Immobilization of Cu(II) in KIT-6 supported Co3O4 and catalytic performance for epoxidation of styrene

Accepted Manuscript Title: Immobilization of Cu (II) in KIT-6 Supported Co3 O4 and Catalytic Performance for Epoxidation of Styrene Author: Baitao Li Xin Luo Yanrun Zhu Xiujun Wang PII: DOI: Reference:

S0169-4332(15)02550-7 http://dx.doi.org/doi:10.1016/j.apsusc.2015.10.131 APSUSC 31612

To appear in:

APSUSC

Received date: Revised date: Accepted date:

10-7-2015 28-9-2015 20-10-2015

Please cite this article as: B. Li, X. Luo, Y. Zhu, X. Wang, Immobilization of Cu (II) in KIT-6 Supported Co3 O4 and Catalytic Performance for Epoxidation of Styrene, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.10.131 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.

Immobilization of Cu (II) in KIT-6 Supported Co3O4 and Catalytic Performance for Epoxidation of Styrene

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Baitao Li*, Xin Luo, Yanrun Zhu, Xiujun Wang*

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Key Laboratory of Fuel Cell Technology of Guangdong Province, School of Chemistry and

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Chemical Engineering, South China University of Technology, Guangzhou 510640, China

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Corresponding author: Baitao Li

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School of Chemistry and Chemical Engineering South China University of Technology

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Guangzhou 510640, China

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E-mail: [email protected]

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Tel/Fax: +86-20-87112943

Co-corresponding author: Xiujun Wang

School of Chemistry and Chemical Engineering South China University of Technology Guangzhou 510640, China

Tel/Fax: +86-20-87112943 E-mail: [email protected]

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Baitao Li et al. Page 2

Abstract KIT-6 is a cage type three dimensional cubic mesoporous silicate with Ia3d type structure, which shows scintillating promise in nanocasting, surface functionality, metal incorporation, and

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pharmaceutics. Nevertheless, little attention was paid to its application as support in heterogeneous catalysts. Cu-containing cobaltosic oxide spinel composite supported by

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mesoporous silica KIT-6 were synthesized via impregnation method and subsequent calcination

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under different temperature. The prepared ordered materials were characterized by X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy, atomic adsorption

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spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results showed that Cu2+ was successfully embedded in spinel structure when calcined at 550 ºC, in contrast, the

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samples through thermal treatment at 250 ºC remained hybrid composition of CuO and Co3O4.

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Catalytic performance of mesoporous materials were evaluated for epoxidation of styrene in the

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presence of tert-butylhydroperoxide as oxidant. Among a range of prepared materials, a significant enhancement in styrene conversion and selectivity of styrene oxide was obtained for

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Cu-spinel catalysts, in comparison with hybrid oxide. A dramatic decrease in catalytic activities was found while KIT-6 support was removed, due to the partial destruction of ordered structure of Cu-Co oxide. Following these results, the catalytic behaviors were chiefly ascribed to copper species and their textural properties. Keywords

Copper-cobalt oxides catalysts, mesoporous materials, spinel phase, epoxidation, styrene

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1 1. Introduction

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Over the recent decades, much interest has been drawn in the studies of mesoporous materials [1-

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4], particularly, ordered mesoporous silica, due to their exceptional properties, such as high

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surface area, uniform pore size distribution, controllable pore volume, good thermal stability, and

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potential functionality [5-7]. Previously, the two dimensional (2D) molecular sieves including

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MCM-41 and SBA-15 were obtained through soft templating techniques using block copolymer

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surfactants, however, these nanoparticles exhibit thin silica wall without interconnectivity

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because of their planar network [8, 9]. It remains a challenge for 2D ordered structure silica to

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cover the applications involving immobilization, diffusion and interaction of large molecules or

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crystals. Therefore, a bicontinuous cubic phase (Ia3d) mesostructure silica KIT-6 synthesized in

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aqueous solution was reported [10, 11]. Typically, as three dimensional (3D) material, KIT-6

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contains interpenetrating channels and precisely controllable pore system via a hydrothermal

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procedure [12]. The formation mechanism of KIT-6, involving a transformation from a lamellar

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phase, is highly depended on initial concentration of n-butanol or acid. Besides, varying the

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hydrothermal synthesis temperature allows efficient tailoring of interconnectivity, capable of

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obtaining the mesopore diameters from 4 to 12 nm [11, 13, 14]. With facile controlled texture

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parameters, KIT-6 shows scintillating promise in nanocasting, surface functionality, metal

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incorporation, and pharmaceutics [6, 15-18]. Nevertheless, little attention was paid to its

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application as support in heterogeneous catalysts.

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Styrene oxide (SO), as a key intermediate for agrochemical, fine chemical, and drug industries, is

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produced via the epoxidation of styrene utilizing oxidizing agents including oxygen,

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hydroperoxide or derivative, tert-buyl hydroperoxide (TBHP), and peracids [19-23].

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Conventionally, a range of heterogeneous catalysts based on precious metal, for instance, gold

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and silver, were employed to enhance the catalytic performance [24-29]. Although remarkable

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yields of target molecule were achieved, precious metal catalysts limited by their low abundance

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and expensive cost, could hardly reflect the demand of usage on a global scale. For years

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mounting efforts devoted to the design and exploitation of cheap metal catalysts for organic

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synthesis, lead to notable activities which are comparable to or even exceed those catalysts

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containing precious metal. For examples, abundant metals such as Fe and Co exhibit impressive

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performance for hydrogenation of C=C or C=O bonds that are catalyzed by Ru, Rh, Pt in general

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[30]. Supported simple transition metal oxides (NiO, CoO, Fe2O3, CuO) have been developed for

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olefins epoxidation [31-35]. Unfortunately, these approaches more or less have disadvantages,

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including supplement with co-feed hydrogen, incomplete or excessive oxidation, metal leaching

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and lengthy preparation.

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Among the first-row transition metals, Cu species, which manifest highly reactivity for

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epoxidation of several terminal olefins, are considered to be alternative compounds with

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applicability for the production of olefin oxides [36-38]. Recent work indicates that metallic

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copper is responsible for the distinctive selectivity in the reaction, but Cu2O is generated

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simultaneously which can restrict the epoxidation [39]. Other studies point to the possibility that

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active phases mainly originate from cupric ions, however, further efforts should be concentrated

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on substrate conversion and selectivity of target product [40-42]. Additionally, anchoring Cu2+

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species onto order mesoporous silica using organic ligands with -NH2 groups, such as Schiff

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bases and 3-aminopropyltriethoxysilane (APTES), was reported, and relative well styrene

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conversion was gained over these complexes [43-45]. On the other hand, some issues, like

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hazardous reactants to handle and tedious organic synthesis to process, should be faced in the

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utilization of these compounds.

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Herein, we report the mesoporous silica KIT-6 supported Cu-containing cobaltosic oxide

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material via a facile preparation and its notable catalytic performance for epoxidation of styrene.

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Characterization details show that activities of the catalysts mainly depend on copper species and

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texture properties.

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2. Experimental Sections

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2.1. Synthesis of Materials.

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2.1.1. Preparation of Cubic Mesoporous KIT-6. KIT-6 was synthesized according to the

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protocol described in literature [10]. Briefly, 12.0 g of Pluronic P123 (EO20PO70EO20, MW =

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5800, Sigma-Aldrich) was dissolved in a mixture of deionized water (434.0 g) and concentrated

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HCl (37%, 23.6 g) under stirring at 35 ºC. 12.0 g of n-butanol was added to the homogeneous

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solution subsequently and the mixture was stirred at 35 ºC for 1 h. 25.8 g of tetraethoxysilane

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(TEOS) was added dropwise and the solution was left stirring at 35 ºC for 24 h, followed by

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hydrothermal treatment at 35 ºC under static condition for another 24 h. The mixture was

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collected via filtration and extraction in ethanol-HCl solution (1 g of as-synthesized silica with a

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mixture of 3 mL of 37% HCl plus 200 mL ethanol). The solid product was then dried overnight

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at room temperature and calcined at 550 ºC under static air atmosphere for 6 h with a

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temperature ramp of 2 ºC min-1.

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2.1.2. Preparation of KIT-6 Supported Cu-containing Cobaltosic Oxide. KIT-6 supported

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Cu-containing cobaltosic oxide was synthesized via an impregnation method described in

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literature [15]. Typically, 2 g of KIT-6 was impregnated with certain molar ratio (Cu/Co = 1/16,

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1/8, 1/4, 1/2) of Cu(NO3)2-Co(NO3)2 ethanol solution (0.8 M total metal ion concentration, 20

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mL), then was stirred under room temperature (25 ºC) for 1 h, followed by drying at 60 ºC

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overnight. The collected solid was divided into two equal portions and calcined under different

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temperature. The series of samples treated by an intermediate calcination process at 250 ºC for 4

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h and an ultimate calcination at 550 ºC for 6 h with a temperature ramp of 2 ºC min-1, are

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denoted as CuS-Co3O4(x)/KIT-6, where x is the initial molar ratio of Cu/Co, and “S” refer to

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spinel type structure. Another series of samples calcined at 250 ºC for 4 h with a temperature

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ramp of 2 ºC min-1, are denoted as CuH-Co3O4(x)/KIT-6, where x is the initial molar ratio of

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Cu/Co, and “H” refer to hybrid metal oxide. Additionally, KIT-6 supported mono-metal oxides

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(CuO/KIT-6 and Co3O4/KIT-6) were obtained following the identical procedure as CuS-

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Co3O4(x)/KIT-6 using the relative precursors.

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2.1.3. Preparation of Cu-containing Cobaltosic Oxide. The removal of silica support of CuH-

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Co3O4(x)/KIT-6 was conducted according to literature [12]. The CuH-Co3O4(x)/KIT-6 was

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dispersed in 2 M NaOH aqueous solution (25 mL for 1 g of silica) under vigorous stirring at ~ 70

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ºC for 4 h. Afterwards, the sediment was separated via centrifugation and washed with deionized

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water until neutralization. Finally, the collected product was dried at 50 ºC and named as CuH-

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Co3O4(x).

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2.2. Catalyst Characterization. Textural and structural properties of catalysts were investigated

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by a combination of X-ray diffraction (XRD), N2 adsorption-desorption, high resolution

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transmission electron microscopy (HRTEM), and atomic adsorption spectroscopy (AAS).

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Chemical states of copper species were studied with Raman spectroscopy and X-ray

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photoelectron spectroscopy (XPS).

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XRD patterns were carried out on a D8 Advance X-ray diffractometer (Bruker) with

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monochromatic Cu Kα (0.154 nm) radiation. The small-angle diffraction peak (2θ = 0.6-3º) were

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recorded with step size of 0.02º and acquisition time of 0.2 s, while the wide-angle diffraction

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peak (2θ = 20-70º) were obtained with step size of 0.02º and acquisition time of 0.1 s. The

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crystal structure was estimated by comparison with Joint Committee on Powder Diffraction

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Standards (JCPDS) database. N2 adsorption-desorption isotherms were measured with a Tristar II

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3020 adsorption analyzer (Micromeritics) at 77 K. The samples were degassed at 150 ºC for 10 h

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before N2-physorption. Brunauer-Emmett-Teller (BET) surface areas were evaluated over the

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relative pressure range from 0.05 to 0.3. Total pore volumes were established by the adsorbed

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volume at a relative pressure of 0.97. Pore size distribution curves were derived from adsorption

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branch using the Barrett-Joyner-Halenda (BJH) method. HRTEM images were taken by a JEM-

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2100F (JEOL) transmission electron microscope with field emission electron source. The

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instrument was operated at the accelerating voltage of 200 kV. The amounts of copper or cobalt

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corresponding to prepared materials were determined by a Z-2000 (Hitachi) graphite furnace

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atomic absorption spectrometer (GFAAS) after decomposition in a mixture of HNO3 and HF

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solution. Raman spectra were performed with a LabRAM Aramis spectrometer (HORIBA Jobin

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Yvon), employing a He-Ne laser of 632.8 nm as excitation source. XPS results were obtained by

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an Axis Ultra DLD (Kratos) spectrometer with an Al Kα (1486.6 eV) radiation operated at 15 kV

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and 10 mA. The binding energy (B. E.) of samples was referenced to C 1S at 284.6 eV.

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2.3. Catalytic Test. The epoxidation of styrene was carried out in a 50 mL round bottom flask

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equipped with a magnetic stirrer and reflux condenser according to the following procedure. 50

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mg of catalyst was added to a mixture consisting of styrene (10 mmol), TBHP (10 mmol, 70

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wt% aqueous solution), and acetonitrile (~ 10 mL, as solvent). Afterwards, the reaction was

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started under continuous stirring, and the vessel was immersed in an oil bath at 70 ºC for 8 h. The

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products were identified and quantified by a gas chromatograph with a capillary column (TM-5,

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30 m × 0.25 mm × 0.25 µm) and a flame ionization detector (FID), using toluene as an internal

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standard. The catalysts were recovered by filtration from the reaction mixture, washed with

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ethanol and dried at 50 ºC for 12 h. The reaction was repeated with recovered catalysts under

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identical conditions.

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3. Results and Discussion

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3.1. Materials Characterization. Effectual synthesis of KIT-6 with large surface area and

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regular pore system was verified by XRD and HRTEM. Analysis on low angle XRD patterns

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(Figure S1 A) ranging from 0.6 to 3º shows characteristic peak corresponding to (211) and (220)

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plane respectively, which reveals the silica materials exhibit a cubic phase with Ia3d symmetry

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[10]. The d211 diffraction peak is located at a relative higher 2θ angle, indicating a cubic

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mesoporous KIT-6 with lower symmetry, as expected from a hydrothermal treatment under 35

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ºC [15]. After impregnation with Cu/Co ethanol solution and calcination at 550 ºC (Figure 1 A),

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although the diffraction intensities for all samples are decreased, all patterns show similar

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features at (211) reflection peak which shifted to a lower 2θ angle with increasing cupper amount.

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It could be reasonably inferred that the ordered cubic structure still remained while the pores of

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KIT-6 were partially filled with cobalt and copper oxides. The d211 values get smaller for CuS-

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Co3O4(1/16)/KIT-6 and CuS-Co3O4(1/8)/KIT-6 in comparison with pristine mesoporous support

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(Table 1), indicating slight shrinkage in the mesoporous framework possibly due to the silicate

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condensation after Cu/Co modification [46]. Notably, the (211) reflection peak of Co3O4/KIT-6

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sample appears at a 2θ angle area much lower than others, suggesting distribution of metal

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oxides in the pore channels has been modified when Cu was introduced.

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As depicted in Figure 1 B, (211) peaks in CuH-Co3O4(x)/KIT-6 series samples calcined at 250 ºC

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are retained and shifted likewise. A growth in intensities is followed the increase of Cu/Co ratios.

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Difference in shapes of (211) peaks between CuS-Co3O4(x)/KIT-6 and CuH-Co3O4(x)/KIT-6

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implies intrinsic structure of catalysts has been changed during the calcination process from 250

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ºC to 550 ºC. Interestingly, CuH-Co3O4(1/2)/KIT-6 and CuO/KIT-6 samples exhibit (211)

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reflection with stronger intensities than others, suggesting these two samples may have

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interaction in common between metal oxide and silica support. As shown in Figure S2 A, all

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diffraction peaks nearly completely vanished after the removal of KIT-6, due to collapse of the

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cubic phase without the ordered silica skeleton.

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Figure 2 shows wide angle results ranging from 20 to 70º of samples with various Cu/Co ratios

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calcined at 250 ºC and 550 ºC, respectively. Obviously, both CuS-Co3O4(x)/KIT-6 (Figure 2 B)

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and CuH-Co3O4(x)/KIT-6 (Figure 2 C) series catalysts exhibit (220), (311), (400), (422), (511),

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(440) plane reflections (JCPDS #42-1467) which are well matched with literatures and

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Co3O4/KIT-6 (Figure 2 A), ascertaining all Co species have been turned into cobaltosic oxide

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after calcination in air [47-49]. Diffraction peaks in CuS-Co3O4(x)/KIT-6 are less broad than

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CuH-Co3O4(x)/KIT-6 (Figure 2 C), due to an inevitable growth in grain size during calcination at

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higher temperature.

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Nevertheless, the existence and quantity of Cu species in prepared materials are rather

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complicated. As seen in Figure 2 C, CuO phase could be hardly found in samples containing

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little amount of Cu, whereas its characteristic reflection peaks appear after the ratio of Cu/Co

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increases to 1/4 and the intensity increases sharply as proportion of Cu doubles. In contrast, in

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CuS-Co3O4(x)/KIT-6 series catalysts (Figure 2 B), diffraction peaks of monoclinic copper oxide

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crystal can never be detected until the ratio of Cu/Co reaches 1/2. The difference between two

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series of samples is attributed to discrepant kind of Cu species which are contained in

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mesoporous silica according to inequable calcination temperature. During preparation of CuH-

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Co3O4(x)/KIT-6, decomposition of nitrates led to a mixture of CuO and Co3O4 partial populated

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in channels of KIT-6 through a 250 ºC thermal treatment in air [15, 50, 51]. Although CuO phase

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was difficult to be detective in low level (Cu/Co = 1/16, 1/8), it became increasingly

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distinguished as the contents of Cu in CuH-Co3O4(x)/KIT-6 samples increased. The distributions

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of Cu species in CuS-Co3O4(x)/KIT-6 samples, by contrast, were widely divergent. It should be

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kept in mind that solid-solid reactions occurred at high temperature (550 ºC), resulting in the

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embedment of Cu2+ in Co3O4 crystalline phase to form doped spinel, while the symmetry,

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morphology and textural parameters of original oxides almost maintained [52, 53]. As

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aforementioned, CuO phase could not be inspected at most cases of CuS-Co3O4(x)/KIT-6 samples

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since copper cations have been embedded in Co3O4 spinel. In addition, the appearance of CuO

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characteristic reflections in CuS-Co3O4(1/2)/KIT-6 was derived from the excess of copper species

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that did not react with Co3O4. The solid-solid reactions also made a difference effecting KIT-6

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support, and that is the reason why 2θ angle areas vary from CuS-Co3O4(x)/KIT-6 to CuH-

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Co3O4(x)/KIT-6. Moreover, the existence of Cu and Co species were reserved when KIT-6 was

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removed, thus CuS-Co3O4(x) samples present similar data at 2θ angle areas ranging from 20 to

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70º (Figure S2 B).

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Morphology information was acquired by HRTEM to check the homogeneity of mesostructure.

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The portions in bright and dark colors correspond to pore wall and pore channels, respectively.

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Obviously, it can be observed that the accessible pores system was present in KIT-6 over a long

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distance (Figure S1 C), and pore size was estimated to be ~ 6 nm, a little larger than previous

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reports due to longer thermal treatment time [10, 11]. The side-view of well ordered linear pore

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arranging is also visible (inset in Figure S1 C). Significantly, HRTEM images in Figure 3 verify

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that the cubic mesoporous architecture was retained after metal oxide loading, which is in good

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agreement with XRD results. The average TEM spacing pore size for each sample loading both

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Cu and Co oxides is estimated to be 8.0 ~ 8.7 nm. Almost no obvious metal oxides grains is

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found on the surface of KIT-6 in CuS-Co3O4(x)/KIT-6 catalysts. However, in CuH-Co3O4(x)/KIT-

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6 samples, clear black spots were visible, indicative for generation of these oxides over the

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support surface in low temperature calcinations. Compared with CuH-Co3O4(x)/KIT-6 (Figure 3

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E-H), CuS-Co3O4(x)/KIT-6 samples (Figure 3 A-D) show more uniform distribution around the

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interconnectivity system of KIT-6, owing to immobilization of Cu2+ in Co3O4 spinel via solid-

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solid reactions. Further evidences were provided in the observation of both Co3O4/KIT-6 and

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CuO/KIT-6 samples (Figure S3 A, B). It is notable that extraordinary quantity of CuO grains

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failed to embed in the pore channels of KIT-6 and released to surface as bulk particles in

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asymmetrical distribution (Figure S3 B), while Co3O4/KIT-6 samples were scattered throughout

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the silica support, resemblance of CuH-Co3O4(x)/KIT-6 series catalysts. Micrographs of materials

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via silica removal process are depicted in Figure S3 C-E. A better maintenance conformal nature

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was found in CuS-Co3O4(1/8)/KIT-6 rather than CuH-Co3O4(1/8)/KIT-6, and the prepared CuO

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without KIT-6 went completely irregular, giving proof of re-arrangement which took place

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across pore system through 550 ºC treatment. Hence, the solid-solid reaction occurred at 550 ºC

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is reliably supposed to be favor of modification for interaction between Cu and Co species,

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which achieved uniform distribution, regardless of agglomeration at higher temperature.

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Textural parameters including surface area, pore volume, and pore size distribution were

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calculated using N2 adsorption-desorption measurements (Table 1). As shown in Figure S1 B and

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Figure 4, both primitive KIT-6 and silica supported materials display type IV isotherms with H1

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hysteresis loops, confirming the presence of typical mesoporous architecture with cylindrical

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pores [45, 54]. Sharp capillary condensation of nitrogen occurred, suggesting narrow pore

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distribution [17], in line with HRTEM study. Less steep slopes obtained in Co3O4/KIT-6 or

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CuO/KIT-6 were assumed that uniformity of pore size turned worse as poor distribution shown

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in TEM images (Figure S3 A, B). The KIT-6 has a BET surface area of 446 m2/g and an

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accessible pore volume of 0.60 m3/g (Table 1). In general, loading of metal oxides caused

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substantial decline in surface area and pore volume, as well as increase in pore size. Furthermore,

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CuS-Co3O4(x)/KIT-6 samples exhibits a BET surface area of ~ 105 m2/g and a pore volume of ~

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0.20 m3/g, and the slightly decrease comparing to CuH-Co3O4(x)/KIT-6 samples (a BET surface

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area of ~ 190 m2/g and a pore volume of 0.25 m3/g) could be recognized as occurrence of

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sintering at higher temperature. It is noted that CuO/KIT-6 has the minimum BET surface area

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and pore volume, due to poor textural properties revealed by XRD and HRTEM. BJH analysis

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on adsorption branch of isotherms reveals that pore diameters for CuH-Co3O4(x)/KIT-6 samples

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(~5 nm) remained similar to KIT-6, while the values increased in CuS-Co3O4(x)/KIT-6 samples

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because of further calcinations. For samples via KIT-6 removing process, BET surface area

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decreased automatically (Table S1) and H3 hysteresis loops were observed in materials

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containing Co skeleton (Figure S4), identified as slit pores, which present rather board pore size

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distribution (inset in Figure S4). These results could be referenced by less ordered matrix of

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relative TEM image. As for CuO synthesized by eliminating KIT-6 support, capillary

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condensation vanished due to the disordered bulk particles with negligible surface area.

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Raman spectra of synthesized materials were employed to assess chemical structure and

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morphology of the metal oxides (Figure 5). For Co3O4/KIT-6 sample, five distinguishable peaks

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located at 197, 484, 525, 619, and 689 cm-1 are assigned to F2g, Eg, F2g, F2g, A1g Raman active

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modes of Co3O4 crystals, respectively, similar to previous literatures [55, 56]. These signals

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originate from lattice vibrations of spinel structure, in which Co2+ and Co3+ are placed at

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tetrahedral and octahedral sites, respectively [57, 58]. And for CuO/KIT-6 sample, three

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characteristic peaks at 295, 345, and 631 cm-1 are identified in the spectrum corresponding to Ag,

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two Bg modes of crystalline copper oxides, with each Cu atom coordinated with four atoms [59-

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61]. The optical properties of samples which consist of Cu and Co oxides in different ratios, vary

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apparently according to calcination temperature. As seen in CuS-Co3O4(x)/KIT-6 with x ranging

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from 1/16 to 1/4, analogous Raman peaks to cobaltosic oxide are observed, while the bands

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belong to CuO are absent. According to previous literature, the spectra covered regions of 600-

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700 cm-1 is associated to vibrations for the motion of corners oxygen atoms in the octahedral unit

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of spinel oxides, thus A1g mode could be regarded as fingerprint for perturbation of the breathing

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vibration of M3+ - O bond upon other atom doping [62]. For CuS-Co3O4(x)/KIT-6 (x = 1/16, 1/8,

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1/4), slight variation in resolution and relative intensity of the A1g mode took place due to the

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augment in components of Cu, insinuating changes in spinel crystallization during the addition of

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copper species [63, 64]. Comparing with XRD results, it is confirmed that these three samples

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deliver a Co3O4 spinel phase doped with Cu. Conversely, a broad shoulder band emerged across

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500-600 cm-1 in all CuH-Co3O4(x)/KIT-6 samples and CuS-Co3O4(1/2)/KIT-6, and A1g mode of

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the materials was broadened and shifted 1-3 cm-1 towards shorter wavenumbers. Referring to

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above Raman spectra of mono oxide catalysts as well as literatures, the broad peaks at 500-600

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cm-1 are probably assigned to the mix of CuO and Co3O4 [65, 66], and the hybrid oxides

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generated red shifts due to lattice strains, heterojunctions, and sample variability [67, 68]. In

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addition, no vibrational modes of Cu2O or CoO were observed in above samples. It could be

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specified that the Cu species were successfully doped in spinel sites of CuS-Co3O4(x)/KIT-6 (x =

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1/16, 1/8, 1/4) samples, however, superfluous Cu2+ remained CuO form as CuH-Co3O4(x)/KIT-6

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in CuS-Co3O4(1/2)/KIT-6. The results kept a high degree of consensus on the observation of

253

XRD.

254

XPS analysis provided further evidence for surface chemical structure and compositions of

255

prepared materials. It is presented in Figure S5 A that Co 2p3/2 and 2p1/2 peaks in CuH-

256

Co3O4(x)/KIT-6 samples appear at 780.1-780.3 eV and 795.1-795.2 eV, respectively, confirming

257

Co3O4 spinel phases were formed on the surface of such materials [69-71]. In contrast, the

258

binding energy (BE) of Co 2p3/2, which is slightly shifted to 779.8-779.9 eV in CuS-

259

Co3O4(x)/KIT-6, can be ascribed to replacement of Co ions (II or III valence) by other metal in

260

the spinel lattice [70, 72-74]. The spin-orbit splitting of ~ 15.1 eV is obtained for a whole range

261

of samples investigated above, in accordance with Co3O4 in literatures [69, 74, 75]. It should be

262

stressed that the intensity of each Co major peak in CuS-Co3O4(x)/KIT-6 is largely similar, while

263

a reduction in intensities owing to the increase in the amount of Cu in CuH-Co3O4(x)/KIT-6 was

264

observed. The phenomenon indicates that the CuS-Co3O4(x)/KIT-6 display a uniform distribution

265

of doped spinel oxides on the surface, fundamentally differently, the quantity of Co3O4 on the

266

surface of CuH-Co3O4(x)/KIT-6 is based on the Cu/Co ratios.

267

In order to account for the electronic structure of copper species at superficial level of the

268

prepared materials, the spectra concerning Cu 2p core level excitation were studied in Figure 6.

269

Since Cu 2p1/2 satellite is hardly indentified for samples in low Cu level, the regions will be

270

skipped for normalization of spectra. Both CuS-Co3O4(x)/KIT-6 and CuH-Co3O4(x)/KIT-6

271

samples show two main peaks center at ~934.5 eV and 954.6 eV associated with Cu 2p3/2 and

272

2p1/2, respectively, accompanied by shake up satellite peaks. It is well known that satellite bands

273

are generated by an electron transfer from a ligand orbital to a 3d orbital of Cu, confirming that

274

Cu species exist in bivalent form with 3d9 structure instead of Cu+ or Cu (0) species that have

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filled d level [76-78]. However, each Cu 2p peak clearly shows a resolved shoulder band,

276

indicating that the Cu2+ components are differentiated in chemical environment. Moreover, the

277

satellite lines observed in CuS-Co3O4(x)/KIT-6 samples with higher temperature treatment

278

present significant decline in intensity compared with CuH-Co3O4(x)/KIT-6 samples. For further

279

clarification of Cu species in the samples, each Cu 2p region is fitted to two doublets using

280

software XPSpeak41 and the BE values were compiled in Table 2. It is observed that Cu 2p3/2 for

281

all spectra presents two peaks at ~935.2 eV (1) and ~933.3 eV (2), while Cu 2p1/2 shows two

282

peak located at ~955.1 eV (1) and ~953.3 eV (2). As reported by previous literature, the Cu

283

component with lower BE of 2p3/2 (933.3-934.0 eV) can be ascribed to tetracoordinated Cu2+

284

ions [79-81], while Cu 2p3/2 located at higher BE (above 935 eV) reveals the existence of

285

octacoordinated Cu2+ species [82, 83]. For CuH-Co3O4(x)/KIT-6 samples, the tetracoordinated

286

copper species with lower BE are probably due to high dispersion of isolated Cu2+ in silica

287

matrix [79, 82], and Cu2+ species placed at higher BE are mainly related to Cu(H2O)62+ complex

288

and other octacoordinated bivalent copper ions according to literatures [80, 84].

289

CuS-Co3O4(x)/KIT-6 samples display Cu 2p BE values of two overlapped bands similar to CuH-

290

Co3O4(x)/KIT-6, whereas the descent in intensity of shake up satellites was detected (Figure 6),

291

indicating a change in environment of Cu atoms occurred under 550 ºC calcination, as satellites

292

bands are sensitive to electron transition from p orbital in ligand to 3d orbital in Cu, which is

293

mentioned above. Furthermore, it should be noticed that an discernible increase in composition

294

of tetracoordinated Cu (2) species was observed in most of CuS-Co3O4(x)/KIT-6 samples (x =

295

1/16, 1/8, 1/4), in contrast to CuH-Co3O4(x)/KIT-6 (Table 2). Based on these results, it is

296

reasonable to infer that Cu2+ was undergone a solid-solid reaction to substitute in

297

tetracoordinated sites of spinel lattice through a 550 ºC calcination, in which transformation from

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distorted octahedral to symmetric tetrahedral geometry resulted in decreased component of

299

octacoordinated Cu species, along with decline in intensity of satellite peaks [53, 65, 72, 84].

300

And for CuS-Co3O4(1/2)/KIT-6 sample, the excess of CuO which did not participate in solid-

301

solid reaction, generated a new phase containing more octacoordinated Cu2+, in line with XRD

302

and Raman results. Interestingly, considerable amount of octacoordinated Cu2+ species were

303

obtained in CuS-Co3O4(x)/KIT-6 samples in spite of high temperature calcinations. The

304

interpretation for this phenomenon is assigned to Jahn-Teller distortion of octahedral Cu2+, in

305

which the energy of the dz2 orbital is lower than the dx2-y2 orbital and is more energetically

306

stabilized for electrons to pair in [72]. Besides, the site preference energy for Cu2+ is close to that

307

for Co3+, enhancing the possibility of Cu2+ filling in octahedral sites of spinel [85]. Additionally,

308

CuO/KIT-6 shows significant shift towards higher BE values for two kinds of Cu 2p peaks

309

according to tetracoordinated and octacoordinated Cu2+ ions in Figure S5 B, suggesting poor

310

distribution of copper species in large grain size of the samples, consistent with TEM images.

311

Superficial analysis results for molar ratios of Cu/Co were listed in Table 3, in comparison to

312

bulk level carried out by AAS. The surface Co/Cu ratios remain at low level in CuS-

313

Co3O4(x)/KIT-6 samples, as the result of uniform distribution and high enrichment of Cu species,

314

mainly due to doped spinel phase with efficient fixation of Cu2+ in lattice. In contrast, the copper

315

concentrations on surface of CuH-Co3O4(x)/KIT-6 samples rise irregularly as anticipated when

316

Co/Cu ratios increase, because the materials are simply mixed of CuO and Co3O4, demonstrated

317

by above measurements. In addition, the bulk ratios of Co/Cu in all materials are well in

318

agreement with initial dosages. As derived from elemental analysis, it could be also concluded

319

that Cu species were substituted in cobaltosic oxides spinel through solid-solid reaction with

320

tuning distribution, identical to XRD, HRTEM, Raman, XPS results.

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3.2. Catalyst Evaluation. The catalytic activities for epoxidation of styrene in the presence of

322

TBHP were displayed in Table 4. Obviously, catalysts without Cu species, either KIT-6 or

323

Co3O4/KIT-6, exhibited rather poor performance with low conversion and TOF. When CuO

324

loading on KIT-6 solely, a little extra improvement in both conversion and selectivity of styrene

325

oxide (SO) was obtained, suggesting Cu2+ hold a dominant position in behaviors of catalysts.

326

However, the activity of CuO/KIT-6 was restricted to several disadvantages as pointed out in

327

characterization, such as inhomogeneous distribution distorted pore system, and narrow surface

328

area. CuS-Co3O4(1/16)/KIT-6 had a higher conversion and better selectivity to target product SO

329

than Co3O4/KIT-6 due to relative small amount of Cu loading.

330

Figure 7 depicts catalytic performance of both CuS-Co3O4(x)/KIT-6 and CuH-Co3O4(x)/KIT-6

331

samples, and significant enhancements were obtained on basis of Cu-Co bi-metal mesoporous

332

materials. Excellent catalytic behaviors were manifested in CuS-Co3O4(x)/KIT-6 materials, in

333

particular CuS-Co3O4(1/8)/KIT-6 had a conversion of 53.8% and a SO selectivity of 82.6%. The

334

results were credibly attributed to high superficial enrichment and uniform distribution of Cu

335

species fixed in lattice of Co3O4 spinel, as well as maintenance of ordered mesostructure in favor

336

of mass transfer. As contents of Cu increased, the conversion decreased gradually while

337

selectivity to SO keep almost constant, indicating that generation of CuO phase may be probably

338

unfavorable to epoxidation of styrene.

339

It could be observed that increasing promotion in catalytic performance emerged in accordance

340

to enlargement of Cu component in CuH-Co3O4(x)/KIT-6 samples. Considering Cu species exists

341

as CuO without intensive interaction with Co3O4, the increase of catalyst performance is merely

342

associated with concentration of Cu2+ on surface, exactly consistent with elemental analysis

343

conducted by XPS. It should be kept in mind that CuH-Co3O4(x)/KIT-6 samples have large pore

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volume and nearly double BET surface areas that presented in CuS-Co3O4(x)/KIT-6, however,

345

the catalytic activities of latter samples via higher temperature calcination indeed surpass the

346

catalysts with better textual parameters. Along with preceding characterization, the Cu2+

347

embedded in spinel lattice, which dispersed in constant concentration on surface of catalysts,

348

played a beneficial influence on catalytic behaviors. Thus, it could be validated that the

349

electronic structure of Cu-Co bimetal mesoporous materials, in particular chemical environment

350

of Cu species, dominates catalytic activities of styrene epoxidation.

351

Since KIT-6 assumes no responsibility for chemical structure other than a carrier, CuS-Co3O4(x)

352

samples via a process of removing the silica support were also investigated for epoxidation of

353

styrene. It is found that conversions of styrene dramatically dropped and tended to towards an

354

equalization of bare CuO through identical elimination process of KIT-6. The loss in activities is

355

considerably related to decrease in symmetry and ordered mesoporous structure, impairing mass

356

transfer over the interface of materials. Furthermore, the exposed metal oxide without support

357

would be inclined to aggregate during the reaction, as epoxidation was an exothermic process. In

358

other words, KIT-6 with ordered mesostructure and interconnectivity not only provided

359

extension in surface area and pore volume, facilitating effective contact of the reactants, but also

360

overcame agglomeration of catalysts to stabilize the active sites. Hence, textural properties of the

361

synthesized materials also play a pivotal role in epoxidation of styrene.

362

The effect of various solvents on the epoxidation of styrene with TBHP is also shown in Table 4.

363

The solvent plays an important role in the epoxidation reactions. The conversion of styrene

364

decreases in the sequence of acetonitrile (53.8%) > dichloroethane (23.8%) > DMF (14.4%) >

365

tert-butanol and pyridine (~ 9%). The acetonitrile were particularly efficient in yielding both

366

high styrene conversion (53.8%) and high epoxide selectivity (83%). The higher catalytic

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activity in acetonitrile was the result of its high polar aprotic solvent with higher dielectric

368

constant [86]. The higher dielectric constant led to the higher concentration of the substrate in the

369

vicinity of the active sites and the better solubility of the substrate and oxidant in the solvent, so

370

that the substrates and oxidant could easily approach the active sites of the catalyst [87, 88].

371

Previous studies had found that DMF was the best solvent in terms of the activity for the styrene

372

oxidation [89, 90], especially when oxygen was used as the oxidant. This behavior may be

373

associated with the high affinity of DMF to oxygen [91].

374

In addition, the influence of reaction conditions including reaction time, and amount of oxidant

375

was studied (Table 4). Obviously, a prolong reaction time (over 12 h) could allow the conversion

376

of styrene to reach 100%, but cause a decline in selectivity of SO (< 30%) due to further

377

oxidation, leading to benzoic acid predominant the product. Similarly, an increase in dosage of

378

TBHP would be advantageous to consume styrene, however, yields of undesired products rose as

379

side reaction occurred more frequently, in line with previous reports [21, 40, 42].

380

Compared with other studies based on copper catalysts for olefins epoxidation, selectivity to SO

381

achieved over CuS-Co3O4(x)/KIT-6 materials is superior to ranges of catalysts reported, allowing

382

convenient separation for desirable product. For instance, the core-shell structure nanopaticles

383

composing of Fe3O4, SiO2, and copper(II) acetylacetonate complexes, presented a styrene

384

conversion of 86.7% and SO selectivity of 51.4%, although the compound were subjected to

385

rather complicated preparation [92]. The CuO coated with SiO2 showed relative good activity in

386

styrene epoxidation in the presence of 5 times TBHP, but 61.2% of selectivity to SO was much

387

lower than for epoxidation of other olefins [41]. The Cu–phthalocyanine catalysts exhibited 50%

388

styrene conversion in epoxidation, however, the result was carried out using 3 times TBHP for

389

24 h, in which had a lower utilization rate of oxidant and poorer TOF than our work [93]. Several

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researchers focus on Cu2+ immobilized with Schiff base modified mesoporous silica, and most of

391

these compounds only manifested selectivities towards SO not more than 70 % with mediocre

392

conversions even after a lengthy reaction time (24 h) [43, 94]. The nanotubes containing Cu2+

393

derived from K4Nb6O17 scrolls displayed better catalytic performance than CuS-Co3O4(x)/KIT-6

394

materials, assigned to Cu2+ in the NbO6 octahedron matrix, which is similar to Cu2+ embedded in

395

the lattice of Co3O4 spinel [42]. In contrast with NbOx, a superiority in price promises practical

396

application for Cu doping Co3O4. In conclusion, KIT-6 supported Cu-Co oxides may be a novel

397

type of compound for catalytic epoxidation of styrene.

398

Generally, recyclability is regarded as an important strength for heterogeneous catalysts. The

399

recycling test using CuS-Co3O4(1/8)/KIT-6 as example was conducted for five cycles, and results

400

were illustrated in Figure 8. In the case of CuS-Co3O4(1/8)/KIT-6, only a trivial drop in

401

conversion about 2% during each cycle was detected, meanwhile, selectivity to target molecular

402

SO remained identical with fresh sample. The content of Cu carried out by AAS for catalyst

403

shows a puny change from 3.14 wt% to 2.97 wt% after the fifth cycle, while the percentage of

404

Co reduce slightly from 27.7 wt% to 24.6 wt%. The recovered catalyst even after 5 recycles

405

maintains the ordered mesostructure and interconnectivity of KIT-6. The above findings reveal

406

that the copper species embedded in Co3O4 lattice are well resistance of leaching, resulting in

407

maintenance for catalytic performance.

408

4. Conclusion

409

In summary, Cu-Co bimetal catalysts supported by KIT-6 were synthesized through a facile

410

impregnation procedure and calcinations under 250 ºC or 550 ºC. The textural studies indicate

411

that the materials retain ordered mesoporous structure and symmetry after metal oxide loading,

412

and exhibit uniform distribution. Furthermore, XPS and Raman spectra investigations reveal that

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Cu2+ was successfully embedded in Co3O4 lattice to form substituted spinel via solid-solid

414

reaction when calcined at 550 ºC, while the materials calcined at 250 ºC remain hybrid of CuO

415

and Co3O4. High concentration Cu2+ species with uniform distribution were inspected on the

416

surface of samples via a 550 ºC calcinations when compared with lower temperature calcinations

417

materials. Series of sample with various Cu/Co ratios were sequentially examined as catalysts for

418

epoxidation of styrene in the presence of TBHP. A significant enhancement in activities was

419

achieved based on the Cu doping Co3O4 spinel catalysts. Especially, Cu doping Co3O4 spinel

420

with a Cu/Co ratio of 1/8 had a conversion of 53.8 % and a styrene oxide selectivity of 82.6 %

421

after 8 h. Combining characterization results, it is credibly concluded that the enhanced catalytic

422

performance is owing to electronic structure of catalysts, in particular the chemical environment

423

of Cu2+, as well as the textural properties of materials.

424

Acknowledgements

425

The work was supported by National Natural Science Foundation of China (Project Nos.

426

21173086, 21543014 and U1301245) and Guangdong Natural Science Foundation (Project No.

427

2014A030313259).

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428 429

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an

us

cr

ip t

682

Ac ce p

te

d

M

691

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Baitao Li et al. Page 35

691

Legends

B

A

CuH-Co3O4(1/16)/KIT-6

Co3O4/KIT-6

ip t

CuH-Co3O4(1/8)/KIT-6 CuH-Co3O4(1/4)/KIT-6

cr us

Intensity (a.u.)

CuS-Co3O4(1/16)/KIT-6

CuH-Co3O4(1/2)/KIT-6

M

CuS-Co3O4(1/4)/KIT-6

an

CuS-Co3O4(1/8)/KIT-6

CuS-Co3O4(1/2)/KIT-6

692 693

1

2 2θ (°)

Ac ce p

0.6

te

d

CuO/KIT-6

3 0.6

1

2

3

2θ (°)

694

Figure 1. Small-angle XRD patterns of different series catalysts with various Cu/Co ratios. (A)

695

CuS-Co3O4(x)/KIT-6 and Co3O4/KIT-6, (B) CuH-Co3O4(x)/KIT-6 and CuO/KIT-6.

Page 35 of 49

Baitao Li et al. Page 36

311

A

Co3O4/KIT-6

220

400

422

B

440

511

ip t

CuS-Co3O4(1/16)/KIT-6

cr

CuS-Co3O4(1/8)/KIT-6

us

Intensity (a.u.)

CuS-Co3O4(1/4)/KIT-6

an

CuS-Co3O4(1/2)/KIT-6

M

C

CuH-Co3O4(1/8)/KIT-6

d

CuH-Co3O4(1/4)/KIT-6

te Ac ce p D

1 11

CuH-Co3O4(1/2)/KIT-6

111

CuO/KIT-6 2 02

110

20

696

30

40

CuH-Co3O4(1/16)/KIT-6

2θ (°)

50

020

1 13

202

60

3 11

220

70

697

Figure 2. Large-angle XRD patterns of various catalysts. (A) Co3O4/KIT-6, (B) CuS-

698

Co3O4(1/x)/KIT-6 , (C) CuH-Co3O4(1/x)/KIT-6, (D) CuO/KIT-6.

Page 36 of 49

us

cr

ip t

Baitao Li et al. Page 37

an

699

Figure 3. HRTEM images of various prepared Cu-Co materials supported by KIT-6. (A) CuS-

701

Co3O4(1/16)/KIT-6,

702

Co3O4(1/2)/KIT-6,

703

Co3O4(1/4)/KIT-6, (H) CuH-Co3O4(1/2)/KIT-6.

(B)

CuS-Co3O4(1/8)/KIT-6,

(C)

CuS-Co3O4(1/4)/KIT-6,

(D)

CuS-

CuH-Co3O4(1/16)/KIT-6,

(F)

CuH-Co3O4(1/8)/KIT-6,

(G)

CuH-

Ac ce p

te

d

(E)

M

700

Page 37 of 49

700

B

A

600 Cu -Co O (1/16)/KIT-6 S 3 4

CuS-Co3O4(1/8)/KIT-6

400

200 100

CuS-Co3O4(1/4)/KIT-6

ip t

300

CuS-Co3O4(1/2)/KIT-6 Co3O4/KIT-6 CuO/KIT-6 0.8

100

CuH-Co3O4(1/4)/KIT-6

20 30 40 Pore diameter (nm)

50

D

dV/dD

CuH-Co3O4(1/8)/KIT-6

10

an

200

M

CuH-Co3O4(1/16)/KIT-6

1.0

d

300

2

us

0.4 0.6 Relative Pressure (p/p0)

C

400

CuH-Co3O4(1/2)/KIT-6

0.2 0.4 0.6 Relative Pressure (p/p0)

Ac ce p

0 0.0

704 705

0.2

te

Volume Adsorbed (cm3/g STP)

0 0.0

cr

500

dV/dD

Volume Adsorbed (cm3/g STP)

Baitao Li et al. Page 38

0.8

1.0

2

10

20

30

40

50

Pore diameter (nm)

706

Figure 4. N2 adsorption-desorption isotherms (A, C) and pore size distribution curves (B, D) of

707

various KIT-6 supported catalysts.

Page 38 of 49

Baitao Li et al. Page 39

CuS-Co3O4(1/16)/KIT-6

ip t

CuS-Co3O4(1/8)/KIT-6 CuS-Co3O4(1/4)/KIT-6

Intensity (a.u.)

cr

CuS-Co3O4(1/2)/KIT-6

us

CuH-Co3O4(1/16)/KIT-6

an

CuH-Co3O4(1/8)/KIT-6

100

708 709

200

A (689) 1g

M

400

CuH-Co3O4(1/2)/KIT-6

F (619) 2g

F (525) 2g

Co3O4/KIT-6

B (631) g

E (484) g

d

Ac ce p

A (295) g B (345) g

te

F (197) 2g

CuH-Co3O4(1/4)/KIT-6

CuO/KIT-6

600

800

1000

Raman Shift (cm-1)

Figure 5. Raman spectra of several KIT-6 supported materials with various Cu/Co ratios.

Page 39 of 49

Baitao Li et al. Page 40

A

B

CuH-Co O (1/16)/KIT-6 3 4

ip t cr

Intensity (a. u.)

Cu -Co O (1/16)/KIT-6 S 3 4

CuH-Co O (1/8)/KIT-6 3 4

an

us

Cu -Co O (1/8)/KIT-6 S 3 4

CuH-Co O (1/4)/KIT-6 3 4

M

Cu -Co O (1/4)/KIT-6 S 3 4

Cu -Co O (1/2)/KIT-6 S 3 4 960

950

945

940

Binding Energy (eV)

935

930 960

955

950

945

940

935

930

Binding Energy (eV)

Ac ce p

710

955

te

d

CuH-Co O (1/2)/KIT-6 3 4

711

Figure 6. Cu 2p spectra of several KIT-6 supported materials with various Cu/Co ratios. (A)

712

CuS-Co3O4(x)/KIT-6 samples, (B) CuH-Co3O4(x)/KIT-6 samples.

Page 40 of 49

Baitao Li et al. Page 41

60

100

80

S-1/16

S-1/8

S-1/4

M

713 714

S-1/2

H-1/16 H-1/8

20

H-1/4

H-1/2

0

d

20

40

an

30

60

Selectivity %

ip t cr

40

us

Conversion %

50

Figure 7. Catalytic performance of several materials for epoxidation of styrene in the presence

716

of TBHP. S-x and H-x refer to CuS-Co3O4(x)/KIT-6 and CuH-Co3O4(x)/KIT-6, respectively.

717

(Reaction condition: styrene, 10 mmol; TBHP, 10 mmol; acetonitrile (solvent), 10 ml; catalyst,

718

50 mg; temperature, 70 oC; reaction time, 8 h. Bars in green and red refer to selectivity to styrene

719

oxide and benzaldehyde, respectively.)

Ac ce p

te

715

Page 41 of 49

Baitao Li et al. Page 42

80

100

80

2nd Cycle

3rd Cycle

722

Ac ce p

te

1st cycle

M

720 721

1st Cycle

d

0

an

20

4th cycle

4th Cycle

2nd cycle

60

40

Selectivity %

ip t cr

40

us

Conversion %

60

20

5th Cycle

0

3rd cycle

5th cycle

723 724

Page 42 of 49

Baitao Li et al. Page 43

725

Figure 8. The recycle results and TEM images of CuS-Co3O4(1/8)/KIT-6 sample for epoxidation

726

of styrene in five cycles. (Reaction conditions are identical to evaluation. Bars in green and red

727

refer to selectivity to styrene oxide and benzaldehyde, respectively )

Ac ce p

te

d

M

an

us

cr

ip t

728

Page 43 of 49

Baitao Li et al. Page 44

Tables Table 1. Textural Parameters of different series of synthesized mesoporous materials. Pore sizeb (nm)

d211d (nm)

a0 e (nm)

Wall thicknessf (nm)

KIT-6 CuS-Co3O4(1/16)/KIT-6

446 97

0.60 0.19

5.0 6.6

7.3 8.1

8.14 7.65

19.9 18.7

5.0 2.8

CuS-Co3O4(1/8)/KIT-6

110

0.18

6.3

8.3

7.93

19.5

3.4

CuS-Co3O4(1/4)/KIT-6

104

0.20

6.5

8.3

8.24

20.2

3.6

CuS-Co3O4(1/2)/KIT-6

112

0.21

6.7

8.7

8.83

21.6

4.1

CuH-Co3O4(1/16)/KIT-6

197

0.26

5.0

8.3

7.95

19.5

4.7

CuH-Co3O4(1/8)/KIT-6

189

0.25

5.0

8.2

8.12

19.9

4.9

CuH-Co3O4(1/4)/KIT-6

191

0.26

5.1

8.4

8.11

19.9

4.8

CuH-Co3O4(1/2)/KIT-6

183

0.26

5.3

8.0

8.11

19.9

4.6

CuO/KIT-6

68

0.12

6.2

8.0

8.93

21.9

4.8

Co3O4/KIT-6

96

0.20

7.2

9.0

9.11

22.3

4.0

Sample

730

a, b

731

c

732

d

733

e

a0 is unit cell parameter and a0 = √6 * d211

734

f

Calculated by the equation d (wall thickness) = 1/2 a0 – d (pore size).

Obtained by TEM analysis.

te

d

Acquired from the adsorption branch.

Determinated from relative peak of XRD patterns using Bragg law.

Ac ce p

735

cr

Pore volumea (cm3/g)

us

SBET (m2/g)

ip t

Pore spacing c (nm)

an

729

M

728

Page 44 of 49

Baitao Li et al. Page 45

Table 2. Cu 2p BE values and relative contents of various mesoporous materials. Binding energy (eV) Cu (2) Cu (1) 2p3/2 2p1/2

Cu (1) 2p3/2

CuS-Co3O4(1/16)/KIT-6

935.5

933.3

CuS-Co3O4(1/8)/KIT-6

935.4

CuS-Co3O4(1/4)/KIT-6

Cu (1)

Cu (2)

955.1

953.3

35.0

65.0

933.3

956.1

953.0

33.8

66.2

935.1

933.3

955.0

953.7

29.7

70.3

CuS-Co3O4(1/2)/KIT-6

935.2

933.4

955.4

953.2

47.8

52.2

CuH-Co3O4(1/16)/KIT-6

935.0

933.3

955.0

953.4

47.3

52.7

CuH-Co3O4(1/8)/KIT-6

935.1

933.0

954.9

953.3

48.0

52.0

CuH-Co3O4(1/4)/KIT-6

934.7

933.3

955.0

953.1

45.7

54.3

CuH-Co3O4(1/2)/KIT-6

935.2

933.9

955.3

953.6

49.4

50.6

CuO/KIT-6

936.9

934.6

954.1

28.6

71.4

us

M

736

956.3

ip t

Cu (2) 2p1/2

cr

Sample

Relative (%)

an

735

Ac ce p

te

d

737

Page 45 of 49

Baitao Li et al. Page 46

Table 3. Elemental analyses for various mesoporous materials

Sample CuS-Co3O4(1/16)/KIT-6 CuS-Co3O4(1/8)/KIT-6

Co and Cu contents (wt. %)a Co Cu 28.7 1.7 27.7 3.1

Co and Cu contents (molar %)a Co Cu 29.1 1.6 28.1 3.0

Co/Cu (molar ratio) Bulka 18.2 9.5

Surfaceb 4.8 2.0

4.8

2.0

2.5

1.2

ip t

737 738

25.1

5.7

25.5

5.3

CuS-Co3O4(1/2)/KIT-6

20.8

9.0

21.2

8.5

CuH-Co3O4(1/16)/KIT-6

28.6

1.5

29.0

1.4

21.1

39.4

CuH-Co3O4(1/8)/KIT-6

25.3

2.7

25.7

2.6

9.8

3.4

CuH-Co3O4(1/4)/KIT-6

23.5

5.1

23.9

4.8

5.0

3.2

CuH-Co3O4(1/2)/KIT-6

21.3

8.7

21.7

8.2

2.6

2.1

CuO/KIT-6

-

28.8

-

27.6

100% Cu

100% Cu

Co3O4/KIT-6

30.2

-

30.6

-

100% Co

100% Co

741

us

an M

Derived from XPS results.

d

b

te

740

Analyzed by AAS.

Ac ce p

739

a

cr

CuS-Co3O4(1/4)/KIT-6

Page 46 of 49

Baitao Li et al. Page 47

Table 4. Performance of various prepared catalysts for epoxidation of styrene Selectivitya (%)

Blank

Dosage of TBHP (mmol) 10

KIT-6 CuS-Co3O4(1/16)/KIT-6 CuS-Co3O4(1/8)/KIT-6

10 10 10

8 8 8

21.1 36.5 53.8

46.7 79.9 82.6

53.0 19.8 17.0

trace trace trace

-31.8 24.8

CuS-Co3O4(1/4)/KIT-6

10

8

42.6

79.5

20.1

trace

10.9

CuS-Co3O4(1/2)/KIT-6

10

8

37.9

CuH-Co3O4(1/16)/KIT-6

10

8

27.0

CuH-Co3O4(1/8)/KIT-6

10

8

42.0

CuH-Co3O4(1/4)/KIT-6

10

8

CuH-Co3O4(1/2)/KIT-6

10

8

CuO/KIT-6

10

8

Co3O4/KIT-6

10

CuS-Co3O4(1/16)

10

CuS-Co3O4(1/8)

10

CuS-Co3O4(1/4)

Reaction Time (h)

Conversion (%)

8

TOFb (h-1)

BA

Others

16.1

35.8

64.2

trace

--

us

trace

5.8

74.7

24.8

trace

23.5

81.2

18.4

trace

19.3

42.2

82.1

17.4

trace

10.8

46.5

74.6

25.1

trace

7.1

38.2

81.0

18.7

trace

2.0

8

27.9

61.3

38.3

trace

--

8

35.6

76.0

23.8

trace

12.1

8

39.4

71.6

28.0

trace

7.1

an

24.2

d

75.6

M

cr

ip t

SO

te

Catalyst

39.5

CuOc

10

8

38.4

81.4

18.1

trace

0.8

Co3O4d

10

8

22.7

62.5

37.2

trace

--

CuS-Co3O4(1/8)/KIT-6e

10

8

14.4

82.3

17.5

trace

6.4

f

10

8

23.8

90.7

9.2

trace

11.1

g

10

8

6.9

1.0

98.3

trace

3.2

h

10

8

9.3

36.4

62.6

trace

4.1

CuS-Co3O4(1/8)/KIT-6

10

4

30.8

85.6

13.9

trace

28.4

CuS-Co3O4(1/8)/KIT-6

10

12

94.9

27.8

31.9

40.3

29.1

CuS-Co3O4(1/8)/KIT-6

10

24

100

9.1

20.6

70.3

15.4

CuS-Co3O4(1/8)/KIT-6

20

8

68.6

65.5

25.1

9.4

31.6

CuS-Co3O4(1/8)/KIT-6

30

8

100

45.2

31.4

23.4

46.1

CuS-Co3O4(1/2)

10

8

74.4

25.3

trace

4.0

10

8

35.6

77.9

21.9

trace

2.1

Ac ce p

741 742

CuS-Co3O4(1/8)/KIT-6 CuS-Co3O4(1/8)/KIT-6 CuS-Co3O4(1/8)/KIT-6

Page 47 of 49

Baitao Li et al. Page 48

743

a

744

phenylacetaldehyde, benzoic acid and polystyrene.

745

b

746

c,d

747

e

N,N-dimethylformamide (DMF) as solvent.

748

f

Dichloroethane as solvent.

749

g

Tert-butanol as solvent.

750

h

Pyridine as solvent.

SO and BA refer to styrene oxide and benzaldehyde, respectively. Other products include

an

us

cr

Obtained via processes of silica removing identical to Cu-Co3O4(x).

M

751 752

d

754

Highlights:

2015-9-28

te

753

ip t

TOF = moles of converted styrene/moles of copper per hour.

Cu-containing cobaltosic oxide composite supported by KIT-6 were synthesized.

756

Calcination temperature (250 and 550 oC) affected the catalyst structure.

757

Cu2+ was successfully embedded in spinel structure when calcined at 550 ºC.

758

Hybrid CuO and Co3O4 were remained in the catalyst through 250 ºC treatment.

759

Enhancement in selectivity of styrene oxide was obtained for Cu-spinel catalyst.

760 761 762

Ac ce p

755

Page 48 of 49

Page 49 of 49

ed

ce pt

Ac

M an

cr

us

ip