Applied Catalysis A: General 450 (2013) 34–41 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General jo ur n al homep age: www.elsevier.com/locate/apcata Sulfonic acid functionalized MCM-41 as solid acid catalyst for tert-butylation of hydroquinone enhanced by microwave heating Eng-Poh Ng a,∗ , Siti Norbayu Mohd Subari a , Olivier Marie b , Rino R. Mukti c , Joon-Ching Juan d a School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM Penang, Malaysia b Laboratoire Catalyse & Spectrochimie, ENSICAEN, Université de Caen, 14000 Caen, France c Division of Inorganic and Physical Chemistry, Institut Teknologi Bandung, Jl Ganesha no. 10, Bandung 40132, West Java, Indonesia d Laboratory of Applied Catalysis and Environmental Technology, School of Science, Monash University, Bandar Sunway 46150, Malaysia a r t i c l e i n f o Article history: Received 25 July 2012 Received in revised form 12 September 2012 Accepted 30 September 2012 Available online 3 November 2012 Keywords: Mesoporous material Sulfonation Sulfonic acid tert-Butylation Microwave synthesis a b s t r a c t Covalently linked sulfonic acid ( SO 3 H) modified MCM-41 mesoporous catalysts was prepared, char- acterized and its catalytic activity under microwave irradiation was evaluated. The NH 2 -MCM-41 was first prepared by anchoring (3-aminopropyl)triethoxysilane (APTES) on Si-MCM-41 and further reacted with 1,4-butane-sultone to yield the desired acid catalyst. The mesophase and porosity of samples were determined by XRD, TEM and N 2 sorption isotherm analyses. The presence of sulfonic acid moiety was confirmed by FT-IR, TG/DTA, sulfur elemental analysis and in situ IR study of pyridine and ammonia adsorptions. The catalyst showed high catalytic activity and high selectivity in tert-butylation of hydro- quinone under microwave irradiation. No leaching problem was observed after several runs, while the catalyst can be recovered and reused without loss of reactivity under the described reaction conditions. © 2012 Elsevier B.V. All rights reserved. 1. Introduction New developments in the chemical industries are driven by environmental regulations, safety, energy efficiencies and the need for improved performance. The increasingly environmental regu- lations require the use of green technology in various areas [1,2]. Particularly, catalysts are attractive in green technology because of their importance in petrochemicals and fine chemicals synthesis. Usually chemical syntheses involve homogeneous catalysts; how- ever, using heterogeneous catalysts such as molecular sieves (e.g. microporous zeolites and mesoporous materials) could be more environment-friendly and cost effective, allowing catalyst separa- tion and reusability [3]. MCM-41 is a structurally well-ordered mesoporous solid, pos- sessing some fascinating properties such as high surface area, uniform pore size (20–100 ˚ A) and relatively hydrophobic nature [4]. It is known that MCM-41 in pure silica form has no substan- tial acidity and exhibits only weak hydrogen bonding sites [5,6]. The incorporation of metals (Al, Ti, Fe, etc.) in MCM-41 framework structure can be performed to generate acid properties [7–10]. On ∗ Corresponding author. Tel.: +60 4 653 4021. E-mail address: epng@usm.my (E.-P. Ng). the other side, functionalizing and supporting some acidic species such as heteropolyacids (HPW) [11–13] and mineral acids (H 3 PO 4 , H 2 SO 4 ) [14–16] offer another promising solutions to generate the acidity. Recently, MCM-41 grafted with sulfonic acid (SO 3 H-MCM-41) has been prepared to catalyze many organic reactions. The mod- ified catalyst improves the solid acidity and at the same time, high surface areas and tunable pore diameters are retained. For instance, SO 3 H-MCM-41 is shown having excellent catalytic activ- ity and selectivity in esterification [17–22], Fischer indole synthesis [23], Claisen–Schmidt condensation [24], Friedel–Crafts alkylation [25,26], Fries and pinacol rearrangements [26], condensation of 2-methylfuran and acetone [27] and transesterification reactions [28]. The results reveal that incorporation of sulfonic acid groups on porous silica supports produces highly convenient solid acid catalysts, exhibiting the advantages of homogeneous catalysts. Basically, covalent anchoring of the sulfonic acid groups to the mesoporous materials surface can be achieved either by a direct synthesis route or by a post synthetic anchoring of 3-(mercaptopropyl)triethoxysilane (MPTES) followed by an oxi- dation step to generate the sulfonic acid groups [17–22,28–30]. However, the use of strong oxidation agent in the oxidization of MPTES tends to lower the ordering of the mesopores. In respect to this, chlorosulfonic acid has recently been proposed as another 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2012.09.055