Mesoporous frameworks, thermal

The thermal stability of mesoporous frameworks substantially increases with an increase in the wall thickness and pore size, which can be varied even for the same template by changing the processing conditions. Ozin et al.55 developed a way to prepare crystalline titania films with a 2D-hexagonal architecture by replacement of ethanol in the Pluronic-containing precursor solution with more hydrophobic butanol-1. The latter promotes phase separation at low surfactant-to-titania ratios, resulting in thicker pore walls, which are more compatible with the crystal growth during subsequent calcination. 

Several factors affect the MTS behavior. These include type of heteroatom T, structure of the solid, T/Si ratio, thermal history and pretreatments. The source of A1 also plays a role, e.g., it is known since long [15-17] that A1 species can be incorporated as T atoms into the inorganic mesoporous framework, provided a monomeric alumina precursor is used in the synthesis. 

Most of the microporous and mesoporous compounds require the use of structure-directing molecules under hydro(solvo)thermal conditions [14, 15, 171, 172]. A serious handicap is the application of high-temperature calcination to develop their porosity. It usually results in inferior textural and acidic properties, and even full structural collapse occurs in the case of open frameworks, (proto) zeolites containing small-crystalline domains, and mesostructures. These materials can show very interesting properties if their structure could be fully maintained. A principal question is, is there any alternative to calcination. There is a manifested interest to find alternatives to calcination to show the potential of new structures. 

Ni [182], V [183], and A1 [184]. SU-M [185] is a mesoporous germanium oxide with crystalline pore walls, possessing one of the largest primitive cells and the lowest framework density of any inorganic material. The channels are defined by 30-rings. Structural and thermal information show that there exists a mismatch between framework stability and template decomposition. The latter requires temperatures higher than 450 °C, while the structure is preserved only until 300 °C. 

Solid-state NMR spectroscopy was used for studying the formation of cubic mesoporous aluminophosphate thin films and powders. The analysis of the initial gel, the as-deposited materials and the thermally-treated materials elucidated the changes in the coordination of phosphorus and aluminium atoms and thus revealed how the framework formation and condensation proceeds. The consolidation process in thin films was different than the process in powders. Most probably this could be attributed to the effect of glass substrate. 

The fraction of octahedrally coordinated aluminium species is much larger in thermally treated aluminophosphate mesoporous thin films than in thermally treated powders. The difference between thin films and powders might be due to a substrate effect that could retard the formation of a well-defined aluminophosphate framework. Indeed, it has been... 

Mesostructured alumina with hexagonal structure can be synthesized in the presence of sodium dodecyl sulfate (SDS), but it was not stable upon surfactant removal. Thermally stable mesoporous alumina has been obtained by nsing triblock copolymer as templates in ethanol solntion. Most alumina mesophases consist of amorphous or semicrystalline framework. Recently, Pinnavaia and coworkers developed a novel three-step assembly method to prepare mesostructured alumina with framework walls composed of crystalline, lathlike y-A Os nanoparticles. ... 

From natural zeolites to the recently discovered meso- and macro-porous materials, the ordered porous frameworks are all constructed by inorganic species. However, in the past ten years, a new family of porous compounds composed of metal-organic frameworks (MOFs) has attracted enormous attention. The main reason is that the poor thermal and chemical stability of MOFs has been somewhat improved. In addition, the discovery of some advantages of MOFs that are lacking in molecular sieves and mesoporous materials has also stimulated the research on MOFs. 

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