Location within zeolite matrix

Powders possessing relatively high surface area and active sites can be intrinsically catalytically active themselves. Powders of nickel, platinum, palladium, and copper chromites find broad use in various hydrogenation reactions, whereas zeolites and metal oxide powders are used primarily for cracking and isomerization. All of the properties important for supported powdered catalysts such as particle size, resistance to attrition, pore size, and surface area are likewise important for unsupported catalysts. Since no additional catalytic species are added, it is difficult to control active site location however, intuitively it is advantageous to maximize the area of active sites within the matrix. This parameter can be influenced by preparative procedures. 

Related to this aim is the preparation of MgO powders by chemical vapor deposition [6], and the dispersion of MgO on Si02 [7] and within the cavities of faujasite zeolites [8]. Noticeably, in the last case, the location of the basic oxide inside a porous matrix was intended for the introduction of an additional shape selectivity effect related to the host structure. However, the access to the faujasite cavities with a diameter of ca. 7 A is limited, and bulky reactant cannot reach the inner catalytic active centers. 

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