Mesoporous solids Subject

It is important atthis point to differentiate between the case of mesoporous solids where the textural parameters can be determined precisely using current models and the case of microporous solids for which the theories proposed to date are still the subject of numerous studies. 

Now, in principle, the angle of contact between a liquid and a solid surface can have a value anywhere between 0° and 180°, the actual value depending on the particular system. In practice 6 is very difficult to determine with accuracy even for a macroscopic system such as a liquid droplet resting on a plate, and for a liquid present in a pore having dimensions in the mesopore range is virtually impossible of direct measurement. In applications of the Kelvin equation, therefore, it is almost invariably assumed, mainly on grounds of simplicity, that 0 = 0 (cos 6 = 1). In view of the arbitrary nature of this assumption it is not surprising that the subject has attracted attention from theoreticians. 

The lamellar—-hexagonal thermal transformation of mesoporous zirconia in the solid state was studied by heating the lamellar form at a fixed temperature for different periods of time. The phase composition of the sample subjected to heat treatment was estimated on the basis of the intensity of the (100) reflection, the ((-spacing showing only small changes in the thermal transformation (Fig. 2). The kinetics of the transformation was studied as a function of time at 373, 403 and 413 K. The transformation was also studied by heating the lamellar sample for a fixed period of 2 h at different temperatures in the range 360-430 K. 

Heferogeneous olefin epoxidation over solid titania-silica catalysts has been the subject of numerous publications in the open literature. The general picture that emerges is that isolated titanium (IV) species on a silica surface or in a zeolife mafrix are responsible for the high epoxidation activity [2]. This picture is supported by model catalyst work on titanium silasesquioxane complexes [3,4] that form active homogeneous epoxidation catalysts [5] and by various successful atfempfs fo prepare well-defined, site-isolated titanium complexes by grafting molecular precursors on mesoporous silica [6-9]. These site-isolated titanium complexes have been shown to possess catalytic activity in olefin epoxidation. 

The Diels-Alder reaction has been shown to be subject to catalysis by a wide range of solid catalysts (see Chapter 4 for some examples). Acidic mesoporous aluminosilicates can be used to catalyse selective Diels-Alder reactions such as that between cyclopentadiene with methyl acrylate. The zinc-exchanged version of the material is particularly effective and compares well to other more established solid acids such as the ion-exchanged clay Zn2+-K10 as well as homogeneous catalysts such as boron trifluoride (Table 2.7).50... 

Mesoporous zirconia is a particulate oxide with properties for several applications such as catalyst or catalyst support [1, 2] and nanocomposite materials (Chap. 25) [3, 4]. Moreover, zirconia nanoparticles are subject of extensive studies dealing with the preparation of piezoelectric, electro-optic, dielectric materials with wide use, and hybrids for solid oxide fuel cells (SOFCs) [3, 5-8]. Zirconia is also a material in ceramic industry [9, 10]. 

After the disclosure of sihca-aliunina-based mesostructures, workers tried to prepare by similar procedures other oxides in a mesoporous form [7]. The resulting solids, though interesting in principle, are usually not yet stable enough for practical catalytic usage sUica-based ordered mesoporous systems still dominate the subject. 

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