Inclusion of Zn into Metallic Ni Enables Selective and Effective

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Inclusion of Zn into metallic Ni enables selective and effective synthesis of 2,5-dimethylfuran from bio-derived 5-hydroxymethylfurfural Xiao Kong, Yifeng Zhu, Hongyan Zheng, Yulei Zhu, and Zhen Fang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01813 • Publication Date (Web): 24 Oct 2017 Downloaded from http://pubs.acs.org on October 26, 2017

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ACS Sustainable Chemistry & Engineering

Inclusion of Zn into metallic Ni enables selective and effective synthesis of 2,5-dimethylfuran from bio-derived 5-hydroxymethylfurfural Xiao Kong,[a] Yifeng Zhu,[b] Hongyan Zheng,[c] Yulei Zhu*[c,d] and Zhen Fang*[a] [a]

College of Engineering, Nanjing Agricultural University, Nanjing 210031, PR China.

[b]

State key laboratory of catalysis, Dalian Institute of chemical physics, Chinese academy of

sciences, Dalian 116023, PR China. [c]

Synfuels China Co. Ltd, Beijing, 101407, PR China.

[d]

State key laboratory of coal conversion, Institute of coal chemistry, Chinese academy of

sciences, Taiyuan 030001, PR China.

Corresponding authors

∗

E-mail address: [email protected] (Zhen Fang), [email protected] (Yulei Zhu).

1

ACS Paragon Plus Environment


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Abstract: 5-Hydroxymethylfurfural (HMF) is an important platform chemical derived from C6 sugars and cellulose. The formed 2,5-dimethylfuran (DMF) via hydrogenolysis of HMF was denoted as a promising and sustainable fuel candidate. The further improvement of DMF yield is the central premise, which based on the elucidation of the relationship between catalytic performance and active sites. Herein, a NiZn alloy catalyst was formed due to Zn inclusion to Ni by controllable reduction of NiZnAl hydrotalcite-derived NiO-ZnO-Al2O3 mixed oxide. The combination of temperature-programmed reduction (TPR), in situ X-ray diffraction (XRD), CO-adsorbed infrared spectroscopy (CO-IR) and X-ray photoelectron spectroscopy (XPS) revealed that the surface of the NiZn catalyst was composed of β1-NiZn while the bulk was composed of α-NiZn. Moreover, the surface Ni atoms were geometrically isolated by Zn atoms and modulated to be electron-rich. Finally, the rate of C=O/C-O hydrogenolysis over C=C/C-C hydrogenation for NiZn alloy catalyst was approximately three times higher than that of monometallic Ni catalyst. A 93.6% yield of DMF was obtained over NiZn alloy catalyst. The greatly improved DMF yield was thus attributed to the electron modification and isolation of Ni atoms due to the formation of NiZn alloy.

Keywords: biomass; 5-hydroxymethylfurfural; hydrogenation; Ni; intermetallic

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Introduction The rapid depletion of fossil resources and the growing concerns about global warming stimulated

the

research

on

clean

biofuel

production

from

renewable

resources.

5-Hydroxymethylfurfural (HMF) is a platform chemical derived from cellulose and C6 sugar. The selective hydrogenolysis of HMF could form 2,5-dimethylfuran (DMF) (Scheme 1), which is an alternative and sustainable fuel with high energy density (30 kJ/cm3) and octane number (RON=119).1 Besides, the unsaturated furanic ring of DMF facilitates the production of various chemicals (e.g., p-xylene) by Diels-Alder reactions, which is also an important process.2,3 Various noble metals (e.g. Pt, Ru and Pd) have been studied for DMF synthesis, while the high price hindered their further application.1,4-10 Design of non-noble catalysts attracts great attention. Especially, bifunctional Ni-based catalysts (e.g., Ni-W2C/AC, NiSi-PS, Ni-Al2O3, Ni/Co3O4 and Ni-Co/C) were demonstrated with high efficiency.11-15 For this process, 2,5-dimethyltetrahydrofuran (DMTHF) and C-C cracking products (e.g., 2-methylfuran, C1-C5 alkane and tetrahydrofuran) are easily formed over some of them (Scheme 1).12,16,17 Development of non-noble catalyst with superior C=O/C-O hydrogenolysis ability and suppressed C=C/C-C session ability is important for achieving high selectivity, which may also have implications for selective hydrogenation of unsaturated aldehydes. (Scheme 1) Alloying and/or fabrication of intermetallic compounds are good choices for catalysts with such ability.18-20 For example, compared with Ni/Al2O3 catalyst, Ni-In intermetallic compound was highly selective for furfural hydrogenation to furfuryl alcohol, due to electron transfer and active-site isolation in the Ni-In intermetallic compound21. Ni-Ga intermetallic compound was proposed for semihydrogenation of phenylacetylene with suppressed ability for complete hydrogenation.20 Ni-Sn-based alloy catalyst exhibited an efficient hydrogenation ability of C=O rather than C=C in the hydrogenation of unsaturated carbonyl compounds.22 Bimetallic Ni-Fe/CNT catalyst was reported with a 91.3% yield of DMF due to the NiFe alloy formation.23 The Zn modified metal catalysts including PtZn, RuZn were also frequently investigated for selective hydrogenation of α,β-unsaturated aldehydes.19,24 The PtZn alloy formation for Pt/ZnO catalyst could change the adsorption mode of arotonaldehyde and exhibited high selectivity for 3



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crotyl alcohol.19 RuZn alloy was reported with changed electron structure enhanced the cyclohexene selectivity from benzene hydrogenation.24 The unique catalytic properties of alloys/intermetallic compounds could be routed from the “electronic effect”, an electron transfer between metals resulting in a modified adsorption/desorption properties, a “geometric effect” leading to weakly π–bonded reactants on top of isolated metal atoms, and a “kinetic effect” due to the decreased availability of hydrogen.25 Yet, fabrication strategy and potential application of the base NiZn alloy were merely reported. Nørskov et al.26 firstly predicted NiZn alloy as a good candidate for acetylene removal with avoiding further C=C saturation, using density functional theory calculations. This result demonstrated that NiZn alloy is promising for reservation of C=C bonds. Rioux group showed that the decrease of adsorption energy of acetylene was the main reason for the enhanced selectivity to ethylene for bulk NiZn.27,28 Moreover, they reported that strong interaction between Ni and ZnO support could contribute the formation of Ni1−xZnx alloy after reduction while decrease the ability of Ni/ZnO to dissociate H2.28 Despite of the modulated catalytic properties, the NiZn alloy catalyst has never been reported for selective hydrogenation of C=O/C-O bonds. Herein, NiZn alloy was determined via reduction of mixed oxide from NiZnAl hydrotalcite due to Zn inclusion to metallic Ni. The NiZn alloy was highly selective for DMF synthesis from HMF with a yield of 93.6%, which was greatly higher than that of monometallic Ni catalyst (Scheme 1). The XRD, TPR, XPS and CO-IR characterizations demonstrated the structural evolution from hydrotalcite precursor to mixed oxides with strong interactions, and then to the NiZn species with an alloy bulk (α-NiZn) and intermetallic overlayer (β1-NiZn). The superior performance of NiZnAl derived catalyst was thus attributed to the modulated electron density and geometric properties of Ni due to NiZn alloy formation. This work also opens up a novel avenue for developing efficient Ni-based catalysts for selective hydrogenation of C=O/C-O versus C=C/C-C bonds.

Experimental Details Catalyst preparation

4


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All the samples were prepared by constant-pH co-precipitation method employing NaOH/Na2CO3 as precipitating agent.29 For NiZnAl catalyst, an aqueous solution containing the Ni(NO3)2•6H2O, Zn(NO3)2•6H2O and Al(NO3)3•9H2O and a solution containing Na2CO3 and NaOH were simultaneously added to beaker under vigorous stirring at 63 oC. The Ni/Zn/Al molar ratio in solution was 1:1:1. The precipitate was aging at 63 oC for 18 h. Then the precipitate was filtered, washed and dried at 63 oC for 24 h and then calcined at 600 oC in air for 4 h. The catalysts with different Ni/Zn ratios were also prepared as references by the constant-pH co-precipitation method as described for NiZnAl catalyst, including NiZnAl(1:3) and NiZnAl(3:1). The NiAl (Ni loading: 28.5 wt. %) and ZnAl (Zn loading: 31.4 wt. %) references were prepared in the similar way.

Catalyst characterization The BET surface area was tested via N2 physical adsorption at -196 oC by a Micromeritics ASAP 2420 instrument. Before tests, the samples were degassed at 90 oC for 1 h and 350 oC for 8 h. XRD pattern of precursor and calcined NiZnAl was recorded by an X-ray diffractometer (MiniFlex II, Rigaku) with Cu kα radiation. In situ XRD patterns of reduced samples were recorded by a Bruker D8 Advance diffractometer with Cu kα radiation at a rate of 10 oC/min under 40 ml/min of 30 vol. % H2/Ar. XRD patterns of used catalyst were performed over a Bruker D8 Advance diffractometer with Cu kα radiation. The ICP experiments were conducted on PerkinElmer Optima2100DV. Temperature programmed reduction (TPR) and H2 temperature programmed desorption (H2-TPD) were conducted on a Tianjin XQ TP-5080 instrument equipped with a TCD detector. For TPR experiment, 20 mg catalyst was loaded into a quartz tube and heated in 30 mL/min of 10 vol. % H2/N2 at a rate of 10 oC/min. For H2-TPD experiment, the catalysts (100 mg) were first reduced at 500 oC for 2 h. The catalysts were then purged with N2 to remove the physisorbed H2 at 50 oC for 1 h until the baseline was smoothing. Subsequently, the catalysts were heated to 750 oC with a rate of 10 oC/min. The surface Ni amounts were estimated from the areas. High-resolution transmission electron microscopy (HRTEM) measurements were carried out on a JEM-2100F operated at 200 keV. X-ray photoelectron spectroscopy (XPS) spectra of reduced catalysts were recorded on a Thermo XPS ESCALAB 250Xi spectrometer equipped with a monochromatic Al Kα (1486.8 eV) source after an in-situ reduction at 500 oC under H2. 5



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Temperature programmed desorption of NH3 (NH3-TPD) experiments were conducted on the AutoChem II. 2920 instrument (Micromeritics, USA) equipped with a mass spectrum detector. The catalysts (100 mg) were reduced in H2 at 500 oC for 2 h and saturated with NH3 and then purged with He to remove the physisorbed NH3 at 100 oC for 30 min. Subsequently, the catalysts were heated to 700 oC with a rate of 10 oC/min. For CO-IR experiments, the catalysts were first reduced in H2 at 500 oC for 2 h and then cooled to room temperature under He to remove the physisorbed H2. After that, the catalysts were adsorbed with CO for 0.5 h at room temperature. Subsequently, the CO was closed and the catalysts were blowed under He flow. The data was recorded every minute and that used in the paper was obtained after blowing 12 min in He at room temperature.

Catalyst tests The tests were performed in a 100 ml tank reactor. Prior to the test, the catalysts were reduced in a quartz tube under H2 flow at 500 oC for 2 h. The reduced catalysts were then protected by 1,4-dioxane and transferred to the reactor. For a typical procedure, the reactor was fed with HMF (1.5 g), 1,4-dioxane (35 ml) and a certain amount of pre-reduced catalyst, then sealed and purged by H2 (5 times). After that, the reactor was filled with 1.5 MPa H2 and heated-up to 180 oC. The timing was started at the moment the temperature reached the desired value. After the test, the reactor was quenched in ice-water, and then the products were analyzed by a GC instrument with a FID detector and a capillary column (J&W DB-WAX). The stability of NiZnAl catalyst for DMF synthesis was also investigated. The catalyst was reused directly after separation by centrifugation, without further washing or other treatment. For the product analyzation, the detector and inlet temperatures were set at 250 oC. The product was analyzed by the following oven heat procedure: started at 40 oC for 6 min, increased the temperature with a rate of 8 oC/min until 220 oC and held at 220 oC for 20 min. The products were identified by GC-MS and comparison of retention times of pure chemicals. The pure chemicals including DMF and DMTHF were purchased from TCI Corporation and used as standard samples. The conversion and selectivity were determined by calibrated area normalization.

Results and discussion 6


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Catalyst Characterization (Figure 1) NiZnAl hydrotalcite was prepared by coprecipitation method with a Ni:Zn:Al nominal molar ratio of 1:1:1 (theoretical Ni loading: 28.5 wt. %, Zn loading: 31.4 wt. %). The hydrotalcite precursor could facilitate the formation of highly dispersed and adjacent Ni and Zn metal oxides, which would benefit the reduction of Zn by spillover of H from Ni.24 The catalysts with different Ni/Zn molar ratios were also investigated, including the ratio of 1:3 and 3:1. The effect of Ni/Zn ratios on the catalytic performace will be discussed in the following part. The NiAl (Ni loading: 28.5 wt. %) and ZnAl (Zn loading: 31.4 wt. %) references were prepared in the similar way. ICP results showed the metal loadings were similar with nominal values (Table 1). XRD patterns of the precursor were shown in Figure S1. The XRD pattern of NiZnAl precursor confirmed the hydrotalcite structure, while ZnAl and NiAl samples exhibited Al(OH)3 phase other than pure hydrotalcite structure. XRD patterns of calcined samples were shown in Figure 1. After calcination, diffraction peaks at 37.2o, 43.3o and 62.9o were observed for NiAl catalyst, which were assigned to NiO. Compared with NiAl catalyst, the NiZnAl displayed peaks that shifted to lower angles, which was characteristics of a larger unit cell. The enlargement of the lattice is rooted from the doping of Zn into NiO due to the strong interaction.28 ZnAl sample exihited obvious peaks assigned to ZnAl2O4. N2 adsorption results of calcined samples revealed that NiZnAl exhibited a slightly lower surface area than NiAl (Table 1). The amount of acid sites was also calculated by NH3-TPD and shown in Table 1. No obvious change of acid amounts was found for NiAl and NiZnAl catalysts. (Table 1) (Figure 2) The reducibility of catalysts was investigated using temperature programmed reduction (TPR) (Figure 2). 20 mg catalysts were used in our case. The theoretical amounts of H to reduce NiO were 0.19 mmol for catalyst of 20 mg. Calibration of TPR area of NiAl catalyst was 0.19 mmol (see supporting information), revealing the total reduction of NiO species (Table 1). NiZnAl showed ~1.9 times H-consumption (0.36 mmol) while ZnAl exhibited almost no H-consumption peak. The promoted H-consumption of NiZnAl indicated the reduction of Zn2+ species. Actually, 7



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Zn2+ species are hard to be reduced to metallic Zn by H2, as indicated by the ZnAl catalyst, despite that H2 treatment could generate the oxygen vacancies. The Zn2+ reduction to Zn0 over NiZnAl catalyst might be arised from the metallic Ni. It is documented that hydrogen is dissociatively adsorbed on metallic Ni to form hydrogen atom, which may spillover to reduce adjacent Zn species, as reported in many catalyst systems (e.g., PtZn, RuZn, PdZn).19,24,30 The excessive H-consumption of NiZnAl was thus ascribed to the reduction of ZnO by spillover H atoms from Ni.31 Besides, NiZnAl catalyst exhibited higher reduction temperature than NiAl, indicating the strong interaction between Ni and the support (ZnO, Al2O3), which hindered the reducibility of Ni species.32 The strong interaction would also benefit the stability of Ni. In all, ZnO was reduced with the help of Ni and further decorate the Ni sites, which would be discussed in the following parts. (Figure 3) To determine the structure of metallic species over the reduced catalysts, XRD experiments for NiAl and NiZnAl catalysts reduced at different temperatures were carried out (Figure 3). NiAl-500 catalyst exhibited the diffraction peaks at 44.5o, 51.8o and 76.4o which correspond to the characteristic metallic Ni (dotted lines). In contrast, the peaks of NiZnAl-500 all shifted to lower angles, which might be caused by the the enlargement of unit cell (i.e., inclusion of Zn into the crystal lattice and formation of a Ni-Zn structure (Ni1-xZnx compound) or overlap of NiO. The characteristic peak at 43.3o may overlap that of metallic Ni diffractions at 44.5o. However, the diffraction peaks of Ni species at 51.8 and 76.4 assigned to Ni also shifted (more clearly in Figure 4). Thus, the shift of diffraction peaks of NiZnAl-500 catalyst is induced by the inclusion of Zn atoms into the crystal lattice. The XRD results of NiZnAl catalysts reduced at higher temperatures (NiZnAl-600 and NiZnAl-700) supported the inclusion of Zn atoms. NiO peaks disappeared for both catalysts while the shift of metallic Ni existed and intensified, confirming the formation of Ni1-xZnx alloy. This is in consistent with the literature reports. Zn-dopped NiO could be formed by calcination of nickel nitrate on a nanoparticulate ZnO support. Subsequently, Ni1−xZnx/ZnO alloy was formed after reduction with x increasing with reduction temperature.28 In detail, the Zn-dopped NiO transformed first to Ni-rich NiZn alloy (α-NiZn, e.g., Ni4Zn, Ni0.87Zn0.13, Ni7Zn3) around 400 oC followed by a transformation to β1-NiZn intermetallic at about 525 oC as detected by X-ray 8


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absorption near-edge structure at a rate of 1.3 °C/min under a 50 mL/min flow of 5% H2/He. Different reduction procedures influenced the specific temperature, as a rate of 10 °C/min under a 40 mL/min flow of 30% H2/N2 was used in our case. Nevertheless, the gradual shift of peaks for NiZnAl catalyst also indicated a transformation process, especially for NiZnAl-700 catalyst. The characteristic peaks based on reported works for Ni4Zn (a kind of α-NiZn) and NiZn (i.e., β1-NiZn) were shown in Figure 3, which is in good accordance with the formation of NiZn alloy over NiZnAl catalyst.28,33 (Figure 4) To determine the evolution during NiZn alloy formation, in situ XRD experiments of the catalysts treated under different temperatures (500 oC, 600 oC and 700 oC) were performed (Figure 4). The XRD spectra of different temperatures were recorded at 3 stages (R1, R2 and R3). R1 represents the spectra collected when temperature was just elevated at object reduction temperature; R2 represents the spectra collected when reduction was just finished; R3 represents spectra collected when the temperature was declined to room temperature. The pink lines at the bottom indicate the characteristic peaks of metallic Ni. Compared with metallic Ni, all catalysts exhibited a shift to lower angles due to Ni1-xZnx formation. Besides, for NiZnAl-500 and NiZnAl-600 catalysts, no other shift of the NiZn alloy peaks was observed during the reduction, due to the good stability of NiZn alloy for both catalysts. Instead, for NiZnAl-700 catalyst, the peaks shifted to higher angles gradually during the process, despite of the more pronounced NiZn alloy peaks than NiZnAl-500 and NiZnAl-600 when the temperature was just elevated at 700 oC (NiZnAl-700, R1). The change of NiZnAl-700 catalyst indicated the change of NiZn alloy. A decomposition behavior of β1-NiZn alloy to α-NiZn alloy in methanol steam reforming at 600 oC was once demonstrated by Friedrich et al., likely following the reaction ZnNi+H2O → Ni70Zn30+ZnO+H234. In our case, the high temperature reduction might contribute the β1-NiZn formation for NiZnAl-700, which undergoes decomposition to α-NiZn gradually. That is, the NiZn intermetallic was oxidized to the NiZn alloy with low Zn content. In conclusion, NiZnAl catalysts reduced at 500 and 600 oC mainly consist of stable α-NiZn, while the higher reduction temperature contributes the formation of unstable β1-NiZn. However, the β1-NiZn decomposed during the reduction process, which transformed into NiZn alloy with lower Zn content. The conclusions are also in good consistent with Rioux’s and Friedrich’s research28,34. 9



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Moreover, NiAl-500 and NiZnAl-500 exhibited similar particle size with 7.3 and 5.8 nm respectively, as calculated by Ni (111) reflection based on Scherrer equation (Table 1). HRTEM was used to confirm the mean particle size of both catalysts. NiAl-500 and NiZnAl-500 exhibited mean sizes of 4.8 and 4.4 nm respectively after counting from the HRTEM images, supporting the formation of highly dispersed particles with similar size. However, for NiZnAl-600 and NiZnAl-700 catalysts, larger particle sizes were observed despite of the formation of NiZn alloy with more Zn content. Thus, to better investigate the effect of NiZn alloy formation, NiAl and NiZnAl catalysts reduced at 500 oC were further compared and tested for HMF hydrogenation by minimizing the size effect. (Figure 5) The Zn-L3M45M45 Auger spectra were also used to investigate the reduction of Zn species for NiZnAl-500 (Figure 5). ZnAl catalyst exhibited a peak at 987.3 eV, which was assigned to the Zn species in ZnAl2O4. NiZnAl catalyst showed two peaks at 988 eV and 991 eV, which were attributed to the ZnO and metallic Zn species respectively.35 The above XPS results confirmed the reduction of Zn species over NiZnAl catalyst under 500 oC, which was in good accordance with XRD results and supported the formation of NiZn alloy. Moreover, we quantitatively analyzed the XPS results of reduced NiZnAl catalysts. The surface Zn/Ni atomic ratio is determined to be 1.16. The enrichment of Zn over the surface is also in accordance with the previous reports on strong metal-support interactions (SMSI) proposed firstly by Tauster et al., whereby the partially-reduced Zn species prefer to migrate over the metallic Ni surface.36,37

The ratio was inconsistent with the

composition of Ni-rich NiZn alloy formation (e.g., Ni4Zn, Ni7Zn3, Ni0.87Zn0.13) while was similar with the NiZn intermetallic (β1-NiZn, 1:1). As Bokhoven et al.30 reported, the intermetallic formation started at the surface and the crystallinity increased with reduction temperature. Thus, the surface atomic ratio supported the existence of β1-NiZn intermetallic, in spite of the undetectable formation in XRD. The β1-NiZn intermetallic was confirmed by XRD at 700 oC. (Figure 6) In situ CO-adsorbed infrared spectra (CO-IR) of reduced catalysts was used to reveal the the electron density of the surface Ni and the binding geometry of CO (Figure 6). The bonding of CO to metal atoms is described in terms of the Ni-C d donation and Ni-C π-backbonding.38 The backbonding is related to the occupancy of the Ni (d) orbitals. NiAl catalyst exhibited a band at 10


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2083 cm-1 and a broad band around 1800 cm-1. The two bands could be assigned to the linear and bridged configuration of CO on Ni respectively, which were associated with the atoms located on the terrace and steps.39,40 Compared with NiAl catalyst, the band at 1800 cm-1 associated with the bridged CO adsorption diminished for NiZnAl, revealing that Zn diluted Ni atoms sufficiently and decreased Ni steps, which support the “active-site isolation” effect.21 This further indicated that the surface of NiZnAl catalyst is composed of β1-NiZn species, since the α-NiZn is composed of random arranged and adjacent Ni atoms. Notably, a 40 cm-1 red shift of CO linear adsorption was observed for NiZnAl, indicating the amount decrease of backbonding of the Ni(d) orbitals.38 This could be induced by electron transfer from Zn to the Ni, according to the electronegativity values of Zn (1.65) and Ni (1.9). This is also supported by the reports of Duan et al., that the addition of electropositive species (In, Ga) metals could enhance the charge density of Ni metals.20,21 Combined with in situ XRD and XPS results, it could be concluded that both Ni-rich NiZn alloy and surface NiZn intermetallic (a typical case of alloy) were present for NiZnAl hydrotalcite derived catalyst after the reduction at 500 oC, which can be clasified to α-NiZn and β1-NiZn phase respectively. The clarification of active species for the traditional NiZnAl hydrotalcite derivd catalyst merits substantial works and the further optimizations are also needed. Besides, the nanosized NiZn alloy compounds with geometric-isolated and electron-efficient Ni properties could greatly alter the adsorption of reactants and catalytic performance for hydrogenolysis of C=O bonds. The formation of Ni-rich alloy and NiZn intermetallic by introducing Zn species could attenuate the adsorption of H atoms, thereby influencing the hydrogenation ability of Ni.28 H2-TPD experiments provide insight into the H2 activation ability of Ni over NiZnAl and NiAl catalysts (Figure S2). Compared with NiAl, a smaller area of H2-TPD peak was observed over NiZnAl. This could be due to the dilution of the Ni sites by Zn inclusion. Besides, an additional broad desorption peak at high temperature was observed for NiZnAl catalyst, which might be attributed to the spillover H2 and/or H2 located in a new surface. In all, the H2-TPD results also supported that the surface structures of NiZnAl and NiAl are different, as discussed in CO-IR results. NH3-TPD experiments were conducted to reveal the effect of Zn addition on catalyst acidity properties (Figure S3). The peaks around 200 oC and 267 oC were observed for NiAl, 11



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corresponding to the weak acid sites, which could be associated with different Al3+ species. Compared with NiAl catalyst, only a slight decrease of desorption area was observed over NiZnAl catalyst. The amounts of acid sites were determined through NH3-TPD results (Table 1). NiAl adsorbed an amount of 0.10 µmolNH3/g, while NiZnAl adsorbed an amount of 0.09 µmolNH3/g. The slight decrese of acid sites might decrease the activity of HMF conversion, due to the fact that Lewis acids are known as active sites benefitting C=O/C-O activation.12 Little works reported the effect of Lewis acid sites for C=C/C-C transformation. Tseng et al.41 experimentally found that the homogeneous Lewis acids remains inactive for C=C activation by attachment of boron Lewis acids to a Ru catalyst, making a superior catalyst for alkyne hydrogenation. Thus, the change of products involves of C=C/C-C hydrogenation (e.g., DMTHF and C-C cracking products) can not be explained by the change of acid sites and effect of acid sites will not be discussed in the following parts.

Catalytic results Catalytic performance of NiZnAl and NiAl for DMF synthesis (Figure 7) NiZnAl and NiAl catalysts upon reduction at 500 oC were tested for HMF hydrogenation and exhibited different catalytic performance (Figure 7). A gradual transformation of HMF and the intermediates

can

be

observed.

The

O-containing

intermediates

mainly

include

2,5-dihydromethylfuran (DHMF), 5-methylfurfuryl alcohol (MFA) and 5-methylfurfural (MFR). A 100% conversion of HMF was observed over NiAl catalyst at 7 h, while HMF was totally converted at 9 h over NiZnAl indicating a slight decrease of activity. As reported in previous works42, the dilution of the Ni site at the surface and electron transfer from Zn to Ni which could occupy the partially vacant d-electron orbital of the Ni atom would decrease the hydrogenation activity. The well-organized metal distributions in the NiZnAl precursor would facilite the formation of highly dispersed Ni sites and benefit the activity. The slight decrease of acid sites over NiZnAl might be also one reason for the slow hydrogenation process, due to the fact that acid sites can benefit the C=O/C-O activation and conversion.12 A control experiment was carried out over ZnAl catalyst at the same condition (Table S1). ZnAl catalyst only exhibited a ~10.1% conversion of HMF, indicating the low hydrogenation ability of ZnAl catalyst. 12


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Further, NiZnAl catalyst exhibited a high DMF yield of 93.6% at at 15 h, which was greatly higher than NiAl catalyst (63.5%) at optimized conditions. Due to the similar particle size and surface acid amounts, the high DMF yield could be attributed to a comprehensive result of the electronic and geometric effect, routed from the Zn inclusion. The enhanced DMF yield could be attributed to the suppressed side-reactions. Firstly, almost no C-C cracking alkanes were obtained over NiZnAl catalyst whereas that increased gradually to ~8% over NiAl after HMF was totally converted. Nørskov et al.43 reported that the Ni step-edge is active for C-C breaking and blocking the Ni steps by alloying with Ag is an effective way to suppress C-C session. Thus, the decreased concentration of Ni steps due to Zn inclusion might be responsible for the suppressed C-C cracking reactions, as illustrated by CO-IR results.32 Secondly, NiZnAl has a low propensity for overhydrogenation of C=C bonds, producing very little DMTHF. Actually, pure Ni has 12 nearest Ni neighbors, while the Ni in β1-NiZn intermetallic is coordinated by 8 nearest Zn neighbors, with 6 Ni atoms slightly further away27. The active site isolation increases Ni-Ni distances on the surface and leads to only weakly π–bonded furan ring on Ni atom.25 Gorte et al.17,44 also concluded that the high DMF yield over the bimetallic surface (e.g., PtCo, PtNi, PtZn) could be attributed to the weakly interacted furan ring. Besides, the hydrogenation of furan ring and C=O follow the nucleophilic and electrophilic addition mechanism, respectively.21 In this work, the electronegative Ni atom prefers to attack C=O, instead of the furan ring. Thus, a greatly enhanced DMF yield was obtained over NiZnAl catalyst. Catalytic performance of NiZnAl catalyst prepared by different methods The NiZn/Al and Ni/ZnAl catalysts with the same preset metal loadings were prepared by impregnation method for a comparasion. NiZn/Al was prepared by the co-impregnation process of the solution of nickel and zinc nitrates onto commercial Al2O3 support. Ni/ZnAl was prepared by the impregnation process of the solution of nickel nitrate onto ZnAl support. ZnAl support was prepared by coprecipitation method similar to preparation of NiZnAl catalyst. The XRD patterns of the calcined samples were shown in Figure S4. The crystalline sizes of NiZn/Al and Ni/ZnAl calculated based on Scherrer equation were 15.6 and 9.9 nm respectively, which were larger than NiZnAl catalyst prepared by co-precipitation method. The catalytic performance of the three catalysts for HMF hydrogenation was shown in Table S2. All catalysts 13



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exhibited a total conversion of HMF after 9 h. NiZnAl catalyst prepared by coprecipitation method exhibited highest DMF selectivity of 59.4%. MFA and DHMF are the main byproducts. NiZn/Al and Ni/ZnAl catalysts prepared by impregnated method showed much lower DMF selectivity due to the insufficient hydrogenolysis of oxygen-containing intermediates of MFA and DHMF. Importantly, all the three catalysts exhibited low yield for the C=C/C-C hydrogenation products. However, the byproducts for NiAl catalyst mainly include DMTHF and C-C cracking products (Figure 7), due to the strong hydrogenation ability for C=C/C-C bonds. In conclusion, the above results demonstrated that NiZn based catalysts are more selective for C=O/C-O hydrogenation compared with monometallic NiAl catalyst. Moreover, the catalyst preparation method has great effect on the catalytic performance. Highly dispersed NiZnAl catalyst prepared by coprecipitation method exhibited superior reactivity. Catalytic performance of NiZnAl catalyst with different Ni/Zn ratios The effect of Ni/Zn ratios on the catalytic performance was also investigated and shown in Table S3. All catalysts exhibited a total conversion of HMF after 9 h. The DMF selectivity increased with increasing Ni/Zn ratio. NiZnAl(3:1) exhibited highest DMF yield of 68.0%. However, the NiZnAl(3:1) catalyst also showed high selectivity of DMTHF due to the strong hydrogenation ability. For NiZnAl(1:3) catalyst, a yield of 36.2% was obtained due to the insufficient hydrogenolysis of MFA and DHMF. The low hydrogenation ability of NiZnAl(1:3) can be assigned to the low Ni contents. Among the three catalysts, NiZnAl catalyst exhibited the best results with a 59.4% yield of DMF, while the MFA and DHMF can be further converted into DMF. The final 93.6% yield of DMF can be achieved over NiZnAl catalyst as demonstrated in Figure 7. In summary, the Ni/Zn ratio has great effect on the catalytic performance of NiZnAl catalyst. The hydrogenolysis ability increased with increasing Ni/Zn ratio. However, too higher Ni/Zn ratio caused the formation of DMTHF and other byproducts. Finally, NiZnAl catalyst with a Ni/Zn ratio of 1:1 exhibited the best performance. Further applications of NiZnAl catalyst (Table 2) 14


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The reactivity of NiZnAl catalyst for HMF hydrogenation was tested at 100 oC for DHMF synthesis. As shown in Table 2, a high DHMF yield was obtained over NiZnAl catalyst, demonstrating the high selectivity for C=O bond with low hydrogenation ability for the furan ring. We also investigated the catalytic performance of NiZnAl for furfural hydrogenation. The products for furfural hydrogenation mainly focused on 2-methylfuran (2-MF) and furfuryl alcohol, which are promising fuel candidate and chemical respectively. Furfuryl alcohol is the intermediate for 2-MF synthesis, in which a deep hydrogenolysis of side hydroxymethyl group can form 2-MF. High yields of 2-MF and furfuryl alcohol were obtained by using furfural as the feedstock. Based on the above results, NiZnAl exhibited superior hydrogenolysis ability for C=O/C-O over C=C/C-C bonds, supporting the mechanisms of Zn inclusion and showing great potential for upgrading of biomass via hydrodeoxygenation. Reusability of NiZnAl catalyst (Figure 8) The stability of NiZnAl catalyst for DMF synthesis was also investigated (Figure 8). In order to track the slight changes in catalyst activity over time, a middle conversion of HMF was chosen. HMF conversion was around 44.3% with the DMF yield of 21.8% in the first run. The O-containing intermediates DHMF and 5-methylfurfuryl alcohol were the main byproducts. After 4 runs, HMF conversion and DMF yield exhibited a great decrease, indicating the deactivation of catalyst. XRD experiments were carried out to investigate the status of catalyst after reaction. As shown in Figure S5, no obvious change was observed for the used NiZnAl catalyst, including the particle size and the Zn inclusion (peak shift), demonstrating the good stability of the NiZn alloy catalyst. The good stability of NiZn alloy could be attributed to the strong interactions between the Ni and Zn species, as indicated by TPR results. For catalyst used for HMF hydrogenation to DMF, the deposition of carbonaceous species easily occurred and was the major deactivation problem, which was also proved by our previous reports.11 Moreover, there were lots of works reported the removal of carbonaceous species to regenerate the deactivated catalyst based on the calcination or reduction processes. For example, Jae et al.6 investigated the Ru/C catalyst for DMF synthesis at 190 oC and found that initial activity of the catalyst was almost completely regained after 15



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regeneration by heating at 573 K under H2 flow for 2 h. Perret et al.45 studied a Ni/Al2O3 catalyst derived from Ni-Al hydrotalcite-like materials for HMF hydrogenation. They also found that the organic impurities chemisorbed on the surface were the main reason for the deactivation, while the activity can be restored after a calcination and reduction at 773 K. However, the regeneration of catalyst was not investigated, which was beyond the scope of this work.

Discussion The active phase Determination of the active phase for NiZnAl is important for a further rational design of selective catalysts for C=O/C-O hydrogenation reactions. As observed from the TPR and XPS results, Zn2+ species were reduced over NiZnAl catalyst. For reduced NiZnAl catalyst, XRD results showed a shift of Ni peaks to low angles, indicating the increase of lattice spacing and formation of Ni-Zn structures. Moreover, pronounced shift was detected over NiZnAl-700. As reported by previous works28,46, different Ni1-xZnx alloy could be formed by changing x value (Zn content). Metallic Ni exhibited fcc crystal structure over NiAl catalyst. Zn inclusion with low content would cause the random substitution of Ni atoms and form the α-NiZn phase (e.g., Ni4Zn, Ni0.87Zn0.13, Ni7Zn3), with retaining the Ni fcc crystal structure but changing the lattice spacing due to the different atom size. At high inclusion content of Zn, a highly ordered intermetallic β1-NiZn (Ni0.5Zn0.5) structure could be formed, constituting of a fc tetragonal super lattice. However, the β1-NiZn was unstable, which could decompose into α-NiZn as demonstrated by our XRD results. A further increase of Zn content induced the β-NiZn phase (e.g., Ni5Zn21) formation. The reduction temperature could modulate the content of Zn inclusion and NiZn alloy compositions, in which the Zn content increased with the reduction temperature. (Figure 9) Herein, 500

o

C was used to reduce NiZnAl derived catalyst and tested for HMF

hydrogenation. Due to the low reduction temperature, low amount of Zn was reduced and included in Ni1-xZnx alloy. Thus, α-NiZn (Ni-rich NiZn alloy) was mainly formed, as confirmed by XRD. On the other hand, the surface Zn/Ni atomic ratio is determined to be 1.16, which is similar with the NiZn intermetallic (β1-NiZn). Moreover, the surface of NiZnAl catalyst was consitituted with isolated and electron density increased Ni sites, as revealed by CO-IR results. This can be 16


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explained by the geometry of isolated Ni sites over the surface, the formation of intermetallic β1-NiZn and the altered electronic structure of Ni sites by electron transfer from Zn atoms. Moreover, bridge adsorption of CO in the IR spectrum for NiZnAl catalyst was not observed, which required a configuration with linked Ni atoms over the surface and can be formed over the Ni-rich NiZn alloy (α-NiZn). β-NiZn could not be obtained in our work while a reduction temperature of ~700 oC are needed on the basis of Ni-Zn bulk phase diagram.47 The structure evolutions can be interpreted by the following steps: 1) NiO-ZnO-Al2O3 oxide formation with strong metal support interaction from NiZnAl hydrotalcite; 2) NiZn alloy formation by Zn inclusion to Ni lattice via reduction treatment (Figure 9A). We steadily reached the conclusion that the NiZnAl catalyst was composed of the nanoparticles with a NiZn intermetalic (β1-NiZn) overlayer and Ni-rich NiZn alloy (α-NiZn) bulk phase, which was different from that of NiAl catalyst. Structure-performance relationship The inclusion of Zn also had great effect on the catalytic performance. Under the similar HMF conversions, the NiZnAl catalyst gave a greatly imporved DMF selectivity than the monometallic NiAl catalyst. The modulated selectivity towards selective C=O hydrogenation is related to the structural alternation by addition Zn, due to the similar particle size and acidity amounts. The rates of C=O/C-O hydrogenolysis over C=C/C-C hydrogenation at similar HMF conversions were calculated for better clarification. The calculation equation was based on the method shown in supplementary material. As shown in Figure 9B, the rate for NiZnAl is 41.2, approximately three times higher than that of NiAl. As reported by Sitthisa et al.48, the planar configurations of furfural on Ni(111) is the optimized geometry, in which carbonyl group (C=O) adsorbed on a bridge site and the furanyl ring plane sitting parallel to the surface across two 3-fold hollow sites. The interaction of the furan ring with the Ni surface is stronger, even than Pd, which can facilitate the hydrogenation reactions49. Thus, the diluted Ni sites would cause a weakly bonded furan ring due to the increased Ni-Ni distance. On the other hand, the Ni step-edge was greatly decreased by the introduction of Zn, which is active for C-C cracking reactions. Finally, the C=C/C-C hydrogenation reactions were suppressed.

17



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The electronic structure was also changed with the formaiton of NiZn alloy (α-NiZn+β1-NiZn), which was different with Ni. As reported for PdZn alloy catalyst, an electronic structure similar with Cu was obtained for PdZn, while Cu was known as highly selective for C=O hydrogenation30. In our case, the NiZn alloy might also exhibit a new electronic structure. From the other point, the electron transfer induced an oxophilic and electron-dense nature of Zn and Ni respectively, which could provide an enhanced interaction with the C=O bond48. The stable η2-(C,O) adsorption over NiZn alloy would benefit the selective hydrogenation of C=O bonds, while the η2-(C,O) species over Ni metal would be converted into a suface acyl species and decomposed subsequently. In conclusion, a greatly improved improved selectivity for DMF was obtained over NiZnAl derived catalyst, due to the formation of surface NiZn intermetallic and Ni-rich NiZn alloy species (combination of α-NiZn and β1-NiZn). Further experiments are needed for the elucidation of the NiZnAl catalyst and for a rational design of NiZn alloy catalyst.

Conclusions This work demonstrated that the surface intermetallic β1-NiZn and bulk α-NiZn alloy could be obtained by reduction of NiZnAl hydrotalcite. The characterizations combining XRD, TPR, XPS and CO-IR show the systematical structural evolution from hydrotalcite precursor to Zn doped NiO, and then to the NiZn species with an alloy bulk (α-NiZn) and intermetallic surface (β1-NiZn). The altered electronic and geometric properties of Ni atoms by NiZn intermetallic formation were further proved by CO-IR and H2-TPD, which influenced the adsorption of reactants and catalytic performance. The final NiZnAl catalyst showed a greatly enhanced DMF yield (93.6%), in compared with that of monometallic Ni catalyst (63.5%). This finding also opens up the application of NiZn alloy catalyst for selective hydrogenation reactions of unsaturated aldehyde.

Supporting Information Calculation method based on H2-TPR for Ni reducibility, calculation method for rates of C=O/C-O and C=C/C-C bonds hydrogenation, H2-TPD and NH3-TPD results of the NiZnAl and NiAl catalysts, XRD results of the catalyst precursor of NiZnAl, NiAl and ZnAl samples, XRD results of NiZnAl catalysts prepared by different methods, XRD results of the fresh and used 18


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NiZnAl catalyst, catalytic performance of ZnAl reference, catalytic performance of NiZnAl prepared by different methods and catalytic performance of NiZnAl catalysts with different Ni/Zn ratio.

Acknowledgements This project was supported by the Major State Basic Research Development Program of China (No.2012CB215305) and National Science Foundation in Jiangsu Province (No. BK20170707).

References (1) Román-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates. Nature 2007, 447, 982-985. (2) Do, P. T. M.; McAtee, J. R.; Watson, D. A.; Lobo, R. F. Elucidation of Diels-Alder Reaction Network of 2,5-Dimethylfuran and Ethylene on HY Zeolite Catalyst. ACS Catal. 2013, 3, 41-46. (3) Shiramizu, M.; Toste, F. D. On the Diels–Alder Approach to Solely Biomass-Derived Polyethylene Terephthalate (PET): Conversion of 2,5-Dimethylfuran and Acrolein into p-Xylene. Chem. -Eur. J. 2011, 17, 12452-12457. (4) Thananatthanachon, T.; Rauchfuss, T. B. Efficient Production of the Liquid Fuel 2,5‐ Dimethylfuran from Fructose Using Formic Acid as a Reagent. Angew. Chem. 2010, 122, 6766-6768. (5) Zu, Y.; Yang, P.; Wang, J.; Liu, X.; Ren, J.; Lu, G.; Wang, Y. Efficient production of the liquid fuel 2,5-dimethylfuran from 5-hydroxymethylfurfural over Ru/Co3O4 catalyst. Appl. Catal. B: Environ. 2014, 146, 244-248. (6) Jae, J.; Zheng, W. Q.; Lobo, R. F.; Vlachos, D. G. Production of Dimethylfuran from Hydroxymethylfurfural through Catalytic Transfer Hydrogenation with Ruthenium Supported on Carbon. ChemSusChem 2013, 6, 1158-1162. (7) Wang, G.-H.; Hilgert, J.; Richter, F. H.; Wang, F.; Bongard, H.-J.; Spliethoff, B.; Weidenthaler, C.; Schüth, F. Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural. Nat. Mater. 2014, 13, 293-300. (8) Mitra, J.; Zhou, X.; Rauchfuss, T. Pd/C-catalyzed reactions of HMF: decarbonylation, hydrogenation, and hydrogenolysis. Green Chem. 2014, 17, 307-313. (9) Gawade, A. B.; Tiwari, M. S.; Yadav, G. D. Biobased Green Process: Selective 19



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

Hydrogenation of 5-Hydroxymethylfurfural to 2,5-Dimethyl Furan under Mild Conditions Using Pd-Cs2.5H0.5PW12O40/K-10 Clay. ACS Sustain. Chem. Eng. 2016, 4, 4113-4123. (10) Nagpure, A. S.; Lucas, N.; Chilukuri, S. V. Efficient Preparation of Liquid Fuel 2,5-Dimethylfuran from Biomass-Derived 5-Hydroxymethylfurfural over Ru–NaY Catalyst. ACS Sustain. Chem. Eng. 2015, 3, 2909-2916. (11) Kong, X.; Zheng, R.; Zhu, Y.; Ding, G.; Zhu, Y.; Li, Y.-W. Rational design of Ni-based catalysts derived from hydrotalcite for selective hydrogenation of 5-hydroxymethylfurfural. Green Chem. 2015, 17, 2504-2514. (12) Kong, X.; Zhu, Y.; Zheng, H.; Li, X.; Zhu, Y.; Li, Y.-W. Ni nanoparticles inlaid nickel phyllosilicate as a metal-acid bi-functional catalyst for low-temperature hydrogenolysis reactions. ACS Catal. 2015, 5, 5914-5920. (13) Yang, P.; Cui, Q.; Zu, Y.; Liu, X.; Lu, G.; Wang, Y. Catalytic production of 2,5-dimethylfuran from 5-hydroxymethylfurfural over Ni/Co3O4 catalyst. Catal. Commun. 2015, 66, 55-59. (14) Huang, Y. B.; Chen, M. Y.; Yan, L.; Guo, Q. X.; Fu, Y. Nickel-tungsten carbide catalysts for the production of 2,5-dimethylfuran from biomass-derived molecules. ChemSusChem 2014, 7, 1068-1072. (15) Yang, P.; Xia, Q.; Liu, X.; Wang, Y. High-yield production of 2,5-dimethylfuran from 5-hydroxymethylfurfural over carbon supported Ni–Co bimetallic catalyst. J. Energy Chem. 2016, 25, 1015-1020. (16) Kong, X.; Zhu, Y.; Zheng, H.; Dong, F.; Zhu, Y.; Li, Y.-W. Switchable synthesis of 2,5-dimethylfuran and 2,5-dihydroxymethyltetrahydrofuran from 5-hydroxymethylfurfural over Raney Ni catalyst. RSC Adv. 2014, 4, 60467-60472. (17) Luo, J.; Yun, H.; Mironenko, A. V.; Goulas, K.; Lee, J. D.; Monai, M.; Wang, C.; Vorotnikov, V.; Murray, C. B.; Vlachos, D. G.; Fornasiero, P.; Gorte, R. J. Mechanisms for High Selectivity in the Hydrodeoxygenation of 5-Hydroxymethylfurfural over PtCo Nanocrystals. ACS Catal. 2016, 6, 4095-4104. (18) Sharafutdinov, I.; Elkjær, C. F.; Pereira de Carvalho, H. W.; Gardini, D.; Chiarello, G. L.; Damsgaard, C. D.; Wagner, J. B.; Grunwaldt, J.-D.; Dahl, S.; Chorkendorff, I. Intermetallic compounds of Ni and Ga as catalysts for the synthesis of methanol. J. Catal. 2014, 320, 77-88. (19) Ammari, F. An emergent catalytic material: Pt/ZnO catalyst for selective hydrogenation of 20


Page 20 of 37

Page 21 of 37

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


crotonaldehyde. J. Catal. 2004, 221, 32-42. (20) Li, C.; Chen, Y.; Zhang, S.; Zhou, J.; Wang, F.; He, S.; Wei, M.; Evans, D. G.; Duan, X. Nickel-Gallium Intermetallic Nanocrystal Catalysts in the Semihydrogenation of Phenylacetylene. ChemCatChem 2014, 6, 824-831. (21) Li, C.; Chen, Y.; Zhang, S.; Xu, S.; Zhou, J.; Wang, F.; Wei, M.; Evans, D. G.; Duan, X. Ni– In Intermetallic Nanocrystals as Efficient Catalysts toward Unsaturated Aldehydes Hydrogenation. Chem. Mater. 2013, 25, 3888-3896. (22) Rodiansono; Khairi, S.; Hara, T.; Ichikuni, N.; Shimazu, S. Highly efficient and selective hydrogenation of unsaturated carbonyl compounds using Ni–Sn alloy catalysts. Catal. Sci. Technol. 2012, 2, 2139-2145. (23) Yu, L.; He, L.; Chen, J.; Zheng, J.; Ye, L.; Lin, H.; Yuan, Y. Robust and Recyclable Nonprecious Bimetallic Nanoparticles on Carbon Nanotubes for the Hydrogenation and Hydrogenolysis of 5-Hydroxymethylfurfural. ChemCatChem 2015, 7, 1701-1707. (24) Wang, J.; Wang, Y.; Xie, S.; Qiao, M.; Li, H.; Fan, K.. Partial hydrogenation of benzene to cyclohexene on a Ru–Zn/m-ZrO2 nanocomposite catalyst. Appl. Catal. A: Gen. 2004, 272, 29-36. (25) Osswald, J.; Kovnir, K.; Armbruster, M.; Giedigkeit, R.; Jentoft, R.; Wild, U.; Grin, Y.; Schlogl, R. Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylenePart II: Surface characterization and catalytic performance. J. Catal. 2008, 258, 219-227. (26) Studt, F.; Abild-Pedersen, F.; Bligaard, T.; Sørensen, R. Z.; Christensen, C. H.; Nørskov, J. K. Identification of non-precious metal alloy catalysts for selective hydrogenation of acetylene. Science 2008, 320, 1320-1322. (27) Spanjers, C. S.; Held, J. T.; Jones, M. J.; Stanley, D. D.; Sim, R. S.; Janik, M. J.; Rioux, R. M. Zinc

inclusion

to

heterogeneous

nickel

catalysts

reduces

oligomerization

during

the

semi-hydrogenation of acetylene. J. Catal. 2014, 316, 164-173. (28) Spanjers, C. S.; Sim, R. S.; Sturgis, N. P.; Kabius, B.; Rioux, R. M. In Situ Spectroscopic Characterization of Ni1–xZnx/ZnO Catalysts and Their Selectivity for Acetylene Semihydrogenation in Excess Ethylene. ACS Catal. 2015, 5, 3304-3315. (29) Pérez-Ramırez, J.; Mul, G.; Moulijn, J. In situ Fourier transform infrared and laser Raman spectroscopic study of the thermal decomposition of Co–Al and Ni–Al hydrotalcites. Vib. Spectrosc. 2001, 27, 75-88. 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

(30) Tew, M. W.; Emerich, H.; van Bokhoven, J. A. Formation and Characterization of PdZn Alloy: A Very Selective Catalyst for Alkyne Semihydrogenation. J. Phys. Chem. C 2011, 115, 8457-8465. (31) Barroso, M. N.; Gomez, M. F.; Arrúa, L. A.; Abello, M. C. Hydrogen production by ethanol reforming over NiZnAl catalysts. Appl. Catal. A: Gen. 2006, 304, 116-123. (32) Rodrı́guez, J. C.; Marchi, A. J.; Borgna, A.; Monzón, A. Effect of Zn Content on Catalytic Activity and Physicochemical Properties of Ni-Based Catalysts for Selective Hydrogenation of Acetylene. J. Catal. 1997, 171, 268-278. (33) Anjaneyulu, C.; Costa, L. O. O. d.; Ribeiro, M. C.; Rabelo-Neto, R. C.; Mattos, L. V.; Venugopal, A.; Noronha, F. B. Effect of Zn addition on the performance of Ni/Al2O3 catalyst for steam reforming of ethanol. Appl. Catal. A: Gen. 2016, 519, 85-98. (34) Friedrich, M.; Teschner, D.; Knop-Gericke, A.; Armbrüster, M. Surface and Subsurface Dynamics of the Intermetallic Compound ZnNi in Methanol Steam Reforming. J. Phys. Chem. C 2012, 116, 14930-14935. (35) Velu, S.; Suzuki, K.; Vijayaraj, M.; Barman, S.; Gopinath, C. S. In situ XPS investigations of Cu1−xNixZnAl-mixed metal oxide catalysts used in the oxidative steam reforming of bio-ethanol. Appl. Catal. B: Environ. 2005, 55, 287-299. (36) Tauster, S. J.; Fung, S. C.; Garten, R. L. Strong metal-support interactions. Group 8 noble metals supported on titanium dioxide. J. Am. Chem. Soc. 1978, 100, 170-175. (37) Tauster, S. J.; Fung, S. C.; Baker, R. T. K.; Horsley, J. A. Strong Interactions in Supported-Metal Catalysts. Science 1981, 211, 1121-1125. (38) Freund, H. J.; Meijer, G.; Scheffler, M.; Schlögl, R.; Wolf, M. CO oxidation as a prototypical reaction for heterogeneous processes. Angew. Chem. Int. Ed. 2011, 50, 10064-10094. (39) Layman, K. A.; Bussell, M. E. Infrared Spectroscopic Investigation of CO Adsorption on Silica-Supported Nickel Phosphide Catalysts. J. Phys. Chem. B 2004, 108, 10930-10941. (40) Paredes-Nunez, A.; Lorito, D.; Schuurman, Y.; Guilhaume, N.; Meunier, F. C. Origins of the poisoning effect of chlorine on the CO hydrogenation activity of alumina-supported cobalt monitored by operando FT-IR spectroscopy. J. Catal. 2015, 329, 229-236. (41) Tseng, K.-N. T.; Kampf, J. W.; Szymczak, N. K. Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal–Ligand Cooperativity Enables Selective Alkyne 22


Page 22 of 37

Page 23 of 37

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


Hydrogenation. J. Am. Chem. Soc. 2016, 138, 10378-10381. (42) Hsu, L. S.; Nesvizhskii, A. I. Experimental and theoretical study of the electronic structures of Ni3Al, Ni3Ga, Ni3In, and NiGa. J. Phys. Chem. Solids 2001, 62, 1103-1109. (43) Vang, R. T.; Honkala, K.; Dahl, S.; Vestergaard, E. K.; Schnadt, J.; Lægsgaard, E.; Clausen, B. S.; Nørskov, J. K.; Besenbacher, F. Controlling the catalytic bond-breaking selectivity of Ni surfaces by step blocking. Nature Mater. 2005, 4, 160-162. (44) Luo, J.; Lee, J. D.; Yun, H.; Wang, C.; Monai, M.; Murray, C. B.; Fornasiero, P.; Gorte, R. J. Base metal-Pt alloys: A general route to high selectivity and stability in the production of biofuels from HMF. Appl. Catal. B: Environ. 2016, 199, 439-446. (45) Perret, N.; Grigoropoulos, A.; Zanella, M.; Manning, T. D.; Claridge, J. B.; Rosseinsky, M. J. Catalytic Response and Stability of Nickel/Alumina for the Hydrogenation of 5-Hydroxymethylfurfural in Water. ChemSusChem 2016, 9, 521-531. (46) Martinez, U.; Asazawa, K.; Halevi, B.; Falase, A.; Kiefer, B.; Serov, A.; Padilla, M.; Olson, T.; Datye, A.; Tanaka, H.; Atanassov, P. Aerosol-derived Ni1-xZnx electrocatalysts for direct hydrazine fuel cells. Phys. Chem. Chem. Phys. 2012, 14, 5512-5517. (47) Okamoto, H. Ni-Zn (nickel-zinc). J. Phase Equilib. 2003, 24, 280-281. (48) Sitthisa, S.; An, W.; Resasco, D. E. Selective conversion of furfural to methylfuran over silica-supported NiFe bimetallic catalysts. J. Catal. 2011, 284, 90-101. (49) Sitthisa, S.; Resasco, D. E. Hydrodeoxygenation of Furfural Over Supported Metal Catalysts: A Comparative Study of Cu, Pd and Ni. Catal. Lett. 2011, 141, 784-791.

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Scheme 1 (A): C=O/C-O hydrogenolysis versus C=C saturation and C-C cracking for selective conversion of HMF (red dotted line: undesired reactions); (B) Modulation of metallic Ni by forming NiZn alloy.

24


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Table 1. Main physiochemical properties of the samples. Ni

Zn

SBET

dNic/dNid

(wt. %)a

(wt. %)a

(m2/g)b

(nm)

NiZnAl

25.0

29.2

143.7

5.8/4.4

0.36

0.09

NiAl

27.8

-

188.3

7.3/4.8

0.19

0.10

ZnAl

-

30.6

97.9

-

0

-

Cat.

H (mmol/g)e

Sacid (µmolNH3/g)f

[a] determined by ICP experiments. [b] determined by N2 physical adsorption. [c] calculated by Ni (200) reflection (2θ=51.8o) based on Scherrer equation after reduction at 500 oC for 2 h. [d] calculated by HRTEM images. [e] Actual amount of H consumed over 20 mg catalyst by H2-TPR analysis. [f] determined by NH3-TPD results.

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Table 2 Catalytic performance of NiZnAl catalyst for HMF and furfural conversion. Feedstock

Conv. (%)

Main products (Sel. (%))

HMFa

100

DHMF (98.2), DHMTHF (1.1)

Furfuralb

100

2-MF (90.8), Furfuryl alcohol (6.2)

Furfuralc

100

Furfuryl alcohol (89.1), 2-MF (4.4)

a

1.5 MPa, 100 oC, 10 h, HMF 1.5 g, catalyst 0.15 g, 1,4-dioxane 35 g. DHMTHF indicates

2,5-dihydroxymethyltetrahydrofuran;

b

1.5 MPa, 220 oC, 6 h, furfural 1 g, catalyst 0.15 g,

1,4-dioxane 35 g. 2-MF indicates 2-methylfuran. Others mainly include 2-methyltetrahydrofuran; c

1.5 MPa, 180 oC, 2 h, furfural 1 g, catalyst 0.15 g, 1,4-dioxane 35 g. Others mainly include

tetrahydrofurfuryl alcohol.

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Figure Captions Figure 1 XRD patterns of calcined catalysts. Figure 2 TPR results of calcined NiZnAl, NiAl and ZnAl catalysts. Figure 3 In situ XRD patterns of reduced catalysts (the number indicates the reduction temperature). Figure 4 In situ XRD patterns of NiZnAl reduced under different reaction temperatures. R1, the XRD of catalyst when reduction temperature was just elevated at object temperature; R2, the XRD of catalyst when the reduction was just finished; R3, the XRD of catalyst when the temperature was cooled down to room temperature. Figure 5 XPS/XAES spectra from Zn-L3M45M45 spectra of reduced NiZnAl and ZnAl samples under 500 oC. Figure 6 CO-IR images of reduced NiZnAl, NiAl and ZnAl catalysts at 500 oC for 2 h. The spectra were obtained after blowing 12 min in He at room temperature. Figure 7 Catalytic performance of HMF hydrogenation over NiAl (a) and NiZnAl (b) catalysts. Reaction conditions: 1.5 MPa, 180 oC, HMF 1.5 g, catalyst 0.15 g. C-C cracking products included the 2-methyltetrahydrofuran, 2-methylfuran, C1-C5 alkane, furan, tetrahydrofuran. (c) Products evolutions for HMF conversion. Figure 8 Reusability of NiZnAl catalyst for HMF hydrogenation to DMF. Reaction conditions: 1.5 MPa, 180 oC, 3 h, 1,4-dioxane 35 g, catalyst 0.15 g, HMF 1.5 g. Figure 9 Structure evolution of NiZnAl catalyst (A) and comparisons of rate for C-O conversion to C-C conversion under similar conversions (B).

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Figure 1 XRD patterns of calcined catalysts.

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Figure 2 TPR results of calcined NiZnAl, NiAl and ZnAl catalysts.

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Figure 3 In situ XRD patterns of reduced catalysts (the number indicates the reduction temperature).

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Figure 4 In situ XRD patterns of NiZnAl reduced under different reaction temperatures. R1, the XRD of catalyst when reduction temperature was just elevated at object temperature; R2, the XRD of catalyst when the reduction was just finished; R3, the XRD of catalyst when the temperature was cooled down to room temperature. The pink lines in the bottom indicate the characteristic peaks of Ni.

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Figure 5 XPS/XAES spectra from Zn-L3M45M45 spectra of reduced NiZnAl and ZnAl samples under 500 oC.

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Figure 6 CO-IR images of reduced NiZnAl, NiAl and ZnAl catalysts at 500 oC for 2 h. The spectra were obtained after blowing 12 min in He at room temperature.

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Figure 7 Catalytic performance of HMF hydrogenation over NiAl (a) and NiZnAl (b) catalysts. Reaction conditions: 1.5 MPa, 180 oC, HMF 1.5 g, catalyst 0.15 g. C-C cracking products included the 2-methyltetrahydrofuran, 2-methylfuran, C1-C5 alkane, furan, tetrahydrofuran. (c) Products evolutions for HMF conversion.

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Figure 8 Reusability of NiZnAl catalyst for HMF hydrogenation to DMF. Reaction conditions: 1.5 MPa, 180 oC, 3 h, 1,4-dioxane 35 g, catalyst 0.15 g, HMF 1.5 g.

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Figure 9 Structure evolution of NiZnAl catalyst (A) and comparisons of rate for C-O conversion to C-C conversion under similar conversions (B).

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Graphical Abstract High yield of DMF (93.6%) was obtained from hydrogenolysis of HMF, which is an important process for sustainable fuel production from biomass.

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Inclusion of Zn into Metallic Ni Enables Selective and Effective

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