Elsevier

Catalysis Today

Volume 116, Issue 2, 1 August 2006, Pages 151-156
Catalysis Today

Development of highly active SO3H-modified hybrid mesoporous catalyst

https://doi.org/10.1016/j.cattod.2006.01.022Get rights and content

Abstract

Ethenylene groups on the framework of hybrid mesoporous ethenylene-silica (HME) were successfully modified by a two-step chemical modification (Diels–Alder reaction, sulfonation) to obtain hybrid mesoporous solid acid catalyst. The pendant phenylene groups were first introduced at the ethenylene sites on the surface by the Diels–Alder reaction with benzocyclobutene. The introduced phenylene groups were then sulfonated by simple treatment with concentrated H2SO4. The successful formation of phenylene–sulfonic acid groups at the ethylene sites was confirmed by 13C and 29Si nuclear magnetic resonance (NMR) analysis. X-ray diffraction (XRD) measurements and N2 adsorption analysis revealed the preservation of the original mesoscopic ordering and mesoporosity after the modification. The resulting material exhibited high activity for various acid-catalyzed reactions and can be used repeatedly without deactivation.

Introduction

The organic tailoring of the internal surface of mesoporous host has recently received great attention in terms of the application in the fields of catalysis, adsorption, and separation [1]. Periodic mesoporous organosilicas (PMOs) [2], [3], [4] are an attractive family of novel mesoporous materials that combine the properties of organic and inorganic components in a composite material. The main focus for developing the PMOs is to introduce bridged-bond organic groups into the highly ordered porous silica framework and thus add either a unique chemical functionality and/or physical property to the materials. To date, several different silicone-bridged organic moieties represented by methylene [4], ethylene [2], [3], [4], ethenylene [3], [5], [6], [7], [8], phenylene [9], [10], [11] and its-derivates [12], [13], [14] have been incorporated into the silicate framework of highly ordered mesoporous materials. Since the framework of PMOs consists of organic–inorganic hybrid network, homogeneous distribution of the organic groups in the pore wall provides smooth accessibility for the reactant molecules and opens a wide range of new and exciting opportunity for designing materials through the chemical modification. In the previous studies, however, the modification of PMOs has been limited in only simple reactions represented by the bromination of ethenylene [3], [5], [7], [8] and the oxidation of mercaptopropyl group [15], [16], [17], [18], [19], [20]. The successful chemical transformation of the organic groups on the surface provides great opportunity of PMOs as a highly functional nanomaterial.

Herein, we proposed the simple methodology to create the hybrid mesoporous solid acid catalyst which has phenylene–sulfonic acid groups as active sites. This proposed approach involves two step chemical reactions shown in Fig. 1; ethenylenes on the surface of hybrid mesoporous ethenylene-silica (HME) are transformed to pendant phenylenes through the Diels–Alder reaction with benzocyclobutene followed by sulfonation of the introduced phenylenes by simple treatment in concentrated H2SO4. In this article, we investigate the change in the structural and chemical properties of hybrid mesoporous material before and after chemical modification. Esterification of acetic acid, Beckmann rearrangement, and pinacol rearrangement were employed as test reactions to examine the acid properties of the prepared samples. As to mesoporous solid acid catalyst containing sulfonic acid groups, propyl sulfonic acid group, which is obtained by the oxidation of mercaptopropyl groups, was generally adopted as an active site and embedded by grafting technique or one-pot synthesis procedure using silsesquioxane precursor with terminal organic group R-Si(OR)3 [15], [16], [17], [18], [19], [20]. However, these modifications suffer from some serious limitations represented by the inhomogeneous distribution of organic groups in the pore, and the loss of mesoscopic ordering and mesoporosity at the oxidation step. Serious problem for use as a solid acid catalyst lies a leaching of sulfur species, which is probably due to the incomplete oxidation of the thiol groups. It is demonstrated that the resulting material exhibits high activity and stability for various acid-catalyzed reactions without deactivation.

Section snippets

Synthesis

In the typical synthesis of hybrid mesoporous ethenylene-silica, 2.0 g of P123 ((HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20OH, BASF) was completely dissolved in 45 mL of water and 30 mL of 4.0 M HCl solution at 40 °C under constant stirring. To this solution was added 3.53 g of bis(triethoxysilyl)ethylene followed by stirring for 24 h at the same temperature. The resulting mixture was then transferred to an autoclave and heated at 100 °C for an additional 24 h under static conditions. The solid product was

Results and discussion

Fig. 1 shows a schematic representation of the synthetic pathway to hybrid mesoporous solid acid catalyst. The ethenylene-bridged silsesquioxane precursor is hydrolyzed and polycondensed in the presence of block copolymer surfactant, P123, to obtain the HME, which has ethenylene moieties in the silica framework. Ethenylene on the surface are successfully transformed through the Diels–Alder reaction with benzocyclobutene, resulting in the formation of pendant phenylenes. This denoted as

Conclusion

A new class of hybrid mesoporous solid acid catalyst was prepared by two-step chemical modification technique. The resulting material has high mesoscopic ordering and mesoporosity without degradation of the original material, and also exhibits stability and high activity in acid-catalyzed reactions. The methodology presented here provides a new route to novel PMOs with applications in a wide range of areas in materials science, including the separation of biomaterials, selective ion exchange,

Acknowledgements

This work was supported by an Industrial Technology Research Grant (2003) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan (Project ID: 03A23010c) and the 21st Century Center of Excellence (COE-21) program of the Ministry of Education, Culture, Sports, Science and Technology, Japan.

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