DOI: 10.1002/chem.201001508 Titanosilicate Beads with Hierarchical Porosity: Synthesis and Application as Epoxidation Catalysts Kaifeng Lin, [a, b] Oleg I. Lebedev, [c] Gustaaf Van Tendeloo, [c] Pierre A. Jacobs, [a] and Paolo P. Pescarmona* [a] Introduction Since the discovery of microporous TS-1 [1] and mesoporous Ti-MCM-41, [2–4] many porous titanosilicates with tetrahe- drally substituted Ti species have been widely studied in an attempt to promote heterogeneous oxidations of various or- ganic substrates with hydrogen peroxide. [5–13] Numerous studies reveal that high specific surface areas and pore ar- chitectures in well-defined micro- and mesoporous struc- tures are pivotal for the success of these titanosilicates as catalysts for heterogeneous oxidations. [14] It is generally ac- cepted that particle size is another structural parameter of these materials, which plays a very important role in hetero- geneous oxidation. [15–18] For example, TS-1 nanoparticles showed much higher activity in phenol hydroxylation than large TS-1 crystals, as a consequence of the strong diffusion limitation experienced by the reactants on reaching the active sites in large crystals. [15] Ti-MCM-41 nanoparticles dis- played higher conversions and initial reaction rates in the epoxidation of cyclohexene than Ti-MCM-41 with micro- metric particle size, because the accessibility of the catalytic Ti species was enhanced in these Ti-MCM-41 nanoparti- cles. [17–19] These results indicate that porous titanosilicates in the form of nanoparticles have many benefits for catalytic applications in various selective oxidations over the corre- sponding large particles. An alternative way to improve the catalytic activity of TS-1 crystals in the epoxidation of large substrates is to increase the accessibility of the Ti sites by creating mesopores in the zeolitic structure. [20, 21] However, a drawback of all these systems in heterogeneous oxidations is their awkward separation from the reaction solution during catalyst recycling, which normally requires high-speed cen- trifugation or special filtration. This hinders recovery of the products and recycling of the catalysts and, therefore, limits broad industrial application of these porous titanosilicates as heterogeneous catalysts in selective oxidations. Furthermore, Abstract: Porous titanosilicate beads with a diameter of 0.5–1.5 mm (TiSil- HPB-60) were synthesized from a pre- formed titanosilicate solution with a porous anion-exchange resin as tem- plate. The bead format of this material enables its straightforward separation from the reaction mixture in its appli- cation as a liquid-phase heterogeneous catalyst. The material displays hier- archical porosity (micro/mesopores) and incipient TS-1 structure building units. The titanium species are predom- inantly located in tetrahedral frame- work positions. TiSil-HPB-60 is a highly active catalyst for the epoxida- tion of cyclohexene with t-butyl hydro- peroxide (TBHP) and aqueous H 2 O 2 . With both oxidants, TiSil-HPB-60 gave higher epoxide yields than Ti-MCM-41 and TS-1. The improved catalytic per- formance of TiSil-HPB-60 is mainly as- cribed to the large mesopores favoring the diffusion of reagents and products to and from the titanium active sites. The epoxide yield and selectivity could be further improved by silylation of the titanosilicate beads. Importantly, TiSil- HPB-60 is a stable catalyst immune to titanium leaching, and can be easily re- covered and reused in successive cata- lytic cycles without significant loss of activity. Moreover, TiSil-HPB-60 is active and selective in the epoxidation of a wide range of bulky alkenes. Keywords: epoxidation · green chemistry · heterogeneous catalysis · hierarchical porosity · titanosilicate beads [a] Dr. K. Lin, Prof. P.A. Jacobs, Prof. P.P. Pescarmona Centre for Surface Chemistry and Catalysis, K. U. Leuven Kasteelpark Arenberg 23-bus 2461, 3001 Heverlee (Belgium) Fax: (+ 32) 16-321998 E-mail: paolo.pescarmona@biw.kuleuven.be [b] Dr. K. Lin Academy of Fundamental and Interdisciplinary Science Harbin Institute of Technology,box-3026 150080 Harbin (China) [c] Dr. O. I. Lebedev, Prof. G. Van Tendeloo EMAT, Physics Department, University of Antwerpen Groenenborglaan 171, 2020 Antwerpen (Belgium) Chem. Eur. J. 2010, 00,0–0  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ÞÞ &1& FULL PAPER