The Design of Supported Metal Composite Oxides by Selective Metal-Support Exchange

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The objective of this work is the systematic preparation of metal catalysts supported on composite oxides and the correlation of catalytic activity with the properties of the support. In an agueous environment, metal oxides develop a surface charge; the pH at which the charge in zero is defined as the "point of zero charge" (pzc). The pzc of pure silica and that of pure alumina are separated by about 4 units. Selective metal-support exchange uses the surface charge to attach catalyst precursors (metal salts) to the support; thus by adjusting the pH one can selectively introduce anionic or cationic catalyst precursors. Furthermore, by preparing composite oxides of silica and alumina, one can, in principle at least, control the pzc. In this study, supported cobalt catalysts are prepared from both anionic and (separately) cationic precursors on a series of silica/alumina composites, and the activities of the catalysts for butene hydrogenation and cyclopropane hydrogenolysis are correlated with the composition of the support and the method of preparation. This work is an effort to introduce scientific principles and methods into preparation of supported catalysts; traditionally these are prepared using "recipes" that represent more of an art than a science. The study is designed in such a way that it can serve as a "template" to obtain design data on a variety of systems. The principles and approches involved are applicable to preparation of reactive ceramic membranes as well.