with well-defined compositions and ordered structures.26–29 Emerging as a new class of crystalline supramolecular assembly, metal–organic frameworks (MOFs) are constructed from metal ions/clusters and organic ligands via coordination bonding.30–39 Apart from high surface areas and tunable pore structures,40–43 the uniformly arranged molecular entities among MOFs enable them to be ideal platforms for embedding dynamic properties and reversible transitions in a coherent fashion. Indeed, thanks to premade compositions and structures, dynamic MOFs with target properties and performances can be facilely gained via implanting flexible,44–46 labile,47 photoactive,48–50 or thermosensitive51,52 functional groups. At current, those dynamical MOFs (also called flexible MOFs)45,53–55 have been engineered for undergoing dynamic responses under physical stimuli such as temperature variation,56–59 mechanical pressure,60–62 light irradiation,63,64 and electric field,65–67 but rarely reported under a driving force like a chemical reaction. In the context of applications, dynamic/flexible MOFs have achieved excellent or even superior performances in gas adsorption,59,68,69 gas purification,70,71 ions sieving,72,73 and catalysis74–79 compared with traditional rigid MOFs. In particular, dynamic/flexible MOFs have been nominated as allosteric enzymes, showcasing tunable catalytic activities in organic transformations.75 Although outstanding properties have been realized, their performance is typically optimized for dedicated products. The design and development of catalytic systems with dynamically switchable activity and selectivity for multipurpose catalytic processes is a promising, yet difficult-to-achieve strategy.80 In this work, a catalytic selectivity-switchable MOF system is developed through the dynamic structure transition between crystalline and amorphous phases triggered by reversible chemical reactions. That is face-centered cubic ( fcu) assembled Pd/Zr-SDC [Zr6O4(OH)4(SDC)6, SDC = 4,4′-stilbenedicarboxylate] and amorphous Pd/Zr-SDC-Br [Zr6O4(OH)4(SDC-Br)6, SDC-Br = 4,4′-(1,2-dibromoethane-1,2-diyl)dibenzoate] intertransformed through dynamic bromination/debromination reactions. As shown in Scheme 1, in the catalytic conversion of vanillin, a model compound of lignin,81,82 crystalline Pd/Zr-SDC mainly transforms vanillin into vanillyl alcohol intermediate via the hydrogenation route (Scheme 1, route I) while amorphous Pd/Zr-SDC-Br switches the major product to the highly calorific 2-methoxy-4-methylphenol via the alternative hydrodeoxygenation route (Scheme 1, route II).83 Benefitting from controlled dynamics between interstructural transitions, more significantly, quasi-crystalline Pd/Zr-SDC-BrX% (X = 70, 50, 20, standing for the bromination ratio of SDC) are further engineered through partial debromination processes for optimizing both high catalytic activity and product selectivity. Impressively, the optimized Pd/Zr-SDC-Br50% exhibits a nearly 100% vanillin conversion and a selectivity up to 99.2% for the high value-added 2-methoxy-4-methylphenol at very mild reaction conditions (i.e. 60 °C and 0.5 MPa H2 pressure). The excellent catalytical performances of optimized Pd/Zr-SDC-Br50% have also been expanded to 10 types of substrates. What's more, no significant loss of catalytic activity and selectivity is observed even after 10 successive reaction cycles. Scheme 1 | Schematic diagram of switching catalytic performances via dynamic structure transitions of MOFs. Download figure Download PowerPoint Experimental Methods Synthesis of Zr-SDC ZrOCl2·8H2O (0.033 g, 0.102 mmol) and formic acid (0.25 mL, 6.427 mmol) were dissolved in 10 mL of dimethylformamide (DMF) in a 15 mL sealed bottle and sonicated at room temperature for 20 min to form a clear solution. Subsequently, 4,4′-stilbenedicarboxylic acid (0.028 g, 0.102 mmol) was added into the above solution and further sonicated for 10 min. The sealed bottle was kept in a 120 °C oven for 24 h. After cooling to room temperature, the product was collected by centrifugation at 6000 rpm for 3 min and washed three times with DMF and ethanol, respectively. The resulting product was dried in a vacuum oven at 50 °C for overnight. Synthesis of Zr-SDC-Br Zr-SDC-Br was obtained from the bromination reaction of Zr-SDC. First, 100 mg of synthesized Zr-SDC was immersed in 10.5 mL of CHCl3 in a 20 mL vial and sonicated for several minutes at room temperature to disperse uniformly. Afterwards, 0.5 mL of 1 mol·L−1 Br2 in CHCl3 solution was added into the above dispersion. The reaction mixture was stirred at 200 rpm for 24 h at 40 °C in a dark environment. After the reaction, the brominated product was collected by centrifugation, washed with fresh CHCl3 multiple times, and then dried under vacuum at room temperature. Synthesis of Pd/Zr-SDC The Pd/Zr-SDC nanocomposite was prepared by a double-solvent approach. Typically, 50 mg of vacuum-dried Zr-SDC was suspended in 10 mL of n-hexane as hydrophobic solvent, and sonicated for 30 min at room temperature to achieve a uniform dispersion. After that, 50 μL of H2PdCl4 solution was slowly added dropwise to the above dispersion under vigorous stirring, and stirred for 2 h. After removing the supernatant, the product was washed three times by centrifugation with 8 mL of ethanol, followed by dispersion into 4 mL of ethanol. Subsequently, 0.25 mL of 0.1 mol·L−1 NaBH4 in ethanol was quickly added to the above mixture with vigorous stirring in an ice bath. After being stirred for 10 min, the obtained sample was collected by centrifugation, washed three times with ethanol, and further dried in vacuum at 50 °C to obtain Pd/Zr-SDC for subsequent catalysis. Synthesis of Pd/Zr-SDC-Br The Pd/Zr-SDC-Br nanocomposite was prepared using the same method as Pd/Zr-SDC, except that Zr-SDC was replaced by Zr-SDC-Br. Synthesis of Pd/Zr-SDC-BrX% The synthesized Pd/Zr-SDC-Br was placed in a tube electric furnace, heated to 220 °C at a rate of 10 °C·min−1 under an argon atmosphere, calcined at constant temperature for a specific time, and then naturally cooled to room temperature to obtain Pd/Zr-SDC-BrX%. The required calcination times for Pd/Zr-SDC-BrX% (X = 70, 50, 20) were 30, 60, and 120 min, respectively. Catalytic reaction The catalytic experiments were performed in a 20 mL Teflon-lined autoclave equipped with a mechanical stirrer and an internal thermocouple. In a typical experiment, 25 mg (0.16 mmol) of vanillin, 5 mg of catalyst, and 4 mL of isopropanol as solvent were sealed in an autoclave. The air in the reactor was replaced with H2 three times and then the reactor was pressurized with H2 to a certain pressure. The autoclave was heated to 60 °C while stirring at 500 rpm for the required time. After a certain reaction time, the autoclave was cooled to room temperature, and the reaction solution was centrifuged for gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis. Similar catalytic reactions were conducted for other substrates using Pd/Zr-SDC-Br50% as the catalyst, with minor adjustments in temperature or reaction time. To assess cycling stability of the Pd/Zr-SDC-Br50% catalyst, the used catalyst was centrifuged, washed, and vacuum-dried overnight before being employed for the subsequent run. More detailed materials, characterizations, synthesis, and computational methods are presented in the Supporting Information. Results and Discussion The prototype Zr-SDC is assembled between the classical 12-coordinated Zr6O4(OH)4 node and the ditopic SDC linker in the fcu arrangement fashion,84–86 which is isoretical to the MOF structure of well-known UiO-series.87 The powder X-ray diffraction (PXRD) pattern of Zr-SDC (brown pattern in Figure 1a) is identical to the simulated one and therefore confirms its crystallography. After complete bromination of the alkene groups of SDC linkers, crystalline Zr-SDC transforms into the amorphous Zr-SDC-Br on the basis of the disappearance of diffraction peaks (orange pattern in Figure 1a). It is well reasoned that the freely rotated C–C single bond88 after bromination makes SDC-Br highly flexible and is therefore no longer able to prop up the crystalline framework. Impressively, the framework crystallinity can be dynamically recovered (blue pattern in Figure 1a) after high-temperature treatment of Zr-SDC-Br at 220 °C under an argon atmosphere, which is ascribed to the re-formation of rigid C=C bonds via the debromination process. The dynamic bromination and subsequent debromination processes are monitored by proton nuclear magnetic resonance (1H-NMR, Figure 1b and Supporting Information Figure S1). The 1H-NMR spectrum of Zr-SDC-Br digested in DCl/DMSO-d6 (orange plot in Figure 1b) clearly demonstrates the formation of SDC-Br linkers according to the emergence of new proton signals at 6.24 ppm accompanying the disappearance of alkene proton signals at 7.45 ppm. Moreover, almost complete debromination of Zr-SDC-Br can also be reversibly obtained as confirmed by the 1H-NMR signals of recovered SDC as the same as the raw one (blue and brown plots in Figure 1b). In addition, the Fourier transform infrared spectroscopy results also confirm the C-Br formation in Zr-SDC-Br, as evidenced by the appearance of a peak at 546 cm−1 and the disappearance of the =C–H vibration peak at 960 cm−1 ( Supporting Information Figure S2). To characterize the well-maintained thermal stabilities of intertransformed MOFs, thermogravimetric analysis (TGA) experiments are performed under nitrogen atmosphere (Figure 1c). Before 200 °C, the residual solvent loss occurs for Zr-SDC which begins to decompose its SDC linkers upon the temperature reaching about 510 °C. In contrast, the TGA curve of the amorphous Zr-SDC-Br after full bromination shows a mass loss of 31.7% between 200 °C and 500 °C, which is attributed to the debromination loss of SDC-Br linkers with a theoretical value of 29.5%. Similarly, the complete decomposition of linkers is also observed at 510 °C, indicating the reserved high thermal stability of Zr-SDC-Br even after the amorphization. As expected, the TGA curve of recovered Zr-SDC via dynamical debromination is basically in line with that of raw Zr-SDC except for the absence of initial solvent loss (brown and blue curves in Figure 1c). In order to further verify the recovered ability of framework porosity, N2 adsorption/desorption isotherms are subsequently collected under 77 K for three types of samples (Figure 1d). The Brunauer–Emmett–Teller (BET) surface area is calculated as 1041 m2·g−1 for raw Zr-SDC. One can see that the seriously decreased surface area (35 m2·g−1) for Zr-SDC-Br is due to its amorphous structure. After reversible linker debromination, the BET surface area of recovered Zr-SDC is greatly increased to 795 m2·g−1 again. Simultaneously, the corresponding pore size distribution of recovered Zr-SDC is also the same as raw Zr-SDC ( Supporting Information Figure S3), further proving the dynamical structure transition triggered by the bromination/debromination processes. Figure 1 | (a) PXRD patterns of as-synthesized Zr-SDC, Zr-SDC-Br, and recovered Zr-SDC. (b) 1H-NMR spectra of Zr-SDC, Zr-SDC-Br, and Zr-SDC recovered after digestion (DCl/DMSO-d6, 293 K). (c) TGA profiles of Zr-SDC, Zr-SDC-Br, and recovered Zr-SDC. (d) N2 adsorption/desorption isotherms (adsorption, filled patterns; desorption, empty patterns) of Zr-SDC, Zr-SDC-Br, and recovered Zr-SDC. Download figure Download PowerPoint Catalytically active Pd nanoparticles (NPs) are then installed into MOFs by a double-solvent method to obtain Pd/Zr-SDC and Pd/Zr-SDC-Br nanocomposites. In order to finely tune catalytic performances, quasi-crystalline Pd/Zr-SDC-BrX% including Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20% with different extents of debromination are further obtained by carefully controlling the debromination time of Pd/Zr-SDC-Br. The corresponding debromination ratios are quantified exactly according to the 1H-NMR spectrum of digested samples in the DCl/DMSO-d6 mixture (Figure 2a and Supporting Information Figure S4). Moreover, TGA curves also confirm the above debromination ratios by calculating mass loss during the debromination process ( Supporting Information Figures S5 and S6). Importantly, the exact debromination ratio of quasi-crystalline Pd/Zr-SDC-BrX% can be carefully controlled by simply varying the heat treatment time as demonstrated by the tiny bromination fluctuations of samples processed from different batches ( Supporting Information Table S1). The developed composite catalysts are further characterized with PXRD (Figure 2b). The crystalline states of Pd/Zr-SDC and Pd/Zr-SDC-Br are nearly unchanged in comparison to pristine Zr-SDC and Zr-SDC-Br, respectively. Figure 2 | (a) 1H-NMR spectra of Pd/Zr-SDC, Pd/Zr-SDC-Br, Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20% after digestion (DCl/DMSO-d6, 293 K). (b) PXRD patterns of Pd/Zr-SDC, Pd/Zr-SDC-Br, Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20%. (c) N2 adsorption/desorption isotherms (adsorption, filled patterns; desorption, empty patterns) and (d) pore size distributions obtained from the isotherms by DFT of Pd/Zr-SDC, Pd/Zr-SDC-Br, Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20%. Download figure Download PowerPoint Note that the unobservable diffraction patterns of Pd NPs ( Supporting Information Figure S7) are ascribed to their tiny installation amounts which are determined using inductively coupled plasma optical emission spectrometry ( Supporting Information Table S2). Upon debromination, quasi-crystalline Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20% gradually recover their ordered crystallinity through dynamic structure transitions. Meanwhile, BET surface areas gradually increase from 255 m2·g−1 to 409 m2·g−1 and further to 622 m2·g−1 for Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20%, respectively, accompanied by the increment of pore volume from 0.21 cm3·g−1 to 0.28 cm3·g−1 and further to 0.42 cm3·g−1 (Figure 2c,d). The morphologies of the resultant Pd/MOF composites are characterized by scanning electron microscopy (SEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The Pd/Zr-SDC, Pd/Zr-SDC-Br20%, Pd/Zr-SDC-Br50%, Pd/Zr-SDC-Br70%, and even amorphous Pd/Zr-SDC-Br coherently show octahedral morphologies embedded throughout Pd NPs ( Supporting Information Figures S8–S10). Taking quasi-crystalline Pd/Zr-SDC-Br50% as a representative example, one can see the typical octahedral morphology with a uniform particle size (Figure 3a). The crystallinity of Pd/Zr-SDC-Br50% is further proved by the high-resolution STEM (HR-STEM) image, which shows the (111) plane of the MOF with a lattice fringe of 1.70 nm (Figure 3c). Moreover, corresponding spots in the hexagonal symmetry (inset in Figure 3c) that evolve from fast Fourier transform (FFT) also reveal its fcu crystal structure. One can figure out the separately embedded Pd NPs (2.3 ± 0.8 nm) from the MOF matrix (Figure 3b and Supporting Information Figure S11). The crystallinity of Pd NPs is verified by their observed lattice fringe of 0.23 nm corresponding to the spacing of (111) plane (Figure 3d). Moreover, energy-dispersive X-ray spectroscopy (EDS) elemental mapping images (blue, purple, and yellow pixels in Figure 3e) indicate uniform dispersion of Zr, Pd, and Br elements, respectively. Figure 3 | Characterization of the Pd/Zr-SDC-Br50% nanocomposite. (a) SEM image of the Pd/Zr-SDC-Br50% nanocomposite. (b) STEM image of a single Pd/Zr-SDC-Br50% nanostructure. (c) HR-STEM image of the Pd/Zr-SDC-Br50% nanocomposite. The inset shows the corresponding FFT pattern with the electron beam perpendicular to its basal plane. (d) HR-STEM image of a Pd nanoparticle. (e) Dark-field TEM image of the Pd/Zr-SDC-Br50% nanocomposite and the corresponding EDS elemental mapping images of Zr, Pd, and Br elements. Download figure Download PowerPoint Vanillin, typically derived from the depolymerization of lignin, is a model compound of biomass phenolic.89,90 The conventional hydrogenation route of vanillin can produce vanillyl alcohol which is a widely used intermediate for the production of epoxy thermosets, food preservatives, and anti-inflammatory drugs.91 Alternatively, the conversion of vanillin to highly calorific 2-methoxy-4-methylphenol via the hydrodeoxygenation route is well accepted as a promising technology to develop fossil fuel-free biomass fuel.92 In this work, the catalytic conversion of vanillin is evaluated at 60 °C and a hydrogen pressure of 0.5 MPa using isopropanol as the solvent, which are considered as very mild conditions applicable for industrial expansions. The performance of the initial Pd/Zr-SDC catalyst shows a turn-over frequency (TOF) of 143 h−1 towards vanillin and a 93.4% selectivity of vanillyl alcohol (Table 1, entry 1). Even lasting a longer reaction time, no further deoxidation process occurs. In sharp contrast, the intertransformed amorphous Pd/Zr-SDC-Br catalyst switches the catalytic process into an alternative hydrodeoxygenation route and offers 2-methoxy-4-methylphenol (56.7%) as the major product (Table 1, entry 2). Nevertheless, the catalytic activity of Pd/Zr-SDC-Br seriously declines to 71 h−1 caused by the porosity collapse in the amorphous state. Aiming to combine the high catalytic activity of Pd/Zr-SDC and the desired product selectivity of Pd/Zr-SDC-Br, dynamically debrominated Pd/Zr-SDC-BrX% are further assessed in catalysis and anticipated to exhibit both high catalytic activity and product selectivity (Table 1, entries 3–5). To one's surprise, the TOF value of converting vanillin is increased to 358 and 717 h−1 for quasi-crystalline Pd/Zr-SDC-Br70% and Pd/Zr-SDC-Br50%, respectively. However, no TOF improvement is further observed for the continuously debrominated Pd/Zr-SDC-Br20% (366 h−1), indicating the optimized catalytic activity acquired by Pd/Zr-SDC-Br50% in return. More impressively, the product selectivities for 2-methoxy-4-methylphenol are greatly boosted to 81.4%, 99.2%, and 98.6% for Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20%, respectively, which also displays a volcano-type selectivity in relation to dynamic debromination. In addition, Zr-SDC and Zr-SDC-Br show no catalytic activity under identical conditions, highlighting the catalytic role of Pd NPs (Table 1, entries 6 and 7). The commercial and catalysts exhibit vanillin conversion activity but the product selectivity to 2-methoxy-4-methylphenol is as as and (Table 1, entries 8 and results have further demonstrated the pivotal role of Pd/Zr-SDC-BrX% in the catalytic selectivity to the optimized Pd/Zr-SDC-Br50% shows both excellent catalytic activity and product selectivity for upgrading vanillin into biomass under the reaction conditions compared with the catalysts ( Supporting Information Table Table 1 | of and Selectivity TOF 1 Pd/Zr-SDC 60 3 143 2 Pd/Zr-SDC-Br 60 5 71 3 Pd/Zr-SDC-Br70% 60 1 358 4 Pd/Zr-SDC-Br50% 60 0.5 0.8 717 5 Pd/Zr-SDC-Br20% 60 1 6 Zr-SDC 60 3 Zr-SDC-Br 60 5 8 60 3 60 3 10 Pd/Zr-SDC recovered 60 4 Pd/Zr-SDC 60 2 5 mg 4 mL hydrogen 0.5 reaction temperature, 60 °C for and which required The TOF was calculated by the of by the of The is with the optimized Pd/Zr-SDC-Br50% as a representative As in Table 1 and Supporting Information Table and are nearly into corresponding product with selectivities at the same reaction conditions. In addition, and also excellent hydrodeoxygenation conversion by the reaction temperature to °C. results a for the developed Pd/Zr-SDC-Br50% catalyst which is promising for further in upgrading biomass into high value-added To the boosted catalytic performances, the states of catalysts are carefully by X-ray spectroscopy Figure show the Pd and Br respectively. The Pd/Zr-SDC nanocomposite shows the peak with a of and for Pd and Pd respectively, which can be to the Pd of Pd peak towards is out for the full brominated Pd/Zr-SDC-Br which partial electron from Pd NPs to SDC-Br Pd/Zr-SDC-Br70%, Pd/Zr-SDC-Br50%, and Pd/Zr-SDC-Br20% Pd peaks at of and for Pd and Pd respectively, which are to the of PdBr2 during the high-temperature debromination process. Meanwhile, the of observed gradually as the debromination of Pd/Zr-SDC-BrX% nanocomposite the Br with corresponding and peaks of and respectively, are from Pd/Zr-SDC-BrX% except for initial SDC-Br the of according to the peak areas as the debromination of Pd/Zr-SDC-BrX% nanocomposite To the of the of of catalytic Pd pristine Pd/Zr-SDC, the of Pd is at (Figure for the of Pd Br towards the as evidenced by the yellow and Pd with of and (Figure respectively. The

Topics & Concepts