Zeolites nano-sized particles

In the next example (Example 2), a different approach for the preparation of zeolite films will be presented. This method was first proposed by Iler in 1979,11321 and involved the assembly of charged nano-sized particles layer by layer to form multilayer films based on electrostatic interaction, hence called the layer-by-layer (LBL) self-assembly technique. 

In recent years, various methods of synthesis of nano-size particle systems have been established. They have used aqueous [22] and non-aqueous [23] solutions, reversed micelles [24], vesicles [24], BLMs [24], surface monolayers [25], clays [26], zeolites [27], Langmuir-Blodgett films [28], peptides [29] aM yeast cells [30], The main idea of the dted variety of synthesis methods is to control the partide size either by spatial conditions (e.g. the size of pores 29], oititi in media [24,27]) or kinetics of synthesis reaction [22]. Another >arameter, which in many cases decreases the partide size, is temperature [2, 1. ... 

In addition, in order to improve the shape selectivity of adsorbents and catalysts, besides adjustment of pore size, the external surface of zeolites also needs to be modified to deactivate the adsorption sites and catalytically active sites present on the external surface which shows no shape selectivity. The external surface modification is especially important for small-particle and nano-sized zeolites. 

From Fig. 6.5a-d and Tables 5.15, 5.16, 5.17 and 5.18 it can be noticed that, SSA increases with the increase in step of recycling of the AAF. bicidentally, contrary to all other AAFs, there is significant increase in the SSA, in the residue, 1.5-PT-36 (refer Fig. 6.5c). This can be attributed to an intensive etching of the ash particles, leading to its dissolution, which helps the development of micro-sized pores in AAFs. In addition, treatment steps of 36 h exhibits trends, contradictory to other trends. This can be attributed to creation of extra fine particles which may be amorphous in nature and nano-sized zeolite crystals. 

Based on the hndings presented in this chapter, it can be concluded that the three-step activation of the hopper ash with NaOH results in minor variation in pH and reduction in electrical conductivity of the supernatant. Such activation is also responsible for reduction in Si and A1 contents of the supernatant, obtained after recycled treatments. Hence, the ftnal grade of the fly ash zeohtes gets improved (with high CEC and specific surface area, enhanced specific gravity, nano-sized fine particles of zeohtes and micro-sized new pores). The three-step activation of the fly ash by adopting the fusion technique has also been found to be effective for zeolitization of the fly ash. However, the presence of impurities in the ash residues obtained from the fusion process makes them inferior as compared to those obtained from the hydrothermal treatment. 

In the present study the effect of zeolite particle size (micro- vs. nano-particles) and N20 concentrations on ODHP is studied over Fe modified BEA zeolites. The feasibility of periodic reactivation over Fe-BEA catalysts by oxygen pulses for continuous C3H6 production has been also evaluated. 

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