Oxidation of cyclohexane to adipic acid catalyzed by Mn-doped titanosilicate with hollow structure

Article abstract of DOI:10.1016/j.catcom.2014.08.026

One-step oxidation of cyclohexane to adipic acid (AA) was carried out at 413 K over manganese-doped titanium silicalite with hollow structure (HTS) using oxygen as oxidant without any initiator or solvent. The catalyst exhibited high conversion (13.4%) and reasonable product (AA) selectivity (57.5%). Hot-separation and catalyst-recycle tests proved that the catalyst acted as a heterogeneous one and it could be reused four times without losing its activity. The synthesized materials were characterized by N₂ adsorption-desorption isotherm, FT-IR, UV-vis and XPS techniques.

Full text of DOI:10.1016/j.catcom.2014.08.026

Oxidation of cyclohexane to adipic acid catalyzed by Mn-doped titanosilicate
with hollow structure
Guoqiang Zou, Wenzhou Zhong, Qiong Xu, Jiafu Xiao, Chang Liu,
Yongqiang Li, Mao Liqiu, Kirk Steven, Dulin Yin
PII:
DOI:
Reference:
S1566-7367(14)00338-0
doi: 10.1016/j.catcom.2014.08.026
CATCOM 4025
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
15 May 2014
12 August 2014
19 August 2014
Please cite this article as: Guoqiang Zou, Wenzhou Zhong, Qiong Xu, Jiafu Xiao, Chang
Liu, Yongqiang Li, Mao Liqiu, Kirk Steven, Dulin Yin, Oxidation of cyclohexane to
adipic acid catalyzed by Mn-doped titanosilicate with hollow structure, Catalysis Com-
munications (2014), doi: 10.1016/j.catcom.2014.08.026
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

ACCEPTED MANUSCRIPT
Oxidation of cyclohexane to adipic acid catalyzed by
Mn-doped titanosilicate with hollow structure
Guoqiang Zou, Wenzhou Zhong*, Qiong Xu, Jiafu Xiao, Chang Liu, Yongqiang Li, Liqiu Mao,
Steven kirk, Dulin Yin*
National & Local United Engineering Laboratory for New Petrochemical Materials & Fine
Utilization of Resources, College of Chemistry and Chemical Engineering, Hunan Normal
University, Changsha 410081, P. R. China
*Corresponding authors: Wenzhou Zhong and Dulin Yin
Tel & Fax: +86-731-8872576
E-mail: zwenz79@163.com (W. Zhong); dulinyin@126.com (D. Yin)
1

ACCEPTED MANUSCRIPT
Abstract
One-step oxidation of cyclohexane to adipic acid (AA) was carried out at 413 K over
manganese-doped titanium silicalite with hollow structure (HTS) using oxygen as oxidant without
any initiator or solvent. The catalyst exhibited high conversion (13.4%) and reasonable product
(AA) selectivity (57.5%). Hot-separation and catalyst-recycle tests proved that the catalyst acted
as a heterogeneous one and it could be reused four times without losing its activity. The
synthesized materials were characterized by N adsorption-desorption isotherm, FT-IR, UV-Vis
2
and XPS techniques.
Key words: Cyclohexane, Adipic acid, Aerobic oxidation, Solvent-free, Mn-HTS
2

ACCEPTED MANUSCRIPT
1. Introduction
The development of a simple and efficient process for the hydrocarbon activation with molecular
oxygen can be one of the key technologies for synthesizing oxygenates, since some industrial
processes are based on these reactions. Among them, the selective oxidation of cyclohexane to AA
is an important reaction due to the fact that AA is a basic material for the production of Nylon-66
(production around million tons per year in the world) [1-3]. At present, it is commercially
produced by a two-step process involving nitric acid oxidation of cyclohexanone and
cyclohexanol (KA oils). These compounds generated from cyclohexane, however, limit the whole
efficiency of the process owing to the low yields (8%) using homogeneous (cobalt-based)
catalysts [4]. More importantly, the use of nitric acid causes some severe environmental problems
in the latter process, since the emission of nitrogen oxides during the synthesis can lead to global
warming and ozone depletion [1, 5]. Alternative routes for synthesis of adipic acid usually need a
number of steps as shown in Scheme 1, and they are too expensive or too complicated to be used
as a commercial process. The direct oxidation of cyclohexane to AA is a promising route for its
application in industrial production, because it completely overcomes the major drawbacks
mentioned above. Currently, direct production of AA from cyclohexane with alkyl hydroperoxide
or O as oxidant has been studied extensively with a catalyst consisting of cobalt salts [6, 7]. From
3
an economic viewpoint, its cost is still prohibitive for less value-added cases. In contrast, a
one-step catalytic cyclohexane oxidation to AA using molecular oxygen as a sole oxidant has been
desired in view of green chemistry.
The challenge of obtaining adipic acid in a manner that is environmentally friendly with low
costs has initiated the search for the direct oxidation of cyclohexane. Lu and co-workers described
3

ACCEPTED MANUSCRIPT
an aerobic catalytic system for the direct production of AA from cyclohexane based on the
Anderson-type [(C H ) N(CH ) ] Mo O catalyst [8]. Yu et al. developed a catalytic method for
18
37 2
3 2 6
7
24
the direct oxidation of cyclohexane with O using N-hydroxyphthalimide (NHPI) or some
2
transition metal species as a key catalyst [9]. These catalytic processes, however, involve the
homogeneous catalytic system. Furthermore, most of the NHPI is decomposed to phthalic acid
and other related byproducts, and the polyoxometalate catalyst is difficult to be recycled. In
contrast to the homogeneous catalytic systems, the heterogeneous systems such as metal-doped
aluminophosphates [10, 11] and carbon nanotubes [12] have only a low efficiency for direct
oxidation of cyclohexane to AA.
The MFI-type titanosilicate, TS-1, has been known for its remarkable catalytic activity in
oxidation of cyclohexane to KA oils at mild conditions with H O [13]. This
2
2
titanosilicate-catalyzed oxidation process is believed to be a “green” route to substitute for old
ones. Following Spinacé’s pioneer work with the TS-1 catalyst, Shi had developed a efficient
titanosilicate catalyst with hollow structure (HTS) for use in the oxidation of cyclohexane and
showed to be more active than TS-1 with H O as oxidant [14]. This reason may be attributed to
2
2
the enhancing of dimensions of the intra-particle pores and can intensify the transport of reactants
and products in and out of the crystal’s channels [15]. On the basis of these results, HTS may
exhibit better selectivity for AA in the aerobic oxidation of cyclohexane, since the diameter of AA
(1.00 nm) is larger than these of cyclohexanone (0.51 nm) and cyclohexanol (0.58 nm). In contrast
to the tremendous progress on titanosilicate catalysts for oxidation of cyclohexane to KA oils with
H O , much less has been reported the titanosilicate-catalyzed aerobic oxidation of cyclohexane to
2
2
AA, which is equally important to be developed from a simple bench-top procedure and to further
4

ACCEPTED MANUSCRIPT
apply it for industrial-scale applications. Herein, we explore an active, selective and green
Mn-HTS catalyst to a one-step aerobic oxidation of cyclohexane to AA under mild reaction
conditions (scheme 2).
2. Experimental
2.1 Synthesis of the catalytic materials and characterization
The HTS was prepared according to the post-synthesis method. First, TS-1 was synthesized from
tetraethyl orthosilicate (TEOS), alkali-free TPAOPH solutions and titanium butoxide (TBOT) with
a composition of SiO :0.4TPAOPH:0.01TiO :40H O. The resultant gel was hydrothermally
2
2
2
treated at 443 K for 3 days under static conditions. The solid product was filtered, washed, dried
and finally calcined at 793 K for 10 h. Secondly, the HTS solid was synthesized by treating with
sulfuric acid solution with a weight ratio of the previous calcined TS-1:sulfuric acid:water =
10:1.0:140, and the acid-treated TS-1 was dispersed in TPAOPH solution in a weight ratio of
molecular sieve:TPAOPH:water = 10:1.5:125. The mixture was then hydrothermally treated at 413
K for 3 days under static conditions. The solid product was filtered, washed, dried and finally
calcined at 793 K for 10 h.
The manganese oxo-species (1.0 wt.% of Mn) were introduced onto the support by the wet
.
impregnation method from EtOH and water (1:1) solution of Mn(Ac) 4H O. Impregnated samples
2
2
were evaporated at 373 K overnight and then calcined at 773 K in air for 3 h (with heating rate 5
◦
C/min). The investigated samples were denoted as xMn-HTS, where x is the manganese content
in support in the weight percentage.
The characterizations of the materials were depicted in Supplementary data, including N2
adsorption, X-ray diffraction, UV–Vis, FT-IR, XPS.
5

ACCEPTED MANUSCRIPT
2.2 Cyclohexane oxidation
The catalytic oxidations were carried out in a 100 mL stainless steel reactor equipped with a
Teflon beaker, magnetic stirrer. In a typical reaction, cyclohexane (119 mmol) was mixed with the
target catalyst and then heated to the reaction temperature under a constant oxygen pressure. After
reaction, the mixture was cooled down, dissolved in ethanol and filtered. Aliquots of the above
mixture (25 μL) were withdrawn by a syringe. Each aliquot was diluted with 0.4 mL of toluene
containing 50 mg of PPh and internal standard (n-hexanol). The yield of cyclohexanol was
3
calculated as a difference between the value obtained by GC and the concentration of cyclohexyl
hydroperoxide determined iodometrically (reduction in cyclohexyl hydroperoxide with PPh gives
3
an additional amount of cyclohexanol). The obtained acid was analyzed by high-performance
liquid chromatography using the external standard method.
3
. Results and Discussion
3.1. Characterization of materials
Mn-HTS was characterized by N adsorption-desorption, XRD, UV-Vis spectroscopy, FT-IR and
2
XPS. N adsorption-desorption images (Fig. 1A and B) depict the textural properties of the
2
material. Apparently, the abrupt closure at p/p = 0.42 on the desorption branch was characteristic
0
of intra-crystalline voids in the samples, accessible only via entrances smaller than 4 nm [15].
Furthermore, Mn-HTS catalysts showed the higher pore diameter than pure HTS because Mn
species with oxygen had a higher bond length than Si-O, indicating incorporation of Mn to form
Si–O–Mn linkages in the zeolite framework sites [16]. XRD images (Fig. 1C) of the catalysts
showed the same main diffraction peaks as those in XRD of normal TS-1 [17], indicating that the
HTS is with MFI topological structure. Mn-HTS catalysts showed no additional diffraction
6

ACCEPTED MANUSCRIPT
intensity, thereby indicating that the Mn species were well dispersed either in the framework or on
the internal surface of support materials. As examined by FT-IR (Fig. 1D), the intra-framework Ti
−
1
and Si–O–Mn linkages formed were characteric by the absorption peak at 966 [18] and 1100 cm
19], which further confirming that the catalysts were with MFI and had the framework Mn.
The corresponding UV–Vis spectrum showed two bands (Fig. 2A), the first band ca. 215 nm,
[
2
−
4+
which was assigned to a charge transfer from O to tetrahedral Ti in the zeolite framework, a
second band around 300 nm indicated that the zeolite contained extraframework Ti species (e.g.,
octahedral Ti sites) [15, 20, 21]. The second assignments might be, however, somewhat hampered
2-
3+
by overlap of signals corresponding to O to Mn electron transition (310 nm) [22]. Fig. 2B
showed the XPS spectra for Ti 2p orbital in HTS and 1% Mn-HTS. The Ti 2p XPS spectra of the
BE (binding energy) of the principal Ti 2p3/2 core electron [23] for the HTS could be
deconvoluted into two contributions: one peak appeared at ca. 458.5 eV, which might be assigned
4+
4+
to the octahedrally coordinated Ti ion and another at ca. 460.0 eV associated Ti in the
tetrahedral coordination within the silica framework. The relative area ratio of the peak at 460.0
eV assigned to tetrahedral Ti species, however, dramatically decreased with the loading of Mn,
suggesting a change in the coordination from tetrahedral to octahedral. This could be attributed to
the change in the coordination number of titanium by the formation of a Ti-O-Mn bond [24]. In
addition, the peaks were shifted in the higher binding energy in the Mn-HTS, which meant the
change of Ti–O bonding strength with the Mn insertion [25]. Mn2p spectrum for 1.0% Mn-HTS
was presented in Fig. 2C. The binding energy value of the Mn 2p3/2 peak was 641.5 eV.
2
+
According to the literature [26], this value indicated that Mn was present as a mixture of Mn ,
3
+
4+
Mn and Mn on the surface of 1.0% Mn-HTS.
7

ACCEPTED MANUSCRIPT
3.2 Catalytic performance of the different catalyst
To understand the influence of the framework of supports, incorporated ion types, and content,
the reactivity of the prepared materials has been tested comprehensively for cyclohexane oxidation
using O as oxidant in a solvent-free system. The results are listed in Table 1. HTS support
2
exhibited the high catalytic activity and AA selectivity compared the reference sample Silicon-1
and TS-1(entries 2-4). These differences might be explained by the following factors [14]: i) the
enrichment of the external surface Ti concentration of HTS led to the better accessibility of Ti
species as a catalytic active site for cyclohexane oxidation (measured from XPS and UV-Vis
spectra; ii) the characteristic hollow structure of HTS could enhance the accessibility of active
centers and diffusion of reactant molecules, thus decreased or even eliminated molecular
diffusions (measured from N adsorption-desorption). Entries 7–10 illustrated the metal-based
2
HTS catalysts (such as Cr-HTS, Fe-HTS, Co-HTS, Mn-HTS) for the oxidation of cyclohexane.
Among them, the catalyst Mn-HMS gave the highest selectivity of AA with a relatively high
cyclohexane conversion, being plausibly attributed to the nature of the metal used (entry 10) [27].
Furthermore, the reference Mn O catalyst showed a low selectivity of AA with 5.2% cyclohexane
3
4
conversion by using 100 mg dosage (entry 5), confirming the important role of Mn species in the
framework of the samples as a highly active component in the oxidation of cyclohexane to AA
(
measured from N adsorption-desorption and XPS). This assertion might also support the
2
difference among the catalytic performance of the different content Mn supported on HTS (entries
0-12). For example, the selectivity of AA was low (36.5%) upon 0.5% Mn-HTS catalyst. The
1
framework Mn(IV)/Mn(III) as strong Lewis acid sites and highly active components could
promote the simultaneous decomposition of peroxide and the production of radicals OH• [28],
8

ACCEPTED MANUSCRIPT
thus accelerating the oxidation of cyclohexanone and enhancing the selectivity of AA. In short, the
synergistic effects among framework Ti, framework Mn and characteristic hollow structure made
Mn-HMS an effective catalyst for the oxidation of cyclohexane to AA under mild conditions.
3.3 Effect of various parameters
In the following experiments, the influence of the amount of catalyst 1% Mn-HTS, reaction
temperature, reaction time, as well as reaction pressure on the cyclohexane-oxidation, was
investigated in a solvent-free system. Fig 3A shows that an increase in the amount of catalyst from
0
3
.03 to 0.10 g resulted in a continuous and considerable increase of cyclohexane conversion from
.3% to 13.4% and AA selectivity from 17.7% to 57.5%, respectively, with a concomitant
decrease in the selectivity of KA oil from 80.7% to 21.0%. However, beyond this amount, the
conversion of cyclohexane and the selectivity of AA increased, which might be attributed to the
so-called “catalyst inhibitor reaction” phenomenon [29]. Fig. 3B illustrates the effect of reaction
temperature on cyclohexane reaction. The conversion of cyclohexane was found to increase with
an increase in reaction temperature and passed through a maximum at 413 K. But the highest
selectivity was obtained at 408 K. A further increase in the reaction temperature resulted in a
decrease of both conversion and selectivity, probably owing to the deep oxidation [30]. Fig. 3C
presented that cyclohexane conversion continuously increased with reaction time. Synchronously,
AA selectivity increased gradually, while KA oil selectivity decreased, the decrease might be due
to its further oxidation of KA oils. Above phenomena might further indicate that KA oil should be
intermediate products, the cyclohexane oxidation process was composed of the process of
converting cyclohexane to KA oil and that of KA oil to AA. Fig. 3D illustrated the effect of
reaction pressure on cyclohexane reaction and the conversion of cyclohexane increased with the
9

ACCEPTED MANUSCRIPT
increasing in reaction pressure and passed through a maximum at 1.4 MPa. But the highest
selectivity was obtained at 1.0 MPa. A further increase in the reaction pressure resulted in a darkly
decrease of both conversion and selectivity, which might be explained by the solubility of oxygen
in the reaction system [31].
3.4 Stability of the catalyst: hot-separation and catalyst-recycle test
Hot catalyst filtration tests [32] were performed to verify the nature of catalysis in the catalytic
systems studied. A hot reaction mixture containing the solid catalyst (1% Mn-HTS) was filtrated
after 3 h, and the oxidation of the mother liquor (filtrate) was followed for another 6 h. As can be
seen from Fig. 4A, the cyclohexane conversion did continue to increase, albeit at a much lower
rate. The persistence of a low activity could be attributed to the thermal autoxidation, initiated by
the oxygenated products, present in the mother liquor [33, 34]. Similar results were observed if the
hot-filtration test was performed after 6 h. Metallic ions like Ti and Mn were detected in the
filtered products solution by ICP-OES analysis and found to be below the detection limit (< 0.04
ppm), implying that Mn-HTS can act as truly heterogeneous catalyst. After four consecutive uses,
the stability of 1% Mn-HTS was confirmed by comparison of the FT-IR and UV−Vis spectra of
the fresh and three times reused (Fig. 1D and Fig. 2A).
In order to check the recycle of the catalyst, four reactions were carried out. After each reaction,
the catalyst was separated by filtration and washed with water and ethanol for several times. Then,
the catalyst was dried at 373 K for 6 h to remove water and ethanol. The regenerated catalyst was
used for the recycling study under the same reaction conditions. The results on the fresh and
regenerated catalyst were shown in Fig. 4B. It could be seen that the conversion of cyclohexane on
the regenerated catalyst was slightly lower than that on fresh catalyst. The selectivity of AA on
1
0

ACCEPTED MANUSCRIPT
regenerated catalyst was almost equal with that over fresh catalyst. These results disclosed that the
catalyst was stable and could be reused after the reaction.
3.5 The proposed reaction mechanism
Based on the results presented here, as well as those in previous studies [21, 35], three main
conclusions emerge: (i) cyclohexane oxidation takes place on Ti sites mainly located in the
external surface, (ii) the hollow structure of HTS favors the accessibility of active centers and
diffusion of reactant molecules, and (iii) the reaction proceeds through radical intermediates. In
the present reaction, the diameter of cyclohexane is 0.49 nm and that of the products cyclohexanol,
cyclohexanone, cyclohexyl hydroperoxide (CHHP) and AA should be 0.58, 0.51, 0.69 and 1.0 nm,
respectively. The hollow structure and Ti sites in the external surface therefore are more adapted
for the production of bulky AA comparison of cyclohexanol and cyclohexanone. Similar reports
also showed that Ti-loaded zeolites with larger channels appear more adapted for the oxidation of
bulky molecules [36]. The oxidation of cyclohexane in this process first involves noncatalytic
autoxidation of cyclohexane by oxygen to CHHP. Subsequently, the bulky Ti(OOCh) species was
possibly formed by the reaction of TiOH with CHHP, and the homolytic fragmentation of
Ti(OOCh) can yield Ti-centered radical species such as Ti(IV)-O• or Ti(IV)-OO• [21, 37]. The
species was generally regarded as active centers for cyclohexane oxidation (Scheme 3). The
3+
presence of Mn sites further increased the formation of CyOO•, which propagated the reaction
with formation of cyclohexyl radical, thereby increasing the conversion. Additionally, adsorption
of cyclohexanone on the Mn-doped catalyst surface might facilitate the aH-abstraction from
cyclohexanone by CyOO•, by forming the cyclohexane-1,2-dione product, thus enhancing the AA
formation rate [38]. This was in agreement with the observed relative high AA selectivity (84.5%)
11

ACCEPTED MANUSCRIPT
with high cyclohexanone conversion (40.5%) in the oxidation pure cyclohexanone experiment
(Table 1, entry 5).
4
. Conclusion
In this paper, an efficient catalyst system for oxidation of cyclohexane to AA was developed
using Mn-HTS as catalyst, molecular oxygen as oxidant in a solvent-free system. The high
selectivity of AA (57.5%) and good cyclohexane conversion (13.4%) could be achieved over
Mn-HTS catalyst in the optimized conditions. The catalyst could be reused with almost the same
activity, with the potential industrial applications.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant No.
20976043)
1
2

ACCEPTED MANUSCRIPT
Reference:
[
[
1] K. Sato, M. Aoki, R. Noyori, Science 281 (1998) 1646-1647.
2] U. Schuchardt, D. Cardoso, R. Sercheli, R. Pereira, R.S. da Cruz, M. C. Guerreiro, D. Mandelli, E.
V. Spinacé, E. L. Pires, Applied Catalysis A: General 211 (2001) 1–17.
[
3] Cavani F., Alini S. In: Sustainable Industrial Processes. Cavani F., Centi G., Perathoner S., Trifiro F.,
eds. Wiley-VCH,Weinheim, 2009, pp. 331-391.
[
[
[
4] T. Ishida, US Patent 3644526 (1972).
5] A. Ravishankara, J.S. Daniel, R.W. Portmann, science 326 (2009) 123-125.
6] T. Maschmeyer, R.D. Oldroyd, G. Sankar, J.M. Thomas, I.J. Shannon, C.R.A. Catlow, J.A.
Klepetko, A.F. Masters, J.K. Beattie, Angew. Chem. Int. Ed. 36 (1997) 1639-1642.
[
[
(
[
[
(
[
[
7] A.J. Bailey, W.P. Griffith, B.C. Parkin, J. Chem. Soc. 11 (1995) 1833-1837.
8] H. Lü, W. Ren, P. Liu, S. Qi, W. Wang, Y. Feng, F. Sun, Y. Wang, Appl. Catal. A: Gen. 441–442
2012) 136-141.
9] T. Iwahama, K. Syojyo, S. Sakaguchi, Y. Ishii, Org. Process Res. Dev. 2 (1998) 255-260.
10] R. Raja, J.M. Thomas, M. Xu, K.D.M. Harris, M. Greenhill-Hooper, K. Quill, Chem. Commun. 4
2006) 448-450.
11] J. Li, X. Li, Y. Shi, D. Mao, G. Lu, Catal. Lett. 137 (2010) 180-189.
12] H. Yu, F. Peng, J. Tan, X. Hu, H. Wang, J. Yang, W. Zheng, Angew. Chem. Int. Ed. 123 (2011)
4
064-4068.
[
[
[
13] E.V. Spinace, H.O. Pastore, U. Schuchardt, J. Catal. 157 (1995) 631-635.
14] C. Shi, B. Zhu, M. Lin, J. Long, R. Wang, Catal. Today 175 (2011) 398-403.
15] Y. Wang, M. Lin, A. Tuel, Micropor. Mesopor. Mater. 102 (2007) 80-85.
1
3

ACCEPTED MANUSCRIPT
[
[
16] M. Selvaraj, T. Lee, J. Phys. Chem. B 110 (2006) 21793-21802.
17] E. Duprey, P. Beaunier, M.-A. Springuel-Huet, F. Bozon-Verduraz, J. Fraissard, J.-M. Manoli,
J.-M. Brégeault, J. Catal. 165 (1997) 22-32.
[
[
18] A.J. de Man, J. Sauer, J. Phys. Chem. 100 (1996) 5025-5034.
19] Y. Meng, H.C. Genuino, C.-H. Kuo, H. Huang, S.-Y. Chen, L. Zhang, A. Rossi, S.L. Suib, J. Am.
Chem. Soc. 135 (2013) 8594-8605.
[
[
20] L. Wang, Y. Liu, W. Xie, H. Wu, X. Li, M. Y. He, P. Wu, J. Phys. Chem. C 112 (2008) 6132-6138.
21] W. Zhou, R. Wischert, K. Xue, Y. Zheng, B. Albela, L. Bonneviot, J.-M. Clacens, F. D. Campo, M.
Pera-Titus, P. Wu, ACS Catal. 4 (2014) 53−62.
[
[
(
[
[
[
[
[
[
[
[
[
[
22] M. Baldi, F. Milella, J.M. Gallardo-Amores, J. Mater. Chem. 8 (1998) 2525-2531.
23] B. Chowdhury, K. Bando, J. Bravo-Suárez, S. Tsubota, M. Haruta, J. Mol. Catal. A: Chem. 359
2012) 21-27.
24] Y. Xu, B. Lei, L. Guo, W. Zhou, Y. Liu, J. Hazard. Mater. 160 (2008) 78-82.
25] M. Kang, M.-H. Lee, Appl. Catal. A: Gen. 284 (2005) 215–222.
26] Y. Dai, X. Wang, Q. Dai, D. Li, Appl. Catal., B 111 (2012) 141-149.
27] J. Li, Y. Shi, L. Xu, G. Lu, Angew. Chem. Int. Ed. 49 (2010) 5392-5399.
28] M.E. Rerek, I. Weil, M. Hill, Coord. Chem. Rev. 105 (1990) 251-268.
29] C.-C. Guo, Q. Liu, X.-T. Wang, H.-Y. Hu, Appl. Catal. A: Gen. 282 (2005) 55-59.
30] X. Liu, J. He, L. Yang, Y. Wang, S. Zhang, W. Wang, J. Wang, Catal. Commun. 11 (2010) 710-714.
31] R. Neumann, M. Dahan, J. Am. Chem. Soc. 120 (1998) 11969-11976.
32] R.A. Sheldon, M. Wallau, I.W.C.E. Arends, U. Schuchardt, Acc. Chem. Res. 31 (1998) 485-493.
33] E. Breynaert, I. Hermans, B. Lambie, G. Maes, J. Peeters, A. Maes, P.A. Jacobs, Angew. Chem. Int.
1
4

ACCEPTED MANUSCRIPT
Ed. 45 (2006) 7584-7588.
[
34] I. Hermans, E. Breynaert, H. Poelman, R.D. Gryse, D. Liang, G.V. Tendeloo, A. Maes, J. Peeters,
P.A. Jacobs, Phys. Chem. Chem. Phys. 9 (2007) 5382-5386
[
[
[
[
35] G.N. Vayssilov, Cat. Rev. 39 (1997) 209-251.
36] A. Corma, M. A. Camblorꢀ ꢁ. ꢂsteveꢀ ꢃ. ꢄartineꢅꢀ ꢆ. ꢁéreꢅ-Pariente, J. Catal. 145(1994) 151-158.
37] D. Srinivas, P. Manikandan, S. C. Laha, R. Kumar, P. Ratnasamy, J. Catal. 217 (2003) 160-171.
38] S. Chavan, D. Srinivas, P. Ratnasamy, J. Catal. 212 (2002) 39-45.
1
5

ACCEPTED MANUSCRIPT
Figure captions:
Fig. 1. (A) N adsorption-desorption isotherms, (B) pore diameter distribution, (C) XRD, (D)
2
FT-IR of samples parent HTS and the xMn-HTS.
Fig. 2. (A) UV-Vis, (B) Ti(2p) core level XPS, (C) Mn(2p) core level XPS of samples parent HTS
and the xMn-HTS.
Fig. 3. Effect of the catalyst amount (A), reaction temperature (B), reaction time (C) and reaction
pressure (D) on the conversion of cyclohexane and AA selectivity over the synthesized 1%
Mn-HTS. (reaction conditions: 10 g cyclohexane, K/A oil is the cyclohexanol and cyclohexanone;
Others include Glutarate acid, Succinate acid and Ester).
Fig. 4. Results of hot-separation (A) and recycle (B) test of 1% Mn-HTS catalyst at 413 K.
(
reaction conditions: 1.0 MPa O , cyclohexane 10 g, catalyst 0.1 g).
2
1
6

ACCEPTED MANUSCRIPT
a
Table 1 Catalytic performance of the different catalyst
c
b
Selectivity (%)
Conversion
%)
Entry
Catalyst
(
CyOH Cyone
SA
--
GA
--
AA
5.8
4.6
--
Othes
14.8
16.4
1.1
1
2
3
4
5
6
Blank
Silicon-1
TS
1.0
1.0
1.7
7.6
5.2
6.2
32.5
32.5
48.4
24.4
36.3
24.5
46.9
46.5
50.5
33.2
26.5
41.5
--
--
--
--
HTS
--
--
30.7
35.2
11.7
2.0
Mn O
--
--
3
4
Mn-Silicon-1
Co-HTS(1%)
Fe-HTS(1%)
Cr-HTS(1%)
Mn-HTS(1%)
Mn-HTS(0.5%)
Mn-HTS(3%)
Mn-HTS(1%)
0.9
2.4
--
1.1
6.2
1.3
1.8
4.5
3.7
5.5
11.9
22.7
44.7
27.7
36.4
57.7
36.5
52.8
85.3
9.3
10.1
2.1
1.8
1.2
8.2
3.7
1.0
7
8
9
8.2
9.2
7.9
8.6
7.5
7.9
43.2
15.3
31.9
17.1
12.0
23.7
12.1
--
21.3
37.0
42.9
22.8
27.5
22.9
--
--
1
0
1
1.8
0.4
3.0
1.7
1
1
2
d
1
3
a
Reaction conditions: 0.1 g of catalyst; 119 m mol (10 g) of substrate; 1.0 MPa O ; 413 K; 6 h.
2
b
Cyclohexane conversion = (the amount (mmol) of starting cyclohexane the amount (mmol) of
cyclohexane recovered)/the amount (mmol) of starting cyclohexane × 100%.
c
Product selectivity = content of this product/Ʃ content (mmol) of each product) × 100%, CyOH:
cyclohexanol, Cyone: cyclohexanone, SA: Succinate acid，GA: Glutarate acid，AA: Adipic acid,
Others: Ester and Cyclohexyl hydroperoxide.
d
Reactant is the cyclohexanone, reaction temperature: 373 K, oxygen pressure: 0.6 MPa.
1
7

ACCEPTED MANUSCRIPT
A
B
C
D
Fig. 1
1
8

ACCEPTED MANUSCRIPT
A
B
Fig. 2
1
9

ACCEPTED MANUSCRIPT
A
B
C
D
Fig. 3
2
0

ACCEPTED MANUSCRIPT
A
B
Fig. 4
2
1

ACCEPTED MANUSCRIPT
Scheme 1 Some alternative routes to adipic acid.
2
2

ACCEPTED MANUSCRIPT
Scheme 2 Illustration for the cyclohexane oxidation over the synthesized catalysts.
2
3

ACCEPTED MANUSCRIPT
Scheme 3 A possible reaction path for oxidation of cyclohexane to AA over Mn-HTS
2
4

ACCEPTED MANUSCRIPT
Graphical abstract
2
5

ACCEPTED MANUSCRIPT
Highlights
►
Mn-HTS exhibits high selectivity for the one-step oxidation of cyclohexane to adipic
acid.
►
The catalyst can be reused and easily separated from the reaction system.
►
Using molecular oxygen as oxidant without any initiator and solvent.
2
6