Pillared layered silicate

Patents assigned to Mobil (217) describe the use of boron trifluoride supported on several porous carriers. BF3 supported on silica was found to exhibit a slightly higher performance with added water in the alkylation of a mixed alkene feed at 273 K. It was also shown that self-alkylation activity was considerably lower than that with HF as catalyst. Another patent (218) describes the use of a pillared layered silicate, MCM-25, promoted with BF3 to give a high-quality alkylate at temperatures of about 273 K. BF3 was also supported on zeolite BEA, with adsorbed water still present (219). This composite catalyst exhibited low butene isomerization activity, which was evident from the inferior results obtained with 1-butene. At low reaction temperatures, the product quality was superior to that of HF alkylate. 

Layered silicate clays intercalated by pillaring poly-oxocations are precursors to an important class of mi-croporous catalysts. Smectite clay was the only host structure known to be pillarable by purely inorganic oxo ions. Recently, layered double hydroxides (LDH) pillaring oxo ions were reported by Pinnavaia and coworkers [79, 80]. 

We have been investigating the use of imogolite as a pillaring agent for smectite clays with layer lattice structures ". The regular intercalation of the tubes within the layered host results in the formation of a tubular silicate-layered silicate (TSLS) complex. These new nanocomposite materials may be viewed as pillared clays in which the pillars themselves are microporous. Significantly, the TSLS structure is thermally stable up to 450 C when montmorillonite is selected as the layered host . 

Figure 6 A conq)arison betweeen the activities of two different layered silicates, magadiite and kenyaite, as a fimction of their interlayer species. Alumina pillared kenyaite appears to have significantly more activity than a comparable pillared magadiite. This indicates a sensitivity towards the layered structure.

Cheng and coworkers at Taiwan University1611 have discussed the silica- and alumina-pillared derivatives of four layered silicates with different charge density and thickness, as well as related synthetic problems. Here, this system will be presented as a typical example. In general, its synthesis includes three steps. 

The diversity of the inclusion of molecules of any type into host lattices which are distinctly inorganic is now becoming apparent [31], Apart from the oxidic zeolites, aluminosilicates and derivatives with other tetrahedral sites, there are the layered silicates and minerals, pillared clays and numerous other intercalation and inclusion systems, including graphite, metal sulfides and metal cyanides [23, 32, 33]. 

Pillared clays, layered silicates whose sheets have been permanently propped open by thermally stable molecular props, were used as templates to load various organic precursors.The pore diameters of resulting carbon materials range from 8 to 22 A, and the mass fractal dimension varies from 2.5 to 2.9, which are accessible to lithium ions when the intercalation process takes place in a lithium secondary battery. An approach to pyrolyse aromatic hydrocarbons such as pyrene within a pillared clay was also reported, in which the pillared clay serves two functions.It acts as the inorganic template around which the carbon can be formed, and it also functions as an acid catalyst to promote condensation of the aromatics similar to the Scholl reaction. The resulting carbon materials have pore sizes from 15 to 50... 

The present work summarizes our efforts to synthesize supergallery pillared derivatives of three general families of layered compounds. The host structures of interest include smectite clays, layered double hydroxides, and layered silicic acids. 

Hydrothermal synthesis of pure dioctahedral 2 1 layer silicates has been attempted to prt uce the starting material for pillared clays. Natural layer silicates have an unreliable quality, and a large variation in the nature and content of impurities. 

Diddams, P.A. et al. 1984. Synthesis, Characterization and Catalytic Activity of Beidellite-Montmorillonite Layered Silicates and their Pillared Analogues. J. Chemical Society (A) Chemical Communications 1340-42. 

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