The Technique of Physically Mixed Catalyst Components

The simplest direct method for testing the cooperative action of catalyst components consists of a comparison of conversion results between experiments where only catalyst particles of type X, only of type F, and where a loose mixture of the same amounts of X and F particles have been placed into the reaction zone, under otherwise similar contact conditions. Polystep action is then indicated if the extent of reaction in the latter case is seen to exceed the sum of the conversions in the two single component contact runs. 

In a given experiment the observed effect may, of course, be immeasurably small due to diffusion effects discussed in Section II,D. In that case, a sufficient lowering of the component particle size may uncover the effect. If the effect can be thus demonstrated to exist, a study of the dependence of catalytic effectiveness on the component particle size can be used to yield information concerning the magnitude of vapor pressure of the intermediates, in accordance with Section II,D,3. 

For porous oxide particles a size-range down to about 60m diameter can be obtained by conventional crushing and grinding techniques. Smaller particle sizes are obtained by conventional ball-milling, thus reaching a size range of the order of 1-5m. 

In studies of dual-functional catalysis the mixed catalyst technique has many advantages, two of which are mentioned. (1) It allows separate and independent preparation of each component for example, a platinum preparation can be made in any manner desired in order to obtain a certain platinum activity without regard to what such procedures might do to the acidic properties of the oxide base, this interdependence always being a matter of concern in conventional direct impregnation techniques. (2) A component s relative activity contribution can be flexibly varied in a perfectly known and controllable manner by simply varying its bulk amount in admixture with the other. 

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