Activity for base-catalyzed reactions and characterization of alumina-supported KF catalysts Original Research Article

Alumina-supported KF (KF/alumina) catalysts containing different amounts of KF were characterized by XRD, XRF, XPS, and 19F MAS NMR to elucidate the catalytically active sites, whose appearance varies much with the pretreatment temperature. The reactions examined are double bond isomerization of 1-butene and 1-pentene, Tishchenko reaction of pivalaldehyde, and Michael addition of nitromethane to butene-2-one. The pretreatment temperature range in which the catalysts exhibited the activities depends on the loading of KF. For the double bond isomerization and Tishchenko reaction, the catalysts loaded with 1.2 and 4.6 mmol KF/g-catalyst exhibited the activities only in the pretreatment temperature range 573–873 K, and the catalyst loaded with 8.2 mmol KF/g-catalyst (Fluka-KF/alumina) exhibited the activities in the range 473–773 K. For the Michael addition, the activity of Fluka-KF/alumina did not vary much with the pretreatment temperature, though the maximum activity was obtained when the sample was pretreated at 623 K.Although the main species containing F was K3AlF6 formed by the reaction of KF with alumina, which was observed by both XRD and 19F MAS NMR, it was not related to the formation of active sites. The surface species relevant to the catalytic activities, in particular for the double bond isomerization and Tishchenko reaction, is the F− containing species which gives a peak at −150 ppm in 19F MAS NMR.