Silicates mesoporous molecular sieves

Since the first synthesis of siliceous mesoporous molecular sieves described in the literature in 1992 [1], several mesoporous materials possessing various T atoms together with Si in the lattice have been prepared. The synthesis and properties of niobium- and siliceous-containing mesoporous sieves of MCM-41 type were first time described by our group [2,3] and almost parallely, Nb-doped mesoporous sieves were synthesized by Zhang and Ying [4]. 

The contents of the current volume presents a sampling of more than 150 oral and poster papers delivered at the Symposium on Access in Nanoporous Materials II held in Banff, Alberta on May 25-28, 2000. The selected papers cover the three main themes of the symposium (i) synthesis of mesoporous silicas, framework-modified mesoporous silicas, and surface-modified mesoporous silicas, (ii) synthesis of other nanoporous and nanostructured materials, and (iii) characterization and applications of nanoporous materials. About 70% of the papers are devoted to the synthesis of siliceous mesoporous molecular sieves, their modification, characterization and applications, which represent the current research trend in nanoporous materials. The remaining contributions provide some indications on the future developments in the area of non-siliceous molecular sieves and related materials. Although the present book does not cover all topics in the area of nanoporous materials, it reflects the current trends and advances in this area, which will certainly attract the attention of materials chemists in the 21st Century. 

The insertion of Ti in the zeolite framework was accompanied by a significant decrease in A1 content (Table 1). However, there was no stoichiometric process between A1 removal and Ti insertion. Moreover, it was found that the treatment of Ig of an aluminum containing beta zeolite with a 75 ml of 3 x 10 M oxalic acid solution decreased the Si/Al ratio from its original value of 30 to 85 due to A1 extraction. Attempts to incorporate Ti into other zeolites like ZSM-12 and mordenite were not successful. Interestingly, the extraction of A1 from these zeolite structures was also unsuccessful with oxalic acid solutions with comparable concentrations. However, preliminary data show that siliceous mesoporous molecular sieves (MCM-41 and HMS) treated similarly with ammonium titanyl oxalate solutions exhibit good epoxidation activity. It is inferred that the presence of framework cations that can be extracted by oxalate species and/or the presence of defect sites in the parent zeolite is a requisite for the subsequent incorporation of titanium. 

The continuous effort of numerous academic and industrial laboratories around the world has resulted in recent years in successful synthesis of a number of new porous materials including new structural types of zeolites and zeolypes, siliceous and non-siliceous mesoporous molecular sieves, mesoporous zeolite single crystals, and micro/mesoporous or micro/macroporous composite materials of different chemical compositions. As a consequence of the success of basic research in this area, zeolites have found new industrial applications. 

Composite Ti02 based catalysts were prepared by means of a modified acid-catalyzed sol-gel method from alkoxide precursor. The preparation was performed at room temperature as described elsewhere [5, 6]. The xerogel obtained at the end of the process was grinded into a fine powder and dried at room temperature. The powder was calcined at 400 °C in a flow of nitrogen for 2 hours to obtain the composite catalysts. Several materials were used as Ti02 supports siliceous mesoporous molecular sieves MCM-41 and MCM-48, synthesized hydrothermally according to the procedure outlined elsewhere [9] ... 

MoOs/siliceous mesoporous molecular sieves [(CF3)2MeCO]2Mo(=CHCMe2Ph)(=N-C6H3-2,6- Pr2)/siliceous mesoporous molecular sieves W catalyst WBrs... 

A fascinating area is micellar autocatalysis reactions in which surfactant micelles catalyse the reaction by which the surfactant itself is synthesized. Thus synthesis of dimethyldoceylamino oxide (reaction between dimethyl dodecyl amine and H2O2) benefits from this strategy. Here an aqueous phase can be used and an organic solvent can be avoided. Synthesis of mesoporous molecular sieves benefit through micellar catalysis and silicate polymerization rates have been increased by a factor 2000 in the presence of cetyltrimethyl ammonium chloride (Rathman, 1996). 

The review of Notari (33) covers the synthesis methodologies of titanium silicate molecular sieves available up to 1996. The reviews of Corma (279) and subsequently of Biz and Occelli (280) describe the synthesis of mesoporous molecular sieves. An informative article on the preparation of TS-1 was reported recently by Perego et al. (68). In this section we list some of the recent developments in the synthesis of micro and mesoporous titanosilicate molecular sieves. 

In the present work the synthesis of highly dispersed niobium or titanium containing mesoporous molecular sieves catalyst by direct grafting of different niobium and titanium compounds is reported. Grafting is achieved by anchoring the desired compounds on the surface hydroxyl groups located on the inner and outer surface of siliceous MCM-41 and MCM-48 mesoporous molecular sieves. Catalytic activity was evaluated in the liquid phase epoxidation of a-pinene with hydrogen peroxide as oxidant and the results are compared with widely studied titanium silicalites. The emphasis is directed mainly on catalytic applications of niobium or titanium anchored material to add a more detailed view on their structural physicochemical properties. 

The inclusion of polymeric carbon in channels of the siliceous MCM-41 mesoporous molecular sieve... 

The siliceous MCM-41 mesoporous molecular sieve used as a host was prepared according to [11], C4I2 and C6HI were prepared according to the recipes given in [12]. The stability of both precursors is limited. While C4I2 can be stored in small amounts in a freezer at -30 °C for several months, C6HI is stable only in its n-hexane-ether solution. 

The specific activity of Ti-sites in oxidation with aqueous H202 was shown to decrease from microporous to mesoporous molecular sieves such as MCM-41 and HMS. The surface hydrophilicity of the latter mesoporous silicates is likely one of the main reasons for the low activity of Ti sites.[47] Water molecules adsorbed on the surface silanol groups would limit the access of organophilic reagents to the Ti sites.1751 This can be limited, to a certain extent, by grafting hydrophobic groups on the surface silanols.1761... 

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

The main purpose of this chapter is to review the applications of thermal analysis and calorimetric techniques to the study of catalysts such as oxides, heteropolyanions, hydrotalcites, layered silicates and microporous or mesoporous molecular sieves. A brief summary of studies that made use of calorimetry to characterize crystaUine or amorphous oxides and related materials is also presented. 

TTus paper is concerned with the particular class of molecular sieves having periodic mesoporous structure with pore sizes in the range of 2 to 10 nm. They are comprised of the M41S mesoporous molecular sieves and solids with related structures. In the first part, the preparation methods and characterization techniques will be reviewed and discussed. Silicate-based materials and non-silicate materials will be dealt with separately. In the second part of this review particular emphasis will be put on potential applications reported in both the patent and the open literature. Early progress in tWs field has been presented in the previous Summer School by Casci [37]. Potential catalytic applications of M41S were also reviewed rprPTitlv 1381... 

A new family of silicate/aluminosilicate mesoporous molecular sieves designated as M41S and kanemite were introduced a few years ago (39-43), and NMR investigations have been done to characterize those materials. 

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