Metal-containing zeolite catalysts for the oxidative acetoxylation of propylene

Миначев, Х. М.; Нефедов, О. М.; Харламов, В. В.; Panov, S. Yu.; Politanskii, S. F.

doi:10.1007/bf01417970

Cited by 2 publications

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“…The oxidative acetoxylation of propene to give allyl acetate has been shown to be selectively catalyzed by ion-exchange zeolites: Pd/Cu-erionite, Pd/Cumordenite and Pd/Cu-faujasite give 90%, 70% and 40% selectivity, respectively. However, the alkali metal ions present in the zeolite before replacement by Pd and Cu may also affect the activity and selectivity of this reaction (20). The direct catalytic oxidation of ethylene with dioxygen to give acetaldehyde with Pd 11 and Cu 1 * in concentrated chloride solution is known as the homogeneous Wacker process.…”

Section: Metal Catalyzed Shape Selectivity In Zeolitesmentioning

confidence: 99%

Shape-Selective Catalysis with Zeolites and Molecular Sieves

Khouw

Davis

1993

ACS Symposium Series

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The types of shape selective catalysis that occur in zeolites and molecular sieves are reviewed. Specifically, primary and secondary acid catalyzed shape selectivity and encapsulated metal ion and zero valent metal particle catalyzed shape selectivity are discussed. Future trends in shape selective catalysis, such as the use of large pore zeolites and electro-and photo-chemically driven reactions, are outlined. Finally, the possibility of using zeolites as chiral shape selective catalysts is discussed.Zeolites are crystalline aluminosilicates that are constructed from TO4 tetrahedra (T = tetrahedral atom, e.g., Si, Al); each apical oxygen atom is shared with an adjacent tetrahedron. Thus, the ratio of O/T is always equal to 2. A S1O4 unit in a framework (structure) is neutral since an oxygen atom bridges two Τ atoms and shares electron density with each ( Figure 1). However, since Al is +3, for every aluminum containing tetrahedron there is a net -1 charge which must be balanced by a cation.The tetrahedra are coordinated such that the zeolites have open framework structures with high surface areas. Access to the cavities is possible through voids of various sizes which are of the size of small molecules. Because of these unique properties, zeolites are able to be shape and size selective in catalytic molecular rearrangements.Approximately 70 distinct structures of zeolites and molecular sieves are known (2). There are natural zeolites, synthetic analogues of natural zeolites, and synthetic zeolites with no natural counterparts. Their pore sizes range from 4 Â to 13 À as illustrated in Figure 2. Zeolites with pores that are comprised of eight T-atoms (and eight oxygen atoms) are consider small pore zeolites. They have free diameters of 3.0-4.5 À, e.g., zeolite A. Medium pore zeolites have pores formed by ten T-atom rings with 4.5-6.0 Â free diameter, e.g., ZSM-5. Zeolites with twelve or more T-atoms in rings that make-up the pores are consider large pores zeolites. They have free diameters of 8.0 A or more, e.g., zeolite X and Y (3). To date, no zeolite (aluminosilicate) exists with pores larger than ~ 8 À. In addition to zeolites, there are now many non-aluminosilicate molecular sieves. Referring to Figure 1, if tetrahedra containing aluminum and phosphorous are connected in a strict Al/P = 1, a neutral framework is obtained. The aluminophosphate or AIPO4 is the "3-5" analogue of the "4-4" pure S1O2. Also, other elements can be incorporated into the AIPO4 framework

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Section: Metal Catalyzed Shape Selectivity In Zeolitesmentioning

confidence: 99%