Ordered mesoporous titanosilicates with better catalytically active titanium sites assembled from preformed titanosilicate precursors with zeolite building units in alkaline media Kaifeng Lin, Zhenhua Sun, Sen Lin, Dazhen Jiang, Feng-Shou Xiao * Department of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, 119 Jiefang Road, Changchun 130023, PR China Received 25 December 2003; received in revised form 26 April 2004; accepted 28 April 2004 Available online 4 June 2004 Abstract Mesostructured titanosilicates have been successfully synthesized from the assembly of preformed titanosilicate precursors with CTAB surfactant micelle in both alkaline media (MTS-5) and strongly acidic media (MTS-8). The samples were characterized by powder X-ray diffraction (XRD), nitrogen isotherms, 29 Si MAS NMR, IR, and UV–visible spectroscopy. These materials exhibit highly hydrothermal stability, as compared with Ti-MCM-41. Characterization results indicate that these mesostructured tita- nosilicates of MTS-5 and MTS-8 have TS-1-like titanium species, and that the mesoporous walls contain the primary and secondary building units similar to those in microporous crystal of TS-1 zeolite. In catalytic hydroxylation of 2,3,6-trimethylphenol, MTS-5 and MTS-8 show higher activities in comparison with microporous crystal of TS-1 and mesoporous material of Ti-MCM-41. More importantly, MTS-5 assembled from preformed titanosilicate precursors in alkaline media has higher silica condensation degree, compared with MTS-8 synthesized in strongly acidic media. After heating at 550 °C for 4 h, MTS-5 basically remains its catalytic activities in hydroxylation of phenol and 2,3,6-trimethylphenol, indicating its higher stability of Ti species for calcination. In contrast, calcined MTS-8 shows much lower conversion than as-synthesized MTS-8. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Orderedmesoporoustitanosilicate;Hydrothermalstability;Preformedtitanosilicateprecursors;Zeolitebuildingunits;Ti-MCM-41;TS-1; Catalytic hydroxylation 1. Introduction Selective oxidations of organic compounds over titanium-substituted microporous zeolites and titanium- containing mesoporous materials have received much attention because of their remarkable selective oxidation properties and using in environmentally friendly oxida- tion with H 2 O 2 as the oxidant [1–9]. However, owing to thelimitationofmicroporoussizetheycannoteffectively catalyze oxidation of bulky molecules [10]. Mesoporous materials overcome the limitation of micropores for zeolites and allow the diffusion of bulky molecules [11– 13]. But these materials have some disadvantages in structural integrity and do not show short-range order, which are closer to amorphous nature [14–21]. For example, Ti-MCM-41 shows very low catalytic activity in phenol hydroxylation with H 2 O 2 , compared with TS- 1 zeolite [10]. Therefore, much effort has been taken to combine the advantages of zeolites (high oxidation abilities) and mesoporous materials (larger pores) [10]. Recently, we have reported the synthesis of an or- dered mesoporous titanosilicate (MTS-9) by the assem- bly of preformed titanosilicate precursors with triblock copolymers in a strongly acidic media [22]. Catalytic test shows that MTS-9 exhibits excellent catalytic activities in the oxidation of the small molecules of phenol, sty- rene and also of the bulky molecule of 2,3,6-trimethyl- phenol. Unfortunately, calcination of as-synthesized MTS-9 at 500 °C for several hours results in significant reduction of catalytic activities, which is assigned to * Corresponding author. Tel.: +86-431-8499191; fax: +86-431- 5671974. E-mail address: fsxiao@mail.jlu.edu.cn (F.-S. Xiao). 1387-1811/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2004.04.025 www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 72 (2004) 193–201