Zeolites metal-proton adducts

T. J. McCarthy, G.-D. Lei, and W. M. H. Sachtler, Methylcyclopentane conversion catalysis over zeolite Y encaged rhodium a test for the metal-proton adduct model, J. Catal. 159, 90-98... 

The dependence of the electron deficiency of Pd or Pt particles on the proton concentration of zeolites suggests a direct bond between metal particles and some protons (70). A model is the metal-proton adduct, e.g., [Pd Hm] , where m is the number of protons in the adduct. This leaves still two possibilities for the actual structure of this complex. One might assume that the protons in the adduct are either totally detached from the zeolite wall or that they act as bridges of the type Pd —O2, where Oj stands... 

In these samples the electron deficiency appears clearly related to the proton concentration of the supporting zeolite. The results indicate a direct interaction of Pd with protons, in accordance with the metal-proton adduct model. 

Recent results are presented illustrating principal mechanistic differences between alkane isomerization in liquid acids and over solid acids, including bifunctional catalysts. Isotopic labeling shows that butane isomerization over solid acids proceeds preferentially as a bimolecular process, i.e. via a Cg intermediate, which subsequently decomposes, preferentially into two iso-Cn structures. Bronsted acid sites in zeolites form chemical bonds with metal clusters. The resulting metal-proton adducts function as "collapsed bifunctional sites". 

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