Ultrasonic Synthesis of Silica-Alumina Nanomaterials with Controlled Mesopore Distribution without Using Surfactants Nan Yao, ² Guoxing Xiong,* ,² King Lun Yeung, ‡ Shishan Sheng, ² Mingyuan He, § Weishen Yang, ² Xiumei Liu, ² and Xinhe Bao ² State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P.O. Box 110, Dalian 116023, People’s Republic of China, Department of Chemical Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, SAR, People’s Republic of China, and Research Institute of Petroleum Processing SINOPEC, Beijing 100083, People’s Republic of China Received October 29, 2001. In Final Form: January 29, 2002 A novel sol-gel process has been developed for the synthesis of amorphous silica-aluminas with controlled mesopore distribution without the use of organic templating agents, e.g., surfactant molecules. Ultrasonic treatment during the synthesis enables production of precursor sols with narrow particle size distribution. Atomic force microscopy analysis shows that these sol particles are spherical in shape with a narrow size distribution (i.e., 13-25 nm) and their aggregation during the gelation creates clusters containing similar sized interparticle mesopores. A nitrogen physiadsorption study indicates that the mesoporous materials containing different Si/Al ratios prepared by the new synthesis method has a large specific surface area (i.e., 587-692 m 2 /g) and similar pore sizes of 2-11 nm. Solid-state 27 Al magic angle spinning (MAS) NMR shows that most of the aluminum is located in the tetrahedral position. A transmission electron microscopy (TEM) image shows that the mesoporous silica-alumina consists of 12-25 nm spheres. Additionally, high-resolution TEM and electron diffraction indicate that some nanoparticles are characteristic of a crystal, although X-ray diffraction and 29 Si MAS NMR analysis show an amorphous material. 1. Introduction Mesoporous materials with pore sizes ranging from 2 to 50 nm have applications in shape-selective catalysis and biomolecular immobilization and separation because of their high specific surface areas and large uniform pore sizes. 1-3 Numerous studies on their synthesis, charac- terization, and application have been reported. 4-6 Since the scientists at Mobil Oil Research and Development announced the successful synthesis of mesoporous mo- lecular sieves (M41S) in 1992, 7,8 it has now been well accepted that the formation of such mesoporous materials could occur through several templating pathways such as S + I - ,S - I + ,S + X - I + ,S - X + I - ,S-I, and S 0 I 0 , where S is the surfactant, I is the inorganic precursor, and X is the mediating ions. 9,10 A typical synthesis starts with the formation of organic micellar species in aqueous solution, followed by the polycondensation of an inorganic matrix or shell, and ends with the removal of the organic template. The nature of the interaction between the organic sur- factant and the inorganic matrix is dictated by the synthesis reagents and preparation conditions and is a controlling factor in the physical and chemical properties of the mesoporous materials. 11 Mesoporous silica-alumina materials possess catalytic properties similar to those of the zeolites but without the micropore restrictions. Owing to their controlled meso- porosity and Bro¨nsted acidity, these materials could be used to prepare metal bifunctional catalysts for hydro- isomerization, as well as in the hydrocracking of long- chain paraffins (e.g., n-alkane). 12,13 Until now, none has described a method for the synthesis of mesoporous material without the aid of surfactant. This paper reports a new templateless procedure for preparing narrow pore sized mesoporous materials. The approach is based on the simple idea that the regular packing of nanometer sized sol spheres can create a network of narrow meso- porous channels. The synthesis procedure utilizes a new sol-gel process to obtain nanometer sized precursor particles of narrow size distribution from inexpensive inorganic salts. The absence of surfactant and the use of inorganic salts instead of organometallic precursors contribute to the reduction in cost and pollution during the manufacture of these materials. 2. Experimental Section 2.1. Synthesis Method. All the chemicals used in the material synthesis were A.R. grade, and the water was deionized and twice distilled. A measured amount of ammonium hydroxide * To whom correspondence may be addressed. E-mail: gxxiong@ ms.dicp.ac.cn. ² Chinese Academy of Sciences. ‡ The Hong Kong University of Science and Technology. § Research Institute of Petroleum Processing SINOPEC. (1) Corma, A. Chem. Rev. 1997, 97, 2373. (2) Diaz, J. F.; Balkus, K. J., Jr. J. Mol. Catal. B: Enzym. 1996, 2, 115. (3) Suib, S. T. Curr. Opin. Solid State Mater. Sci. 1998, 3, 63. (4) Aguado, J.; Serrano, D. P.; Romero, M. D.; Escola, J. M. J. Chem. Soc., Chem. Commun. 1996, 765. (5) Corma, A.; Iglesias, M.; Sanchez, F. Catal. Lett. 1996, 39, 153. (6) Tanev, P. T.; Chibwe, M.; Pinnavaia, T. J. Nature 1994, 368, 321. (7) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710. (8) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T-W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834. (9) Huo, Q.; Margolese, D. I.; Ciesla, U.; Feng, P.; Gier, T. E.; Sieger, P.; Leon, R.; Petroff, P. M.; Schu¨ th, F.; Stucky, G. Nature 1994, 368, 317. (10) Tanev, P. T.; Pinnavaia, T. J. Chem. Mater. 1996, 8, 2068. (11) Biz, S.; Occelli, M. L. Catal. Rev.-Sci. Eng. 1998, 40 (3), 330. (12) Corma, A.; Martinez, A.; Pergher, S.; Peratello, S.; Perego, C.; Bellusi, G. Appl. Catal., A 1997, 152, 107. (13) Calemma, V.; Peratello, S.; Perego, C. Appl. Catal., A 2000, 190, 207. 4111 Langmuir 2002, 18, 4111-4117 10.1021/la0116084 CCC: $22.00 © 2002 American Chemical Society Published on Web 04/09/2002