2.0 to 2.5


Figure 11. TEM image of wormlike mesoporous TUD-1.

single-peak XRD patterns. On the other hand, they exhibit higher Br0nsted acidity compared to aluminum-containing MCM-41. The Pt-impregnated forms of Al-MMSX become efficient catalysts for the hydroconversion of «-heptane. At low Si/Al ratio (e.g., X = 10) the materials have total conversions and selectivity comparable to that of USY zeolite (Si/Al = 21) [124]. Further studies of these materials confirmed that these materials with disordered pores can be good candidates for catalysts [125].

The existence of disordered short channels in these wormlike silicas can be detected by TEM observation of samples incorporating with heavy metals such as Pt [123]. The high flexibility of the mesopores in these nonperiodic phases leads to easy control of the morphology [127]. It is also possible to make very small particles [128] for application in the realm of catalysis or homogeneous large area thin films [129] and monoliths [130], which have wide applications in the electrochemical industry.

In summary, during the last 10 years, many ordered meso-porous silicas have been synthesized using several different mechanisms. The structures of most phases have been determined (Table 1). To date, these structures discovered have symmetries of P6mm (two-dimensional), P63/mmc, cmm, Fm3m, Ia3d, Im3m, Pm3n, Fd3m, etc. Several nonperiodic phases were also fabricated. Variation of the pore sizes in these materials has been extensively investigated. The shapes of pores can be cylindrical, spherical with windows, bottlelike, wormlike, etc. Incorporation of chemically active inorganic or organic groups into the mesoporous particles is an important direction of development in the field of advanced material research.

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