Fluorine-modified Mg–Al mixed oxides: A solid base with variable basic sites and tunable basicity

Abstract

The fluorine-modified Mg–Al mixed oxides were synthesized by thermal decomposition of the fluorine-containing Mg–Al hydrotalcites, and their physicochemical properties were characterized by ICP, TGA, XRD, FTIR, CO 2-TPD and N 2 adsorption/desorption techniques. It was found that weak basic sites were gradually transformed into moderate and strong basic sites during thermal decomposition, and thus weak basic sites (OH − groups), moderate basic sites (Mg–O, Mg–F and Al–O pairs) and strong basic sites (coordinatively unsaturated F − and O 2− ions) were all produced in the as-prepared samples. Furthermore, the basicity of moderate basic sites could be controlled by the change of fluorine content, which caused the change in the amounts of Mg–F pairs. In the synthesis of propylene glycol methyl ether from methanol and propylene oxide, the base-catalytic performance of the obtained samples was shown to be closely associated with their moderate basic sites.