Chitosan CoreâShell Hybrid-Microsphere-Supported Pd

Article Cite This: Ind. Eng. Chem. Res. 2017, 56, 12655-12662

pubs.acs.org/IECR

Silica/Chitosan Core−Shell Hybrid-Microsphere-Supported Pd Catalyst for Hydrogenation of Cyclohexene Reaction Luyao Ma, Yechao Su, Jian Chen, and Jianhong Xu* The State Key Lab of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China ABSTRACT: This paper presents a simple microfluidic method to prepare monodispersed palladium nanoparticles supported on silica/ chitosan core−shell hybrid microspheres. Because a large amount of −NH2 provided by chitosan has a strong force with metal ions, Pd nanoparticles loaded on the microspheres kept monodispersed and had a mean diameter of only 2−3 nm. In addition, the core−shell structure indicating that the chitosan was mainly distributed on the shell of the microspheres results in that palladium is mainly loaded on the shell too, which can effectively reduce mass transfer distance between reactant and catalyst. Therefore, the supported Pd catalyst showed a superb catalytic performance through the hydrogenation of cyclohexene. Furthermore, silica/chitosan-supported catalyst can be reused many times without an obvious loss of its activity, and it will have promising application in other similar hydrogenation reactions.

1. INTRODUCTION Palladium (Pd) is a significant noble metal catalyst, which is widely applied in the processes of organic synthesis, such as hydrogenation,1−4 dehydrogenation,5,6 oxidation,7,8 and carbon−carbon (C−C) cross-coupling reaction,9,10 especially in catalytic hydrogenation. The supported Pd catalyst has been extensively studied in recent years due to its high activity. It has been mentioned that material and structure of the support play a significant role in the catalyst’s performance.11 To improve the catalytic performance of the supported Pd catalyst, suitable support materials should be selected and appropriate support structures should be designed for specific chemical reactions. For most hydrogenation reaction catalyzed by palladium, one of its remarkable characteristics is that its intrinsic kinetics is extremely fast, which means the hydrogenation process is mass-transfer limited. To intensify the reaction process, mass transfer resistance needs to be reduced. Core−shell structured support can selectively load metal nanoparticles on the shell layer due to its affinity with metal ions, effectively reducing the mass transfer resistance in the process of hydrogenation.11,12 In addition, it has been reported that the magnitude of the interaction between the support and the metal ions will have a great influence on the catalytic activity of the metal nanoparticles.13,14 First, larger interaction between the support and the metal ions is beneficial to get metal nanoparticles with small size and narrow distribution by reducing the agglomeration of metal nanoparticles in the reduction process, which shows superior catalytic activity during hydrogenation. Moreover, the stronger interaction can effectively reduce the loss of metal nanoparticles during the long-term use of hydrogenation. Thus, the appropriate support material and loading method need to be selected to enhance © 2017 American Chemical Society

the interaction between the support and the noble metal ion Pd2+. Polymer supports usually have better interaction with Pd through the coordination between heteroatom such as N and O on the branches of polymer molecules.15,16 Chitosan is a biocompatible and low-cost polymer material containing a large number of amino in its molecule, which has strong chelating characteristics with metal ions.17 The chelation is some kind of chemical interaction, which is apparently stronger than physical adsorption between inorganic carrier and metal ions. Besides, it has been reported that silica−chitosan hybrid materials exhibit an enhanced mechanical property compared with other hybrid materials because of addition of silica,18,19 so the silica/chitosan hybrid material is a good choice of support for noble metal nanoparticles. In our previous work, silica/chitosan hybrid microspheres with different structure were designed and prepared by suitable microfluidic devices for catalyst support in organic reactions.20 To specifically increase the catalytic performance for the masstransfer-limited hydrogenation reaction, silica/chitosan core− shell hybrid microspheres with silica core and chitosan shell was fabricated in this work using a developed simple microfluidic approach. The prepared silica/chitosan-supported Pd catalysts were applied in the hydrogenation of cyclohexene and exhibited a superb catalytic performance, long-term stability, and outstanding mechanical strength. Received: Revised: Accepted: Published: 12655

September 3, 2017 October 10, 2017 October 14, 2017 October 25, 2017 DOI: 10.1021/acs.iecr.7b03667 Ind. Eng. Chem. Res. 2017, 56, 12655−12662

Article

Industrial & Engineering Chemistry Research

Figure 1. (a) Schematic diagram of microfluidic device. (b) Micrograph of the silica/chitosan droplets. (c, d, e) SEM image on surface and inner structure of the microspheres.

2. MATERIALS AND METHODS 2.1. Materials and Chemicals. Chitosan (2 w/w %, deacetylation degree below 95%, average molecular weight of 600 kDa, Sinopharm chemical reagent Co., Ltd., Beijing, P.R. China) aqueous solution with acetic acid (2 w/w %, VAS Chemical Co., Ltd., Tianjin, P.R. China) was used as the middle fluid. A silica sol was prepared by TOES (2%), which was dissolved in the acetic acid (2 w/w %) aqueous solution and stirred over 6 h to serve as the inner fluid. N-octanol (VAS Chemical Co., Ltd., Tianjin, P.R. China) was used as the continuous phase. N-octane (100.0 g) with cross-linking reagent, glutaraldehyde (1.03 g), and surfactant, Span 80 (2.0 g, VAS Chemical Co., Ltd., Tianjin, P.R. China) was used as the solidification bath. Palladium chloride (Alfa Aesar, Tianjin, P.R. China), cyclohexene (Alfa Aesar, Tianjin, P.R. China), hydrogen, and N,N-dimethylformamide (Alfa Aesar, Tianjin, P.R. China) were used in the reaction. 2.2. Microfluidic Device. The scheme diagram of the experiment device is provided in Figure 1a. A circular glass capillary (0.3 mm × 0.6 mm) is tapered to approximately 150 μm in tip using a micropipette puller (P-97, SUTTER Co.Ltd., USA) for the inner fluid. This glass capillary is inserted into a second glass capillary (0.7 mm × 1.0 mm), the orifice of which is tapered to approximately 350 μm for the middle fluid. Next,

the orifices of those two compound capillaries are inserted into a third glass capillary (1.05 mm × 1.5 mm) to form the coaxial structure. The third glass capillary is inserted as the continuous phase inlet, and another Teflon tube is inserted into this capillary as the multiphase flow collected channel. These fluids are pumped into the microchannel through three microsyringe pumps and three gastight microsyringes. The droplets are collected with a solidification bath, which is placed on a shaker. 2.3. Preparation of Monodispersed Silica/Chitosan Core−Shell Hybrid Microspheres. To prepare silica/ chitosan core−shell hybrid microspheres, the inner and middle fluids were injected as the dispersed phase into the microchannel and broken into monodispersed droplets under the shearing force of the continuous flow at the intersection. The droplets were formed in the Teflon tube and collected in the solidification bath, where the Schiff’s base reaction between chitosan and glutaraldehyde and the extraction of water out of droplets in n-octanol were used to presolidify the droplets. Then the microspheres were washed with n-octane and submerged in the n-octane for 16−24 h to realize different gelation extent of silica. By adjusting the presolidification time in the solidification bath and the gelation time in the n-octane, the microspheres’ structure could be controlled precisely. 12656

DOI: 10.1021/acs.iecr.7b03667 Ind. Eng. Chem. Res. 2017, 56, 12655−12662

Article


gas and air is 30 and 300 mL/min, respectively. The external standard method is used to analyze the composition of the product. First, cyclohexane solutions of different concentration are injected into the GS as the standard samples to get their corresponding integration of the peak of cyclohexane. Then the standard curve is obtained by fitting the concentration data as X-axis and the peak area data as Y-axis. Therefore, if the value of peak area of cyclohexane in an unknown sample is measured, the concentration of cyclohexane in this sample can be determined using the standard curve.

Finally, the spheres were freeze-dried and the silica/chitosan core−shell hybrid microspheres were obtained. 2.4. Preparation of Pd-Loaded Silica/Chitosan Core− Shell Hybrid Microspheres. On the basis of our previous work,20 a suitable pattern was chosen to get the Pd-loaded microspheres. A conical flask with different amounts of hybrid microspheres, PdCl2, and 50 g of aqueous solution was shaken in a water-bath shaker at room temperature for a fixed time. Then the hybrid microspheres with Pd2+ were separated and mixed with 0.1 g of NaBH4 in 50 g of aqueous solution, and the mixture was shaken in the water-bath shaker at room temperature for another 2 h. At last, the resulting hybrid microspheres were separated from the mixture, washed, and freeze-dried. 2.5. Catalytic Hydrogenation of Cyclohexene. A total of 10.0 mg of the prepared catalyst was packed in a tubular reactor, which was made of Teflon, with an inner diameter of 3 mm. The total length of the reactor was 6 cm. In each experiment, the cyclohexene, dissolved in DMF as liquid reagent, was pumped at a predetermined flow rate of 0.1 mL/ min by a pump. Hydrogen gas flowed from a cylinder through a mass flow controller and was mixed with the liquid reagent in a T-type micromixer. Then the gas−liquid mixture flowed into the tubular reactor packed with the prepared catalyst, which was immersed in a water bath to keep the temperature constant. A back-pressure regulator (BPR) was used to adjust the reaction pressure from 0.1−0.3 MPa. The reactor was connected to a phase separator with an inner diameter of 10 mm and a height of 10 cm. The gas−liquid system flowed into the middle position of the phase separator and was separated into two phases immediately for the large density difference. After the reaction reached the steady state, the liquid product was collected for analysis. The conversion ratio of cyclohexene is calculated as eq 1, and the space time is defined as eq 2: X = Ccyclohexane/C0cyclohexene

(1)

τ = V /v0

(2)

3. RESULTS 3.1. Preparation and Characterization of the Monodispersed Silica/Chitosan Core−Shell Hybrid Microspheres. After optimization, the typical silica/chitosan core− shell hybrid microspheres (2.0 wt % chitosan in the inner fluid and 2.0 wt % TEOS in the middle fluid, presolidified for 20 min and gelated for 20 h) were used to characterize the structures. Figure 1b shows that the droplets possess uniform size distributions well as good sphericity. After subsequent rinsing and freeze-drying, it was observed under SEM that the microspheres had good sphericity and a uniform size distribution in Figure 1c. Furthermore, as shown in Figure 1d and e, both the outside and inside of these microspheres had large pores, which means there are abundant adsorption sites for catalyst to be loaded and can effectively reduce the inner mass transfer resistance for the catalytic hydrogenation. In our previous work, the distribution of chitosan and silica in core− shell hybrid microspheres was calculated according to the energy spectrum results because there was Si only in silica and C in chitosan.11 If the value of (Siout/Siin)/(Cout/Cin) is closer to 1, the distribution of silica and chitosan in the microspheres is much more uniform. If the value is far from 1, that means there is less silica in the shell layer and more silica in the core; 0.499 is the value for core−shell hybrid microspheres and 0.908 is the value for homogeneous hybrid microspheres, which shows that silica and chitosan are nonuniformly distributed in the microspheres with most silica in the core and chitosan in the shell, and they subsequently form a core−shell structure. In addition, we used mercury injection apparatus to characterize the microspheres’ large pore distribution. Average large pore diameter was 46.58 μm, and porosity was up to 61.44%, as shown in Table 1. Besides, N2 adsorption and

where Ccyclohexane means the concentration of cyclohexane after the reaction, while C0cyclohexene means the initial concentration of cyclohexene. V means the volume of the reactor, and v0 means the flow rate at the entrance. 2.6. Analysis and Characterization. The preparation process and overall morphology of the droplets and microspheres were observed using an optical microscope (Type BX61, Olympus, Japan) and an online CCD (Pixelink, Canada). The detailed structures of microspheres were observed through a scanning electron microscopy (SEM, TM3000, Hitachi, Japan) and a transmission electron microscopy (TEM, HT7700, Hitachi, Japan). Mercury injection apparatus (Autopore IV 9510, Allied Domecq PLC) was used to characterize the macropore structure of the microspheres. The element valence of the catalyst was obtained using X-ray photoelectron spectroscopy (XPS) in a PHI Quantera SXM system (ULVAC-PHI Inc., Kanagawa, Japan) with a monochromatic Al KR source and a charge neutralizer. The product of hydrogenation was analyzed by gas chromatography (GC) 7890A with a flame ionization detector (FID) made by Agilent. The chromatographic column is HP-INNOWAX polyethylene glycol with the model of 19091N-133. The injector temperature, detector temperature, and oven temperature are 533, 493, and 333 K, respectively. Nitrogen gas is used as the carrier gas with a flow rate of 30 mL/min. The flow rate of hydrogen

Table 1. Pore Structure Data of Porous Silica/Chitosan Microspheres

chitosan/silica microspheres

surface area (multipoint BET) (m2/g)a

pore volume (BJH method) (mL/g)a

6.825

0.015

porosity (%)b

total pore volume (cm3/g)b

average pore diameter (μm)b

61.44

7.24

46.58

a Measured by nitrogen sorption analysis. intrusion porosimetry characterization.

b

Measured by mercury

desorption experiments were conducted to further characterize their pore structure. The surface area calculated by BET method and pore volume calculated by BJH method were 6.825 m2/g and 0.015 mL/g, also shown in Table 1. The load efficiency of the catalyst on the support influences the catalytic activity significantly, so it is necessary to study adsorption properties of the hybrid microspheres. Figure 2 12657


Article


indicates that the microspheres in this work show good adsorption ability for Pd(II) and can be used as a suitable support of Pd referring to other works about the supported Pd catalyst. 3.2. Preparation and Characterization of Supported Pd Catalysts. X-ray photoelectron spectroscopy characterization was conducted to further verify the ion chelation interaction during the loading of Pd(II) on microspheres. Figure 3 shows the N1s and Pd3d XPS spectra. In the chelation process, the free electron orbital of element Pd was fit in by the surplus pair electrons of N, leading to the increase in binding energy of element N and decrease in binding energy of element Pd accordingly.21−23 As shown in Figure 3a and b, the binding energy of element N in microspheres increased to 399.56 eV from 399.29 eV after chelation with Pd(II). On the other hand, Figure 3c and d show that the binding energies of Pd3d5/2 and Pd3d3/2 were 342.9 and 337.7 eV when Pd existed as Pd(II), and then they decreased to 340.8 and 335.5 eV, respectively, after reduction by NaBH4, which indicates that Pd element existed as Pd(0).21−23 From the results of XPS above, it can be illustrated that Pd interacts with the support through ion chelation in the microspheres, with which the prepared catalysts would perform higher stability than other Pd heterogeneous catalysts prepared from direct sediment and impregnation method. Figure 4 shows the HR-TEM images of the prepared catalyst to observe the crystal structure, dispersity of Pd nanoparticles, and Pd loading order. As shown in Figure 4a and b, Pd nanoparticles are monodispersed, and their size was uniform

Figure 2. Adsorption kinetic curves of Pd(II) by hybrid microspheres at 25 °C.

shows the adsorption of Pd(II) by the microspheres at 25 °C. It can be observed that the adsorption process contained two stages. In the first stage, the adsorption amount of Pd(II) reached 50.75 mg/g in merely 10 min. After that, the adsorption rate suddenly decreased to a very low level so that the adsorption amount was increased only 10 mg/g in 12 h. This phenomenon may be caused by the decrease of concentration gradient of Pd(II). The adsorption result

Figure 3. (a, b) Normalized intensity of X-ray photoelectron spectroscopy for element N before and after adsorption. (c, d) Normalized intensity of X-ray photoelectron spectroscopy for element Pd before and after reduction. 12658


Article


Figure 4. (a, b) TEM characterization of Pd nanoparticles on hybrid microspheres and their size distribution with loading amounts of 10 mg/g and 30 mg/g. (c) TEM characterization of lattice fringes of Pd nanoparticles on hybrid microspheres. (d) XRD characterization of hybrid microspheres after Pd loading. The peak and its corresponding structures have been marked.

after adsorption and reduction on microspheres, with no apparent metal aggregation. Figure 4a and b also show that the Pd nanoparticles had average size of 2−3 nm calculated by the software of NanoMeasurer. Besides, the lattice fringes with the spacing of 0.224 nm of the nanoparticles can be clearly observed in Figure 4c. The exact lattice spacing of [1,1,1], which is proved to be the main catalytic crystal in hydrogenation reaction, was 0.224 nm.24 Moreover, X-ray diffraction characterization on the prepared catalyst was conducted to confirm the catalytic crystal. As shown in Figure 4d, an obvious diffraction peak was observed at 40°, implying that the main exposure crystal of Pd(0) was [1, 1, 1], which approximately has a lattice spacing of 0.224 nm and was consistent with the results of TEM. In addition, the first peak indicates the existence of noncrystalline structure such as silica (PDF: 29−0085) in the microspheres. 3.3. Performance of Supported Pd Catalysts in Hydrogenation of Cyclohexene. The supported Pd catalyst was packed in a mini fixed-bed reactor for the hydrogenation of cyclohexene to test its catalytic activity. Figure 5a and b show the effects of the gas/liquid ratio and reaction temperature on the conversion ratio of this reaction, respectively. The conversion ratio of cyclohexene increased at first and then decreased with the increase of the gas/liquid ratio. This phenomenon may be attributed to two reasons. On one hand, the mixing of gas and liquid was gradually enhanced with the increase of the gas/liquid ratio, which was conducive to the process of hydrogenation. On the other hand, the increase of the gas/liquid ratio would lead to the decrease of residence

time, which could lessen the contacting time between the mixture and the catalyst, resulting in the reduction of the conversion. The increase of the temperature would make the hydrogenation reaction faster, as shown in Figure 5b. Therefore, when the cyclohexene’s initial concentration was 1000 ppm, the conversion ratio of cyclohexene could reach 100% at 340 K by the catalyst with a Pd loading amount of 30 mg/g with the fixed gas/liquid ratio of 25 and pressure of 0.1 MPa. As expected, the silica/chitosan microspheres without Pd loading showed absolutely no catalytic activity for this reaction. The catalyst with a Pd loading amount of 30 mg/g has the higher activity than the catalyst with a Pd loading amout of 10 mg/g. This may be caused by two factors. First, the average Pd nanoparticle size did not become larger with the increase of the loading amount because of the chelation, as shown in Figure 5b, which implies that the supported catalyst with a larger Pd loading amount would provide more active sites for the hydrogenation. Besides, the core−shell structure ensured that the mass transfer resistance that played a decisive role for the rate of hydrogenation could be further reduced as the increased amount of Pd was much more loaded on the shell layer of the microsphere rather than core. The effects of pressure and cyclohexene’s initial concentration on conversion were studied as well, as shown in Figure 5c. It can be seen that the increase of the pressure would result in a little faster hydrogenation reaction rate. As to cyclohexene’s initial concentration, the conversion would decrease largely 12659


Article


Figure 5. (a) Effect of the gas/liquid ratio on conversion. The temperature was fixed at 300 K. (b) Effect of the temperature and loading amount on conversion. The gas/liquid ratio was fixed at 25. (c) Effect of the inlet pressure and loading amount on conversion. The temperature was fixed at 300 K, and the gas/liquid ratio was fixed at 25.

Table 2. Comparison between Different Catalysts or Conditions sample

loading amount (mg/g)

initial concentration (wt %)

reaction temperature (K)

TOF (min−1)

ref

chitosan/silica microspheres chitosan/silica microspheres chitosan/silica microspheres chitosan/silica microspheres porous glass beads Ir/H-ZSM-5 (HF)

30 30 30 30 31.8 30

0.1 0.2 0.5 5 100 100

300 300 300 300 298 398

0.38 0.69 1.54 5.89 1.12 1.97

this work this work this work this work ref 1 ref 28

The values of the observable kinetic orders, n and m, and of the apparent activation energy Eapp corresponding to the power-law model can be derived from the two-type sites model. The results show that these parameters, n, m, and Eapp are dependent on the surface coverage of cyclohexene and H2 of the operating conditions. The increase of temperature has almost no effect on the surface coverage but will significantly reduce the Eapp, and then increase the kp, so the reaction can be obviously enhanced. On the other hand, the increase of pressure will lead to a higher surface coverage of H2 and a higher m, which can help to enhance the reaction, but meanwhile the higher pressure will make the Eapp become larger to slow the reaction down; thus, the conversion of cyclohexene is not very sensitive to the change of pressure due to its two opposite results. To compare the catalytic activity of the different catalysts, the turnover frequency (TOF) for hydrogenation of cyclohexene in different references or conditions was calculated separately, and the results are shown in Table 2. The TOF would be greatly

with the cyclohexene in the entrance getting thicker and thicker. The mechanism and kinetics of hydrogenation of cyclohexene have been reported in the literature.25−27 The two-type sites model has been built to predict the influence of temperature and pressure on the reaction rate and is in good agreement with the experiment results. It may provide a rational explanation to the effects of temperature and pressure in this work. The empirical power-law model is used to analyze the kinetic data: ( −rCE) = k p × CCE n × C H m

(3)

where CCE means the concentration of cyclohexene, while CH means the concentration of H2. rCE represent the reaction rate of cyclohexene. kp is a kinetic constant dependent on the apparent activation energy Eapp, which is mainly decided by temperature. 12660


Article


Figure 6. (a) Effect of the time of reuse on conversion. The gas/liquid ratio was fixed at 25, and the loading amount of Pd was 30 mg/g. (b, c) TEM characterization of Pd nanoparticles on hybrid microspheres and their size distribution after 7 days’ reuse.

between support and Pd offered by chelation. However, the conversion actually decreased slightly from 91.3% to 84.1% after operation for 42 h. This phenomenon might be due to the slight increase of the average Pd nanoparticle size in the microspheres, also shown in Figure 6c.

raised with the concentration of cyclohexene in the entrance getting higher. When the initial concentration of cyclohexene reached 5 wt %, the TOF was 5.89 min−1 in this work. Under almost the same loading amount and temperature, the Pd supported on porous glass beads prepared by Shen et al.1 showed a TOF of 1.54 min−1 with even pure cyclohexene as the liquid reactant. Besides, the Ir/H-ZSM-5 (HF) catalyst prepared by Aboul-Gheit et al.28 has the best performance with the TOF of 1.97 min−1 at 125 °C. Therefore, the silica/ chitosan core−shell hybrid-microsphere-supported Pd catalyst showed higher catalytic activity. 3.4. Study of Catalytic Stability of Silica/Chitosan Core−Shell Hybrid Microspheres as Catalyst Supports. The catalytic stability of silica/chitosan core−shell hybridmicrosphere-supported catalyst was also studied based on the optimized conditions (the gas/liquid ratio was fixed at 25 and the loading amount of Pd was 30 mg/g). The supported catalyst was reused and recycled in 7 days, 6 h per day continuously. The conversion was measured every hour to get an average conversion result for each day. As shown in Figure 6a, the prepared supported catalyst could be reused for 7 days with no obvious activity loss, which indicated that the catalyst had good stability and maintained good catalysis performance even after several days. TEM images of the recycled catalysts would help us to understand its excellent catalytic performance better. As shown in Figure 6b, the supported Pd nanoparticles kept welldispersed and no obvious aggregation occurred after 7 days’ reuse, which was mainly attributed to the strong interaction

4. CONCLUSION In this paper, silica/chitosan core−shell hybrid microspheres with uniform size distribution as well as good sphericity were prepared by a facile microfluidic method. The presolidification time and gelation time were adjusted to optimize the structure of microspheres for the loading of Pd(II) and catalytic hydrogenation. Palladium ions were mainly adsorbed onto the shell layer of microspheres via chelation and then reduced to Pd(0) by NaBH4 at room temperature. TEM images showed that Pd nanoparticles loaded on the microspheres were monodispersed and had an average diameter of 2−3 nm with fcc (face-centered cubic) structure. The silica/chitosan core−shell hybrid microspheres with Pd nanoparticles loading were used as the catalyst for hydrogenation of cyclohexene and the catalytic performance of hydrogenation of cyclohexene under different operating condition in a fixed bed reactor had been studied in detail. The results showed the catalyst had good catalytic performance compared with catalysts prepared in other references due to its core−shell structure and the chelation between Pd(II) and chitosan. Moreover, the supported catalyst had excellent stability with relatively high catalytic performance for 7 days 12661


Article


(15) Berguerand, C.; Yuranov, I.; Cárdenas-Lizana, F.; Yuranova, T.; Kiwi-Minsker, L. Size-controlled Pd nanoparticles in 2-butyne-1, 4-diol hydrogenation: support effect and kinetics study. J. Phys. Chem. C 2014, 118 (23), 12250−12259. (16) Luo, C.; Zhang, Y.; Wang, Y. Palladium nanoparticles in poly (ethyleneglycol): the efficient and recyclable catalyst for Heck reaction. J. Mol. Catal. A: Chem. 2005, 229 (1), 7−12. (17) Liu, G.; Hou, M.; Song, J.; Jiang, T.; Fan, H.; Zhang, Z.; Han, B. Immobilization of Pd nanoparticles with functional ionic liquid grafted onto cross-linked polymer for solvent-free Heck reaction. Green Chem. 2010, 12 (1), 65−69. (18) Lan, W.; Li, S.; Xu, J.; Luo, G. One-step synthesis of chitosansilica hybrid microspheres in a microfluidic device. Biomed. Microdevices 2010, 12 (6), 1087−1095. (19) Narayanan, R. K.; Nethran, N. K.; Devaki, S. J.; Rao, T. P. Robust polymeric hydrogel using rod-like amidodiol as crosslinker: Studies on adsorption kinetics and mechanism using dyes as adsorbate. J. Appl. Polym. Sci. 2014, 131 (18), 1. (20) Cui, Q.; Zhao, H.; Luo, G.; Xu, J. An efficient chitosan/silica composite core-shell microspheres supported Pd catalyst for aryl iodides Sonogashira coupling reactions. Ind. Eng. Chem. Res. 2017, 56, 143. (21) Barr, T. L. An ESCA study of the termination of the passivation of elemental metals. J. Phys. Chem. 1978, 82 (16), 1801−1810. (22) Sohn, Y.; Pradhan, D.; Leung, K. Electrochemical Pd nanodeposits on a Au nanoisland template supported on Si (100): Formation of Pd− Au alloy and interfacial electronic structures. ACS Nano 2010, 4 (9), 5111−5120. (23) Li, Y.; Jang, B. W. Non-thermal RF plasma effects on surface properties of Pd/TiO 2 catalysts for selective hydrogenation of acetylene. Appl. Catal., A 2011, 392 (1), 173−179. (24) Silvestre-Albero, J.; Rupprechter, G.; Freund, H.-J. Atmospheric pressure studies of selective 1, 3-butadiene hydrogenation on Pd single crystals: effect of CO addition. J. Catal. 2005, 235 (1), 52−59. (25) Cazaña, F.; Jimaré, M.; Romeo, E.; Sebastián, V.; Irusta, S.; Latorre, N.; Royo, C.; Monzón, A. Kinetics of liquid phase cyclohexene hydrogenation on Pd−Al/biomorphic carbon catalysts. Catal. Today 2015, 249, 127−136. (26) Siegel, S.; Ohrt, D. The Kinetics and Mechanism of the Hydrogenation of Cyclohexene Catalyzed by Chlorotris (triphenylphosphine) rhodium (I) in Benzene. Inorg. Nucl. Chem. Lett. 1972, 8 (1), 15−19. (27) Voorhoeve, R.; Stuiver, J. The mechanism of the hydrogenation of cyclohexene and benzene on nickel-tungsten sulfide catalysts. J. Catal. 1971, 23 (2), 243−252. (28) Aboul-Gheit, A. K.; Aboul-Gheit, N. A. Iridium/H-ZSM-5 zeolite catalyst promoted via hydrochlorination or hydrofluorination for the hydroconversion of cyclohexene. Appl. Catal., A 2006, 303 (2), 141−151.

without an obvious activity loss, and it will have promising application in other similar hydrogenation reactions.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jianhong Xu: 0000-0002-3550-1345 Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS The authors gratefully thank the support of the National Natural Science Foundation of China (21322604, 21476121). REFERENCES

(1) Shen, C.; Wang, Y.; Xu, J.; Wang, K.; Luo, G. Size control and catalytic activity of highly dispersed Pd nanoparticles supported on porous glass beads. Langmuir 2012, 28 (19), 7519−7527. (2) Kidambi, S.; Dai, J.; Li, J.; Bruening, M. L. Selective hydrogenation by Pd nanoparticles embedded in polyelectrolyte multilayers. J. Am. Chem. Soc. 2004, 126 (9), 2658−2659. (3) Montsch, T.; Heuchel, M.; Traa, Y.; Klemm, E.; Stubenrauch, C. Selective hydrogenation of 3-Hexyn-1-ol with Pd nanoparticles synthesized via microemulsions. Appl. Catal., A 2017, 539, 19−28. (4) Thompson, S. T.; Lamb, H. H. Catalysts for selective hydrogenation of furfural derived from the double complex salt [Pd (NH 3) 4](ReO 4) 2 on γ-Al 2 O 3. J. Catal. 2017, 350, 111−121. (5) Jeon, H.-j.; Chung, Y.-M. Hydrogen production from formic acid dehydrogenation over Pd/C catalysts: Effect of metal and support properties on the catalytic performance. Appl. Catal., B 2017, 210, 212−222. (6) Peters, T.; Liron, O.; Tschentscher, R.; Sheintuch, M.; Bredesen, R. Investigation of Pd-based membranes in propane dehydrogenation (PDH) processes. Chem. Eng. J. 2016, 305, 191−200. (7) Xie, S.; Liu, Y.; Deng, J.; Zhao, X.; Yang, J.; Zhang, K.; Han, Z.; Arandiyan, H.; Dai, H. Effect of transition metal doping on the catalytic performance of Au−Pd/3DOM Mn 2 O 3 for the oxidation of methane and o-xylene. Appl. Catal., B 2017, 206, 221−232. (8) Liu, C.-H.; Lin, C.-Y.; Chen, J.-L.; Lu, K.-T.; Lee, J.-F.; Chen, J.M. SBA-15-supported Pd catalysts: The effect of pretreatment conditions on particle size and its application to benzyl alcohol oxidation. J. Catal. 2017, 350, 21−29. (9) Shi, Z.; Li, B.; Wan, X.; Cheng, J.; Fang, Z.; Cao, B.; Qin, C.; Wang, Y. Suzuki−Miyaura Coupling Reaction by PdII-Catalyzed Aromatic CH Bond Activation Directed by an N-Alkyl Acetamino Group. Angew. Chem., Int. Ed. 2007, 46 (29), 5554−5558. (10) Marion, N.; Navarro, O.; Mei, J.; Stevens, E. D.; Scott, N. M.; Nolan, S. P. Modified (NHC) Pd (allyl) Cl (NHC= N-heterocyclic carbene) complexes for room-temperature Suzuki− Miyaura and Buchwald− Hartwig reactions. J. Am. Chem. Soc. 2006, 128 (12), 4101−4111. (11) Zhao, H.; Xu, J.; Lan, W.; Wang, T.; Luo, G. Microfluidic production of porous chitosan/silica hybrid microspheres and its Cu (II) adsorption performance. Chem. Eng. J. 2013, 229, 82−89. (12) Wen, X.; Li, R.; Yang, Y.; Chen, J.; Zhang, F. An egg-shell type Ni/Al 2 O 3 catalyst derived from layered double hydroxides precursor for selective hydrogenation of pyrolysis gasoline. Appl. Catal., A 2013, 468, 204−215. (13) Liao, X.; Zhang, Y.; Hill, M.; Xia, X.; Zhao, Y.; Jiang, Z. Highly efficient Ni/CeO 2 catalyst for the liquid phase hydrogenation of maleic anhydride. Appl. Catal., A 2014, 488, 256−264. (14) Regenhardt, S. A.; Meyer, C. I.; Garetto, T. F.; Marchi, A. J. Selective gas phase hydrogenation of maleic anhydride over Nisupported catalysts: effect of support on the catalytic performance. Appl. Catal., A 2012, 449, 81−87. 12662


Chitosan CoreâShell Hybrid-Microsphere-Supported Pd

Recommend Documents

Chitosan CoreâShell Hybrid-Microsphere-Supported Pd