Effect of adsorption of potassium iodide on catalytic activity of plate-type Raney nickel.

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An experimental investigation was made of the adsorptive activity of Raney nickel catalyst toward potassium iodide over a wide KI concentration range and of the change with KI adsorption of hydrogenating activity toward unsaturated alcohol and ketone. Adsorbed amounts of K+ and I− ions were determined by potentiometry and radioactivity measurement. The adsorptive activity vs. I− concentration relation yields a definitive break at equilibrium concentration 5.5×105 mol dm−3 (surface coverage 26%), the adsorption features in the lower and higher ranges relative to the break point being approximately represented by Freundlich's and BET equations, respectively. Adsorption sites effective for I− ion in the Freundlich region disappear almost completely when the catalyst is preheated at 600 °C. The surface coverage causing the hydrogenation activity to decrease by 50% is 3% for allyl alcohol and 0.3% for 2-butanone. With allyl alcohol, however, even such a catalyst as has preadsorbed ca. 5-monolayer amount of I− ions possesses a 33% residual activity, though catalyst coverages over 26% result in only a little decrease in activity. These results suggest that the adsorption sites in the Freundlich region may function as strong catalytically active centers for the hydrogenation, which are unstable to heating.
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