Platinum determining chemisorbed sites

Only a few years after the existence of active centers was first postulated, Dohse and coworkers in 1930 ( ) determined the site density by what amounts to determining the number of chemisorbed reactant molecules when the reaction is zero order. For isopropanol dehydration over alumina they found a site density— asji min their alumina had a normal surface area—of about 10 cm. In 1937 Kubokawa ( ) used a poisoning method, measuring the amount of mercuric ion which inhibited > 2 decomposition over platinum black. Balandin and Vasser i rg obtained in 1946 ( ) a site density of the order of 10 cm for the dehydration of isopropanol over a mixed oxide of zinc and alumina. 

With the mechanism of hydrogenation of the double bond not being known, the determination of the structural parameters presents a difficult problem. This is related to the question of a correct choice of the reaction site. Ruiifika et al. (78) report correlation of the reaction rates of hydrogenation of 15 olefins on three platinum catalysts in ethanol (48). The existence of an associatively chemisorbed olefin was assumed in this correlation, and the mechanisms of simultaneous and stepwise addition of hydrogen particles were considered. 

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