Modified zeolites, advantages

Researchers state that modified zeolite has the following potential advantages ... 

The use of surfactant-modified zeolite (SMZ) as a permeable barrier sorbent may offer several unique advantages when dealing with mixed contaminant plumes. Zeolites are hydrated aluminosilicate minerals characterized by cage-like structures, high internal and external surface areas, and high cation exchange capacities. Both natural and synthetic zeolites find use in industry as sorbents, soil amendments, ion exchangers,... 

Since then chemists worldwide have prepared numerous tailor-made modified zeolites, and the synthetic potential for the production of organic intermediates and high-value fine chemicals is enormous. How can the success of this new class of catalysts in industry and academe be explained It is due to the outstanding catalytic properties of the zeolites. No other class of catalysts offers so much potential for variation and so many advantages in application. Their advantages over conventional catalysts can be summarized as follows ... 

The wide-pore H-Beta zeolite has strong Bronstcd acid hydroxyl groups and other advantage chemical environment which govern the adsorption and consecutive conversion of methanol to dimethyl ether and further to hydrocarbons, mostly isobutane. This character can be modified by Fe ion-exchange. 

Dispersion of POMs onto inert solid supports with high surface areas is very important for catalytic application because the surface areas of unsupported POMs are usually very low (—10 m2g). Another advantage of dispersion of POMs onto inert supports is improvement of the stability. Therefore, immobilization of POMs on a number of supports has been extensively studied. Silica and active carbon are the representative supports [25], Basic supports such as MgO tend to decompose POMs [101-104], Certain kinds of active carbons firmly entrap POMs [105,106], The maximum loading level of POMs on active carbons is 14 wt% [107], Dispersion of POMs onto other supports such as zeolites, mesoporous molecular sieves, and apatites, is of considerable interest because of their high surface areas, unique pore systems, and possibility to modify their compositions, morphologies, and sorption properties. However, a simple impregnation of POM compounds on inert supports often results in leaching of POMs. 

Recently Mikae et al. (66) showed that NaY zeolite impregnated with NaCl solution can be used as a para selective catalyst for chlorination of chlorobenzene, which is indeed another example of zeolite modified advantageously by means of monolayer dispersion of salts. 

Zeolites also appear to be suitable supports for the formation of small bimetallic clusters between components which are immiscible as bulk metals. The Ru/Ni zeolite Y methanation catalyst is an interesting example (234) where the properties of a single active metal component could be advantageously modified. 

The following examples reflect the main advantages of SIMS analysis the microanalysis of elements at trace level in the case of catalytic cracking catalysts (FCC). the sensitivity to light elements for the study of coke distribution and the possibility of providing composition profiles on zeolites modified by chemisorption of metals. 

The zeolites and modified clays (PIL-clays) are suitable products over which metallic phases can be dispersed to obtain a bifunctional catalysts providing the acid and basic centres on the mentioned structures. In addition, clays and zeolites have the advantage as supports that they are chemically and physically robust and inexpensive [1]. In our study we chose the hydrogenation of acetone, in which acetone is competitively transformed through bifunctional catalysts into 2-propanol (IPA) and methyl isobutyl ketone (MIBK). 

A huge number of catalysts for the cyclization of citronellal to isopulegol have been described. Newer developments offer advantages in diastereoselectivity and yield through the use of modified silicon dioxides or zeolites [82c]-[82e],... 

For application of zeolites as catalysts in industrial processes, high activity and easy removal of coke deposits are required. To meet these requirements, small crystals of zeolites (0.5-1.0 (im) should be advantageously used. On the other hand, the para-shape selectivity of zeolites in alkylaromatic transformations is connected especially with large crystals of the ZSM-5 zeolite structure, modified by silicon, boron, magnesium and phosphorus [1-5], However, no definite conclusion has been drawn on the contribution of various species to restricted transport of the bulkier isomers through the zeolite crystals, selectivity of the initial... 

The development of catalytic converters has recently encompassed the use of zeolites, e.g. Cu-ZSM-5 (a copper-modified ZSM-5 system), but at the present time, and despite some advantages such as low light-off temperatures, zeolite-based catalysts have not shown themselves to be sufficiently durable for their use in catalytic converters to be commercially viable. 

More and more, solid catalysts like zeolites, clays or resins are used instead of traditional catalysts. Thus, zeolites are good catalysts for the acylation of non-heterocyclic aromatic compounds, both in the gas phase [2] and in the liquid phase [3]. The acylation of thiophene and of furan can also be carried out in the gas phase with M-5 catalysts [4]. Lasdo and co-woikers have shown that modified clays like montmorillonite doped with ZnCl2 can catalyse the reactioi of arenes with substituted benzoyle chlorides in good yields [5] (70 to 100%). Delmas and co-workers have reported the acylation of furan by carboxylic acids with nafion-H [6] (sulfonic resin) and duolite [7] (ion exchanged phosphonic resin). One of the advantages of these catalysts is the safety of environment. Actually, the use of homogeneous catalysts causes problems of corrosion, waste and troublesome workups [8,9]. 

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