Y dealuminated

When 1,2-dichlorobenzene in hydrogen-saturated deionized water was exposed to a slurry of palladium catalyst (1%) at room temperature, benzene formed via the intermediate chlorobenzene. The reaction rate decreased in the order of MCM-41 (mesoporous oxide having a silicon aluminum ratio of 35) > alumina > Y (dealuminated zeolite having a silicon aluminum ratio of 15). It appeared the reaction rate was directly proportional to the surface area of the support catalyst used (Schiith and Reinhard, 1997). 

DEALUMINATIQN OF ZEOLITE Y Dealumination is an important process to improve the thermal stability and resistance to acid of zeolite. This is one of the main techniques for preparing zeolite catalysts (US-Y). New pores (mesopores) have been introduced during hydrothermal treatment (Fig.4), which were directly confirmed by electron microscopy. The density of mesopores depended on the degree of dealumination and the size distribution of mesopores... 

Fyfe et al. (155) also recorded spectra of samples of zeolite Y dealuminated using silicon tetrachloride vapor. This method is discussed in detail in Section... 

Scheme 8 Metal transition complexes grafted on the surface of a) Y dealuminated zeolite b) silica gel.

Fig. 6.7 Schematic representation of the zeolite Y dealumination process steps...

Zeolites Y dealuminated by Si/Al substitution using SiCU (DAY-S) and dealuminated thermochemically in steam (DAY-T) were investigated by X-ray powder diffraction, infrared spectroscopy and wet chemical methods. The dependence of lattice constants (a) on the molar ratio X = (1+Si/Al) show non-ideal solid solution behaviour. In a first approximation the change in a (in nm) can be described as a = 0.187x+2.412, for 0.1 < x < 0.5. For x < 0.1 the change in lattice constant saturates towards a = 2.425 nm. A similar shift in the double ring mode (wdr) is observed, tailing off. 

Figure 2. Wavenumber of the asymetric TO stretching as a function of A1 content in faujasites o as synthesised in the laboratory p commercially available steamed Y dealuminated with (NH4)2SiF6 dealuminated with SiCU.

The effect of cationic EFAL species on catalytic activity, has been shown by comparing steam stabilized and zeolite Y dealuminated by (KH4)2SiFj treatment. While Creighton et al. (100) found the same selectivity, Beyerlain et al. (101) show that clean framework "fresh" zeolite Y dealuminated by (NH4)2SiFs, gave a lower i-butane cracking activity that the same sample after mildly steamed. 

Fig. 3.70 (a)Change in wavenumber of the hydroxyl vibrating in the large cavities as a iunc-tion of Si/Al ratio. From left to right A, GeX, X, Y, chabazite, L, Q, dealuminated Y, dealuminated Y, offretite, mordenite, clinoptilolite, dealuminated Y, dealuminated mordenite, ZSM—5. 

Fig. 7. a High-resolution electron micrograph of zeolite Y dealuminated with SiCl along the [110] zone axis b selected area diffraction pattern corresponding to this zone axis and c [100] projection of the framework [150]... 

An amorphous component such as silica-alumina is added to the catalyst, for a sort of pre-cracking of the large molecules (greater than about C25), which cannot enter the zeolite pores. The smaller fragments may then react in the zeolite. Middle distillates maximum yield is achieved by the use of dealuminated Y zeolites. 

Hydrolysis oftricaprylin in trimethylpentane by Fusarium solani pisi recombinant cutinase immobilized on various zeolites (NaA, NaX, NaY, LZY-82, dealuminated Y) was investigated in order to assess the effect of chemical composition (Si/Al ratio), hydrophilic character and acidity on the catalytic activity [221]. The adsorption of... 

Keywords Two-Dimensional correlation, Infrared spectroscopy, Dealuminated H-Y zeolite, Bronsted acidity, MQ-MAS NMR. 

Acidic micro- and mesoporous materials, and in particular USY type zeolites, are widely used in petroleum refinery and petrochemical industry. Dealumination treatment of Y type zeolites referred to as ultrastabilisation is carried out to tune acidity, porosity and stability of these materials [1]. Dealumination by high temperature treatment in presence of steam creates a secondary mesoporous network inside individual zeolite crystals. In view of catalytic applications, it is essential to characterize those mesopores and to distinguish mesopores connected to the external surface of the zeolite crystal from mesopores present as cavities accessible via micropores only [2]. Externally accessible mesopores increase catalytic effectiveness by lifting diffusion limitation and facilitating desorption of reaction products [3], The aim of this paper is to characterize those mesopores by means of catalytic test reaction and liquid phase breakthrough experiments. 

Liquid-phase breakthrough experiments were also developed in order to characterize mesopores. The principle of the methodology relied on the analysis of the diffusion and adsorption of molecular probes with various molecular dimensions and adsorption strength. The relative proportion of occluded and accessible mesopores in the studied dealuminated Y zeolite could then be estimated. To allow this estimation, it is necessary to use molecular probes that can or cannot penetrate into the microporosity of the Y zeolite (see Figure 2). 

It was found that more than 70 % of the mesopore volume of the highly dealuminated Y zeolite was externally accessible [7]. Interestingly these results are in accordance with... 

These data clearly indicate that the NiMCM-36 catalyst exhibits very interesting properties for ethylene oligomerization, by comparison with the microporous NiMCM-22 zeolite at both reaction temperatures (70 and 150°C, respectively). Compared with other catalysts, the NiMCM-36 behaviour is intermediate between Ni-exchanged dealuminated Y zeolite and Ni-exchanged mesoporous materials. Taking into account that the amount of Ni2+ sites is near the same for all samples (Table 1), in order to explain these differences in catalytic behaviors, two mains categories of properties could be considered (i) the concentration and strength of acid and nickel sites and (ii) the diffusional properties (determined by the size and the architecture of pores). 

J.-F. Chapat, A. Finiels, J. Joffre, and C. Moreau, Synthesis of butyl-a and / -d-glucopyranosides in the presence of dealuminated H-Y faujasites Kinetic study, mechanism, stereoelectronic effects, and microreversibility principle, /. Catal., 185 (1999) 445—453. 

C. Buttersack and D. Laketic, Hydrolysis of sucrose by dealuminated Y-zeo-lites, /. Mol. Cat., 94 (1994) L283-L290. 

The microwave technique has also been found to be a potential method for the preparation of the catalysts containing highly dispersed metal compounds on high-porosity materials. The process is based on thermal dispersion of active species, facilitated by microwave energy, into the internal pore surface of a microporous support. Dealuminated Y zeolite-supported CuO and CuCl sorbents were prepared by this method and used for S02 removal and industrial gas separation, respectively [5], The results demonstrated the effective preparation of supported sorbents by micro-wave heating. The method was simple, fast, and energy-efficient, because the synthesis of both sorbents required a much lower temperature and much less time compared with conventional thermal dispersion. 

Figure 15, Dealumination of zeolite Na-Y using SiClk vapor studied by 29Si-MAS NMR at 79.8 MHz. Key top, parent Na-Y zeolite and bottom, after treatment with SiClk. (Reproduced from Ref. 30. Copyright 1982, American Chemical Society.)...

MEDISORBON An adsorptive process for removing mercury and dioxins from flue-gas. The adsorbent is a dealuminated zeolite Y manufactured by Degussa. For mercury removal, the zeolite is impregnated with sulfur. Developed in 1994 by Lurgi Energie und Umwelt and piloted in Germany and The Netherlands. 

The preparation methods of aluminum-deficient zeolites are reviewed. These methods are divided in three categories (a) thermal or hydrothermal dealumination (b) chemical dea-lumination and (c) combination of thermal and chemical dealumination. The preparation of aluminum-deficient Y and mordenite zeolites is discussed. The structure and physico-chemical characteristics of aluminum-deficient zeolites are reviewed. Results obtained with some of the more modern methods of investigation are presented. The structure, stability, sorption properties, infrared spectra, acid strength distribution and catalytic properties of these zeolites are discussed. 

Zeolite dealumination was first reported by Barrer and Makki (1), who progressively removed aluminum from clinoptilolite by treating the zeolite with hydrochloric acid of different strengths. Subsequent dealumination studies were carried out primarily on mordenite (2-5) and Y zeolites. 

An example of such thermal dealumination is the formation of ultra-stable Y zeolites (USY zeolites). McDaniel and Maher (6) reported the preparation of two types of ultrastable Y zeolites (a) one type prepared by the hydrothermal... 

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