Nanosized zeolite particles

The use of Nafion/silica composite and zeolite catalysts in this kind of reaction has been studied. The comparison of zeolites with these new materials seems interesting because excellent catalytic performance of such ion exchange resins in several reactions were found.This new material can be considered as nanosized Nafion particles entrapped within a porous silica matrix. Thus the surface area of the dispersed Nafion in the composite is much larger than that of the... 

On the other hand, the literature on fluoride crystallization is scarce, in spite of the recent work on nanosized fluoride particles for applications in optics or catalysisInterest in fluorides is mainly driven by their properties as crystallization agents for the synthesis of zeolites or phosphate-based materials and more recently of metal organic frameworks ° (MOF). Mixed anions (fluoride-phosphate, fluoride-carboxylate...) build three-dimensional 3D open frameworks for gas storage (CO2), catalysis or emerging applications (the symbols OD, ID, 2D, 3D, characteristic of the dimensionality of the frameworks, are used throughout this chapter). 

Zeolites and zeolite-like materials with their well-organized and regular systems of pores and cavities represent almost ideal matrices to host nanosized particles. The high thermal and chemical stability of zeolite-like matrices would afford the nanocomposites which could operate in a broad range of temperatures and in various media. 

X-rav diffraction. Appearance of diffraction peaks consistent with an individual non-zeolitic phase shows unambiguously the formation of oxide particles much more than nanosized [7]. Though the lack of such peaks does not mean the contrary. 

Incorporation of metals or metal oxides into zeolite cavities leads to the formation of nanosized clusters exhibiting different catalytic properties from the bulk materials. These metal particles are usually introduced into zeolite channels through ion-exchange followed by reduction or oxidation/reduction to get their final dispersions. Metal clusters can also be formed via zeolite impregnation by corresponding azides from methanolic solutions followed by thermal decomposition. " Catalytic activities of the bifunctional or basic catalysts prepared using these methods can be successfully combined with shape-selective properties of parent zeolites. 

Zhang et al. (2001) studied the HTT effects on the structure of zeolite HZSM-5 (with micro-and nanosized particles) using (Figure 2.96), Al, and Si solid-state MAS NMR. The thermal stability of nanosized HZSM-5 ( 70 nm) is lower than that of microsized particles ( 1 J.m) due to dealumination and desilicification. After HTT at 700°C, the Brpnsted acid sites (6h = 3.9 ppm) disappear (as well as nonframework AlOH at 8h = 2.7 ppm) in nanosized HZSM-5 in contrast to microsized HZSM-5 (Figure 2.96). However, the silanol peak at 1.7 ppm increases for nanosized particles. For microsized particles, the dealumination process is dominant. Upon HTT, the amorphous silica can heal dealuminated fragments. Therefore, the hydrothermal stability of nanosized HZSM-5 particles is similar to that of the microsized HZSM-5 (Zhang et al. 2001). 

In a great number of cases, zeolites are used as auxiliary elements. They may act either as a framework to stabilize the sensor material, as filter layers (either catalytic or size restrictive) to enhance selectivity of a sensitive film, or as a preconcentrator of specific analytes from diluted solutions. For example, due to excellent chemical and thermal stability, zeolites can be used as a substrate to prepare compounds and devices with desirable fundamental physical and chemical properties (Xu et al. 2006). For example, inorganic or organic compounds, metal and metal-organic compounds, and their clusters can be assembled into the pores and cages in zeohtes. Some nanosized metal or metal oxide particles have been successfully inserted into the caves and the pores or highly dispersed on the external surface of zeohtes. 

The bulk phase (phase A) is typically a polymer the dispersed phase (phase B) represents the inorganic particles, which maybe zeolite, carbon molecular sieves, or nanosized particles. Thus, MMMs have the potential to achieve higher selectivity, permeability, or both, relative to the existing polymeric membranes, resulting from the addition of the inorganic particles with their superior inherent separation characteristics. 

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