Zeolitic catalysts

Increasing the surface-to-bulk ratio of the sample to be studied. This is easily done in the case of highly porous materials, and has been exploited for the characterization of supported catalysts, zeolites, sol-gels and porous silicon, to mention a few. 

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

Faujasite is a naturally occurring mineral, having a specific crystalline, alumina-silicate structure, used in the manufacturing of the FCC catalyst. Zeolite faujasite is a synthetic form of the mineral. 

There is a real opportunity to reduce biodiesel production costs and environmental impact by applying modem catalyst technology, which will allow increased process flexibility to incorporate the use of low-cost high-FFA feedstock, and reduce water and energy requirement. Solid catalysts such as synthetic polymeric catalysts, zeolites and superacids like sulfated zirconia and niobic acid have the strong potential to replace liquid acids, eliminating separation, corrosion and environmental problems. Lotero et al. recently published a review that elaborates the importance of solid acids for biodiesel production. ... 

Consider the conversion of methanol in a 50-L reactor (volume of catalyst) similar to that shown in Figure 1.2 (which operates like a CSTR). The reactor contains 800 g of catalyst (zeolite H-ZSM5), and the space time through the reactor is 0.1 h The methanol feed rate is 1.3 kg h-1. For each reaction temperature, determine the yield and selectivity to each olefin, and comment on your results. 

Test Conditions 40 WHSV,493°C,4 Cat/Oil,West Texas Gas Oil Catalyst Zeolite in Semisynthetic Matrix... 

Nuclear magnetic resonance (NMR) spectroscopy is most frequently used to analyze liquid samples, but in the magic angle spinning (MAS) mode, this spectroscopy can also be employed to characterize solid catalysts, zeolites in particular [116-120], For example, the 29Si NMR signal can... 

Alkylglucosides are a class of valuable commercial surfactants, particularly for cosmetics applications because of their biocompatibility. They are obtained by acetalization of carbohydrates with fatty alcohols in the presence of acid catalysts. Zeolites and MCM-41 have been used as acidic catalysts to achieve the acetalization of glucose with alcohols of different chain lengths [45, 46]. Shape selectivity effects decrease the amount of oligomers formed and the activity and selectivity can be controlled with the Si/Al ratio. 

In the following decades, researchers in catalysis turned their efforts to controlhng molecular structure as well as size. The catalyst zeolite paved the way. In the late 1960s, researchers at Mobil Oil Co. were able to s)uithesize zeolite by deliberately designing and preparing the structure of catalysts at the atomic and molecular levels. The resulting nanostructured crystalline material (ZSM-5)—with a 10-atom ring and pore size of 0.45-0.6 nm—enabled the control of selectivity in petrochemical processes at the... 

Scheme 4.4 Insertion of CO2 into epoxides and cleavage of cyclic carbonates. Step 1. Catalyst MgO, CaO. Step 2. Catalyst zeolites exchanged with alkah and/or earth metal ions.

Chu, Y.F. and Chester, A.W. (1986) Reactions of isobutane with butene over zeolite catalysts. Zeolites, 6, 195-200. 

In this paper we report the use of supported heteropoly acid (silicotungstic acid) and supported phosphoric acid catalysts for the acylation of industrially relevant aromatic feedstocks with acid anhydrides in the synthesis of aromatic ketones. In particular, we describe the acylation of thioanisole 1 with iso-butyric anhydride 2 to form 4-methyl thiobutyrophenone 3. The acylation of thioanisole with acetic anhydride has been reported in which a series of zeolites were used as catalysts. Zeolite H-beta was reported to have the highest activity of the zeolites studied (41 mol % conversion, 150°C) (2). 

Since 1981, three-way catalytic systems have been standard in new cars sold in North America.6,280 These systems consist of platinum, palladium, and rhodium catalysts dispersed on an activated alumina layer ( wash-coat ) on a ceramic honeycomb monolith the Pt and Pd serve primarily to catalyze oxidation of the CO and hydrocarbons, and the Rh to catalyze reduction of the NO. These converters operate with a near-stoichiometric air-fuel mix at 400-600 °C higher temperatures may cause the Rh to react with the washcoat. In some designs, the catalyst bed is electrically heated at start-up to avoid the problem of temporarily excessive CO emissions from a cold catalyst. Zeolite-type catalysts containing bound metal atoms or ions (e.g., Cu/ZSM-5) have been proposed as alternatives to systems based on precious metals. 

In the first chapter, Bates and van Santen summarize the theoretical foundations of catalysis in acidic zeolites. Being the most important crystalline materials used as catalysts, zeolites have been the obvious starting point for applications of theory to catalysis by solids and surfaces. Impressive progress has been made in the application of theory to account for transport, sorption, and reaction in zeolites, and the comparisons with experimental results indicate some marked successes as well as opportunities for improving both the theoretical and experimental foundations. 

Using zeolite catalysts, the NOy reduction takes place inside a molecular sieve ceramic body rather than on the surface of a metallic catalyst (see Molecularsieves). This difference is reported to reduce the effect of particulates, soot, S02/S03 conversions, heavy metals, etc, which poison, plug, and mask metal catalysts. Zeolites have been in use in Europe since the mid-1980s and there are approximately 100 installations on stream. Process applications range from use of natural gas to coal as fuel. Typically, nitrogen oxide levels are reduced 80 to 90% (37). 

The enhanced diffusivity of polynuclear compounds in sc C02 has been utilized to enhance catalyst lifetimes in both 1-butene/isoparaffin alkylations (Clark and Subramaniam, 1998 Gao et al., 1996). The former may be catalyzed using a number of solid acid catalysts (zeolites, sulfated zeolites, etc.), and the use of sc C02 as a solvent/diluent permits the alkylations to be carried out at relatively mild temperatures, leading to the increased production of valuable trimethylpentanes (which are used as high-octane gasoline blending components). The enhancement of product selectivity in the latter process is believed to result from rapid diffusion of ethylbenzene product away from the Y-type zeolite catalysts, thus preventing product isomerization to xylenes. 

Another option is encapsulating the homogeneous complex in an (inorganic) cage, creating a ship-in-a-bottle hybrid catalyst. Zeolites are often used for trapping large... 

Catalyst Zeolite Low metals cycles High metals cycles... 

Whereas solid acid catalysts (zeolites) have been intensively studied, only recently has the use of basic solid catalysts received substantial interest for production of intermediate and fine chemicals [1], Heterogeneous catalytic transformations are environmentally friendly compared with processes requiring neutralization and... 

As for other recyclable heterogeneous catalysts, zeolites and related materials can also contribute to the development of environmentally friendly processes in the synthesis of bulk and fine chemicals. The concept of a biomass refinery, capable of separating, modifying and exploiting the numerous constituents of renewable resources, is gaining worldwide acceptance today with a very broad outlook. This chapter has attempted to show that this particular area of carbohydrate chemistry is in itself very rich, both in already acquired knowledge and potential future developments. 

In order to get acidic zeolite catalysts, zeolites are ion exchanged with ammonium cations ... 

Since acidic or basic sites may interact with each other, the site density ought to be determined. Moreover, an attempt should be made to describe the site location, particularly in the case of microporous acid catalysts (zeolites). 

H Pfeiffer, D Freude, M Hunger, Nuclear Magnetic Resonance Studies on the Acidity of Zeolites and Related Catalysts, Zeolites 1985, 15, 274... 

The gas phase acid-catalyzed synthesis of pyridines from formaldehyde, ammonia and an alkanal is a complex reaction sequence, comprising at least two aldol condensations, an imine formation, a cyclization and a dehydrogenation (9). With acetaldehyde as the alkanal, a mixture of pyridine and picolines (methylpyridines) is formed. In comparison with amorphous catalysts, zeolites display superior performance, particularly those with MFI or BEA topology. Because formation of higher alkylpyridines is impeded in the shape-selective environment, the lifetime of zeolites is much improved in comparison with that of amorphous materials. Moreover, the catalytic performance can be enhanced by doping the structure with metals such as Pb, Co or Tl, which assist in the dehydrogenation. 

A1C13 > stoichiometric amount 1,2-Dichloroethane as solvent Batch reactor Hydrolysis at the end of reaction Destruction of the catalyst Zeolite catalyst No solvent Continuous reactor No water Periodic catalyst Regeneration... 

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