Zinc Oxide Supported trans-CoD(p-Cl)PPCl-Type Metalloporphyrins

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Zinc oxide supported trans-CoD(p-Cl)PPCl type metalloporphyrins catalyst for cyclohexane oxidation to cyclohexanol and cyclohexanone with high yield Yujia Xie, Fengyong Zhang, Pingle Liu, Fang Hao, and Hean Luo Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 02 Feb 2015 Downloaded from http://pubs.acs.org on February 4, 2015

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Industrial & Engineering Chemistry Research

Zinc oxide supported trans-CoD(p-Cl)PPCl type metalloporphyrins catalyst for cyclohexane oxidation to cyclohexanol and cyclohexanone with high yield Yujia Xie; Fengyong Zhang; Pingle Liu*; Fang Hao; Hean Luo College of Chemical Engineering, Xiangtan University, Xiangtan 411105, China

1

ACS Paragon Plus Environment


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Abstract Direct functionalization of saturated C-H bonds by metalloporphyrin catalysts is among the topical and challenging areas within the chemical industry and the synthetic chemistry. In this work, supported CoD(p-Cl)PPCl metalloporphyrin catalysts were prepared and characterized. It has been found that the CoD(p-Cl)PPCl/ZnO catalyst shows better catalytic activity than the supported catalyst (ZrO2, MCM-41, kaolin, Zr(OH)2 and BM) in cyclohexane oxidation with dioxygen. The effects of the reaction pressure, reaction temperature and reaction time on the catalytic activity were considered by the supported CoD(p-Cl)PPCl/ZnO catalyst. The CoD(p-Cl)PPCl/ZnO catalyst can be facilely recovered and was recycled up to seven times without signiﬁcant decrease in catalytic performance. The average cyclohexane conversion and selectivity to KA oil are 10.98% and 84.34% respectively, and the turnover number is 2.10 x 107.

Keywords Trans-CoD(p-Cl)PPCl types metalloporphyrins; ZnO; cyclohexane oxidation; cyclohexanol; cyclohexanone

1. Introduction Functionalization of inert alkanes to more valuable products (e.g., carboxylic acids, alcohols, ketones) has attracted much attention

1-6

. Generally, catalytic oxidation of C–H bond in saturated hydrocarbons under mild

conditions is a key step in the oxyfunctionalization of organic compounds. Although many types of metalloporphyrins (MPs) have been largely studied for their catalytic performance in oxidation reactions, the application of metalloporphyrins in the synthetic chemistry and the chemical industry is not popular because of its economic problem. Selective oxidation of hydrocarbons and other organic compounds is still a challenging and promising subject 7. Cyclohexane oxidation with air or dioxygen in the absence of additives and solvents is one of the most important industrial process to produce KA oil (cyclohexanol and cyclohexanone) or adipic acid, the key intermediates for the production of caprolactam, nylon-6,6 and nylon-6 8, 9. In industrial cyclohexane auto-catalytic oxidation process, cyclohexane conversion is about 3-5%, and the selectivity to KA oil is about 80% since the main oxidation product cyclohexyl peroxide need to undergo a decomposition process to form cyclohexanol and cyclohexanone. As to cyclohexane catalytic oxidation process, the selectivity to KA oil is about 75% at the cyclohexane conversion of 8-10%. The cytochrome P-450 monooxygenase enzyme can oxidize saturated hydrocarbons to alcohol under mild conditions in organisms and is able to effectively and stereospecially catalyze the hydroxylation and epoxidation of hydrocarbons in the metabolic system. Like cytochrome P-450, metalloporphyrins have been proven to be efficient 2


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biomimetic catalysts, which are known to activate and transport dioxygen, and then transform hydrocarbons into the corresponding oxygenic compounds under mild conditions 10, 11. However, the metalloporphyrins are inclined to aggregation through π-π interactions or decompose in homogeneous catalytic oxidation systems 12. Furthermore, it is difficult to recover and recycle from the homogeneous media at the end of the reaction. For this reason, immobilization of metalloporphyrins on the supports is an effective method to overcome the above drawbacks 13. The efficiency and selectivity of oxidation processes depend on the microenvironment that the metallopophyin macrocycle creates around the metal center. In addition, much efforts have been devoted to develop heterogeneous metalloporphyrin catalysts on various supports 14-25.

Scheme 1. The cyclohexane oxidation reaction catalyzed by supported CoD(p-Cl)PPCl.

In this paper, some different supports were used to prepare supported CoD(p-Cl)PPCl catalysts. And the supported metalloporphyrins catalysts were applied in catalytic oxidation of cyclohexane with dioxygen (Scheme 1). CoD(p-Cl)PPCl/ZnO catalyst shows better catalytic performance and presents great industrial application value than the supported catalyst (ZrO2, MCM-41, kaolin, Zr(OH)2 and BM).

2. Experimental 2.1. Reagents Aluminum nitrate nonahydrate (98%), Zinc sulfate, ammonia (NH3 27%), Kaolin (Al2O3.2SiO2.2H2O), and other agents were all obtained from Aladdin Reagent. Boehmite (γ-AlOOH, BM) was synthesized according to literature procedures

26

. The supports of ZnO was synthesized according to literature procedures. No impurities

were found in the cyclohexane by GC analysis before use. 2.2. Preparation of CoD(p-Cl)PPCl complexes 5-(4-chlorophenyl)dipyrromethane

27

(2.0 mmol) and benzaldehyde (2.0 mmol) was dissolved in CH2Cl2 (200

mL) under argon at room temperature. After a homogenous solution was obtained, TFA (4.0 mmol) was added and the reaction mixture was stirred at room temperature for 3 h. Chloranil (3.0 mmol) was added and stirring was continued for 3 h. The reaction was terminated by addition of triethylamine (1 mL). The mixture was passed 3



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through column chromatography (alumina, CH2Cl2) and eluted with CH2Cl2 until the eluant was no longer dark. The collected eluant was concentrated. The resulting crude product was purified by column chromatography on silica gel (CH2Cl2/hexanes=5:2). The D(p-Cl)PPCl (0.25 mmol) was dissolved and refluxed in DMF (50 mL). Then, cobalt acetate (1.5 mmol) was added in three portions within 30 min. The evolution of the reaction was monitored by TLC. The solvents were pulled into water. The mixture was filtered and washed with water. The resulting solid was vacuum-dried. The titled compound was obtained in yields between 96%. 2.3. Preparation of supported CoD(p-Cl)PPCl catalyst CoD(p-Cl)PPCl was prepared by following literature procedures

26

. The MCM-41 and kaolin supported

CoD(p-Cl)PPCl catalysts were prepared by following literature procedures catalysts were prepared by following literature procedures

22, 26

14

. Other supported CoD(p-Cl)PPCl

. The support was added to 250 mL of ethanol in a

three-necked flask with high stirring for 1 h. Subsequently, 0.030 mmol of CoD(p-Cl)PPCl ethanol solution were slowly added into the above suspension and stirred for another 40 min, and the mixture was heated to 50 oC with rapid stirring for 6 h. The light-brown suspension was filtered and washed with distilled water, and the cake was vacuum-dried at 170 oC for 10 h, then washed in Soxhelt apparatus for 48h with 280 mL of CH2Cl2 in order to remove the weakly adsorbed metalloporphyrin on the surface. Finally, the solids were dried at 60 oC for 6 h. 2.4. Catalysts characterization 2.4.1. UV-vis UV-vis spectra was obtained by UV-2550 spectrophotometry with a scan range of 300-800nm for CoD(p-Cl)PPCl metalloporphyrin using 1cm quartz cuvette. The supported CoD(p-Cl)PPCl catalyst was characterized by using barium sulphate as reference, a small amount of BaSO4 was pressed into thin pellets, and some samples were put on the pellets and pressed again, then it was placed in the sample holder to assay the spectra. 2.4.2. Thermal analysis TG/DTG curves were carried out on a TGA Q50 using air as purge gas (80 mL min-1). The temperature is between 30 and 800 oC with a heating rate of 10 oC/min. 2.4.3. X-ray diffraction analysis X-ray diffraction (XRD) patterns were collected on a Japan Rigaku D/Max 2550 VB+ 18 kW X-ray diffractometer under the conditions of 40 kV, 30 mA, Cu Ka radiation, with a scanning rate of 2o/min in the range 4


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of 2θ = 20o–80o. 2.4.4. Nitrogen physical adsorption Specific surface area, pore volume and pore size distribution of the samples were obtained from the nitrogen adsorption-desorption on a Quantachrome NOVA-2200e automated gas sorption system. 2.4.5. Inductively coupled plasma (ICP) The amount of CoD(p-Cl)PPCl per gram of support was determined by Inductively Coupled Plasma Atomic Emission Spectometer (IRIS Intrepid II XSP ICP-AES) (Thermo Electron Co.) under a microwave pressure digestion (MDS 200; CEM) with hydrofluoric and aquaregia. The samples were digested by a traditional acid method (HF, HNO3, HClO4 and HCl), diluted adequately and analyzed for Co 14. 2.5. Procedures for the catalytic test Cyclohexane oxidation was carried out in a 50 mL autoclave reactor with a magnetic stirrer in the absence of solvent. Typically, catalysts and cyclohexane (185mmol) were added into the autoclave reactor. And the reactor was sealed and heated to the setting temperature. Then it was pressurized to the setting pressure with the molecular oxygen under stirring. After the reaction, the reactor was cooled to the ambient temperature. The mixture was dissolved in ethanol and the catalysts were removed by filtration. And the catalysts were washed in alcohol, dried and then recycled in the next reaction. The samples of the reaction mixture were identified by GC–MS and LC-MS. The acid in the product can mainly be attributed to the succinic acid, glutaric acid and adipic acid. The cyclohexanol and cyclohexanone in the product were analyzed by gas chromatography with the internal standard method using chlorobenzene as the internal standard. The total acid in the product was analyzed by the chemical titration method. The total ester in the product was analyzed by the chemical titration method with a solution of hydrochloric acid.

3. Results and discussion 3.1. Characterization of the catalysts Supported CoD(p-Cl)PPCl shows bright red in color, which indicates that metalloporphyrin is successfully supported on the supports. The results of UV-vis absorption measurements of supported CoD(p-Cl)PPCl are shown in Figure S1. Generally, porphyrin has one soret band and four Q band absorption peaks in the ultraviolet visible region. And the number of Q band usually reduces to one or two owing to the increase of symmetry of the molecular structure when metalloporphyrins form. The soret band shows variable degrees of redshift or blueshift. 5



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The results of UV-vis absorption in Figure S1 confirm that the metalloporphyrin species are loaded on the supports. Thermal analysis was used to testify the stability of the supported catalysts designed for oxidation reactions. For all samples, the weight losses of the supported catalysts during 140-160 oC indicate that it was too small to change the structure of the complexes. This can also be seen from the corresponding DTG curves (Figure S4a-f). Thus, the structure of the supported catalysts will not lead to decomposition during cyclohexane oxidation process carried out at 150-160 oC. The XRD patterns of the supported CoD(p-Cl)PPCl catalysts exhibit characteristic peaks of the corresponding support. And the typical peaks pattern for all the supports and supported metalloporphyrins are in agreement with the literature 26. The nitrogen adsorption–desorption isotherms and pore size distributions of supported CoD(p-Cl)PPCl catalysts are shown in Figure S2 and Figure S3. The adsorption isotherms of CoD(p-Cl)PPCl/BM and CoD(p-Cl)PPCl/Zr(OH)2 are type IV with the hysteresis loop of type H2. The adsorption isotherms of CoD(p-Cl)PPCl/ZnO and CoD(p-Cl)PPCl/kaolin are type Ⅲ with the hysteresis loop of type H3. The adsorption isotherms of CoD(p-Cl)PPCl/ZrO2 are type Ⅲ with the hysteresis loop of type H2. The adsorption isotherms of CoD(p-Cl)PPCl/MCM-41 are type IV with the hysteresis loop of type H1. CoD(p-Cl)PPCl/BM and CoD(p-Cl)PPCl/MCM-41 show relative larger pore size of 3.4 nm and 3.7 nm, and CoD(p-Cl)PPCl/Zr(OH)2 shows relative smaller pore size of 1.7 nm. The amount of metalloporphyrin on the support was determined by Inductively Coupled Plasma Atomic Emission Spectometer (IRIS Intrepid II XSP ICP-AES) 14. The results of the amount of CoD(p-Cl)PPCl are show in Table S1. 3.2. Catalytic performance The catalytic performance of the supported CoD(p-Cl)PPCl catalysts were tested in cyclohexane oxidation. The results are shown in Table 1. It can be seen from Table 1 that the cyclohexane conversion and the selectivity to KA oil are greatly influenced by the different supports. The support can behave like an electron-withdrawing substituent, that is, the electronic density of cobalt ions in supported metalloporphyrins changes with the support 28. And the existence of the supports could also change the reaction rate of cyclohexane hydroxylation with the metalloporphyrin catalysts. Under the same reaction conditions (entries 1-6 and 7-12), the CoD(p-Cl)PPCl/ZnO catalyst

presents

the best

catalytic

performance

with

the

highest

selectivity to

KA oil,

while

CoD(p-Cl)PPCl/Zr(OH)2 catalyst doesn't show catalytic activity. The selectivity to KA oil of different supported 6


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CoD(p-Cl)PPCl catalysts decreased in order of ZnO＞BM＞ZrO2 ＞MCM-41＞kaolin＞ Zr(OH)2. Different supports can provide a different micro-environment in cyclohexane oxidation reactions, which change the ability of activating oxygen molecules 20, 26, 29. Zinc oxide can be easily prepared in nanoparticle form of high surface energy and good thermal stability. It also possesses an oxygen atom acting as an electron pair donor. Thus providing an opportunity of coordination to the metal ion of the metalloporphyrin. Metalloporphyrin can be firmly adsorbed onto its surface. Comparing the consequences of the supported catalysts, it could find that CoD(p-Cl)PPCl/ZnO catalyst is better than the others. The appropriate pore diameter of the carrier can improve stability and catalytic activity of supported catalyst. The synergistic effect on micro-environment and the pore diameter could give rise to the order of the selectivity to KA oil. It presents great industrial application value. Table 1. Results of cyclohexane oxidation catalyzed by different carrier supported catalyst

Entry

Conversion (%)

K-A Selectivity (%)

1a

CoD(p-Cl)PPCl/BM

6.17

84.27

0.38

6.40

2a

CoD(p-Cl)PPCl/ZnO

6.23

89.40

0.41

9.72

3

a

CoD(p-Cl)PPCl/ZrO2

6.05

80.16

0.42

2.03

4

a

CoD(p-Cl)PPCl/MCM-41

4.08

0.36

5a

CoD(p-Cl)PPCl/Zr(OH)2

-

78.43

0.40

-

-

-

6

a

CoD(p-Cl)PPCl/kaolin

8.06

77.30

0.52

5.18

7

b

CoD(p-Cl)PPCl/BM

14.02

68.12

0.59

14.48

8b

CoD(p-Cl)PPCl/ZnO

13.09

72.12

0.63

20.43

b

65.14

0.80

5.03

CoD(p-Cl)PPCl/ZrO2

15.00

b

CoD(p-Cl)PPCl/MCM-41

13.50

58.59

0.79

1.18

11b

CoD(p-Cl)PPCl/Zr(OH)2

0.33

-

-

0.09

CoD(p-Cl)PPCl/kaolin

18.18

57.76

0.84

11.68

9

10

12

b

a

Reaction conditions: cyclohexane (20 mL), catalysts (CoD(p-Cl)PPCl ), 155 C for 2h, oxygen pressure (1 MPa);

b

Reaction conditions: cyclohexane (20 mL), catalysts (CoD(p-Cl)PPCl ), 155 oC for 2h, oxygen pressure (2 MPa);

c

K/A (mol ration)

TON (x106)c

Catalysts

o

The turnover number (TON) is the value of 2h reaction time, calculated by mol product (ketone + alcohol + acid + ester)/ mol CoD(p-Cl)PPCl;

“-” = no reaction.

In metalloporphyrins/O2 system (Figure S6), supported metalloporphyrin catalyst Co(III)D(p-Cl)PPCl/ZnO loses a chlorine radical to form Co(II)D(p-Cl)PP /ZnO, which combines with an oxygen molecule to form an activated radical species Co(III)OOD(p-Cl)PP /ZnO, and then form O-O active species (Co(III)D(p-Cl)PP/ZnO)2OO. And the intermediate Co(Ⅳ)=OD(p-Cl)PP /ZnO can easily capture a hydrogen atom from cyclohexane to afford an alkyl radical and then form the products

22, 30

. The chlorine radical can also easily capture a hydrogen atom from

cyclohexane to afford an alkyl radical, which combines with an oxygen molecule to form the activated peroxoradicals species (ROO ), then it may form organic acids. The existence of the different supports hindered 7



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the supported catalysts and dioxygen to form the active species Co(IV)=OD(p-Cl)PP /ZnO, which can capture a hydrogen atom from cyclohexane to afford an alkyl radical and then form the products. That is，the steric hindrance of different support shows different impacts on the oxygen activation ability of the supported metalloporphyrin catalysts

31-33

. The supported catalysts have shown a lower conversion of cyclohexane in comparison with

homogeneous systems. This steric hindrance leads to increase the selectivity to KA oil and prevents from further oxidation of KA oil to byproducts. It may be the reason why the supported catalyst presents better catalytic performance than the unsupported metalloporphyrin. 3.3. Effect of reaction pressure Table 2. Effect of reaction pressure with CoD(p-Cl)PPCl/ZnO

K-A Selectivity (%)

K/A(mol ration)

TON (x107)b

5.51

90.56

0.36

0.86

1.5

11.13

84.19

0.53

1.74

3a

2.0

14.32

77.10

0.68

2.23

4a

2.5

16.69

69.56

0.74

2.60

5a

3.0

18.88

65.89

0.88

2.95

Entry

Reaction pressure (MPa)

1a

1.0

2a

Conversion (%)

a

Reaction conditions: cyclohexane (20 mL), CoD(p-Cl)PPCl/ZnO catalysts (CoD(p-Cl)PPCl 0.092 mg), 155oC for 2h, oxygen pressure;

b

The turnover number (TON) is the value of 2h reaction time, calculated by mol product (ketone + alcohol + acid + ester)/ mol CoD(p-Cl)PPCl.

Table 2 demonstrates the effect of reaction pressure on cyclohexane oxidation catalyzed by CoD(p-Cl)PPCl/ZnO catalyst. The reaction pressure has a great effect on the cyclohexane conversion and the selectivity to KA oil. As shown in Table 2, the cyclohexane conversion increase markedly and the selectivity to KA oil decrease significantly with the increment of reaction pressure. Meanwhile, the TON and the mol ration of K/A also increase markedly with pressure. The higher reaction pressure causes the higher oxygen concentration in the liquid phase, which may lead to further oxidation of KA oil to byproducts. In literature

34

, cyclohexane oxidation with oxygen

has obtained the yield of 90%. In this mentioned literature, the oxidation products were determined by GLC analysis based on the starting acetaldehyde using an internal standard. It was assumed that 2 moles of acetaldehyde were necessary for ketone or diol formation. In our research, the cyclohexanol and cyclohexanone in the product were analyzed by gas chromatography with the internal standard method using chlorobenzene as the internal standard. The total acid and ester in the product were analyzed by the chemical titration method. The analytical method and the calculation basis are different between our research work and the mentioned literature. Furthermore, we know that industrial cyclohexane oxidation process include non-catalytic oxidation process and catalytic 8


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oxidation process, as to non-catalytic oxidation process, the per pass conversion of cyclohexane is only 3-5%, and the selectivity to KA oil is about 80% since the main oxidation product cyclohexyl peroxide need to undergo a decomposition process to form cyclohexanol and cyclohexanone. As to cyclohexane catalytic oxidation process, the selectivity to KA oil is about 75% at the cyclohexane conversion of 8-10%. Thus it can be seen that the results of our research work is good. 3.4. Effect of reaction temperature The effects of reaction temperature on the cyclohexane oxidation are shown in Table 3. The cyclohexane conversion and the selectivity to KA oil change with the increment of temperature. At lower temperature, there is not enough energy to activate the reaction, the phenomenon that the supported catalyst undergoes induction and activation in different reaction temperature exists. Comparing the consequences of entry 1 and 2, it could find that the cyclohexane conversion increases obvious and the selectivity to KA oil reduces slightly when the temperature increases from 145 oC to 150 oC. From 150 oC to 155 oC, however, the cyclohexane conversion is almost unchanged and the selectivity to KA oil decreased with the increment of reaction temperature, the reason may be that cyclohexanone and cyclohexanol are more readily oxidizable than cyclohexane. Table 3. Effect of reaction temperature with CoD(p-Cl)PPCl/ZnO

Entry

Reaction temperature (oC)

Conversion (%)

K-A Selectivity (%)

K/A(mol ration)

TON (x107)b

1a

145

3.44

90.69

0.90

0.54

2a

150

11.92

87.61

0.61

1.86

3a

155

11.13

84.19

0.53

1.74

a

Reaction conditions: cyclohexane (20 mL), CoD(p-Cl)PPCl/ZnO catalysts (CoD(p-Cl)PPCl 0.092 mg), 2h, oxygen pressure (1.5 MPa);

b


3.5. Effect of reaction time Table 4 shows the effects of reaction time on cyclohexane oxidation catalyzed by CoD(p-Cl)PPCl/ZnO. Under the chosen experimental conditions, because of the induction period, the cyclohexane conversion and the yield of the KA oil are extremely low with the reaction time changing from 0 to 30 min, the cyclohexane conversion and the yield of the KA oil increase quickly with the increment of reaction time from 30 to 90 min (entries 1-3), the cyclohexane conversion and selectivity changes very little from 90 to 180 min (entries 3-6), the reduction in selectivity may be attributed to further oxidation of cyclohexanol and cyclohexanone (entry 6).

9



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Table 4. Effect of reaction time with CoD(p-Cl)PPCl/ZnO

Entry

Reaction time (min)

Conversion (%)

K-A Selectivity (%)

K/A(mol ration)

TON (x107)b

1a

30

1.63

89.62

1.03

0.25

2a

60

8.16

84.44

0.53

1.27

3a

90

10.57

85.15

0.54

1.65

4a

120

11.13

84.19

0.53

1.74

5a

150

11.21

84.03

0.56

1.75

6a

180

11.37

82.76

0.57

1.77

a

Reaction conditions: cyclohexane (20 mL), CoD(p-Cl)PPCl/ZnO catalysts (CoD(p-Cl)PPCl 0.092 mg), 155oC, oxygen pressure (1.5 MPa);

b


3.6. Recycle of the CoD(p-Cl)PPCl /ZnO catalyst Table 5. Recycle of CoD(p-Cl)PPCl/ZnO catalyst

Conversion (%)

K-A Selectivity (%)

K/A(mol ration)

TON (x107)b

1a

11.13

84.19

0.53

1.74

2

10.57

84.93

0.53

1.77

3

10.86

84.38

0.54

1.98

Catalysts

Entry

CoD(p-Cl)PPCl/ZnO

4

11.55

83.67

0.57

2.15

5

10.05

85.05

0.49

2.26

6

11.50

84.16

0.55

2.39

7

11.23

84.02

0.52

2.44

Average

10.98

84.34

0.53

2.10

a

Reaction conditions: cyclohexane (20 mL), CoD(p-Cl)PPCl/ZnO catalysts (CoD(p-Cl)PPCl 0.092 mg), 155oC for 2h, oxygen pressure (1.5MPa);

b

The turnover number (TON) is the value of 2h reaction time, calculated by mol product (ketone + alcohol + acid + ester)/ mol CoD(p-Cl)PPCl.

Recycling tests with repeated use of CoD(p-Cl)PPCl/ZnO catalyst in seven consecutive reactions were carried out under the typical reaction conditions, the recycled catalysts were washed with alcohol, dried and then used for the next reaction. The results are shown in Table 5. It can be seen from Table 5 that the catalytic activity and selectivity to KA oils are almost unchanged. The average TON is 2.10 x 107. As shown in Figure S5, CoD(p-Cl)PPCl/ZnO are so tightly adsorbed on the ZnO that the supported metalloporphyrin displayed a peak at 430nm in the UV-Vis spectrum (Figure S5a), it may because some of the Co porphyrins on the surface of the solid catalyst were destroyed by O2, an intensity of which gradually decreased with the continuous recovery and reuse of the supported catalyst after the 7th cyclohexane oxidation run (Figure S5b). It indicates that CoD(p-Cl)PPCl/ZnO has been immobilised on ZnO, it has undergone no change in its macrocyclic complex structure. Furthermore, unsupported catalysts are difficult to recover and reused. Compared with the industrial cyclohexane oxidation 10


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process, the advantages of the ZnO supported CoD(p-Cl)PPCl catalyst were obvious.

4. Conclusion Different kinds of supported metalloporphyrin catalysts were prepared and characterized. The supported catalysts were used to mimic cytochrome P-450 in cyclohexane oxidation process. The appropriate pore diameter and micro-environment of the support can improve the stability and catalytic activity of the catalysts. In general, ZnO supported metalloporphyrin catalysts (CoD(p-Cl)PPCl/ZnO) show better catalytic performance. It gives the average selectivity to KA oil of 84.34% at the cyclohexane conversion of 10.98% and TON reaches to 2.10 x 107 after seven times recycle. Compared with today’s industrial cyclohexane oxidation process, supported metalloporphyrin catalyst (CoD(p-Cl)PPCl/ZnO) presents great industrial application value.

Auther information Corresponding Author *E-mail: [email protected]. Tel.: (+86)-731-58293545. Fax: (+86)-731-58298267.

Acknowledgment This work was supported by the NSFC (21276218), SRFDP(20124301110007), Scientiﬁc Research Fund of Hunan Provincial Education Department (13k043, CX2012B253), and the project of Hunan Provincial Science and Technology Department (2012FJ1001).

Supporting Information Further complementary information about preparation of zinc oxide-supports, UV-vis spectra of carrier and supported CoD(p-Cl)PPCl/Z, N2 adsorption–desorption isotherms and BJH pore size distribution of CoD(p-Cl)PPCl/Z catalyst, proposed mechanisms of the supported catalyst (CoD(p-Cl)PPCl/Z), TG and DTG CoD(p-Cl)PPCl/Z, and UV-Vis spectra of supported CoD(p-Cl)PPCl/ZnO and recovered CoD(p-Cl)PPCl/ZnO after 7th run. This material is available free of charge via the Internet at http: //pubs.acs.org.

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Zinc Oxide Supported trans-CoD(p-Cl)PPCl-Type Metalloporphyrins

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