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Chemical dealumination

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. [Pg.157]

Combination of thermal and chemical dealumination. This is a two-step method which was applied in the preparation of aluminum-deficient mordenite (4,5) and Y zeolites (28,29). In some instances the two-step treatment was repeated on the same material, in order to obtain a higher degree of dealumination (5,28). [Pg.162]

Gnep et al. (91) investigated toluene disproportionation and coke formation over chemically dealuminated mordenite. [Pg.194]

Chemically dealuminated Y zeolite was prepared starting from NHa exchanged Y (2.5 Si/Al ratio) using the procedure of Skeels... [Pg.102]

The fact that catalysts prepared from hydrothermally and chemically dealuminated zeolites are similar may be related to the catalyst... [Pg.108]

Metals passivation compliments the latest generations of FCC catalysts octane catalysts based on USY zeolite technology and chemical dealumination. Octane catalysts equilibrate at lower unit cell sizes, resulting in minimization of hydrogen transfer reactions (15). Commercial tests have demonstrated that antimony does not affect the zeolite unit cell size (9). [Pg.192]

We found the acidity of chemically dealuminated mordenites shows a large variation with aluminum content (Figure 9). The alpha values decrease over five orders of magnitude as the aluminum content decreases from four aluminum atoms per unit cell down to 0.8 Al/unit cell. If the Bronsted acid sites associated with boron are of equal strength as those associated with... [Pg.388]

Chemical dealumination involves reaction of the zeolite framework with any one of a variety of reagents(2). In this work, zeolites were reacted with ammonium hexafluorosilicate in aqueous solution(9-12) to prepare dealuminated products. Aluminum was extracted from the zeolite framework and removed from the crystal as a soluble fluoroaluminate complex the resulting lattice vacancies are believed to be filled by silicon in solution. Composition profiles of chemically dealuminated zeolites (AFS) are homogeneous and indicate the entire crystal is accessible for dealumination(13). Sorption data indicate that AFS zeolites do not possess a secondary pore system although pore blockage may occur due to occlusion of fluoroaluminate species(13). [Pg.32]

The hydrothermally dealuminated zeolites (USY-1 and USY-2) used in this study were plant-grade materials and were used without further exchange. The chemically dealuminated zeolites (AFS-1 and AFS-2) were prepared in our laboratory following the method of Breck and Skeels(12). The AFS samples were washed thoroughly until residual fluoride was no longer detected in the filtrate AFS-1 received additional warm-water washes to reduce further fluoride levels in the solid. AFS samples were prepared so as to have the same extent of framework dealumination as the USY samples. [Pg.32]

Table III shows XRD and porosimetry data for calcined USY and AFS zeolites. All samples show shrinkage of the unit cell to comparable values following calcination. As a result, calcined samples are compared at similar silica-alumina framework ratios. All calcined samples have well developed microporous structures and comparable total pore volumes. These porosimetry data confirm that the hydrothermally dealuminated materials contain a significant fraction of mesopores relative to chemically dealuminated materials. The extensive washing given to AFS-1 results in higher micropore surface area and volume compared to AFS-2 and suggest that AFS-2 contains occluded fluoroaluminate and fluorosilicate compounds within the microporous structure. Table III shows XRD and porosimetry data for calcined USY and AFS zeolites. All samples show shrinkage of the unit cell to comparable values following calcination. As a result, calcined samples are compared at similar silica-alumina framework ratios. All calcined samples have well developed microporous structures and comparable total pore volumes. These porosimetry data confirm that the hydrothermally dealuminated materials contain a significant fraction of mesopores relative to chemically dealuminated materials. The extensive washing given to AFS-1 results in higher micropore surface area and volume compared to AFS-2 and suggest that AFS-2 contains occluded fluoroaluminate and fluorosilicate compounds within the microporous structure.
The acidity of high-silica zeolites produced either by direct synthesis or by chemical dealumination of parent zeolites (either by steaming and acid leaching or by SiCfi vapor treatment), which makes it possible in principle to extract the aluminum from the network without the structure collapsing, was extensively studied in the 1990s. [Pg.425]

Characterisation of the textural properties of chemically dealuminated Y zeolites... [Pg.717]

The main objective of this work is to analyse the effect of chemical dealumination by ammonium hexafluorosilicate treatment on the textural properties of Y zeolite. [Pg.717]

The physicochemical properties of the different beta samples (before impregnation of platinum) are presented in Table 1. It can be seen that the chemically dealuminated HP c nd HP p r samples have a similar bulk Si/Al ratio, which would be very close to the framework Si/Al ratio, as both samples are practically free of EFAL species. By ccHitrast, the steamed HP, sample has the same bulk Si/Al ratio than the parent Hp sample, as it contains all the EFAL generated, but the framework Si/Al ratio should be very close to that of the chemically dealuminated catalysts, as mdicated by the Si MAS-NMR analysis. The XPS results indicate that steaming of HP sample did not produce an... [Pg.458]

Chemical stability is an extremely important characteristic of HDV s, but one that has received relatively limited mention in the literature. Most reported studies have dealt with just two sorts of environments The first are those encountered in chemical dealumination processes—strong acids, chelating agents (e.g., EDTA, or soluble silicon sources (e.g., amnionium f luorosilicate). [9,10,11] The second deals with catalytic process environaients—ammonia vapor in hydrocrackers [12,13] or vanadic acid in fluid crackers [14]. Essentially no studies directed towards the specific needs of the catalyst manufacturer are available. [Pg.306]

Chemical dealumination route. This technique has been used for decades, and it involves acids (including inorganic and organic acids), alkalis, salts in solution which react with the zeolite for dealumination, or else involves inorganic ligands such as F ... [Pg.361]

Chemical Dealumination and Silicon Enrichment of Zeolites Liquid Phase Dealumination and Silicon Enrichment... [Pg.364]

Modification of Zeolites. The purpose of any modification is to improve catalytic properties. The most common modification is the dealumination of zeolites which has been shown to increase crystalline thermal stability. Three dealumination procedures can be used (35) chemical dealumination, thermal or hydrothermal dealuminatTon and combination of thermal and chemical dealuminations. [Pg.265]

Five dealuminated Y zeolites were prepared from the parent commercial NaY zeolite (ACC, India) by chemical dealumination with H4EDTA [17] as follows the zeolite sample was suspended in distilled water and heated upto 100"C under reflux. To this required amount of 0.3% H4EDTA solution (adjusted to get different degree of dealumnation) was added slowly over a period of 5 h. Dealuminated samples were washed with hot water and dried at 120°C. The samples were designated as DAY-n, where n represents experiment number. [Pg.690]

Pretreatment Effects.- In this section, we discuss the changes in selectivity by hydrothermal treatment, chemical dealumination,... [Pg.246]

Pellet et al. investigated in detail the effect of the Al content of Y and ultrastable Y (USY) zeolites on gasoline selectivity in a MAT unit. The total Al content was varied by chemical dealumination, while the relative amount of NFA was varied by the severity of the steam treatment. Crystallinity and unit cell measurements quantified the amorphous SiAlO and the NFA respectively. Results indicate that the gasoline selectivity is inversely proportional to the total amount of Al present, i.e., increases with increasing Si enrichment. It is also Inversely... [Pg.247]

Pretreatmeht processes for zeolite catalysts include ion exchange and Si/Al ratio enhancement (A1 stripping). Ion exchange can be either to remove, e.g. Na, or to insert, e.g.. Re. Si/Al enhancement can be by hydrothermal treatment, chemical dealumination by, e.g., silicon halides, or a combination. Poisons such as pyridine or heavy metals may be present in the feed or be preintroduced. Coke is generally an Inevitable side product of hydrocarbon reactions, and is progressively added to the catalyst. [Pg.276]

Acidity of modified HY zeolites prepared by combination of chemical dealumination and hydrothermal treatment have been characterized by IR, MAS NMR and w-butylamine titration. The results showed that by increasing the level of dealumination, the total amount of acid sites decreased while the strongest acid sites (Ho S -8.2) increased. The strength population profile of acid sites revealed that only the aluminum atoms associated with the stronger acid sites (-8.2 < Ho < -5.6) were extracted from the framework during the dealumination steps. These results were correlated with the population of Si(nAl) groupings... [Pg.213]


See other pages where Chemical dealumination is mentioned: [Pg.161]    [Pg.559]    [Pg.64]    [Pg.108]    [Pg.108]    [Pg.109]    [Pg.540]    [Pg.36]    [Pg.36]    [Pg.460]    [Pg.362]    [Pg.371]    [Pg.372]    [Pg.265]    [Pg.26]    [Pg.246]    [Pg.248]    [Pg.213]   
See also in sourсe #XX -- [ Pg.25 ]

See also in sourсe #XX -- [ Pg.364 , Pg.371 ]




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