Crystallization of Zeolites under Microwave Irradiation

Sometimes the interpretations conflict with each other. The mechanism for the acceleration effect of microwaves on the reactions and molecular sieve crystallization needs to be studied in a more in-depth way. 

The crystallization of microporous compounds under microwave irradiation was developed in the 1970s, and was characterized by mild conditions, low energy consumption, rapid reaction, small particles, and uniform particle-size distribution. For example, under microwave irradiation and normal pressure, zeolite NaA could crystallize with a high crystallinity in a short time, even less than 1 minute. Thus, this new synthesis approach can quickly and continuously produce molecular sieves with low energy consumption. The microwave synthesis of zeolite NaA and microporous AIPO4-5 and the ion exchange reaction of zeolite Ce-/i will be discussed in detail later in this section. The successful synthesis of microporous FeAPC 4-5, CoAPO-5, CoAPO-44, VPI-5/771 zeolites Na-X, Na-Y, ZSM-5, and TS-1,[78] the preparation of molecular sieve membranes/791 the dispersion of salts or oxides into the channels of molecular sieves, and the modification or functionalization of the channel or structure of the molecular sieves under microwave irradiation have been reported as well/801 

The effect of aging of the parent mixture on the microwave synthesis of zeolite NaA was studied by P.M. Slangen et al. in 1997.[81] The gel composition of the studied system was 1.5 Na20 1.0 A1203 1.0 Si02 96.5 H20. The gels, aged at ambient temperature for various times, were cooked under microwave irradiation for 5 min at 100 °C and the results are summarized in Table 3.12. 

Numerous microporous crystallines with various structure types have been successfully synthesized by using microwave irradiation in the last decade. Compared with conventional hydrothermal synthesis, microwave synthesis has many advantages, such as narrow particle-size distribution, controllable morphology, broader parent mixture composition, and short crystallization time. It can be expected that microwave synthesis will play an important role in the rapid, energy-saving, and continuous production of microporous compounds. 

Because of its unique heating mechanism, microwave irradiation has a special effect on the ion-exchange behavior of zeolite molecular sieves. Compared with traditional ion-exchange of rare-earth ions, microwave-irradiation-conducted ion-exchange has many 

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