CATALYTIC BEHAVIOR OF MULTIPHASIC OXIDE CATALYSTS CONTAINING LANTHANIDES (LA, CE, PR, SM, TB) IN THE SELECTIVE OXIDATION OF ISOBUTENE TO METHACROLEIN

The catalytic performances of five lanthanide oxides (La2O3, Sm2O3, Ce O2, Pr6O11 and Tb4O7) for the selective oxidation of isobutene to meth acrolein are evaluated within the framework of the remote control mech anism. Mechanical mixtures of these oxides with typical donor (Sb2O4) or acceptor (MoO3) phases of spill-over oxygen were prepared and teste d for their activity in the isobutene-to-methacrolein oxidation at 400 degrees C. Amongst the five lanthanide oxides tested, only CeO2 and P r6O11 were found to display significant cooperation effects for the in vestigated reaction, with enhanced yields and selectivity for partial oxidation and concomitant decrease of CO2 production. The fresh and us ed catalysts were characterized by X-ray diffractometry, and the occur rence of solid state reactions between the partner oxides outside the reaction conditions was investigated in parallel in the temperature ra nge 400-500 degrees C. No new phase was observed in the case of the mi xtures with La2O3, Sm(2)O3, CeO2 and Tb4O7. Account taken of the absen ce of any new phase in the CeO2-MoO3 system, it can be concluded that CeO2 is a potential donor of spill-over oxygen. The situation in the M oO3-Pr6O11 mixtures is more complex, owing to the generation of variou s praseodymium molybdates, together with the oxocarbonate Pr2CO5. The latter phase was shown to have no intrinsic tendency to produce methac rolein, but it seems that some of the praseodymium molybdates present in the working catalysts may exhibit noticeable catalytic properties.