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

Alumina-supported KF (KF/alumina) catalysts containing different amounts of KF were characterized by XRD, XRF XPS, and F-19 MAS NMR to elucidate the c atalytically active sites, whose appearance varies much with the pretreatme nt temperature. The reactions examined are double bond isomerization of 1-b utene and 1-pentene, Tishchenko reaction of pivalaldehyde, and Michael addi tion 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 lo aded with 1.2 and 4.6 mmol KF/g-catalyst exhibited the activities only in t he 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 ra nge 473-773 K, For the Michael addition, the activity of Fluka-KF/alumina d id not vary much with the pretreatment temperature, though the maximum acti vity was obtained when the sample was pretreated at 623 K. Although the main species containing F was K(3)AIF(6) formed by the reactio n of KF with alumina, which was observed by both XRD and F-19 MAS NMR, it w as not related to the formation of active sites. The surface species releva nt to the catalytic activities, in particular for the double bond isomeriza tion and Tishchenko reaction, is the F- containing species which gives a pe ak at - 150 ppm in 19F MAS NMR. (C) 2000 Elsevier Science B.V. All rights r eserved.