Acid-base properties and active site requirements for elimination reactions on alkali-promoted MgO catalysts

Base-catalyzed elimination reactions were studied on MgO and alkali-modified MgO catalysts using 2-propanol as a probe reactant. The effect of the acid-base properties on the catalyst activity and selectivity was investigated by modifying the surface properties of MgO with 1 mol% of alkaline metals. Group IA metals promote the formation of medium- and high-strength basic sites, thereby increasing the basic site density and strength. The addition of alkaline promoters improves the MgO activity for 2-propanol conversion reactions. The selectivity toward dehydration or dehydrogenation products depends on the base site nature, so that intermediate-strength base sites promote acetone formation, whereas high-strength base sites selectively yield propylene. 2-Ppropanol decomposition to acetone and propylene is proposed to take place via an E-1cB mechanism in two parallel pathways sharing a common 2-propoxy intermediate. (C) 2000 Elsevier Science B.V. All rights reserved.