Kinetics of zeolites

Bosnar, S., Antonie, T., Bronic, J. and Subotic, B. Mechanism and kinetics of the growth of zeolite microcrystals. Part 2 Influence of sodium ions concentration in the liquid phase on the growth kinetics of zeolite A microcrystals, Microporous Mesoporous Mater., 2004, 76, 157-165. 

Kinetics of Zeolite Formation. Since the D5R synthesis mechanism, if operative, is clearly disturbed by DMSO (vide supra), we also carried out a number of time-dependent syntheses in the absence of DMSO in the hope of being able to relate the kinetics with the D5R concentration present. Starting from a molar composition of 40 Si02 1 A OjX 5 NaOH 1000 H20 X at T - 190 °C, various organics and/or seed crystals (X) were added and the solid products were characterized after various synthesis times. Properties of the products obtained when the highest crystallinities were reached are summarized in Table II. 

The induction periods of both zeolite X and zeolite Na-Pc shortens and the maximal yield of zeolite X increases, respectively, with the increased time of gel ageing. All kinetics of zeolite X and zeolite Na-Pc, respectively, can be mathematically expressed by the simple kinetic equation (5,23-26),... 

Fig 11 Crystallization kinetics of zeolite Beta, from reference hydrogels, at... 

Figure 5.Crystallization kinetics of zeolite ZSM-48 in presence of Li+, Na+ and K+ ions, without A1 (a) and in presence of 0.5 mole AI2O3 in the gel (b) 5Na20 2.5HMBr2 (0 or 0.5)Al2C>3 60SiO2 3000H20.

Nucleation and crystallisation kinetics generally follow S-shaped crystallisation curves as shown for zeolite A in Figs. 8.28 and 8.29. This means that a rather long incubation time or nucleation period precedes the crystallisation (compare Figs. 8.28b for zeolite A and 8.29b for ZSM5). The general trend in the kinetics of zeolite (ZSM5) synthesis can be summarised as follows ... 

Predictability of activity, selectivity, and stability based on known structures of catalysts can be considered the main aim of the theoretical approaches applied to catalysis. Here, for a particular class of heterogeneous catalysts, namely, acidic zeolites, we present the theoretical approaches that are available to accomplish this goal, which lead to a better understanding of molecular motion within the zeolitic micropores and the reactivity of zeolitic protons. It is not our aim to introduce the methods as such, since introductory treatments on those can be found elsewhere. Rather we focus on their application and use to solve questions on mechanisms and reactivity in zeolites. The discussion is focused on an understanding of the kinetics of zeolite-catalyzed reactions. 

We are concerned with the kinetics of zeolite-catalyzed reactions. Emphasis is put on the use of the results of simulation studies for the prediction of the overall kinetics of a heterogeneous catalytic reaction. As we will see later, whereas for an analysis of reactivity the results of mechanistic quantum-chemical studies are relevant, to study adsorption and diffusion, statistical mechanical techniques that are based on empirical potentials have to be used. 

Figure 6 shows the variations with time of the silicate and aluminate concentrations, expressed as Si02 and A1203, in the mother liquor. The formation kinetic of zeolite X, obtained by x-ray quantitative analysis, using molecular sieve 13X of Union Carbide as reference, is reported in... 

Figure 12. Crystallization kinetics of zeolite X from pumices at 3 different finenesses, treated at 65°C with S/L = 1/25 and 18% NaOH solution Fraction passing at 320 mesh ...

Crystallization fields of zeolites growing from homocationic Na gels at around 100 °C have been studied extensively at a number of laboratories (cf. 3,11, 21). Sand and coworkers recorded the coexisting phases for different reaction times (19). The kinetics of zeolite crystallization in the Na system also has received attention (12, 14, 15). Studies of low-temperature crystallizations from Li gels, on the other hand, have been much more limited (13). 

P-23 - The influence of different silica sources on the crystallization kinetics of zeolite beta... 

Kinetics of Zeolitic Solid Acid-Catafyzed AUgrlation of Isobutane with 2-Butene... 

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