Catalyst continued zeolite

As was shown here in some examples, the field of catalysis over zeolites, although marnre, is still very much alive. The chemists who work with the synthesis zeolites continue to be very creative, the focus now being placed on the synthesis of materials that can catalyze reactions other than the acidic ones and/or reactions of bulkier molecules, that is, synthesis of zeolites with larger micropores or with a very large external surface, such as nanosize and delaminated zeolites. New concepts related to the mode of action of zeolite catalysts continue to emerge, as shown here with the shape selectivity of the external surface. These concepts are particularly useful to scientifically design selective and stable catalysts. 

Of the various mechanical properties of a formed catalyst containing zeolite, attrition resistance is probably the most critical. This is particularly the case for FCC catalysts because of the impact on the addihon rate of fresh catalyst, particulate emissions of fines and overall catalyst flow in the reactor and regenerator. Most attrition methods are a relative determination by means of air jet attrition with samples in the 10 to 180 xm size range. For example the ASTM D5757 method attrites a humidified sample of powder with three high velocity jets of humidified air. The fines are continuously removed from the attrition zone by elucidation into a fines collection assembly. The relative attrition index is calculated from the elutriated fines removed at a specific time interval. 

Molecular sieve zeolites have become established as an area of scientific research and as commercial materials for use as sorbents and catalysts. Continuing studies on their synthesis, structure, and sorption properties will, undoubtedly, lead to broader application. In addition, crystalline zeolites offer one of the best vehicles for studying the fundamentals of heterogeneous catalysis. Several discoveries reported at this conference point toward new fields of investigation and potential commercial utility. These include phosphorus substitution into the silicon-aluminum framework, the structural modifications leading to ultrastable faujasite, and the catalytic properties of sodium mordenite. 

Existing processes can be improved by simple exchange of conventional catalysts with zeolite catalysts however, the process and the reaction parameters continue to be the same. 

Insofar as heterogeneous Cu(I)-catalyzed click chemistry is concerned, new catalysts continue to appear. Nanoparticles of copper can be generated and used in aqueous solution, from which crystalline products often precipitate. Inclusion of copper (as CuCl) into Lewis acidic zeolites, using in particular Cu(I)-USY (pore size 6-8 A), is one such catalyst employed in toluene. Other solvents such as DCM, CH3OH, CH3CN, and benzene were not recommended, and yields of 1,4-disubstituted triazoles can be highly variable. 

In 1962, the most important catalytic breakthrough of the FCC process took place when a component, known as Zeohte-Y, was added to the active alumina catalyst. It has been found that by adding small amounts of zeolite into the matrix of the older sihca-alumina catalyst, a new catalyst was produced. Such a catalyst had an outstanding performance, much better than any catalyst before. The zeolite catalyst greatly improved the gasoUne yield (Table 1). The first commercial zeolite catalysts were introduced in 1964, and zeoUte catalysts continue being used today. 

The development of ultrastable Y-zeolite catalyst led to the production of gasoline with higher olefin content and increased octane niunber. However, the need for improved catalysts continued because the zeohte was not sufficiently stable and the motor octane number did not rise as much as the research octane number. As discovered previously with other zeolites in the 1960 s, partial exchange of USY-zeolite with rare earth (REUSY) gave better stability as well as activity and provided more branched hydrocarbons and aromatics. Both motor octane number and gasoline production could thus be increased. 

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). 

In the present study the effect of zeolite particle size (micro- vs. nano-particles) and N20 concentrations on ODHP is studied over Fe modified BEA zeolites. The feasibility of periodic reactivation over Fe-BEA catalysts by oxygen pulses for continuous C3H6 production has been also evaluated. 

EBMax A continuous, liquid-phase process for making ethylbenzene from ethylene and benzene, using a zeolite catalyst. Developed by Raytheon Engineers and Constructors and Mobil Oil Corporation and first installed at Chiba Styrene Monomer in Japan in 1995. Generally similar to the Mobil/Badger process, but the improved catalyst permits the reactor size to be reduced by two thirds. 

Corma and Renz6 developed an effective heterogeneous catalyst system. Incorporation of tin into a beta zeolite network (Sn-Beta) gave a catalyst that was used to convert citronellal 5 to racemic isopulegol (6, Equation (3)) with 85% diastereoselectivity. It was calculated that each metal site performed 11,500 reaction cycles. No leaching of the tin was detected. This catalyst system is advantageous over normal Lewis acids, since precautions against humidity are not required, and it is suitable for use in a fixed bed continuous reactor. 

The liquid phase alkoxylation of limonene (3) with C4-C4 alcohols to 1-methyl-4-[a-alkoxy-isopropyl]-l-cyclohexene (5) was carried out both in batch and continuous fixed-bed reactor at 60 °C on various acidic catalysts (Scheme 3.1) [16]. The best yields were obtained in batch (85%) or continuous reactor (81%) using a /1-type zeolite with Si02/Al203 = 25. 

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