Silica framework silicas, microporosity

Figure 10a shows the conversion of reactant A, isophthalaldehyde, as a function of time for both the imprinted silica 2 and the surface-functionalized material (comprising a monolayer of aminopropyl groups covalently attached to the surface of a mesoporous silica) [45]. Both the imprinted material and surface-functionalized material catalyzed the reaction of A to B. This was evident in the high turnover frequencies of367 and 74 turnovers per amine site per hour for the surface-functionalized and imprinted silicas, respectively. Although both materials showed catalytic turnover, the turnover frequency observed in the imprinted silica may have been slightly mass-transfer-limited due to the microporosity of the silica framework. However, the imprinted material did not catalyze the production of C to the same... 

Carbons prepared from sucrose have surface areas up to 1500 m g , and pore volumes up to 1 cm g (Table 1). These carbons also have micropore volumes of around 0.210 cm g, which is likely related to the intrinsic microporosity of the carbon precursor. For both samples a capillary condensation occurs in the p/po range between 0.1-0.4 and 0.3-0.6, which clearly indicates that the structural porosity of the silica framework is replicated in the carbon. The pore size distributions for these carbons are very narrow with peak maxima at 1.2 nm and 1 nm, for T30 SUC and T60 SUC, respectively. Additionally, a slight development of complementary mesoporosity (estimated from the amount of nitrogen adsorbed at p/po > 0.7) can be seen, accounting for 6 % and 7 % of the total pore volume. 

Microporous crystalline solids in which transition metals are tetrahedrally substituted via template-mediated hydrothermal synthesis have remarkable properties in selective oxidation reactions [66]. Unfortunately, the microporous structure and the rigidity of the crystalline frameworks limit the substitution degree, variety of substituted metal, and their general applicability. For this reason, the amorphous microporous mixed oxides (AMMs) with uniform microporosity and wide compositional variability are devoid of Bronsted acidity, but are not associated with the redox-active elements. However, metals such as Ti, V, and Mo incorporated in amorphous silica were good catalysts in allylic oxidation or epoxidation of olefins [67]. 

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