Elsevier

Catalysis Communications

Volume 21, 5 May 2012, Pages 68-71
Catalysis Communications

Short Communication
Highly efficient epoxidation of styrene and α-pinene with air over Co2+-exchanged ZSM-5 and Beta zeolites

https://doi.org/10.1016/j.catcom.2012.01.029Get rights and content

Abstract

Co2+-exchanged zeolites (prepared simply by ion-exchange method) have been used in the epoxidation of styrene and α-pinene with air, in which Co-ZSM-5 and Co-Beta without any organic Schiff-base ligand or additive behaved as highly efficient catalysts. Co-ZSM-5 and Co-Beta achieved 88.4–92.4 mol% conversion with the overall selectivity of 94.6–96.6% for the epoxidation of styrene, and 92.8–90.6 mol% conversion with the selectivity of 86.1–88.3% for the epoxidation of α-pinene, respectively. Recycling studies and control experiments showed the stability and recyclability of Co-ZSM-5 and Co-Beta in the epoxidation reaction.

Graphical abstract

Simple Co2+-exchanged ZSM-5 and Beta present highly catalytic epoxidation activity. Co-ZSM-5 and Co-Beta achieve 88.4–92.4 mol% conversion of styrene with the overall selectivity of 94.6–96.6% for styrene oxide, and 92.8–90.6 mol% conversion of α-pinene with the selectivity of 86.1–88.3% for α-pinene oxide, respectively.

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Highlights

► Co-ZSM-5 and Co-Beta are prepared by a simple ion-exchange route. ► Both show high activities for the epoxidation of styrene and α-pinene with air. ► These solids are highly reusable heterogeneous catalysts.

Introduction

The catalytic epoxidation of alkenes to produce epoxides is an important industrial reaction, since epoxides are key building blocks in organic synthesis [1], [2]. Over the past decade, with respect to environmental and economic consideration, the epoxidation of alkenes by H2O2 [3], [4], [5], molecular oxygen or air [6], [7], [8], [9] has attracted much attention, and great effort has focused on the discovery of efficient catalyst [10], [11], [12], [13], [14]. Due to triplet ground state of O2 disfavoring reactions with singlet organic compounds, the epoxidation of alkenes with O2 was generally carried out in the presence of co-reductants like H2, alcohols and aldehydes [15], [16], [17], [18]. In 2004, Tang et al. [19], [20] firstly reported that Co2+-exchanged faujasite-type zeolites could efficiently catalyze the epoxidation of styrene with O2 in the absence of co-reductant. Later, Co-containing X-type zeolites modified by alkali and alkaline metals [21], [22], Co-TUD-1 [23], cobalt-substituted SBA-15 [24] and Ag-based catalyst Ag-γ-ZrP [25] were also prepared and applied in the epoxidation of alkenes with O2. However, these catalytic systems contain four defects, i.e. high cobalt content (ca. 8.8 wt.%), complicated preparation procedure of catalyst, pure oxygen as oxidant or low selectivity to epoxide.

Recently, our group [26], [27] has reported that Co-ZSM-5 coordinated with bi-/tridentate Schiff-base ligands catalyzed highly selective epoxidation of alkenes with dry air. Based on the above work, our new progress firstly shows that, the selective epoxidation of styrene and α-pinene with dry air can be efficiently conducted over simple Co2+-exchanged zeolites with a low Co content (ca. 1.2 wt.%), in which no organic Schiff-base ligand or additive is required.

Section snippets

Preparation of catalysts

Zeolites (Na-ZSM-5, Na-Beta, Na-Y, K-3A, and Na-4A) were commercial products. Co2+ cations or other transition metal ions were introduced into zeolites by conventional ion-exchange method, i.e. 5.0 g of zeolite was treated at 363 K overnight with an aqueous solution (250 ml) containing 1.3 mmol of Co(Ac)2·4H2O or other salts like Zn(Ac)2·2H2O, Mn(Ac)2·4H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Cr(NO3)3·9H2O, and Fe(NO3)3·9H2O. The solid powder was recovered by filtration, washed several times with hot

Characterization of catalysts

Fig. 1 showed the XRD patterns of Co2+-exchanged zeolites, in which there was no obvious change in the crystalline structure of zeolites that had undergone ion-exchange treatment as compared to those of the parent zeolites (Fig. S1, Supplementary data).

BET surface areas and pore sizes of various zeolites determined by BET analysis were given in Table 1, in which both parameters exhibited the same decrease order of Co-Y > Co-Beta > Co-ZSM-5 > Co-4A > Co-3A. Co contents and Si/Al ratios of Co-zeolites

Conclusions

Transition metal ions (Co2+, Fe3+, Ni2+, Cu2+, Mn2+, Cr3+, and Zn2+) exchanged zeolites have been prepared by a simple route. Co-ZSM-5 and Co-Beta displayed the highest activities for the epoxidation reaction, in which Co-ZSM-5 and Co-Beta achieved 88.4–92.4 mol% conversion with the overall selectivity of 94.6–96.6% for the epoxidation of styrene, and 90.6–92.8 mol% conversion with the selectivity of 86.1–88.3% for the epoxidation of α-pinene, respectively. Solvents, oxidants and initiators

Acknowledgments

The authors acknowledge the funding supports provided by the National Natural Science Foundation of China (Nos. 20901023, 21173073), by the 2007 excellent mid-youth innovative project of HPED of China (no. T200701), and by the key project of HPSTD of China (no. 2008CAD030). Dr. D. Zhou thanks the financial support by Chen Guang Scheme of Wuhan City (no. 201050231087).

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