Basicity-Tuned Hydrotalcite-Supported Pd Catalysts for Aerobic

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Basicity-tuned hydrotalcite supported Pd catalysts for aerobic oxidation of 5-hydroxymethyl-2-furfural under mild conditions Yanbing Wang, Kai Yu, Da Lei, Wei Si, Yajun Feng, Lan-Lan Lou, and Shuangxi Liu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00965 • Publication Date (Web): 03 Aug 2016 Downloaded from http://pubs.acs.org on August 6, 2016

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ACS Sustainable Chemistry & Engineering

Basicity-tuned hydrotalcite supported Pd catalysts for aerobic oxidation of 5-hydroxymethyl-2-furfural under mild conditions

Authored by Yanbing Wang a,b, Kai Yu b*, Da Lei a,b, Wei Si a, Yajun Feng b, Lan-Lan Lou a,c, and Shuangxi Liu a,c,d**

a

Institute of New Catalytic Materials Science and Key Laboratory of Advanced

Energy Materials Chemistry (Ministry of Education), School of Materials Science and Engineering, Nankai University, Tianjin 300350, People's Republic of China b

MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of

Environmental Science and Engineering, Nankai University, Tianjin 300350, People's Republic of China c

National Institute of Advanced Materials, Nankai University, Tianjin 300350, People's Republic of China

d

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, People's Republic of China

* Corresponding author: Tel: +86-22-85358635; E-mail: [email protected] ** Corresponding author: Tel/Fax: +86-22-23509005; E-mail: [email protected]

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Abstract An

environmentally

benign

and

homogeneous

base-free

route

for

5-hydroxymethyl-2-furfural (HMF) aerobic oxidation to 2,5-furandicarboxylic acid (FDCA) in water was reported using Mg-Al-CO3 hydrotalcite supported Pd nanoparticles (xPd/HT-n) as catalyst. The influences of Mg/Al molar ratio of hydrotalcite and Pd loading amount on the catalytic performance of these catalysts were originally systematically investigated. These catalysts exhibited excellent catalytic activity and FDCA selectivity in the HMF oxidation, especially for 2%Pd/HT-5 and 2%Pd/HT-6, >99.9% FDCA yield were achieved for 8 h under ambient pressure and homogeneous base-free conditions. The remarkably improved catalytic performance could be attributed to the suitable basicity of Mg-Al-CO3 hydrotalcite and the abundant OH- groups on the surface of hydrotalcite. The plausible reaction mechanism was proposed based on the results of a series of controlled experiments. Furthermore, these catalysts were quite stable and could be reused at least five times without obvious loss in reaction activity.

Keywords Mg-Al-CO3 hydrotalcite; Homogeneous base-free; 5-Hydroxymethyl-2-furfural; Aerobic oxidation; Basicity-tuned.

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Introduction For the numerous impacts of the increased emission of greenhouse gases and the depletion of fossil fuels, biomass, as a sustainable and green candidate resource, has considerable potential to serve as both renewable energy and alternative feedstock for chemical industry1-4. 5-Hydroxymethyl-2-furfural (HMF), a versatile intermediate from inexpensive and plentiful cellulosic derivate C6 carbohydrates, has been effectively synthesized and used as a key precursor for the production of biodiesel and fine chemicals5. The final oxidation product of HMF, 2,5-furandicarboxylic acid (FDCA), is one of the selected top value added platform chemicals from biomass. It could be a monomer for the production of new polyesters and nylons6 as a hopeful alternative to widely used terephthalic acid, which is currently applied for the production of polyethylene terephthalate (PET). Therefore the oxidation of HMF to FDCA is considered as an important and valuable reaction for biorenewable resource. As a furan derivate with an aldehyde group and a hydroxymethyl group, HMF could be oxidized to several possible products, such as 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 5-formyl-2-furancarboxylic acid (FFCA), and final product FDCA. In order to design a green synthesis method from HMF to FDCA without classic stoichiometric oxidants, various catalysts have been developed, including noble metal nanocatalysts7-33, transition metal catalysts34-38, and enzyme catalysts39, 40. Transition metal catalysts sometimes needed organic solvents and exhibited lower activity and FDCA yield34-38, while supported noble metal nanocrystals showed desirable activity and FDCA selectivity with H2O as reaction

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medium and O2 as oxidant13-15, 18, 22-24. Thus the studies on supported noble metal nanocatalysts received much attention in the last decades. Pd7, Ru8-11, Au12-17, Pt18-21 and their bimetal nanoparticles22-26 were supported onto the surface of carbon18, 19, 22, 26

, zeolite14, and metal oxides23, 30, 31, etc. Under carefully adjusted conditions, most of

these catalysts were efficient in the oxidation of HMF. Especially, Villa et al.

22

reported Au8-Pd2/AC as a highly active and stable catalyst to convert 200 folds (molar ratio) HMF to FDCA in 2 hours. However, under normal conditions, high oxygen pressure (up to 4 MPa) and high homogeneous base concentration (up to 10 equivalents of NaOH) were required in these reaction systems. From green chemistry point of view, converting HMF to FDCA using molecular oxygen as oxidant and H2O as reaction medium under ambient pressure and homogeneous base-free condition was an amazing and promising route. Mg-Al hydrotalcite as a solid base catalyst with diverse and tunable functions for a wide range of applications exhibited great potential in the oxidation of biomass derivates12, 13, 41-45

. Recently, Gupta et al.13 reported hydrotalcite supported Au nanoparticles and

their use in the oxidation of HMF by O2 under ambient pressure in the absence of homogeneous base. A total conversion of HMF to FDCA could be achieved after 7 h. Ardemani et al.12 focused on the effect of metallic gold nanoparticles concentration onto the hydrotalcite surface on the catalytic activity of Au/hydrotalcite catalyst for aerobic oxidation of HMF and explored the reaction mechanism through operando XAS study. Hydrotalcite supported Pt42-44 and Pt-Au45 were also applied as catalysts for the selective oxidation of glycerol and 1,2-propanediol in homogeneous base-free

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aqueous solution. However, to the best of our knowledge, there is not any research that employs the hydrotalcite supported Pd nanoparticles as catalyst for aerobic oxidation of HMF. Moreover, seldom related research has focused on the influence of basicity of hydrotalcite on the catalytic performance of noble metal/hydrotalcite catalysts. In this work, the Pd nanoparticles were supported onto the surface of Mg-Al-CO3 hydrotalcites with different Mg/Al molar ratios and the obtained catalysts were used in the oxidation of HMF by molecular oxygen in water under ambient pressure and homogeneous base-free conditions. The effect of hydrotalcite basicity on the catalytic activity was originally investigated and the plausible reaction mechanism was proposed. A highly efficient and quite stable catalyst could be obtained for HMF aerobic oxidation to FDCA by tuning the basicity of hydrotalcite.

Experimental Materials All chemicals were obtained from commercial sources and used as received. HMF (97%) and FDCA (98%) were purchased from Heowns Biochemical Technology Co.,Ltd. HMFCA (98%) was obtained from Matrix Scientific. FFCA (98%) was provided by Toronto Research Chemicals Inc. DFF (98%) was supplied by Sun

Chemical

Technology

Co.,Ltd.

Magnesium

nitrate

hexahydrate

(Mg(NO3)2·6H2O), aluminum nitrate nonahydrate (Al(NO3)3·9H2O), urea (CO(NH2)2), sodium hydroxide (NaOH), potassium chloride (KCl) and palladium chloride (PdCl2) were purchased from Aladdin Industrial Corporation. Activated carbon was purchased

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from Beijing HWRK Chem Co.,Ltd. Characterization Powder X-ray diffraction (XRD) patterns were recorded on a Bruker D8 FOCUS diffractometer with Cu Kα (λ=1.541 Å) operating at 40 kV and 40 mA collected in the 2θ of 5–80º with a scanning rate of 0.2º s-1. X-ray photo-electron spectroscopy (XPS) spectra were obtained using a Kratos Axis Ultra DLD spectrometer employing a monochromatized Al Kα X-ray source (hν=1486.6 eV). Survey spectra were recorded with a pass energy of 160 eV, and high resolution spectra with a pass energy of 40 eV. All binding energies (BEs) were corrected with reference to the C1s peak (BE=284.6 eV) of carbon contaminants as an internal standard. Transmission electronic microscope (TEM) images were obtained by an FEI Tecnai G2 F20 instrument. The sample powder was dispersed by ultrasonic in ethanol and dropped onto a formvar stabilized with carbon support film for observation. The content of metal ion in solution was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) on an IRIS Intrepid II XSP instrument from Thermo Fisher Scientific Inc. The pH values were detected by a Rex PHS-3C pH meter equipped with an E-201-C pH electrode from INESA Scientific Instrument Co.,Ltd. The pulse CO chemisorption experiments were performed on a Micromeritics ChemiSorb 2750 Analyzer with a TCD detector at 303 K. Pulses of 10% CO/He were introduced to the catalyst until three successive peaks showed the same peak area. A CO/Pd stoichiometry of 1 was used for calculations46. The reaction solutions were analyzed using an Agilent 1200 series high-performance liquid chromatography (HPLC) equipped with a Waters

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Atlantis T3 column (column oven at 308 K) and a UV-Vis detector operating at 271 nm. 1 mmol/L H3PO4 aqueous solution was used as mobile phase at a flow rate of 1.0 mL/min. Synthesis of hydrotalcite with different Mg/Al molar ratios Mg-Al-CO3 hydrotalcite with different Mg/Al molar ratios were prepared using urea decomposition method as follows: a desired amount of Mg(NO3)2·4H2O and Al(NO3)3·9H2O with a certain molar ratio (Mg/Al=3, 4, 5, 6) were dissolved in water and mixed with a urea solution under stirring. The molar ratio of urea/(Mg+Al) in resulting mixture was maintained at 3.3. This solution was transferred into a closed Teflon vessel in a stainless steel autoclave and crystallized in an oven at 373 K for 24 h. The white solid sample was collected by filtration, washed with water until the filtrate was neutral and dried in oven overnight at 373 K. According to the difference of Mg/Al molar ratio, the obtained samples were marked as HT-n (n=3, 4, 5 or 6). Synthesis of hydrotalcite supported Pd catalysts PdCl2 (0.1 mmol) and KCl (0.2 mmol) were dissolved in 10 mL H2O under stirring for 1 h. Then a desired amount of HT-n was added into the resulting orange solution and the obtained brown suspension was kept under continuous stirring overnight at 303 K. The solid sample was collected by filtration, washed with 2 L water, dried at 373 K and reduced in hydrogen/argon mixture (10%) at 473 K for 2 h to give the catalysts xPd/HT-n. The nominal Pd content (x) in the final catalyst was 1 or 2 wt%, while the results of ICP-AES investigation revealed that the actual Pd loading were 1.03 wt% and 2.14 wt%, respectively. For comparison, the activated

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carbon supported Pd catalysts were synthesized through the same method and denoted as 1%Pd/C and 2%Pd/C. HMF oxidation A suspension of 0.4 mmol HMF and 0.1 g catalyst in 10 mL H2O was heated to 373 K at reflux and bubbled with O2 flow (100 mL/min) with stirring for a certain time. 50 µL reaction mixture was taken out when needed and diluted with 15 mL H2O. Then this liquid sample was syringe-filtered through a 0.2 µm PTFE membrane and analyzed by HPLC.

Results and Discussion Catalyst characterization The obtained HT-n and xPd/HT-n materials were characterized by XRD, TEM and XPS. Figure 1 shows the XRD patterns of as-synthesized HT-n and xPd/HT-n materials. All the obtained HT-n materials exhibited a typical layered double hydroxide (LDH) structure, the characteristic diffraction peaks of (003), (006), (009), (015), (018), (110) and (113) can be perfectly indexed (JCPDS 70-2151). Moreover, no other crystalline phases were observed from the XRD patterns. After loading Pd nanoparticles on HT-n, these characteristic peaks were still well identified. No obvious diffraction peaks of Pd were found from the XRD patterns of xPd/HT-n catalysts due to the low loading amount and small particle size of Pd nanoparticles. The basicities of obtained HT-n materials with different Mg/Al ratios were detected by Hammett indicator titration method according to the reported method47. No color change was observed with adding brilliant cresyl blue (pKa = 11) or

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2,4-dinitroaniline (pKa = 15) as indicators, whereas the alkaline induced color appeared using phenolphthalein (pKa = 9.6) and bromothymol blue (pKa = 7.2) as indicators. It could be concluded that the basic sites of synthesized HT-n materials were mainly derived from weak basic sites (OH- groups, H− = 7.2-9.8) and medium basic sites (Mg–O pairs, H− = 9.8-11), since the strong basic sites (O2−, H− = 11-15.0) weren’t detected47. The basicities of HT-n materials were quantitatively detected by titration using standard benzoic acid solution and the results are listed in Table 1. It could be found that the medium basic sites (mainly derived from Mg–O pairs) of obtained HT-n materials increased regularly with the rise of Mg/Al ratio, while HT-5 exhibited the highest alkali quantity for the weak basic sites (mainly derived from OH- groups) and the total basic sites (Mg–O pairs and OH- groups). In addition, the actual Mg/Al ratios of HT-n materials measured by ICP-AES were similar with the predicted values. Figure 2 describes the TEM images and the Pd particle size distribution of obtained xPd/HT-n catalysts. It could be found that Pd nanoparticles were uniformly dispersed on the surface of hydrotalcites and the average diameters of Pd nanoparticles ranged from 2.7 nm to 3.3 nm. As described in the high-resolution image of 2%Pd/HT-5 catalyst (Figure 2G), the interplanar distance of 0.21 nm suggested that Pd (111) was the dominant crystal plane in these catalysts. The XPS spectra of xPd/HT-5 catalysts are shown in Figure 3. Peaks corresponding to elements Pd, Mg and Al were clearly distinguished. No peak of Cl 2p was detected from the wide-scan spectra indicating the totally removal of chloride

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from K2PdCl4. The Pd 3d5/2 and Pd 3d3/2 peaks with binding energy at 335.8 eV and 341.0 eV could be assigned to Pd0 nanoparticles48, 49. No Pd 3d5/2 and Pd 3d3/2 peaks derived from Pd2+ were observed from Figure 3(C), which indicated that Pd2+ was entirely reduced to Pd0. By comparing Figure 3(A) with 3(B), it could be found that the intensity of Pd 3d peaks significantly enhanced and the peak area ratio of Pd 3d/(Mg 2s+Al 2p) was doubled with the increase of Pd loading amount from 1% to 2% in xPd/HT-5 catalysts. This result is in good agreement with the ICP-AES characterization of xPd/HT-5 catalysts. Effect of hydrotalcite basicity on the catalytic performance To investigate the effect of hydrotalcite basicity on the catalytic performance for HMF oxidation, the obtained xPd/HT-n were employed as catalysts in the aerobic oxidation of HMF and the results are shown in Figure 4 and Figure 5. It could be observed that HMF could be completely converted to oxidation products over most of obtained xPd/HT-n catalysts at ambient pressure for 7 h in the absence of homogeneous base. No side reaction of HMF was detected by quantitative HPLC determination. It indicates that Mg-Al-CO3 hydrotalcite is a high-performance and environmentally benign alternative catalyst support for HMF oxidation. It was also clearly demonstrated from Figure 4 and Figure 5 that the catalytic performance of xPd/HT-n was obviously related to the Mg/Al molar ratio of Mg-Al-CO3 hydrotalcite. As Mg/Al molar ratio increased from 3 to 5, the activity of xPd/HT-n catalysts remarkably improved, whereas the catalyst activity was decreased when Mg/Al molar ratio furtherly increased from 5 to 6. Both the catalysts

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1%Pd/HT-5 and 2%Pd/HT-5 exhibited the best catalytic performance among the obtained catalysts with the same Pd loading. It suggested that Mg-Al-CO3 hydrotalcite with Mg/Al molar ratio close to 5 has the most positive effect for HMF oxidation. Taking into account the negligible difference of crystallinity of HT-n materials with different Mg/Al molar ratios and Pd nanoparticle sizes of xPd/HT-n catalysts, the conclusions could be drawn that the basicity of Mg-Al-CO3 hydrotalcite could obviously influence the catalytic performance of xPd/HT-n catalysts for HMF oxidation and HT-5 was the most suitable support for xPd/HT-n catalysts. The basicity characterization (as described in Table 1) showed that basic sites in obtained HT-n materials were mainly derived from OH- groups and Mg–O pairs. The aldehyde group of HMF could be nucleophilic attacked by OH- groups on hydrotalcite. Then a catalytic dehydrogenation reaction could take place on active nano Pd particles and thus the carboxyl group would be generated. Therefore, the notably enhanced catalytic performance of xPd/HT-5 compared with xPd/HT-6 could be attributed to the increased weak basic sites (OH- groups) of HT-5. The pH values of reaction solution catalyzed by 2%Pd/HT-5 were detected using a pH meter at hourly intervals. Furthermore, in order to figure out whether some soluble homogeneous bases exist, the reaction solution was filtrated by a 0.22 µm filter to exclude the solid-base catalyst. Table 2 lists the pH values of reaction solutions before and after filtration. It could be found that the pH value of reaction solution containing 2%Pd/HT-5 catalyst was 9.0, while it gradually decreased from 9.0 to 8.0 through 3 h reaction, which could be derived from the generation of acid

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products, such as HMFCA, FFCA and FDCA. When the solid-base catalyst was filtrated from the reaction solution, the pH values of filtrate were in the range of 7.7-6.6. The near-neutral pH values of filtered reaction solution suggested that the activation of substrates mainly occurred on the surface of solid-base catalysts. Effect of Pd loading on the catalytic performance The Pd loading on xPd/HT-n catalysts was another important factor to influence the catalytic performance of xPd/HT-n catalysts. In this work, 1%Pd/HT-n and 2%Pd/HT-n catalysts were synthesized and used in the aerobic oxidation of HMF under the same dosage. The reaction results are described in Figure 4 and Figure 5. The actual Pd loading of these catalysts were detected by ICP-AES, which was in full accordance with the nominal Pd content. The TEM images of 1%Pd/HT-n and 2%Pd/HT-n catalysts (as shown in Figure 2) confirmed that Pd nanoparticles were uniformly dispersed on support surface and the average particle size of Pd was similar for these catalysts. No obvious agglomeration of Pd nanoparticles was observed for 2%Pd/HT-n although the Pd loading on the surface of HT-n had doubled. It could be found that with the increase of Pd loading from 1% to 2%, the yield of FDCA was significantly improved. More than 90% of HMF was oxidized to FDCA in 7 h over 2%Pd/HT-n catalysts. However, among 1%Pd/HT-n catalysts, only 1%Pd/HT-5 exhibited comparable catalytic performance with 2%Pd/HT-n catalysts. It could be attributed to the fact that more Pd nanoparticles were involved in the oxidation reaction and more catalytic active sites were provided when 2%Pd/HT-n were used as catalysts.

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While the phenomenon could also be observed from Figure 4 and Figure 5 that 2%Pd/HT-3 and 2%Pd/HT-4 exhibited lower initial reaction rate than 1%Pd/HT-3 and 1%Pd/HT-4. It could be explained by that the amount of OH- groups on hydrotalcite played a key role in the oxidation of HMF. Even though more Pd active sites were involved in the reaction, the catalysts 2%Pd/HT-n cannot perform better than 1%Pd/HT-n in initial reaction rate when the Mg/Al molar ratio of hydrotalcite was low. However, when the Mg/Al molar ratio of hydrotalcite was high, the abundant OH- groups and more Pd active sites on the surface of hydrotalcite could significantly motivate the HMF oxidation. 2%Pd/HT-5 exhibited the best catalytic efficiency, 99.4% HMF conversion and 91.9% FDCA yield were obtained through 3 h oxidation under mild conditions. After 7 h of reaction, >99.9% HMF conversion and >98% FDCA yield could be obtained over 2%Pd/HT-5 and 2%Pd/HT-6. Further prolonging the reaction time to 8 h, >99.9% FDCA yield could be achieved over these two catalysts. In order to compare catalytic activity of 1%Pd/HT-5 and 2%Pd/HT-5 more quantitatively, turnover frequency (TOF) results were calculated from the conversion at 10 min reaction using the equation (1) as follows. In this equation, Pd dispersion is the ratio of surface Pd to total Pd of the catalyst, which was determined through CO chemisorption and the values were 36% for 1%Pd/HT-5 and 38% for 2%Pd/HT-5. nHMF/nPd means the molar ratio of HMF to Pd. The calculated TOF value of 1%Pd/HT-5 is 0.48 min-1 and that of 2%Pd/HT-5 is 0.86 min-1. The TOF value of 2%Pd/HT-5 is about 1.8 times as high as that of 1%Pd/HT-5, which further

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indicated the excellent catalytic performance of 2%Pd/HT-5 in the aerobic oxidation of HMF under mild conditions. ( ) =

(%)×( / ) ()× !

(1)

Plausible reaction mechanism The synthesized xPd/HT-n catalysts exhibited excellent catalytic performance in the aerobic oxidation of HMF under mild conditions. To investigate the role of Mg-Al-CO3 hydrotalcite in this reaction, a series of controlled experiments were carried out and the results are listed in Table 3. It could be found that HT-5 had no detectable activity in this reaction system. Without adding any base, the 1%Pd/C and 2%Pd/C catalysts exhibited relatively much lower catalytic activity (HMF conversion99.9% after five runs, which indicated that the 2%Pd/HT-5 catalyst is quite stable. The used 2%Pd/HT-5 catalyst for five runs was characterized by XRD, TEM and ICP-AES. Figure 7 shows the XRD patterns of fresh and used 2%Pd/HT-5 catalyst. It could be found that the characteristic diffraction peaks of hydrotalcite were maintained and the intensities of these peaks decreased slightly after five runs, which could be attributed to the Mg leaching from hydrotalcite support (about 3% of Mg was leaching after each run). The TEM images of used 2%Pd/HT-5 catalyst (as shown in Figure 8) displayed that the Pd nanoparticles still uniformly dispersed on the surface of support. No obvious agglomeration of Pd nanoparticles was observed and the average diameter of Pd nanoparticles was kept at 3.0 nm after five runs. The Pd content of used 2%Pd/HT-5 catalyst was determined by ICP-AES and only 0.02% of Pd was leached from catalyst after five runs. It means that the obtained xPd/HT-n catalysts were quite stable in this aerobic oxidation system and could be recycled at least five times without significant loss in reaction activity.

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A series of Mg-Al-CO3 hydrotalcites with different Mg/Al molar ratios were synthesized and employed as matrixes to support Pd nanoparticles. According to the results of basicity determination by Hammett indicator titration, the basicities of obtained Mg-Al-CO3 hydrotalcite materials were studied. The obtained catalysts were characterized by XRD, TEM, and XPS. The typical LDH structure of Mg-Al-CO3 hydrotalcite and uniform dispersion of Pd nanoparticles on hydrotalcite surface were confirmed. The Mg/Al molar ratio and Pd loading amount were found to have significantly influences on the activity and selectivity of these catalysts. The optimized Mg/Al molar ratio of Mg-Al-CO3 hydrotalcite is 5 for this reaction system, which could be attributed to the highest alkali quantity for weak basic sites (OH- groups) of HT-5. The catalyst 2%Pd/HT-5 exhibited the best catalytic activity and FDCA selectivity, >99.9% FDCA yield were achieved for 8 h under mild conditions. According to the results obtained in this work, the plausible reaction mechanism of aerobic oxidation of HMF over Mg-Al-CO3 hydrotalcite supported Pd catalysts was proposed. Furthermore, these catalysts were quite stable in this reaction system, and could be easily recovered by centrifugation and reused at least five times without significant loss in reaction activity.

Associated Content Supporting Information TEM image of HT-5 hydrotalcite, high-resolution XPS spectra of K 2p region for xPd/HT-5 catalysts and spectra of Mg element for HT-n samples, catalytic

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performance of 1%Pd/HT-5 under different HMF/Pd molar ratios, catalyst stability tests with lower HMF conversions.

Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 21203102), the Tianjin Municipal Natural Science Foundation (Grant Nos. 14JCQNJC06000, 14JCZDJC32000 and 15JCTPJC63500) and MOE (IRT13R30).

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References: (1) Serrano-Ruiz, J. C.; Luque, R.; Sepulveda-Escribano, A. Transformations of Biomass-derived Platform Molecules: From High Added-value Chemicals to Fuels via Aqueous-phase Processing. Chem. Soc. Rev. 2011, 40, 5266-5281. (2) Shuttleworth, P. S.; De bruyn, M.; Parker, H. L.; Hunt, A. J.; Budarin, V. L.; Matharu, A. S.; Clark, J. H. Applications of Nanoparticles in Biomass Conversion to Chemicals and Fuels. Green Chem. 2014, 16, 573-584. (3) Besson, M.; Gallezot, P.; Pinel, C. Conversion of Biomass into Chemicals over Metal Catalysts. Chem. Rev. 2013, 114, 1827-1870. (4) Sheldon, R. A. Green and Sustainable Manufacture of Chemicals from Biomass: State of the Art. Green Chem. 2014, 16, 950-963. (5) van Putten, R.-J.; van der Waal, J. C.; de Jong, E.; Rasrendra, C. B.; Heeres, H. J.; de Vries, J. G. Hydroxymethylfurfural, A Versatile Platform Chemical Made from Renewable Resources. Chem. Rev. 2013, 113, 1499-1597. (6) Eerhart, A. J. J. E.; Faaij, A. P. C.; Patel, M. K. Replacing Fossil Based PET with Biobased PEF; Process Analysis, Energy and GHG Balance. Energy Environ. Sci. 2012, 5, 6407-6422. (7) Siyo, B.; Schneider, M.; Pohl, M.-M.; Langer, P.; Steinfeldt, N. Synthesis, Characterization, and Application of PVP-Pd NP in the Aerobic Oxidation of 5-Hydroxymethylfurfural (HMF). Catal. Lett. 2014, 144, 498-506. (8) Gorbanev, Y.; Kegnæs, S.; Riisager, A. Effect of Support in Heterogeneous Ruthenium Catalysts Used for the Selective Aerobic Oxidation of HMF in Water.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Top. Catal. 2011, 54, 1318-1324. (9) Gorbanev, Y.; Kegnæs, S.; Riisager, A. Selective Aerobic Oxidation of 5-Hydroxymethylfurfural in Water over Solid Ruthenium Hydroxide Catalysts with Magnesium-based Supports. Catal. Lett. 2011, 141, 1752-1760. (10) Artz,

J.;

Palkovits,

R.

Base-Free

Aqueous-Phase

Oxidation

of

5-Hydroxymethylfurfural over Ruthenium Catalysts Supported on Covalent Triazine Frameworks. ChemSusChem 2015, 8, 3832-3838. (11) Nie, J.; Xie, J.; Liu, H. Activated Carbon-supported Ruthenium as an Efficient Catalyst for Selective Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran. Chinese J. Catal. 2013, 34, 871-875. (12) Ardemani, L.; Cibin, G.; Dent, A. J.; Isaacs, M. A.; Kyriakou, G.; Lee, A. F.; Parlett, C. M. A.; Parry, S. A.; Wilson, K. Solid Base Catalysed 5-HMF Oxidation to 2,5-FDCA over Au/hydrotalcites: Fact or Fiction? Chem. Sci. 2015, 6, 4940-4945. (13) Gupta, N. K.; Nishimura, S.; Takagaki, A.; Ebitani, K. Hydrotalcite-supported Gold-nanoparticle-catalyzed Highly Efficient Base-free Aqueous Oxidation of 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid under Atmospheric Oxygen Pressure. Green Chem.2011, 13, 824-827. (14) Cai, J.; Ma, H.; Zhang, J.; Song, Q.; Du, Z.; Huang, Y.; Xu, J. Gold Nanoclusters Confined in a Supercage of Y Zeolite for Aerobic Oxidation of HMF under Mild Conditions. Chem.–Eur. J. 2013, 19,14215-14223. (15) Casanova, O.; Iborra, S.; Corma, A. Biomass into Chemicals: Aerobic Oxidation

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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of 5-Hydroxymethyl-2-furfural into 2,5-Furandicarboxylic Acid with Gold Nanoparticle Catalysts. ChemSusChem 2009, 2, 1138-1144. (16) Saha,

B.;

Dutta,

S.;

Abu-Omar,

M.

M.

Aerobic

Oxidation

of

5-Hydroxylmethylfurfural with Homogeneous and Nanoparticulate Catalysts. Catal. Sci. Technol. 2012, 2, 79-81. (17) Gorbanev, Y. Y.; Klitgaard, S. K.; Woodley, J. M.; Christensen, C. H.; Riisager, A. Gold-Catalyzed Aerobic Oxidation of 5-Hydroxymethylfurfural in Water at Ambient Temperature. ChemSusChem 2009, 2, 672-675. (18) Ait Rass, H.; Essayem, N.; Besson, M. Selective Aqueous Phase Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Pt/C Catalysts: Influence of the Base and Effect of Bismuth Promotion. Green Chem. 2013, 15, 2240-2251. (19) Davis, S. E.; Benavidez, A. D.; Gosselink, R. W.; Bitter, J. H.; de Jong, K. P.; Datye, A. K.; Davis, R. J. Kinetics and Mechanism of 5-Hydroxymethylfurfural Oxidation and Their Implications for Catalyst Development. J. Mol. Catal. A: Chem. 2013, 388-389, 123-132. (20) Siankevich, S.; Savoglidis, G.; Fei, Z.; Laurenczy, G.; Alexander, D. T. L.; Yan, N.; Dyson, P. J. A Novel Platinum Nanocatalyst for the Oxidation of 5-Hydroxymethylfurfural

into

2,5-Furandicarboxylic

Acid

Under

Mild

Conditions. J. Catal. 2014, 315, 67-74. (21) Davis, S. E.; Zope, B. N.; Davis, R. J. On the Mechanism of Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Supported Pt and

22


Page 23 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Au Catalysts. Green Chem. 2012, 14, 143-147. (22) Villa, A.; Schiavoni, M.; Campisi, S.; Veith, G. M.; Prati, L. Pd-modified Au on Carbon as an Effective and Durable Catalyst for the Direct Oxidation of HMF to 2,5-Furandicarboxylic Acid. ChemSusChem 2013, 6, 609-612. (23) Albonetti, S.; Lolli, A.; Morandi, V.; Migliori, A.; Lucarelli, C.; Cavani, F. Conversion of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Au-based Catalysts: Optimization of Active Phase and Metal–support Interaction. Appl. Catal., B: Environ. 2015, 163, 520-530. (24) Albonetti, S.; Pasini, T.; Lolli, A.; Blosi, M.; Piccinini, M.; Dimitratos, N.; Lopez-Sanchez, J. A.; Morgan, D. J.; Carley, A. F.; Hutchings, G. J.; Cavani, F. Selective Oxidation of 5-Hydroxymethyl-2-furfural over TiO2-supported Gold– Copper Catalysts Prepared from Preformed Nanoparticles: Effect of Au/Cu Ratio. Catal. Today 2012, 195, 120-126. (25) Pasini, T.; Piccinini, M.; Blosi, M.; Bonelli, R.; Albonetti, S.; Dimitratos, N.; Lopez-Sanchez, J. A.; Sankar, M.; He, Q.; Kiely, C. J.; Hutchings, G. J.; Cavani, F.

Selective

Oxidation

of 5-Hydroxymethyl-2-furfural using

Supported

Gold-copper nanoparticles. Green Chem. 2011, 13, 2091-2099. (26) Wan, X.; Zhou, C.; Chen, J.; Deng, W.; Zhang, Q.; Yang, Y.; Wang, Y. Base-Free Aerobic Oxidation of 5-Hydroxymethyl-furfural to 2,5-Furandicarboxylic Acid in Water Catalyzed by Functionalized Carbon Nanotube-Supported Au–Pd Alloy Nanoparticles. ACS Catal. 2014, 4, 2175-2185. (27) Yi, G.; Teong, S. P.; Li, X.; Zhang, Y. Purification of Biomass-Derived

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Page 24 of 42

5-Hydroxymethylfurfural and Its Catalytic Conversion to 2,5-Furandicarboxylic Acid. ChemSusChem 2014, 7, 2131-2135. (28) Zope, B.; Davis, S.; Davis, R. Influence of Reaction Conditions on Diacid Formation

During

Au-Catalyzed

Oxidation

of

Glycerol

and

Hydroxymethylfurfural. Top. Catal. 2012, 55, 24-32. (29) Davis, S. E.; Houk, L. R.; Tamargo, E. C.; Datye, A. K.; Davis, R. J. Oxidation of 5-Hydroxymethylfurfural over Supported Pt, Pd and Au Catalysts. Catal. Today 2011, 160, 55-60. (30) Triebl, C.; Nikolakis, V.; Ierapetritou, M. Simulation and Economic Analysis of 5-Hydroxymethylfurfural Conversion to 2,5-Furandicarboxylic Acid. Comput. Chem. Eng. 2013, 52, 26-34. (31) Menegazzo, F.; Fantinel, T.; Signoretto, M.; Pinna, F.; Manzoli, M. On the Process for Furfural and HMF Oxidative Esterification over Au/ZrO2. J. Catal. 2014, 319, 61-70. (32) Zhou, C.; Deng, W.; Wan, X.; Zhang, Q.; Yang, Y.; Wang, Y. Functionalized Carbon Nanotubes for Biomass Conversion: The Base-Free Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Platinum Supported on a Carbon Nanotube Catalyst. ChemCatChem 2015, 7, 2853-2863. (33) Liu, B.; Ren, Y.; Zhang, Z. Aerobic Oxidation of 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid in Water under Mild Conditions. Green Chem. 2015, 17, 1610-1617. (34) Partenheimer, W.; Grushin, V. V. Synthesis of 2,5-Diformylfuran and

24


Page 25 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Furan-2,5-Dicarboxylic

Acid

by

Catalytic

Air-Oxidation

of

5-Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal/Bromide Catalysts. Adv. Synth. Catal. 2001, 343, 102-111. (35) Deng, J.; Song, H.-J.; Cui, M.-S.; Du, Y.-P.; Fu, Y. Aerobic Oxidation of Hydroxymethylfurfural and Furfural by Using Heterogeneous CoxOy–N@C Catalysts. ChemSusChem 2014, 7, 3334-3340. (36) Zhang, Z.; Liu, B.; Lv, K.; Sun, J.; Deng, K. Aerobic Oxidation of Biomass Derived 5-Hydroxymethylfurfural into 5-Hydroxymethyl-2-furancarboxylic Acid Catalyzed by a Montmorillonite K-10 Clay Immobilized Molybdenum Acetylacetonate Complex. Green Chem. 2014, 16, 2762-2770. (37) Saha, B.; Gupta, D.; Abu-Omar, M. M.; Modak, A.; Bhaumik, A. Porphyrin-based Porous Organic Polymer-supported Iron(III) Catalyst for Efficient Aerobic Oxidation of 5-Hydroxymethyl-furfural into 2,5-Furandicarboxylic Acid. J. Catal. 2013, 299, 316-320. (38) Zuo, X.; Venkitasubramanian, P.; Busch, D. H.; Subramaniam, B. Optimization of Co/Mn/Br-Catalyzed

Oxidation

of

5-Hydroxymethylfurfural

to

Enhance

2,5-Furandicarboxylic Acid Yield and Minimize Substrate Burning. ACS Sustainable Chem. Eng. 2016, 4, 3659–3668. (39) Dijkman, W. P.; Fraaije, M. W. Discovery and Characterization of a 5-Hydroxymethylfurfural Oxidase from Methylovorus sp. Strain MP688. Appl. Environ. Microb. 2014, 80, 1082-1090.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 42

(40) Dijkman, W. P.; Groothuis, D. E.; Fraaije, M. W. Enzyme-Catalyzed Oxidation of 5-Hydroxymethylfurfural to Furan-2,5-dicarboxylic Acid. Angew. Chem. Int. Ed. 2014, 53, 6515-6518. (41) Takagaki, A.; Takahashi, M.; Nishimura, S.; Ebitani, K. One-Pot Synthesis of 2,5-Diformylfuran from Carbohydrate Derivatives by Sulfonated Resin and Hydrotalcite-Supported Ruthenium Catalysts. ACS Catal. 2011, 1, 1562-1565. (42) Tongsakul, D.; Nishimura, S.; Ebitani, K. Effect of Stabilizing Polymers on Catalysis of Hydrotalcite-Supported Platinum Nanoparticles for Aerobic Oxidation of 1,2-Propanediol in Aqueous Solution at Room Temperature. J. Phys. Chem. C 2014, 118, 11723-11730. (43) Tsuji, A.; Rao, K. T. V.; Nishimura, S.; Takagaki, A.; Ebitani, K. Selective Oxidation of Glycerol by Using a Hydrotalcite-Supported Platinum Catalyst under Atmospheric Oxygen Pressure in Water. ChemSusChem 2011, 4, 542-548. (44) Tongsakul, D.; Nishimura, S.; Thammacharoen, C.; Ekgasit, S.; Ebitani, K. Hydrotalcite-Supported Platinum Nanoparticles Prepared by a Green Synthesis Method for Selective Oxidation of Glycerol in Water Using Molecular Oxygen. Ind. Eng. Chem. Res. 2012, 51, 16182-16187. (45) Tongsakul,

D.;

Nishimura,

S.;

Ebitani,

K.

Platinum/Gold

Alloy

Nanoparticles-Supported Hydrotalcite Catalyst for Selective Aerobic Oxidation of Polyols in Base-Free Aqueous Solution at Room Temperature. ACS Catal. 2013, 3, 2199-2207. (46) Zhang, C.; Li, Y.; Wang, Y.; He, H. Sodium-Promoted Pd/TiO2 for Catalytic

26


Page 27 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Oxidation of Formaldehyde at Ambient Temperature. Environ. Sci. & Technol. 2014, 48, 5816-5822. (47) Zeng, H.-Y.; Xu, S.; Liao, M.-C.; Zhang, Z.-Q.; Zhao, C. Activation of Reconstructed Mg/Al Hydrotalcites in the Transesterification of Microalgae Oil. Appl. Clay Sci. 2014, 91–92, 16-24. (48) Zhang, Z.; Zhen, J.; Liu, B.; Lv, K.; Deng, K. Selective Aerobic Oxidation of the Biomass-derived Precursor 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid under Mild Conditions over a Magnetic Palladium Nanocatalyst. Green Chem. 2015, 17, 1308-1317. (49) Ma, Z.; Yang, H.; Qin, Y.; Hao, Y.; Li, G. Palladium Nanoparticles Confined in the Nanocages of SBA-16: Enhanced Recyclability for the Aerobic Oxidation of Alcohols in Water. J. Mol. Catal. A: Chem. 2010, 331, 78-85. (50) Shumaker, J. L.; Crofcheck, C.; Tackett, S. A.; Santillan-Jimenez, E.; Crocker, M. Biodiesel Production from Soybean Oil using Calcined Li–Al Layered Double Hydroxide Catalysts. Catal. Lett. 2007, 115, 56-61. (51) Fraile, J. M.; García, N.; Mayoral, J. A.; Pires, E.; Roldán, L. The Influence of Alkaline Metals on the Strong Basicity of Mg–Al Mixed Oxides: The Case of Transesterification Reactions. Appl. Catal. A: Chem. 2009, 364, 87-94. (52) Cross, H. E.; Brown, D. R. Entrained Sodium in Mixed Metal Oxide Catalysts Derived from Layered Double Hydroxides. Catal. Commun. 2010, 12, 243-245. (53) Savara, A.; Chan-Thaw, C. E.; Rossetti, I.; Villa, A.; Prati, L. Benzyl Alcohol Oxidation on Carbon-Supported Pd Nanoparticles: Elucidating the Reaction

27



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Mechanism. ChemCatChem 2014, 6, 3464-3473. (54) Davis, S. E.; Ide, M. S.; Davis, R. J. Selective Oxidation of Alcohols and Aldehydes over Supported Metal Nanoparticles. Green Chem. 2013, 15, 17-45. (55) Lolli, A.; Albonetti, S.; Utili, L.; Amadori, R.; Ospitali, F.; Lucarelli, C.; Cavani, F. Insights into the Reaction Mechanism for 5-Hydroxymethylfurfural Oxidation to FDCA on Bimetallic Pd–Au Nanoparticles. Appl. Catal., A: Chem. 2015, 504, 408-419. (56) An, G.; Ahn, H.; De Castro, K. A.; Rhee, H. Pd/C and NaBH4 in Basic Aqueous Alcohol: An Efficient System for an Environmentally Benign Oxidation of Alcohols. Synthesis 2010, 3, 477-485. (57) Yamaguchi, K.; Mizuno, N. Supported Ruthenium Catalyst for the Heterogeneous Oxidation of Alcohols with Molecular Oxygen. Angew. Chem. Int. Ed. 2002, 41, 4538-4542. (58) Mori,

K.;

Hara,

T.;

Hydroxyapatite-Supported

Mizugaki, Palladium

T.;

Ebitani,

Nanoclusters:

K.; A

Kaneda, Highly

K.

Active

Heterogeneous Catalyst for Selective Oxidation of Alcohols by Use of Molecular Oxygen. J. Am. Chem. Soc. 2004, 126, 10657-10666.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 Characterization of the Mg/Al molar ratio and basicity of HT-n materials Alkali quantity (mmol/g) Sample Mg/Al molar ratio a H− ≥7.2 b

H− ≥9.6 c

9.6≥H− ≥7.2 d

HT-3

2.7

0.68

0.28

0.40

HT-4

3.9

0.95

0.48

0.47

HT-5

4.9

1.42

0.61

0.81

HT-6

5.8

1.34

0.70

0.64

a

Detected by ICP-AES.

b

The indicator was bromothymol blue.

c

The indicator was phenolphthalein.

d

Caculated through the equation: Alkali quantity(9.6≥H− ≥7.2) = Alkali quantity(H−

≥7.2) - Alkali quantity(H− ≥9.6)

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 2 pH values of reaction solutions using 2%Pd/HT-5 as catalyst pH values of

pH values of

reaction solution

filtered solution

0

9.0

7.7

1

8.2

7.7

2

8.1

7.3

3

8.0

6.6

Reaction time (h)

30


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3 Catalytic aerobic oxidation of HMF into FDCA with different catalystsa Yield (%)

Time

HMF Conversion

(h)

(%)

HMFCA

FFCA

FDCA

HT-5

7

0.0

0.0

0.0

0.0

1%Pd/C

7

30.3

9.6

87.8

2.5

2%Pd/C

3

26.2

8.3

87.1

4.6

1%Pd/C + HT-5

7

78.1

23.1

44.8

32.0

1%Pd/HT-5

7

99.0

5.1

3.7

91.3

2%Pd/C + HT-5

3

74.6

24.6

33.8

41.6

2%Pd/HT-5

3

99.4

1.3

6.3

92.4

2%Pd/C+HT-5 leaching

3

28.2

16.2

73.8

9.9

Catalysts

a

Reaction conditions: HMF 40 mmol L-1, H2O 10 mL, 373 K, with O2 bubbling.

31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. XRD patterns of HT-n (A), 1%Pd/HT-n materials (B) and 2%Pd/HT-n materials (C). Figure 2. TEM images with Pd particle size distribution of the catalysts of 1%Pd/HT-n (A-D for n=3, 4, 5 and 6) and 2%Pd/HT-n (E-H for n=3, 4, 5 and 6). Figure 3. XPS spectra of 1%Pd/HT-5 (A, C) and 2%Pd/HT-5 (B, D). Figure 4. Reaction profiles for the oxidation of HMF with 1%Pd/HT-n catalysts at ambient pressure, Reaction conditions: HMF 40 mmol L-1, H2O 10 mL, HMF/Pd (mol mol-1) = 40, 373 K, with O2 bubbling (100 mL/min). Figure 5. Reaction profiles for the oxidation of HMF with 2%Pd/HT-n catalysts at ambient pressure, Reaction conditions: HMF 40 mmol L-1, H2O 10 mL, HMF/Pd (mol mol-1) = 20, 373 K, with O2 bubbling (100 mL/min). Figure 6. Recycling tests of 2%Pd/HT-5 for the aerobic oxidation of HMF. Figure 7. XRD patterns of (A) fresh 2%Pd/HT-5 and (B) used 2%Pd/HT-5. Figure 8. TEM images with Pd particle size distribution of the used 2%Pd/HT-5 catalyst. Scheme 1. Plausible reaction mechanism of aerobic oxidation of HMF to FDCA over xPd/HT-n catalysts.

32


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Page 33 of 42

(003)

Figure 1.

(110) (113)

(018)

(015)

HT-6

Intensity(a.u.)

(009)

(006)

(A)

HT-5

HT-4

HT-3 10

20

30

40

50

60

70

2Theta (degree)

(B)

Intensity (a.u.)

1%Pd/HT-6

1%Pd/HT-5

1%Pd/HT-4

1%Pd/HT-3 10

20

30

40

50

60

70

2Theta (degree)

(C) 2%Pd/HT-6

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2%Pd/HT-5

2%Pd/HT-4 2%Pd/HT-3 10

20

30

40

50

60

2Theta (degree)

33


70


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2.

34


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Page 35 of 42

Figure 3.

(A)

(B) Counts (s)

Counts (s)

Pd 3d

Pd 3d

Mg 2s

Mg 2s Al 2p

Al 2p

400

350

300

250

200

150

100

50

0

400

350

300

Binding Energy (eV)

250

200

150

100

50

Binding Energy (eV)

Pd 3d5/2

Pd 3d5/2

(C)

(D)

Pd 3d3/2

346

344

342

340

Counts (s)

Pd 3d3/2

Counts (s)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


338

336

346

334

344

342

340

338

Binding Energy (eV)

Binding Energy (eV)

35


336

334

0


Figure 4. 100

HMF HMFCA FFCA FDCA

80

1%Pd/HT-3 60

40

20

Yield/Conversion (%)


100

HMF HMFCA FFCA FDCA

80

1%Pd/HT-4

60

40

20

0

0 0

1

2

3

4

5

6

0

7

1

2

3

4

5

6

7

Time (h)

Time (h) 100

100

80

1%Pd/HT-5 60 HMF HMFCA FFCA FDCA

40

20


80


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 42

1%Pd/HT-6

60

HMF HMFCA FFCA FDCA

40

20

0

0 0

1

2

3

4

5

6

0

7

1

2

3

4

Time (h)

Time (h)

36


5

6

7

Page 37 of 42

Figure 5. 100

100 HMF HMFCA FFCA FDCA

HMF HMFCA FFCA FDCA

80

2%Pd/HT-3 60

40

20



80

2%Pd/HT-4 60

40

20

0

0 0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

Time (h)

Time (h) 100

100

80

80

2%Pd/HT-5

60

40 HMF HMFCA FFCA FDCA

20



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2%Pd/HT-6 60

40

HMF HMFCA FFCA FDCA

20

0

0 0

1

2

3

4

5

6

0

7

1

2

3

4

Time (h)

Time (h)

37


5

6

7


Figure 6.

HMF Conv. (%)

HMF Conv.

FDCA Yield

100

100

80

80

60

60

40

40

20

20

0

0 1

2

3

4

Run

38


5

FDCA Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 42

Page 39 of 42

Figure 7.

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(A)

(B) 10

20

30

40

50

60

2Theta (degree)

39


70

80


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8.

40


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1.

41



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

For Table of Contents Use Only Basicity-tuned hydrotalcite supported Pd catalysts for aerobic oxidation of 5-hydroxymethyl-2-furfural under mild conditions Yanbing Wang, Kai Yu, Da Lei, Wei Si, Yajun Feng, Lan-Lan Lou, and Shuangxi Liu

Mg-Al-CO3 hydrotalcite supported Pd serves as a green and highly efficient catalyst for aerobic oxidation of HMF to FDCA under mild conditions.

42


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Basicity-Tuned Hydrotalcite-Supported Pd Catalysts for Aerobic

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