Article Cite This: Ind. Eng. Chem. Res. 2019, 58, 10844−10854
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Highly Selective Production of 2,5-Dimethylfuran from Fructose through Tailoring of Catalyst Wettability Kaiyue Ji,† Chun Shen,*,†,‡ Jiabin Yin,† Xinqiang Feng,† Hao Lei,† Yuqing Chen,† Nan Cai,† and Tianwei Tan*,† †
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Beijing Key Laboratory of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, No. 15 of North Three-Ring East Road, Chaoyang District, Beijing 100029, PR China ‡ The State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China S Supporting Information *
ABSTRACT: Aiming at the highly selective production of 2,5-dimethylfuran (DMF) from fructose, a one-pot strategy and bifunctional catalysts with different surface wettability were specially designed. The hydrophobic surface assisted in weakening side reactions and promoting the adsorptive property for the hydrogen donator. The as-prepared Pd/ PDVB-S-143 catalyst showed high activity and good stability: Yield of 94.2% was obtained under mild reaction conditions, and no loss in activity was observed after 5 cycles. From the standpoint of green and sustainable chemistry, there may be several possible advantages. HMF separation is avoided, reducing the amount of organic solvent and energy expenditure for purifying HMF; besides, polymethylhydrosiloxane (PMHS) was used as the hydrogen source, increasing the convenience and efficiency of the whole process. Overall, this work demonstrates a successful strategy for rational design and preparation of novel catalysts with both high activity and superior selectivity during biomass upgrading. catalyze HMF into DMF under mild reaction conditions.11 Gortea et al. used bimetallic Pt alloys with Ni, Zn, or Cu to reach a higher selectivity to DMF, up to 98%.12 Furthermore, to limit the expense of catalyst, various research efforts substituted noble catalysts by non-noble catalysts, without hampering the selectivity for DMF from HMF. Wang et al. used Ni/Co3O4,13 whereas Zhu et al. developed Ni−Si−PS.14 Fu et al. exploited Ni-WC/AC and Cu−Co@C was explored by Yuan et al.15,16 In recent studies, some unique insights were focused on feasible application of other hydrogen source, such as cyclohexanol, which was applied by Li et al., who used nitrogen-doped carbon-decorated copper catalyst and Ni−Fe alloy yielding 96.1% and >97.0% DMF from HMF respectively.17,18 Li and Fan et al. investigated CuNi bimetallic as electrode, creatively electro-synthesizing DMF from HMF with water as hydrogen source.19 Although all these above-mentioned catalysts have exhibited a potential to achieve the production of DMF from HMF on a largescale, the high cost of HMF and its highly difficult separation from solvents severely restricted their further
1. INTRODUCTION The increasing depletion of fossil fuel movtivates research of producing biomass-based liquid fuels. It has been estimated that one-third of transportation fuels consumed in the USA could be obtained from a renewable resource.1,2 2,5Dimethylfuran (DMF) is identified as one of the best potential additive liquid fuels, with a higher octane number of 119, an ideal boiling point (92−94 °C), and an energy content 31.5 MJ/L, similar to that of gasoline (35 MJ/L) and exceeding that of ethanol (23 MJ/L). Compared with ethanol, DMF has a moreover lower latent heat of vaporization (300 vs 710 MJ/L), a lower oxygen content (O/C = 0.17 vs 0.5), and water miscibility (2.3 g/L), which favor the processes of purification and distillation as well as further application such as direct use as a fuel additive and its possible conversion into p-xylene via a Diels−Alder reaction with ethylene.3−7 The initial strategy for producing DMF stems from the hydrogenolysis of the biomass-based compound 5-hydroxylmethylfurfural (HMF), obtained by acid-catalyzed dehydration of C-6 sugars (e.g, fructose, glucose).8 Previous works such as Rauchfuss et al. utilized Pd/Carbon as catalyst to determine the mechanisms of decarbonylation, hydrogenation, and hydrogenolysis of HMF.9 Schuth et al. reported a DMF yield up to 98% on Pt−Co nanoparticles encapsulated in hollow carbon spheres.10 Wang et al. prepared Ru/Co3O4 to © 2019 American Chemical Society
Received: Revised: Accepted: Published: 10844
March 19, 2019 May 28, 2019 May 30, 2019 May 30, 2019 DOI: 10.1021/acs.iecr.9b01522 Ind. Eng. Chem. Res. 2019, 58, 10844−10854
Article
Industrial & Engineering Chemistry Research
Figure 1. (a) SEM images of Pd/PDVB-S-143; (b−d) TEM images of Pd/PDVB-S-143; (e) size distribution histogram of Pd/PDVB-S-143.
application.20−22 Therefore, a strategy of one-pot production of DMF from the raw material would be a promising pathway for the direct conversion of biomass into useful biofuels. Dumesic et al. initially conceived a tandem reaction combing HCl with bimetallic CuRu/carbon as catalysts for directly converting fructose into DMF.23 Thananatthanachon and Rauchfuss utilized formic acid to achieve the cascading reaction from fructose to DMF over Pd/C.24 Wei et al. applied a catalysis system composed of a mixture of AlCl3 with H3PO4 and Ru/C for the one-pot conversion of fructose to DMF.25 In the work of Jaehoon and co-workers, Pd species was loaded on a Zr-based metal−organic framework (UIO66), and 70.5 mol % DMF was achieved from fructose through one-pot conversion.26 However, two factors heavily hamper the application of this simple mixture strategy. The first relates to the general feature of inorganic acids with related issues of difficult recovering and equipment corrosion; the second comprises the low yield of DMF obtained directly from fructose. Normally, two ingredients are essential to obtain DMF from fructose (i.e., acid sites for the dehydration and
metal sites for HDO). In this respect, Fang et al. anchored palladium (Pd) on heterogeneous acid, and achieved a yield 85% DMF from fructose coupled with polymethylhydrosiloxane (PMHS).27 Moreover, the intermediates and side products seem to be the main limitations in yielding DMF from fructose.3,21,28,29 One of the notorious problems is the extremely high activity of HMF, which serves as a vital precursor of occurring side reactions in producing DMF. It hampers the production of DMF from fructose and is hence unfavorable.30−32 Efficiently producing HMF and raising its stability in the reaction system are hence crucial preconditions to guarantee a high yield of DMF in the whole process. Recent advancements in interfacial materials with special wettability have already been applied to many areas.33−38 In the heterogeneous catalyst, suitable wettability of the catalyst could improve the product selectivity, such example as oxidation of ethylbenzene, the major product was transferred from phenylethanol (64.5% selectivity) to acetophenone (84.6% selectivity) after introduction of superhydrophobic surface.39 In the work of Xiao et al., the highly selective 10845
DOI: 10.1021/acs.iecr.9b01522 Ind. Eng. Chem. Res. 2019, 58, 10844−10854
Article
Industrial & Engineering Chemistry Research Table 1. Property of the Various PDVB Catalysts compound
acid density (mmol/g)a
Pd amount (wt %)b
CA (deg)
SBET (m2/g)c
Vp (cm3/g)d
Dp (nm)e
PDVB-155 Pd/PDVB-153 PDVB-S-145 Pd/PDVB-S-143 Pd/PDVB-S-103 Pd/PDVB-S-0 Pd/PDVB-SS-140 Pd/PDVB-S-144
0 0 0.35 0.3 0.25 0.24 0.49 0.31
0 0.76 0 0.79 0.7 0.85 0.74 0.74
155 153 145 143 103 0 140 144
848.1 833.5 815.7 790.5 750.4 693.1 743.8 770.4
1.84 1.82 1.84 1.8 1.89 1.92 1.83 1.79
13 12.7 12.9 12.8 9.8 11.5 12.5 12.6
a
Measured by acid−base titration. bMeasured by ICP-MS. cBET surface area. dTotal pore volume. eAverage pore size. fCatalyst after 5 cycles.
Figure 2. (a) FT-IR spectra of Pd/PDVB-S-143 and Pd/PDVB-S-0. (b) 13C MAS NMR spectra of Pd/PDVB-S-143. (c) 13C MAS NMR spectra of d/PDVB−S-I. (d) XPS analysis for Pd 3d spectra of Pd/PDVB-S-143. (e) TG-Curve of Pd/PDVB-S-143 and Pd/PDVB-S-0.
wettability might also affect the whole reaction pathway. The catalytic activity is intimately related to the surface wettability in all these steps since it significantly affects the affinity of the catalyst toward the reactants, intermediates and products, especially in liquid−solid biphasic catalysis.41−46 In view of the crucial support chemistry to attach metal sites and exert profound influences on the affinity toward various
production of HMF from fructose (99.0% yield of HMF) has been realized by adjusting catalyst wettability: It is reported that the superhydrophobic surface assists in avoiding HMF decomposition and improves the stability of HMF in the reaction system.40 To our knowledge, the influence of wettability might not be confined to a sole reactant, and slight changes in catalyst 10846
DOI: 10.1021/acs.iecr.9b01522 Ind. Eng. Chem. Res. 2019, 58, 10844−10854
Article
Industrial & Engineering Chemistry Research
giving a steep rise at a relative pressure of 0.7−0.95, indicating the presence of a mesoporous structure. Correspondingly, the pore size distributions further confirm the mesoporous structures in the range of 10−50 nm (Figure S3). Other BET results are given in Table 1. PDVB-155 has the largest surfaces area of 848 m2/g, while the reduction in the surface area of other samples are attributed to the introduction of sulfonic groups or MEBA, as also demonstrated previously.48 Figure 2a shows the FT-IR spectra of Pd/PDVB-S-A 143 and Pd/PDVB-S-0. They exhibit several characteristic peaks of a copolymeric framework: The peak around 3023 cm−1 results from C−H stretching vibrations in the benzene ring, and those at 1601, 1510, and 1448 cm−1 are also ascribed to the existence of benzene ring. Both samples show a peak at 1694 cm−1 which is assignable to ν(CO) of acylamide on pyrrolidinone;49 Pd/ PDVB-S-0 presents a pair of consecutive vibration peaks around 1664 cm−1, proving the existence of extra ν(CO) of acylamide which belongs to MEBA embedded into the PDVB backbones. Moreover, an obvious peak at 1009 cm−1 is assignable to ν(C−S), and bands at 1039, 1128, 1179 cm−1 correspond to ν(OSO) indicating the presence of sulfonic groups in both samples. Furthermore, a comparison of the PDVB-S-A before and after Pd NPs deposits (Figure S4) detected no obvious differences regarding the characteristic peaks of S element in FT-IR on both samples. Solid-state 13C NMR spectra (Figure 2b,c) analyzes Pd/ PDVB-S-143 and Pd/PDVB-S-0 respectively. The board overlapping peak at 28 and 40 ppm is ascribed to a methylene unit that connected with ketone and other carbon atoms in the alkyl-chain, respectively. A sharpened peak at 127 ppm corresponds to C9 and C10 atoms, while 144 ppm refers to C8 and C11 of the benzene ring. For the acylamide, a weak peak at 174 ppm is related to the C4 atom in Pd/PDVB-S-143. In contrast, Pd/PDVB-S-0 exhibits an intense peak at the same ppm resulting from introducing extra MEBA in the backbones, and an acute peak at 63 ppm is ascribed to C14 atom on Pd/ PDVB-S-0. These observations confirm the existence of MEBA in the polymeric backbone in Pd/PDVB-S-0 and reflect the copolymerization of DVB and other functioned groups as shown in Scheme S1 for the chemical structures. The metallic nature state of Pd NPs in Pd/PDVB-S-143 is investigated by X-ray photoelectron spectroscopy (XPS). Figure 2d shows the XPS signals in the binding energy region of 330−348 eV which is fitted to two sets of peaks, corresponding to Pd 3d5/2 and Pd 3d3/2 on Pd 3d spectrum.50 The relatively lower binding energy set of spin−orbit doublet at 336.4 (3d5/2) and 341.5 eV (3d3/2) is attributed to Pd(0) species, and the other set of doublets at 338.4 (3d5/2) and 343.7 eV (3d3/2) is related to Pd(II) species. The Pd 3d core level is deconvoluted into two spin−orbit split components with binding energies of 336.4 and 338.2 eV. The component at 336.4 eV is assigned to Pd(0), slightly higher than the one for clean Pd metal (334.6 eV).50 Quantitative calculation of the peak area in Figure 2d indicates that the major part of the Pd NPs is Pd(0), while the rest of the balance is in the Pd(II) state because the surface of Pd NPs is easily reoxidized when exposed to air. Moreover, the peak intensities of N 1s XPS data (Figure S4) among Pd/PDVB-S-X (X = 0, 103, 143) are strengthened with the increased amount of MEBA indicating the extra introduction of N on Pd/PDVB-S-103 and Pd/ PDVB-S-0.51 In addition, S 2pXPS spectrum of both Pd/ PDVB-S-143 and Pd/PDVB-S-0 (Figure S4) result in the same
reactants due to a wetting discrepancy in different catalysts, our research utilizes the flexible features of polydivinylbenzene (PDVB) through selecting or designing task-specific monomers to realize an adjustment of the catalyst wettability arbitrarily and introduced acid sites. A simple method in situ reduction with alcohol solution45−47was then adopted by anchoring Pd as metal sites to achieve the tandem reaction and produce DMF from fructose directly and efficiently coupled with PMHS. Catalytic performances of catalysts with different wettability were investigated in DMF production from fructose. A possible reaction pathway was proposed based on the analysis of behavior of different catalysts.
2. RESULTS AND DISCUSSION 2.1. Synthesis and Characterizations of Catalysts. Scheme S1 outlines the synthetic routes of copolymerization and the corresponding catalyst decorated with Pd nanoparticles, noted as Pd/PDVB-S-X [X is the contact angle (CA) of the catalyst and water droplet]. The three steps involved include the following: (i) build the copolymer with different surface wettability by adjusting the ingredients during the hydrothermal process (considering the hydrophilic nature of the N,N-methylenediacrylamide (MEBA) unit, copolymers with higher hydrophilicity would be synthesized by increasing MEBA amount); (ii) to acquire acid sites, by grafting sodium p-styrenesulfonate onto the backbone of PDVB and then the obtained polymer was ion-exchanged with sulfuric acid, substituting Na+ for H+; (iii) to immobilize Pd nanoparticles (NPs) by reducing the palladium precursor K2PdCl4 with ethylene glycol/glycerol. Starting compositions for synthesizing catalysts with various surface wettability are listed in Table S1. Images of the water contact angle within different catalysts in Figure S1 show a sheer framework based on PDVB present the maximum CA of 155°. The value dropped from 155 to 145° after the introduction of sulfonic groups onto PDVB backbones. Moreover, PDVB-S-111 and PDVB-S-0 were obtained when molar ratios of PDVB/MEBA were 10 and 5, respectively.45 The scanning electron microscopy (SEM) image (Figure 1a) indicates that the morphology of these polymers is loose but highly cross-linked. Transmission electron microscopy (TEM) images are depicted in Figure 1b−d, indicating that Pd NPs are uniformly dispersed on the catalyst surface, with a mean diameter of 4.4 nm (Figure 1e). Similarly, both Pd/PDVB-S103 and Pd/PDVB-S-0 exhibit average diameters of Pd NPs of 4.6 nm (Figure S2), indicating that introducing extra MEBA onto backbones of PDVB exerts little influence on the size distributions of Pd NPs. Besides, lattice fringes with a width of 0.23 nm, which contributed to Pd (1 1 1) planes could be clearly observed in all the samples (Pd/PDVB-S-X) (Figures 1d and S2). The amount of Pd loaded is detected by ICP-MS, as shown in Table 1. Since values vary insignificantly regardless of the surface wettability, results revealing that Pd NPs could be deposited on the supporting materials stably and reliably. Moreover, acid−base titration was used to verify the acid amounts of all the samples (Table 1). Copolymers with different wettabilities and the same amounts of p-styrenesulfonate give the similar results of acid amounts. The nitrogen isotherms of Pd/PDVB-S-143, Pd/PDVB-S103, and Pd/PDVB-S-0 catalysts are shown in Figure S3. All the nitrogen sorption isotherms present typical type-IV curves, 10847
DOI: 10.1021/acs.iecr.9b01522 Ind. Eng. Chem. Res. 2019, 58, 10844−10854
Article
Industrial & Engineering Chemistry Research Table 2. Catalytic Performances under Different Conditions in the Direct Production of DMF from Fructose yield (%) no.
catalyst
F/Mb
X (%)
DMF
DMTHF
HMF
MFA
MFF
DHMF
HDO
1 2 3 4c 5c 6c 7d 8e 9 10 11f
Pd/PDVB-S-143 Pd/PDVB-S-103 Pd/PDVB-S-0 Pd/PDVB-S-143 Pd/PDVB-S-103 Pd/PDVB-S-0 Pd/PDVB-S-143 Pd/PDVB-S-143 Pd/PDVB-S-143 Pd/PDVB-153 Pd/PDVB-SS-140
100 100 100 50 50 50 100 100 200 100 100
>99 >99 >99 >99 98.1 >99 >99 >99 >99 >99 >99
94.2 43.1 10 92.1 49.6 12.8 18.9 52.5 63.4 34.6 90.1
4 2.8 1 5.4 3.1
