文摘
The ceria- and lanthana-modified MFI zeolites were prepared and extensively investigated to verify the function of lanthanide oxides as blocking modifiers. Their catalytic behavior in the methanol-to-olefin (MTO) conversion was explained by the characterization results regarding crystallinity, agglomeration, porosity, surface composition, and the uptakes of o-xylene and methanol. The ceria impregnated on the MFI formed nano-sized small particles with two oxidation states of +3 and +4 (Ce2O3 and CeO2) on the surface and was located predominantly on the external surface. So, the ceria impregnation maintained the porosity and activity of the MFI, and induced little change in the conversion and product composition of MTO. However, the lanthana impregnated on the MFI dispersed as a single lanthana (La2O3) phase in its micropores, as well as on the external surface. The blocking of the micropores and reduction of acidity by lanthana impregnation lowered the activity of the lanthana-modified MFI in MTO. The ceria located on the external surface of MFI did not have any negative effects on the catalytic performance, while the lanthana dispersed in the micropores lowered the conversion in MTO. The locations and dispersed states of ceria and lanthana were systematically discussed in the relation to their catalytic performance as blocking modifiers.
