Alkaline earth metal oxides with high-surface-area

The most general methodology followed to prepare alkaline earth metal oxides as basic catalysts consists of the thermal decomposition of the corresponding hydroxides or carbonates in air or under vacuum. BaO and SrO are prepared from the corresponding carbonates as precursor salts, whereas decomposition of hydroxides is frequently used to prepare MgO and CaO. Preparation of alkaline earth metal oxides with high surface areas is especially important when the oxide will be used as a basic catalyst, because the catalytic activity will depend on the number and strength of the basic sites accessible to the reactant molecules, which is dependent on the accessible surface area. 

Conjugate addition of methanol to a,jS-unsaturated carbonyl compounds forms a new carbon-oxygen bond to yield valuable ethers. Kabashima et al.[70] reported the conjugate addition of methanol to 3-buten-2-one on alkaline oxides, hydroxides and carbonates at a temperature of 273 K. The activities of the catalyst follow the order alkaline earth metal oxides > alkaline earth metal hydroxides > alkaline earth metal carbonates. All alkaline earth metal oxides exhibited high catalytic activities. The yields obtained after 10 min in a batch reactor with MgO, CaO or SrO exceeded 92 %, whereas with BaO the yield was lower (72 %), probably because of its low surface area (2m2g ). As observed for other reactions, the catalytic activity of MgO strongly depends on the pretreatment temperature. 

Photoluminescence spectra of high surface area samples of alkaline earth oxides have been reported by Tench et al. [39] and interpreted in terms of the radiative decay of surface excitons. Representative data obtained by Tench et al. [39c] with microcrystalline MgO smoke (obtained by combustion of the metal in oxygen) are reproduced in Fig. 5, together with their schematic model for surfaces of the cubic MgO microcrystallites and their modification by exposure to water vapour. 

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