IR STUDY OF ALKENE ALLYLIC ACTIVATION ON MAGNESIUM FERRITE AND ALUMINA CATALYSTS

The interaction of propene and butenes with a butene oxydehydrogenatio n catalyst, MgFe2O4, and with an isomerization catalyst, gamma-Al2O3, have been studied by FTIR spectroscopy. Allyloxy species (prop-2-en-1- oxides from propene and but-3-en-2-oxide from but-1-ene) were observed over MgFe2O4, while allyl species (prop-2-en-1-yl from propene, but-3 -en-2-yl from but-1-ene and 2-methylprop-2-en-1-yl from isobutene), th ought to be sigma-bonded to Al3+ ions, were observed over gamma-Al2O3. It is proposed that in all cases the allylic C-H bond is heterolytica lly broken at cation-anion couples (M(n+)O(2-)) to give rise to anioni c allyls. However, when the cation is reducible, as on the Fe3+ centre s of magnesium ferrite, the allyl anion is further rapidly oxidized to allyloxy species that, at high temperature, can act as cationic allyl s which interact weakly with oxide anions. From propene, the cationic allyls can act as symmetric species, as is expected for acrolein synth esis.