Role of basic and acidic centers of MgO and modified MgO in catalytic transfer hydrogenation of ketones studied by infrared spectroscopy

In this study our aim was to identify the active sites and the surface spec ies responsible for deactivation of MgO during catalytic transfer hydrogena tions (CTH) of ketones using alcohols as hydrogen donors. Our previous stud ies showed that deactivation of MgO could be prevented by previous treatmen t with chloromethanes. Therefore the surface species formed during the reac tion were studied before and after treatment with chloroform or chloroform- d by in situ infrared spectroscopy (IR). As a result, it was concluded that the reaction requires the presence of surface basic and acidic centers. Th e presence of Lewis acid centers was not necessary, the reaction could proc eed on weakly acidic surface Bronsted sites, as the alterations in intensit y and position of the nu(OH) bands indicated. Modification with chloroform resulted also in the generation of surface OH groups with a proper acidity for the reaction. The shift in carbonyl vibrations led us to the conclusion that Lewis acid and base centers were responsible for the catalyst poisoni ng, so covering these acid sites by Cl- led to a stable catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.