Open-framework materials treatment

Treatment of the open-framework materials at high vacuum and 70 °C results in collapse of the pores that are readily visible in the X-ray crystal structure (Fig. 13) and a nonporous structure (surface area[Pg.267]

The open frameworks of zeolites are slightly less stable than the corresponding condensed structures [15,16] into which they will transform during severe thermal treatment. Nevertheless, the difference in energy between a-quartz, the most stable polymorph of silica, and siliceous faujasite, one of the most open and least stable, is only about 15 kj mol k The extensive occurrence of aluminosilicate zeolites and their widespread utility in industry therefore depend heavily upon both the strengths of their T-O bonds (e.g. Si-O 466 kJ mol ), which render them stable with respect to framework rearrangement. The challenge with many of the newer materials is that their stability with respect to transformation into alternative condensed structures is considerably lower and they frequently collapse on dehydration or other means of activation. It is for this reason that only a small subset of the many open-framework families of materials can be rendered truly nanoporous,... 

The development of mesoporous materials with more or less ordered and different connected pore systems has opened new access to large pore high surface area zeotype molecular sieves. These silicate materials could be attractive catalysts and catalyst supports provided that they are stable and can be modified with catalytic active sites [1]. The incorporation of aluminum into framework sites of the walls is necessary for the establishment of Bronsted acidity [2] which is an essential precondition for a variety of catalytic hydrocarbon reactions [3], Furthermore, ion exchange positions allow anchoring of cationic transition metal complexes and catalyst precursors which are attractive redox catalytic systems for fine chemicals [4]. The subject of this paper is the examination of the influence of calcination procedures, of soft hydrothermal treatment and of the Al content on the stability of the framework aluminum in substituted MCM-41. The impact on the Bronsted acidity is studied. 

Zeolites are microporous crystalline aluminosilicates with a channel-like or cagelike pore structure with pore-opening sizes in the range of 0.3 to 1.5 nm [13]. The spatially periodic pore structure and well-defined nanospaces of zeolites offer opportunities to control the nanostructure and morphology of microporous carbon materials at the nanometer level. As schematically illustrated in Figure 2.1, zeolite pores can be filled wifh a carbon precursor such as furfuryl alcohol (FA). After a proper treatment, followed by removal of the zeolite framework, a carbon nanostructure with pores replicated from the zeolite framework is obtained. Over the past decade, many zeolite templates (e.g., zeolite Y, zeolite (3, and ZSM-5) and carbon precursors (e.g., FA, phenol-formaldehyde, and sucrose) have been... 

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