Catalyst aluminosilicate zeolite

Zeolite A [1318-02-1] Zeolite (aluminosilicate) Zeolite catalysts Zeolite L Zeolites... 

Catalytic cracking is a process that is currently performed exclusively over fluidized catalyst beds. The fluid catalytic cracking (FCC) process was introduced in 1942 and at that time replaced the conventional moving bed processes. These early processes were based on acid-treated clays as acidic catalysts. The replacement of the amorphous aluminosilicate catalysts by Faujasite-type zeolites in the early-1960s is regarded as a major improvement in FCC performance. The new acidic catalysts had a remarkable activity and produced substantially higher yields than the old ones. 

Aluminum (properly called aluminium, but the former name prevails in North America) is found in combination with Si and 0 as aluminosilicates in rocks, and as its ore, bauxite. The metal finds use in vehicles, aircraft, packaging, cookware, construction materials, etc., while aluminum salts are used in baking powders, water treatment, and dyeing of textiles. Aluminum oxide is widely used as a refractory and as a support for catalysts. Aluminosilicate catalysts such as zeolites are of key importance in the chemical and petroleum industries. 

The fundamental carbonium ion-type reactions of olefins— including double bond and carbon skeleton isomerization, polymerization, isotopic exchange, and hydrogen transfer—have been reviewed earlier (62). The importance of a thorough understanding of the nature of olefin transformations over zeolite catalysts cannot be underestimated. Probably the most important and frequently recurring pattern is the transfer or redistribution of hydrogen that is observed with olefins over acidic crystalline aluminosilicate catalysts. 

Solid catalysts such as zeolite (aluminosilicate), heteropolyacids and their alkali or alkaline earth metal salts on a metal oxide support and basic resins have been used as catalysts to manufacture polysulfides. 

Significant advances resulting from the use of aluminosilicate solids were made during the last few years [3-6] and the first industrial application of zeolites in large scale Friedel-Crafts acylations was reported very recently [7]. However, most of the efforts devoted so far focused on the acylation of aromatic compounds. To the best of our knowledge, recourse to heterogeneous aluminosilicate catalysts for the acylation of alkenes has not yet been reported. Conventional methods for alkene acylation [8] involve the use of Br0nsted or Lewis acids such as sulfuric acid [9], boron trifluoride [10], zinc chloride [11], or... 

A large amount of information has been published on catalytic cracking with molecular shape-selective catalysts, such as natural or synthetic crystalline aluminosilicates. Several excellent reviews have appeared on the chemistry of catalysis with zeolites (52, 53). Literature on hydrocracking of pure hydrocarbons and simple mixtures of hydrocarbons with zeolite-containing catalysts is limited. However, numerous patents on the use of zeolites in hydrocracking catalysts and published... 

At high temperatures (above 200 °C) these polymers are dehydrogenated to carbon, a process known as coking. Especially catalysts with acidic or hydrogenating/ dehydrogenating properties cause coking. Coking on acid centers is observed with zeolite and aluminosilicate catalysts and with acidic supports. The extent of coke formation depends directly on the acidity. 

The selectivity varies with catalysts (improved with zeolites, that are acid-base aluminosilicate catalysts) and surfaces (faces of crystals). 

Pillared montmorillonites were used to oligomerize propylene at 30-50 atm [68]. One of the catalysts was pillared with a mixed aluminum-zirconium polymer. The PILCS were much less active than H-zeolite omega or an aluminosilicate catalyst. However, the selectivity for gasoline was greater. The Al-Zr PILC exhibited a high selectivity for aromatics and less coke formation than the Al-PILC. The observed behavior was attributed to the large niimber of Lewis acid sites relative to Br nsted acid sites and to the microporosity of the PILCS. 

Microporous catalysts are heterogeneous catalysts used in catalytic converters and for many other specialized applications, because of their very large surface areas and reaction specificity. Zeolites, for example, are microporous aluminosilicates (see Section 14.19) with three-dimensional structures riddled with hexagonal channels connected by tunnels (Fig. 13.38). The enclosed nature of the active sites in zeolites gives them a special advantage over other heterogeneous catalysts, because an intermediate can be held in place inside the channels until the products form. Moreover, the channels allow products to grow only to a particular size. 

Zeolites form a unique class of oxides, consisting of microporous, crystalline aluminosilicates that can either be found in nature or synthesized artificially [J.M. Thomas, R.G. Bell and C.R.A. Catlow in Handbook of Heterogeneous Catalysis (Ed. G. Ertl, H. Knbzinger and J. Weitkamp) (1997), Vol. 1, p. 206, VCH, Weinheim.]. The zeolite framework is very open and contains channels and cages where cations, water and adsorbed molecules may reside and react. The specific absorption properties of zeolites are used in detergents, toothpaste, and desiccants, whereas their acidity makes them attractive catalysts. 

The hydroamination of alkenes has been performed in the presence of heterogeneous acidic catalysts such as zeolites, amorphous aluminosilicates, phosphates, mesoporous oxides, pillared interlayered clays (PILCs), amorphous oxides, acid-treated sheet silicates or NafioN-H resins. They can be used either under batch conditions or in continuous operation at high temperature (above 200°C) under high pressure (above 100 bar). 

Zeolites are hydrous aluminosilicates that are widely used as catalysts in the chemical process industry. Zeolite A is usually synthesized in the sodium form from aqueous solutions of sodium... 

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