SORPTION AND ACTIVATION OF HYDROCARBONS BY MOLECULAR-SIEVES

Substantial progress has been made recently in the understanding of so rption and activation of alkanes. This progress reflects the emergence of new theoretical and experimental results, leading to a more quanti tative picture of the elementary steps involved in the ordering of alk anes in molecular sieves and their chemical interaction with the acid site. Conversion of n-alkanes over various zeolites is now well unders tood to depend mainly upon the concentration of reactants sorbed. The sorption enthalpy and entropy of these molecules are linearly related and this relationship,is characteristic of a particular molecular siev e (compensation effect). The interfacial chemistry that alkanes and al kenes undergo involves ionic species only in their transition state, w hereas the stable intermediates are covalently bound. This leads to a description of the chemical transformations that resemble nucleophilic and electrophilic substitutions.