Formation of superbase sites on alkaline earth metal oxides by doping of alkali metals

The generation of superbase sites by doped alkali metals (Li, Na, and K) on alkaline earth metal oxides (MgO, CaO, SrO, and BaO) has been examined. In catalytic activity for the double bond migration of 4,4-dimethyl-1-pentene and 2,3-dimethyl-1-butene, a large increase in the generation of superbase sites was observed with Na- and K-doped MgO, owing to an electron, or pair ed electrons, being trapped. The increase in base-catalytic activity was ve ry small for the other materials. The spin concentration of NO22- radicals, formed by the selective adsorption of NO on strong base sites, was determi ned using ESR. The results are well explained by an increase in site genera tion. When the ionic radius of the alkali metal is smaller than that of the oxide cation, the alkali cation adsorbs onto the superbase sites, which ar e activated by trapped electron(s). The adsorption of small alkali cations interferes with the electrical inductive effect. In the cases of Na- and K- doping on MgO, the adsorption of the alkali cations on the superbase site r esulted in an unstable state, due to insufficient area for their adsorption . As a result, the alkali cations migrated, leading to an increase in site generation. The ratio of the ionic radii of the alkali metal/alkaline earth metal must be 1.46 or larger for the generation of superbase sites.