Two reactions, two sites, two adsorption coefficients: a kinetic and mechanistic study of the dehydration of 2-octanol on amberlyst®15 catalyst

On dry Amberlyst®15 catalyst at 80 °C, 2-octanol undergoes irreversible dehydration to water and octenes. Ether formation is negligible, and reversible alkene double bond isomerization is slow. Kinetic data indicate that two different types of catalytic sites are active. On one site, all adsorbates have large (> 10) adsorption coefficients, and dehydration occurs here by a single site mechanism; on the second site, all adsorbates (except water) have small (< 0.2) adsorption coefficients. Dehydration and alkene double bond isomerization occur on both sites but at separate rates on each site. The site with weak adsorption loses activity rapidly as water forms, while the site with strong adsorption remains active much longer than the other and catalyzes most of the dehydration. Water adsorbs strongly to both sites and inhibits dehydration and double bond isomerization both by competing for vacant active sites and by displacing adsorbed 2-octanol (but not alkenes) directly from the active sites. The existence of two different types of active sites that lose activity at substantially different rates early in the reaction sometimes confounds the interpretation of initial rate data.