Mesoporous alkali-exchanged

Alkali-exchanged mesoporous molecular sieves are suitable solid base catalysts for the conversion of bulky molecules which cannot access the pores of zeolites. For example, Na- and Cs-exchanged MCM-41 were active catalysts for the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate (pKa=10.7) but low conversions were observed with the less acidic diethyl malonate (pKa=13.3) [123]. Similarly, Na-MCM-41 catalyzed the aldol condensation of several bulky ketones with benzaldehyde, including the example depicted in Fig. 2.38, in which a flavonone is obtained by subsequent intramolecular Michael-type addition [123]. 

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

Similarly the alkali metal-exchanged titanium beta was shown to be an effective catalyst for olefin epoxidations with TBHP [47]. Titanium has also been incorporated into mesoporous molecular sieves, such as MCM-41, by framework substitution [48] or by grafting Ti(IV) species to the internal surface by reaction... 

Micro- and meso- Alkali ion-exchanged zeolites and mesoporous materials... 

The development of environmentally friendly solid catalysts for the production of fine chemicals has known a recent growing interest and recent review articles have been devoted to catalysis by solid bases. Several solid bases have been proposed such as alkali ion-exchanged zeolites [1], alkaline oxides supported on microporous [2] and mesoporous solids [3], sodium metal clusters in zeolites... 

MCM-22 (Si/Al =12) and MCM-36 pillared with Si02 (Si/Al = 29) were modified by ion exchange of alkali cations. A critical point was the pH of the solution, which should be adjusted to about 9 and 4, respectively. At pH 9 the pillared mesoporous structure of MCM-36 was destroyed as indicated by nearly amorphous XRD patterns and severely reduced BET surface areas. The degree of exchange decreased from Na to Cs (except the lowest value for Li). In spite of this, the basic character in both series increased from Li to Cs as demonstrated by IR spectra of adsorbed pyridine and TPD of ammonia. 

Walton K. S., Abney M. B., Levan M. D. CO adsorption in Y and X zeolites modified by alkali metal cation exchange. Microporous and Mesoporous Materials 91(1-3), 78-84 (2006). 

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