Mechanism of 1,2-dichloroethane dehydrochlorination on the acid sites of oxide catalysts as studied by IR spectroscopy

摘要

The adsorption of 1,2-dichloroethane on zeolite HZSM-5 and gamma-Al2O3 at temperatures from 25 to 400A degrees C was studied by Fourier transform IR spectroscopy. The forms of adsorbed 1,2-dichloroethane and the products of its conversion at the Bronsted and Lewis acid sites of catalysts were identified. The kinetics of 1,2-dichloroethane conversion on the surface of catalysts was studied by in situ Fourier transform IR spectroscopy. It was demonstrated that 1,2-dichloroethane was dehydrochlorinated at the Lewis sites of gamma-Al_2O_3 even at 100A degrees C, whereas the reaction came into play at the Bronsted sites of zeolite HZSM-5 only at 200A degrees C. It was found that, at the Lewis acid sites of catalysts, the resulting vinyl chloride underwent oligomerization with the intermediate formation of a dimer (1,3-dichloro-2-butene), whereas the formation of 1,3-dichloro-2-butene at the Bronsted sites of zeolite HZSM-5 was not observed. The mechanisms of 1,2-dichloroethane conversions at Lewis and Bronsted acid sites were proposed.