Al2O3 Catalyst for

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Highly Dispersed Manganese Based Mn/N−C/Al2O3 Catalyst for Selective Oxidation of the C−H Bond of Ethylbenzene Wan-Fei Xu, Wen-Jing Chen, De-Chang Li, Bin-Hai Cheng, and Hong Jiang* CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China Ind. Eng. Chem. Res. Downloaded from pubs.acs.org by NEW JERSEY INST OF TECHNOLOGY on 03/05/19. For personal use only.

S Supporting Information *

ABSTRACT: The solvent-free oxidation of ethylbenzene to acetophenone with high conversion rate and selectivity is of great importance. Herein, a catalyst composed of nitrogen-doped carbon and mesoporous alumina supported manganese (Mn) was prepared by pyrolysis and calcination. We demonstrated its excellent catalytic activity (27.8%), selectivity (>99%), and stability (without a significant decrease over eight cycles) for the solvent-free oxidation of ethylbenzene with molecular oxygen. In the heterogeneous catalytic system, phenanthroline had two functions. First, it acted as a versatile chelating ligand to lock Mn and improve its dispersity. Second, it served as a nitrogen source to provide doped pyridine-N (9.4%), which promoted the adsorption and bond breaking of molecular oxygen. More abundant active Mn in the bulk phase than on the surface guaranteed the stability and reusability of the catalyst. Meanwhile, the mesoporous aluminum oxides provided a stable support for active components and adsorption sites for reactants.

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INTRODUCTION

reported for the oxidation of ethylbenzene in solvent-free catalytic system. Second, the conversion rate and selectivity of ethylbenzene are the main factors that can affect a heterogeneous and solvent-free catalytic system. Transition-metal-based catalysts were widely used as alternatives to noble metallic catalysts in the oxidation of alkyl aromatics.7,10,13 Manganese (Mn)-based catalysts exhibited superior catalytic performance for ethylbenzene oxidation by O2 compared with other transition metals. However, these reactions were usually performed under liquid-phase conditions. Conversion and selectivity were also not perfect, and it has been reported that only 29% conversion and 85% selectivity were obtained under harsh conditions (10 bar, 110 °C for 6 h).14 To enhance the catalytic performance of heterogeneous catalysts, heteroatom doping (especially nitrogen and oxygen) is considered as one of the most promising candidates,15−17 in which the inherent electron density, spin density, and advanced forms of porosity speed up the electron and/or ion transfer18,19 and contribute to catalytic performance. Qu et al.20 synthesized N-doped graphene quantum dots by facile hydrothermal synthesis route, and the quantum yield could reach 78% and 10 times higher than that of P25 TiO2 under visible light irradiation.

The selective oxidation of ethylbenzene to acetophenone is an important reaction because the product is a crucial platform molecule serving as an intermediate in the production of fine chemicals and pharmaceuticals, such as perfumes, pharmaceuticals, resins, alcohols, esters, and aldehydes.1,2 Conventionally, acetophenone is synthesized by the Friedel−Crafts acylation of arenes by strong acid (e.g., H2SO4 and HF),3 Lewis acids (e.g., AlCl3, BF3, and FeCl3),4,5 or by the oxidation of alkylarenes with stoichiometric inorganic oxidants (e.g., TBHP and H2O2).6,7 However, these reagents are relatively expensive, and could produce noxious and corrosive wastes. Meanwhile, separating catalysts from a reaction mixture renders the process tedious on the industrial scale and thus limits their application. Hence, developing a heterogeneous and solvent-free catalytic system with high selectivity and activity for ethylbenzene oxidation is important. In this catalytic system, the molecular oxgen and porous materials supported metals are promising components. First, molecular oxygen is taken as an ideal oxidant because of its natural, environmentally friendly, and inexpensive characteristics.8−11 Currently, molecular oxygen has been successfully adopted to oxidize alkyl aromatics and produce aromatic ketones in acetic acid media by using the homogeneous cobalt acetate catalyst.12 However, this method has some operational problems associated with corrosive solvents and poor catalyst reusability. Although molecular oxygen has been utilized in different scenarios, it has not been © XXXX American Chemical Society

Received: Revised: Accepted: Published: A

October 29, 2018 February 15, 2019 February 26, 2019 February 26, 2019 DOI: 10.1021/acs.iecr.8b05328 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

ambient dried, ground to a fine powder, and annealed in a tubular furnace initially in Ar atmosphere at 800 °C for 1 h and subsequently in ambient atmosphere at 300 °C for 1 h at 5 °C/ min heating rate. The product was Mn/N−C/Al2O3. Mn/ Al2O3 and N−C/Al2O3 were then prepared by the same procedure without adding any nitrogen precursor or Mn salt. To compare the effects of different transition metals, FeCl2· 4H2O, CoCl2·6H2O, or NiCl2·6H2O was used to replace MnCl2·4H2O, and the other processes were conducted in the same manner. To verify the effect of pretreatment at 800 °C, we calcined the powder obtained by grinding at 300 °C for 2 h under ambient conditions without pretreatment at 800 °C. Catalytic Activity and Reusability Measurement. Catalytic activity of the oxidation of ethylbenzene with molecular O2 was determined in a 25 mL Parr reactor. (Anhui Kemi Machinery Technology Co., Ltd., China). Reactor temperature was monitored with a PID temperature controller and heated in a separate heating furnace. Pressure was determined with a piezometer. The catalytic hydrogenation of aromatic nitro compound was carried out with an initial O2 (99.999%) pressure of 8 bar and 120 °C for 6 h. In a typical experiment, 10 mL of reaction substrate and 50 mg of catalyst were mixed without any solvent in an autoclave. The reactor was purged with 8 bar O2 three times to remove air before sealing tightly and pressurizing to 8 bar with O2. The reactants were stirred at 500 rpm and 120 °C for 6 h. The remaining O2 was carefully vented after the autoclave was naturally cooled to room temperature (25 °C). The products and catalyst were separated by centrifugation and stored in a freezer (4 °C) for subsequent analyses. The contents of products were analyzed by gas chromatography (GC) and gas chromatography−mass spectrometry (GC-MS). For reusability tests, the reaction conditions were maintained the same as above-mentioned except for the use of the recovered catalyst. The catalyst was recovered by centrifugation and used for the next run immediately without rinsing, drying, or any other post-treatment. Characterizations. The morphology of the samples was investigated using a field-emission SEM (Zeiss Supra 55, Germany) and JEM-2100F field-emission TEM (JEOL, Japan). BET surface area was determined by nitrogen adsorption with a Micromeritics ASAP 2020 Plus analyzer at −196 °C over P/P0 = 0.0−1.0. Approximately 0.1 g of the sample was used for each analysis. Determination of surface chemical composition (C, O, N, and Mn) was carried out on XPS with Al Kα (hv = 1486.6 eV), which was provided by ESCALAB 250 (Thermo-VG Scientific, UK). The binding energy of C 1s (287.5 eV) was used as a reference to calibrate the binding energy of the catalysts. Baseline calibration was conducted by the Shirley method. All binding energies obtained were precise to within ±0.2 eV. Powder XRD patterns were obtained using a Rigaku D/maxγA rotating-anode diffractometer equipped with Cu-kα radiation (λ = 1.54056 Å) within 20°−70° scan range. The contents of products were analyzed on a GC (GC1690, Hangzhou Kexiao Chemical Equipment Co., Ltd., China) equipped with an OV-1701 column (30 m × 0.32 mm i.d. × 1 μm film thickness) and GC−MS (Thermo Trace GC Ultra with an ISQ i mass spectrometer) equipped with an SE-30MS capillary column (50 m × 0.25 mm i.d. × 0.25 μm film thickness). All the detectors used were flame ionization detector (FID). An X Series 2 (Thermo fisher Scientific, USA) inductively coupled plasma atomic emission spectrom-

Third, porous supports with well-ordered pores, high surface area, uniform pore-size distribution, and large pore volume are necessary for heterogeneous catalysts.21,22 For instance, Chen et al.13 successfully prepared methyl modified Co-SiO2 nanocomposite (Me-Co-SiO2) and applied it to oxide ethylbenzene by molecular O2. Though the conversion rate reached 39.0%, the selectivity was only 77.2% and the SiO2 based catalysts were not stable. Compared with SiO2, alumina has several attractive features, such as intermediate metal− support interaction strength, good mechanical properties, adjustable pore structure, and high resistance to attrition, which benefit metal dispersity and catalyst recovery.23−25 On the basis of the above-mentioned factors influencing the catalytic performance in ethylbenzene oxidation and our previous research on pyrolysis method,26,27 we herein synthesized a nitrogen-doped carbon and alumina (Mn/N− C/Al2O3) supported manganese based catalyst by pyrolysis of the precursors of Mn, 1,10-phenanthroline (PNL), and alumina. Pyrolysis was divided into two steps; the first was conducted under Ar atmosphere, and the second was calcinated in air to obtain oxidized-state Mn. 1,10-PNL, which contains two pyridinic-type nitrogen species, was used as a nitrogen source that can decompose into N-containing small molecules and deposited in situ on alumina to enhance its electrical properties efficiently and provide more active sites for catalytic reactions.28,29 Meanwhile, as a versatile chelating ligand in coordination chemistry, 1,10-PNL can produce homogeneous and stable metal complexes by chelating Mn ions during preparation, which may significantly improve the dispersity of Mn.30 The as-prepared Mn/N−C/Al2O3 catalyst was systematically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR). Catalytic activity and selectivity toward the solvent-free oxidation of ethylbenzene by O2 were evaluated. The synergistic effect of doped N and Mn species was investigated by a series of controlled experiments and characterization.

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MATERIALS AND METHODS Materials. Al(OH)3, FeCl2·4H2O, CoCl2·6H2O, NiCl2· 6H2O, MnCl2·4H2O, NaOH, hydrochloric acid (HCl), nitric acid (HNO3), and 1,10-PNL (>99%) were supplied by Sinopharm Chemical Reagent Co.. All reagents were used without further purification. Catalyst Preparation. Preparation of Boehmite (Aluminum Oxyhydroxide, γ-AlOOH). γ-AlOOH is the precursor of γ-alumina, which has a high surface area and is widely used as a support of refining catalysts. A classic method of synthesizing γ-AlOOH was performed. First, 34 g of Al(OH)3 was added to 75 mL of 40 wt % NaOH solution, which was then heated to dissolve aluminum hydroxide and properly supplemented with water during the process. Second, pH was adjusted to 8.5−9.0 with hydrochloric acid solution (1:1, v/v), and the mixture was aged for 2 h at 60 °C. At the end of aging, the precipitate was filtered and washed with hot deionized water to remove Na+ and Cl−. Cl− was detected with 1 M silver nitrate solution. Preparation of Mn/N−C/Al2O3. MnCl2·4H2O (99 mg, 0.5 mmol) and PNL (1.0 mmol) were stirred in ethanol (20 mL) for 15 min at room temperature. Then, the mixture was stirred in a water bath at 60 °C for 1 h. The support AlOOH (691.2 mg) was added, and the mixture was stirred at room temperature overnight. The residue was rotary evaporated, B

DOI: 10.1021/acs.iecr.8b05328 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article


Figure 1. (a) XRD patterns of Al2O3 and Mn/N−C/Al2O3; (b) representative SEM image of Al2O3; SEM image (c) and BSE image (d) of Mn/ N−C/Al2O3Al2O3; (e) SEM image and (f) BSE image of Mn/Al2O3.

Figure 2. Representative EM images of (a, c) Mn/N−C/Al2O3 and (b, d) the energy-dispersive spectrometer of corresponding circle region.

process, catalysts were pretreated in Ar at 100 °C for 2 h to remove impurity gas and water in the system.

etry (ICP-AES) spectrometer was used to determine the amount of Mn encapsulated in Al2O3. A H2 temperature program reduction characterization (H2TPR) with a thermal conductivity detector (TCD) was conducted to study the reductive behaviors of samples. During experiments, the samples were exposed to 10% (v/v) H2/Ar at a flow rate of 5 cm3 min−1, and the temperature was increased from 100 to 750 °C (heating rate = 5 °C min−1). Before a TPR

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RESULTS AND DISCUSSION Structure and Composition Analyses. Figure 1a depicts the powder XRD patterns of Al2O3 and Mn/N−C/Al2O3. No difference exists in the shape of the peaks between the two samples. The presence of the alumina peak and the absence of C


Article


Figure 3. N2 adsorption−desorption isotherms of (a) Al2O3 and (b) Mn/N−C/Al2O3, inset is pore size distribution based on the desorption branch of BJH model.

stronger monolayer−-multilayer adsorption compared with Al2O3. BJH model analysis reveals that the pore volume and pore diameter of Mn/N−C/Al2O3 are ca. 0.24 cm3/g and ca. 9.95 nm, respectively, whereas those of Al2O3 are ca. 0.22 cm3/ g and ca. 4.53 nm, respectively. Although both Al2O3 and Mn/ N−C/Al2O3 predominantly exhibit a mesoporous nature according to IUPAC classification,33 the pore size of Mn/ N−C/Al2O3 increase compared with that of Al2O3. The pore size of Mn/N−C/Al2O3 is concentrated in two intervals (35 and 73 Å) and that of Al2O3 is on 39 Å. By comparing the curves of Al2O3 and AlOOH (Figure S1), it can be found that the heating treatment did not affect the pore size distribution of Al2O3. As a catalyst support, alumina was used to increase the dispersion of active metals and contact area with reactants. To verify this conjecture, we prepared Mn/N−C material without Al2O3 addition. The specific surface area of Mn/N−C is 10.21 m2/g, obviously lower than the 75.12 m2/g of Mn/N− C/Al2O3, whereas the content of Mn in Mn/N−C is definitely higher than that in Mn/N−C/Al2O3. Thus, the Al2O3 addition greatly improved the dispersion of Mn. After the Mn loading, the specific surface area of Al2O3 decreased from 256.86 to 75.12 m2/g (Table 1), which may because the complex of phenanthroline and Mn entered and filled part of the pores of Al2O3.

the Mn peak are observed, suggesting that Mn exists mainly in amorphous form or at a lower-level content. As shown in the SEM images (Figures 1b, c), the substrate surface is extremely rough and has flowerlike folds in the local area, which provide a large surface area that benefits the mass transfer and reaction. However, no difference after Mn loading and no pattern of Mn are observed, confirming that Mn mainly exists in amorphous form. To verify the existence of Mn, backscattered electron (BSE) images were obtained, in which a higher atomic number means a stronger backscatter.31 The atomic number of Mn far exceeds that of aluminum, leading to a large difference in contrast, which indicates the brightest dots in the picture may be Mn. The uniform distribution of bright spots on the basement confirmed the homogeneous dispersion of Mn, which can be attributed to the complexation of phenanthroline to Mn2+ during the preparation stage (Figure 1d). In contrast, a large bright spot can be seen in the BSE image of Mn/Al2O3 (Figure 1e, f), which means a part of Mn agglomerates into large particles. Therefore, the phenanthroline played an important role in the dispersion of the active metal Mn. To further explore the form of Mn, we obtained TEM images. As shown in Figure 2a, c, Mn in any pattern is not observed and only flake alumina is present. The images clearly display the uniform pores after the Mn ions were incorporated, indicating that the mesoporous structure did not change during synthesis, which agree well with the results of XRD and BET analyses. Several different regions were randomly selected for electronic energy spectrum analysis (Figures 2b and 2d), and the contents of the specific elements are shown in Table S1. Results show that Mn was homogeneously dispersed in alumina. XRD and surface imaging analyses indicate that amorphous Mn was uniformly loaded on the alumina supports while the surface structure of supports remained unchanged after thermal treatment. The nitrogen adsorption−desorption analysis was performed to further confirm the porous structure of Al2O3 before (Figure 3a) and after (Figure 3b) loading. Before loading, the nitrogen adsorption−desorption isotherm of Al2O3 exhibits a typical characteristic of type V isotherm, which shows pore condensation and hysteresis. The initial part is related to adsorption isotherms of type III, which is caused by relatively weak attractive interactions between adsorbent and adsorbate.32 After loading, the nitrogen adsorption−desorption isotherm of Mn/N−C/Al2O3 exhibits a typical characteristic of type-IV curve with an almost horizontal plateau at low relative pressures, and the initial part can be attributed to a relatively

Table 1. Pore Structure of Various Catalysts sample AlOOH Al2O3 Mn/N−C/ Al2O3 Mn/N−C

surface area (m2/g)

BJH pore size D (Å)

pore volume (cm3/g)

256.86 283.87 75.12

45.31 40.58 99.48

0.22 0.31 0.24

10.21

69.05

Fe > Co > Ni. Hence, Mn is the best choice among the transition metals that we examined (Table 2). A series of solvent-free catalytic oxidation processes of ethylbenzene was conducted at different temperatures and pressures (Table 3). Oxidation cannot occur when pressure

Table 2. Solvent-Free Oxidation of Ethylbenzene with Molecular O2 Using Various Catalystsa

entry

catalyst

conv. (%)e

sel. (%)e

1 2 3 4 5 6 7 8 9 10 11

no catalyst Al2O3 N−C/Al2O3 Mn/Al2O3 N−C/Al2O3 Mn/N−C/Al2O3b Mn/N−C/Al2O3c Mn/N−C/Al2O3d Fe/N−C/Al2O3 Co/N−C/Al2O3 Ni/N−C/Al2O3

6.7 6.8 6.8 18.1 7.8 27.8 19.5 21 25.1 12.7 6.2

80 78 75 82 63 >99 >99 >99 >99 >99 >99

a

Reaction conditions: 10 mL of ethylbenzene, 50 mg of catalyst, 120 °C, 8 bar O2, 6 h. bMn/N/Al2O3 was calcinated under an Ar atmosphere at 800 °C for 1 h and under ambient atmosphere at 300 °C for 1 h at the heating rate of 5 °C/min. cMn/N/Al2O3 was calcinated under an Ar atmosphere at 800 °C for 1 h at the heating rate of 5 °C/min directly. dMn/N/Al2O3 was calcinated under an ambient atmosphere at 500 °C for 2 h at the heating rate of 5 °C/min directly. eConversion and selectivity were determined by GC (internal standard: n-dodecane).

Table 3. Solvent-Free Oxidation of Ethylbenzene with Molecular O2 by Mn/N−C/Al2O3 at Different Initial Pressure and Temperaturea

N−C/Al2O3 can be attributed to the synergistic interaction among Mn and phenanthroline. The function of N is mainly reflected in two aspects. First, as discussed above, in the preparation stage, N-containing phenanthroline was acted as a ligand to form coordination bonds with Mn ions, and then loaded on the support to improve the content and dispersion of the active metal. Second, a part of N is retained in the material after heat treatment, which existed mainly in forms of pyridinic N bonded with Mn and graphitic N. The MnNx is normally an effective catalyst for the oxidation reaction.38 The N-doped carbon has little direct catalytic activity in this oxidation reaction, which can be proved by catalytic performance of N− C/Al2O3 in the later section. However, the presence of Ndoped carbon may assist in enhancing the catalytic effect of Mn by improving the adsorption and bond breaking of oxygen. Carbon atoms linked to nitrogen atom have a higher positive charge density. For instance, pyridinic N possesses one lone electron pair except for the one electron donated to the conjugated π bond system. Delocalized π electrons are capable of nucleophilic attack, endowing the carbon with Lewis basicity. This can enhance the adsorption of O2 and intermediates, which has been widely accepted by researchers.39,45 The charge delocalization induced by nitrogen atoms can also change the chemisorption mode of O2. Detailedly, undoped carbon atoms adsorb oxygen atoms with monatomic end-on adsorption mode (Pauling model), whereas doped carbon atoms with nitrogen atoms adsorb oxygen atoms with diatomic side-on adsorption mode (Yeager model). This effectively weakens the O−O bond and facilitates the reduction of O2 under the catalysis of Mn.40,41 To confirm this hypothesis, urea was used as a chelating ligand and N source instead of phenanthroline. Keeping other experimental conditions unchanged, we prepared a new catalyst sample

entry

pressure (bar)

T (°C)

conv. (%)b

sel. (%)b

1 2 3 4 5 6 7 8

8 8 8 8 7 6 5 4

140 120 100 80 120 120 120 120

30.5 27.8 2.1 0 26.6 23.4 4.6 0

>99 >99 >99 >99 >99 >99 -

a

Reaction conditions: 10 mL Ethylbenzene, 50 mg catalyst, 6 h. Conversion and selectivity were determined by GC (internal standard: n-dodecane).

b

and temperature are low, and high pressure and temperature benefit the reaction. A higher conversion rate can be obtained when the pressure and temperature are both high. On one hand, oxygen molecules are used as a reactant and need to be transferred from gas to liquid phase, and high pressure is beneficial to phase transfer of gas. On the other hand, high temperature helps increase the kinetic constants of the reaction, increase the saturated vapor pressure of the liquid phase, and finally increase the pressure of the reaction system. Study on Reaction Kinetics. We also studied the reaction kinetics in the solvent-free oxidation of ethylbenzene with molecular O2 at 8 bar and 120 °C over Al2O3, Mn/N−C/ Al2O3, and blank catalysts, respectively (Figure 6). An induction period of 3 h was observed before the reaction started, which agrees well with the previous reports.46,47 It was F


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Figure 6. (a) Reaction kinetics in the solvent-free oxidation of ethylbenzene with molecular O2 over Mn/N−C/Al2O3. Reaction conditions: 50 mg of catalyst, 10 mL of ethylbenzene, 120 °C, 8 bar. (b) Schematic diagram for the action mechanism of the Mn/N−C/Al2O3.

indicated that the decline of catalytic activity was attributed to the leaching of Mn. According to ICP-AES analysis, the content of Mn in bulk Mn/N−C/Al2O3 (12.23 wt %, Table S7) is higher than the content on surface (7.76 wt %, Table S3). Given that the detection depth of XPS is only several nanometers and ICP-AES measures the metal content in the whole sample matrix, it suggests that Mn is mainly dispersed in the bulk alumina instead of adsorbing on the surface. The active components in the bulk phase are more stable, and then benefit for the stability and reusability of the catalyst.

deemed that some changes occurred in the Mn species during the induction period due to the interaction between Mn and reactants. New active Mn species (the exact structure of the active Mn species has not been proposed) formed through the coordination with the byproduct benzoic acid, and this process took some time.47 The kinetic curve of alumina was almost the same as that in the blank, showing that alumina had little effect on the promotion of dynamics. About 7.2% conversion of acetophenone was obtained after 8 h of reaction when Al2O3 was used alone, whereas the conversion rate was greatly improved and reached 30.4% when the catalyst was replaced with Mn/N−C/Al2O3 under the same conditions. In addition, the reaction rate constant of Mn/N−C/Al2O3 was significantly better than that of Al2O3. A simple catalytic process is proposed based on literatures (Figure 6b).48,49 The catalyst adsorbs and activates oxygen to produce radical •O−O−Mn/ N−C/Al2O3, which will attack β-H in ethylbenzene to produce intermediates. The catalyst then continues to attack another H to produce acetophenone. Recycle Capability. Stability and reusability are always used to assess heterogeneous catalysts. In this sense, Mn/N− C/Al2O3 was utilized in successive runs without any post treatment. As shown in Figure 7, in the initial eight cycles, sufficient catalytic activity could be preserved and the conversion rate keeps a steady value. After that, the activity of catalyst began to decline; in the ninth cycle, Mn/N−C/ Al2O3 only had 25% yield. One cause of catalyst deactivation is the loss of the active component. ICP-AES results (Table S6)

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CONCLUSIONS We prepared nitrogen-doped carbon and alumina supported manganese based material and demonstrated its excellent catalytic activity, high selectivity, and good stability for the solvent-free oxidation of ethylbenzene with molecular oxygen. In the heterogeneous catalytic system, phenanthroline contributed to locking more Mn, and Mn and phenanthroline had a synergistic effect on molecular oxidation. In the oxidation process, Mn2+ was the major active component that catalyzed the reaction, and the abundant active components in the bulk phase guaranteed the stability and reusability of the catalyst. These findings can guide the design of highly active, highly selective, and reusable heterogeneous catalysts for challenging molecule syntheses.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.8b05328. Tables S1−S7 and Figures S1−S2 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail:[email protected]. ORCID

Hong Jiang: 0000-0002-4261-7987 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from National Natural Science Foundation of China (21677138, 41601203), the Key Special Program on the S&T for the

Figure 7. Reuse of Mn/N−C/Al2O3, reaction conditions: 10 mL of ethylbenzene, 50 mg of catalyst, 120 °C, 8 bar O2, 6 h. The target product yields were determined by GC (internal standard: ndodecane). G


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(19) Dou, S.; Shen, A.; Tao, L.; Wang, S. Molecular doping of graphene as metal-free electrocatalyst for oxygen reduction reaction. Chem. Commun. 2014, 50, 10672−10675. (20) Qu, D.; Zheng, M.; Du, P.; Zhou, Y.; Zhang, L.; Li, D.; Tan, H.; Zhao, Z.; Xie, Z.; Sun, Z. Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts. Nanoscale 2013, 5, 12272−12277. (21) Raja, R.; Sankar, G.; Thomas, J. M. Powerful redox molecular sieve catalysts for the selective oxidation of cyclohexane in air. J. Am. Chem. Soc. 1999, 121, 11926−11927. (22) Kuwahara, Y.; Tsuji, K.; Ohmichi, T.; Kamegawa, T.; Mori, K.; Yamashita, H. Waste-slag hydrocalumite and derivatives as heterogeneous base catalysts. ChemSusChem 2012, 5, 1523−1532. (23) Lu, A. H.; Schüth, F. Nanocasting: a versatile strategy for creating nanostructured porous materials. Adv. Mater. 2006, 18, 1793−1805. (24) Borg, Ø.; Eri, S.; Blekkan, E. A.; Storsæter, S.; Wigum, H.; Rytter, E.; Holmen, A. Fischer−Tropsch synthesis over γ-aluminasupported cobalt catalysts: effect of support variables. J. Catal.2007,248, 89−100. (25) Gangwar, J.; Gupta, B. K.; Tripathi, S. K.; Srivastava, A. K. Phase dependent thermal and spectroscopic responses of Al2O3 nanostructures with different morphogenesis. Nanoscale 2015, 7, 13313−13344. (26) Chen, S.-Q.; Chen, Y.-L.; Jiang, H. Slow pyrolysis magnetization of hydrochar for effective and highly stable removal of tetracycline from aqueous solution. Ind. Eng. Chem. Res. 2017, 56, 3059−3066. (27) Liu, W.-J.; Jiang, H.; Yu, H.-Q. Development of biochar-based functional materials: toward a sustainable platform carbon material. Chem. Rev. 2015, 115, 12251−12285. (28) Kong, X.-k.; Sun, Z.-y.; Chen, M.; Chen, C.-l.; Chen, Q.-w. Metal-free catalytic reduction of 4-nitrophenol to 4-aminophenol by N-doped graphene. Energy Environ. Sci. 2013, 6, 3260−3266. (29) Shang, L.; Zeng, B.; Zhao, F. Fabrication of novel nitrogendoped graphene−hollow AuPd nanoparticle hybrid films for the highly efficient electrocatalytic reduction of H2O2. ACS Appl. Mater. Interfaces 2015, 7 (1), 122−128. (30) Sammes, P. G. G. Y. 1, 10-Phenanthroline: a versatile ligand. Chem. Soc. Rev. 1994, 23, 327−333. (31) Goldstein, J.; Newbury, D. E.; Echlin, P.; Joy, D. C.; Romig, A. D. J.; Lyman, C. E.; Lifshin, E. Scanning Electron Microscopy and X-ray Microanalysis, 3rd ed.; Kluwer Academic/Plenum Publishers: New York, 2003. (32) Ryu, Z.; Zheng, J.; Wang, M.; Zhang, B. Characterization of pore size distributions on carbonaceous adsorbents by DFT. Carbon 1999, 37, 1257−1264. (33) Rouquerol, J.; Fairbridge, C. Recommendations for the characterization of porous solids (Technical Report). Pure Appl. Chem. 1994, 66, 1739−1758. (34) Nesbitt, H.; Banerjee, D. Interpretation of XPS Mn (2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO2 precipitation. Am. Mineral. 1998, 83, 305−315. (35) Gómez, S.; Giraldo, O.; Garcés, L. J.; Villegas, J.; Suib, S. L. New synthetic route for the incorporation of manganese species into the pores of MCM-48. Chem. Mater. 2004, 16, 2411−2417. (36) Sheng, Z.-H.; Shao, L.; Chen, J.-J.; Bao, W.-J.; Wang, F.-B.; Xia, X.-H. Catalyst-free synthesis of nitrogen-doped graphene via thermal annealing graphite oxide with melamine and its excellent electrocatalysis. ACS Nano 2011, 5, 4350−4358. (37) Artyushkova, K.; Kiefer, B.; Halevi, B.; Knop-Gericke, A.; Schlogl, R.; Atanassov, P. Density functional theory calculations of XPS binding energy shift for nitrogen-containing graphene-like structures. Chem. Commun. 2013, 49, 2539−2541. (38) Arshadi, M.; Ghiaci, M.; Rahmanian, A.; Ghaziaskar, H.; Gil, A. Oxidation of ethylbenzene to acetophenone by a Mn catalyst supported on a modified nanosized SiO2/Al2O3 mixed-oxide in supercritical carbon dioxide. Appl. Catal., B 2012, 119−120, 81−90.

Pollution Control, and Treatment of Water Bodies (2017ZX07603-003).

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REFERENCES

(1) Seddon, K. R.; Stark, A. Selective catalytic oxidation of benzyl alcohol and alkylbenzenes in ionic liquids. Green Chem. 2002, 4, 119− 123. (2) Acharyya, S. S.; Ghosh, S.; Bal, R. Surfactant promoted synthesis of CuCr2O4spinel nanoparticles: A recyclable catalyst for one-pot synthesis of acetophenone from ethylbenzene. Ind. Eng. Chem. Res. 2014, 53, 20056−20063. (3) Olah, G. A. In Friedel-Crafts and Related Reactions; WileyInterscience: New York, 1963−1964; Vol. I−IV. (4) Clark, J. H.; Kybett, A. P.; Landon, P.; Macquarrie, D. J.; Martin, K. Catalytic oxidation of organic substrates using alumina supported chromium and manganese. J. Chem. Soc., Chem. Commun. 1989, No. 18, 1355−1356. (5) Lee, D. G.; Spitzer, U. A. Oxidation of ethylbenzene with aqueous sodium dichromate. J. Org. Chem. 1969, 34, 1493−1495. (6) Deng, D.; Chen, X.; Yu, L.; Wu, X.; Liu, Q.; Liu, Y.; Yang, H.; Tian, H.; Hu, Y.; Du, P.; Si, R.; Wang, J.; Cui, X.; Li, H.; Xiao, J.; Xu, T.; Deng, J.; Yang, F.; Duchesne, P. N.; Zhang, P.; Zhou, J.; Sun, L.; Li, J.; Pan, X.; Bao, X. A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature. Sci. Adv. 2015, 1, e1500462. (7) Liu, W.; Zhang, L.; Liu, X.; Liu, X.; Yang, X.; Miao, S.; Wang, W.; Wang, A.; Zhang, T. Discriminating catalytically active FeNx species of atomically dispersed Fe−N−C catalyst for selective oxidation of the C−H bond. J. Am. Chem. Soc. 2017, 139, 10790− 10798. (8) Joseph, J. K.; Jain, S. L.; Sain, B. Covalently anchored polymer immobilized Co(II) phthalocyanine as efficient catalyst for oxidation of mercaptans using molecular oxygen as oxidant. Ind. Eng. Chem. Res. 2010, 49, 6674−6677. (9) Sharma, S.; Sinha, S.; Chand, S. Polymer anchored catalysts for oxidation of styrene using TBHP and molecular oxygen. Ind. Eng. Chem. Res. 2012, 51, 8806−8814. (10) Liang, Y.-F.; Jiao, N. Oxygenation via C−H/C−C bond activation with molecular oxygen. Acc. Chem. Res. 2017, 50, 1640− 1653. (11) Parreira, L. A.; Menini, L.; Gusevskaya, E. V. Palladium catalyzed oxidation of renewable terpenes with molecular oxygen: oxidation of [small alpha]-bisabolol under chloride-free conditions. Catal. Sci. Technol. 2014, 4, 2016−2022. (12) Maeda, T.; A. K. P. a. D. H JP 07196573. 1995. (13) Chen, C.; Shi, S.; Wang, M.; Ma, H.; Zhou, L.; Xu, J. Superhydrophobic SiO2-based nanocomposite modified with organic groups as catalyst for selective oxidation of ethylbenzene. J. Mater. Chem. A 2014, 2, 8126−8134. (14) Novak Tušar, N.; Laha, S. C.; Cecowski, S.; Arčon, I.; Kaučič, V.; Gläser, R. Mn-containing porous silicates as catalysts for the solvent-free selective oxidation of alkyl aromatics to aromatic ketones with molecular oxygen. Microporous Mesoporous Mater. 2011, 146, 166−171. (15) Duan, X.; Sun, H.; Wang, Y.; Kang, J.; Wang, S. N-dopinginduced nonradical reaction on single-walled carbon nanotubes for catalytic phenol oxidation. ACS Catal. 2015, 5, 553−559. (16) Imran Jafri, R.; Rajalakshmi, N.; Ramaprabhu, S. Nitrogen doped graphene nanoplatelets as catalyst support for oxygen reduction reaction in proton exchange membrane fuel cell. J. Mater. Chem. 2010, 20, 7114−7117. (17) Yuan, C.; Liu, X.; Jia, M.; Luo, Z.; Yao, J. Facile preparation of N- and O-doped hollow carbon spheres derived from poly(ophenylenediamine) for supercapacitors. J. Mater. Chem. A 2015, 3, 3409−3415. (18) Hui, Z.; Xiaolei, W.; Xuexia, L.; Xiurong, Y. Integrated synthesis of poly(o-phenylenediamine)-derived carbon materials for high performance supercapacitors. Adv. Mater. 2012, 24, 6524−6529. H


Article

Industrial & Engineering Chemistry Research (39) Maldonado, S.; Stevenson, K. J. Influence of nitrogen doping on oxygen reduction electrocatalysis at carbon nanofiber electrodes. J. Phys. Chem. B 2005, 109, 4707−4716. (40) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science 2009, 323, 760−764. (41) Shao, Y.; Zhang, S.; Engelhard, M. H.; Li, G.; Shao, G.; Wang, Y.; Liu, J.; Aksay, I. A.; Lin, Y. Nitrogen-doped graphene and its electrochemical applications. J. Mater. Chem. 2010, 20, 7491−7496. (42) Escax, V.; Impéror-Clerc, M.; Bazin, D.; Davidson, A. Nanocasting, templated syntheses and structural studies of manganese oxide nanoparticles nucleated in the pores of ordered mesoporous silicas (SBA-15). C. R. Chim. 2005, 8, 663−677. (43) Parida, K. M.; Dash, S. S. Manganese containing MCM-41: Synthesis, characterization and catalytic activity in the oxidation of ethylbenzene. J. Mol. Catal. A: Chem. 2009, 306, 54−61. (44) Zhang, Q.; Wang, Y.; Itsuki, S.; Shishido, T.; Takehira, K. Manganese-containing MCM-41 for epoxidation of styrene and stilbene. J. Mol. Catal. A: Chem. 2002, 188, 189−200. (45) Szymański, G. S.; Grzybek, T.; Papp, H. Influence of nitrogen surface functionalities on the catalytic activity of activated carbon in low temperature SCR of NOx with NH3. Catal. Today 2004, 90, 51− 59. (46) Kuwahara, Y.; Yoshimura, Y.; Yamashita, H. Liquid-phase oxidation of alkylaromatics to aromatic ketones with molecular oxygen over a Mn-based metal−organic framework. Dalton T. 2017, 46, 8415−8421. (47) Kuwahara, Y.; Yoshimura, Y.; Yamashita, H. In situ-created Mn (iii) complexes active for liquid-phase oxidation of alkylaromatics to aromatic ketones with molecular oxygen. Catal. Sci. Technol. 2016, 6, 442−448. (48) Yoshino, Y.; Hayashi, Y.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Catalytic oxidation of alkylbenzenes with molecular oxygenunder normal pressure and temperature by N-Hydroxyphthalimide combined with Co(OAc)2. J. Org. Chem. 1997, 62, 6810−6813. (49) Luo, J.; Peng, F.; Yu, H.; Wang, H.; Zheng, W. Aerobic liquidphase oxidation of ethylbenzene to acetophenone catalyzed by carbon nanotubes. ChemCatChem 2013, 5, 1578−1586.

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Al2O3 Catalyst for

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