Nano-sized zeolite

A new composite containing montmorillonite and zeolite Beta is prepared by in situ crystallization. Nano-zeolite Beta grows on montmorillonite. The composite possesses a dual system of micropore, originated from zeolite Beta, and mesopore of size around 50nm, due to the abundance of interspace formed by montmorillonite laminaes. Compared with catalyst MoNi/Beta, more i-C8 is produced on catalyst MoNi/composite, when n-Cg is used for feedstock for hydroisomerization. This results from the high diffusion created by composite and the short channel of nano-size zeolite Beta. 

In recent years, there has been a growing interest in the synthesis and application of nano-scale zeolites. Zeolites with a crystal size smaller than 100 nm are the potential replacement for existing zeolite catalysts and can be used in novel environmentally benign catalytic processes. It is well known that the crystal size of zeolites has a great effect on their catalytic properties. The improved catalytic activity and selectivity as well as lower coke formation and better durability can be obtained over nano-sized zeolite crystals [2]. 

Early reports include a patent from W.R. Grace describing nano-sized zeolite X and Y, another from Mobil for nano-sized MFl catalysts and a third describing the preparation of nano-sized zeolite L [147-149]. The explosion of nanotechnology research in the past few decades has led to an enormous number of additional... 

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. 

Fully dispersed nano-size zeolitic imidazolate frameworks embedded in PBI have been used in gas separation membranes [26]. The loading with these specific nanoparticles overcomes the low permeability of neat PBI. The membranes exhibit high transparency and mechanical flexibility, and an enhanced... 

Moermans et al. (2000) prepared PDMS membranes filled with colloidal silicate-1 and applied these membranes in the PV of EtOH-water mixtures. The nano-sized zeolites showed much improved PV results compared with the micron-sized silicate m branes. Both the flux and the selectivity were drastically increased at the highest loading. The best results were obtained with the PDMS membrane containing 40 wt% of silycated nano-sized siUcate-1. 

Jiang LY, Chung TS, Cao C, Huang Z, Kulprathipanja S. Fundamental understanding of nano-sized zeolite distribution in the formation of the mixed-matrix single and dual-layer asymmetric hollow fiber membranes. J Membr Sci 2005 252(l-2) 89-100. 

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. 

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. 

Derouane, E. G., Schmidt, L, Lachas, H., and Christensen, C. J. H. 2004. Improved performance of nano-size H-BE A zeolite catalysts for the Friedel-Crafts acetylation of anisole by acetic anhydride. Gatal. Lett. 95 13-17. 

Ab-initio quantum chemical calculations at the HF/3-21G level of theory were applied to consider the nature of the active sites of sodalite P-cage of the LTA type zeolite and faujasite structures. Especially, the nature of sodium, potassium and silicon atoms encapsulated within the sodalitic P-cage, and their structural and molecular parameters have been described. We have shown that up to four sodium and four potassium atoms as well as five silicon atoms could be encapsulated within the sodalite P-cage. The unique properties of these nano-size materials relate directly to the encapsulated guest atom containing fragments stabilized within the sodalite P-cage of the LTA type zeolite or faujasite structures. 

S. Anandan, M. Yoon, Photocatalytic activities of the nano-sized Ti02-supported Y-zeolites , Journal of Photochemistry and Photobiology C Photochemistry Reviews, 4, 5-18, (2003). 

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. ... 

Fodor, D., Pacosovd, L., Krumeich, F., and van Bokhoven, J-A. (2014) Facile synthesis of nano-sized hollow single crystal zeolites under mild conditions. Chem. Commun., 50, 76-78. 

As zeolitization of fly ash is a complex phenomenon. Fig. 6.18 intends to simplify complex effects of successive activations of the fly ash, in three-steps. In such a situation, grinding of a residue, may cause peeling off and crumbling the deposited crystals of the FAZ (refer Fig. 6.14) and thus exposes the roughened boundary of impurities, IMP from Step-1 and Step-2. In fact, the activated boundary contains many nano-sized pores, as observed in Fig. 6.14b-g, which... 

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. 

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