CHARACTERIZATION OF POROUS LANTHANUM OXIDE CATALYSTS - MICROSCOPIC AND SPECTROSCOPIC STUDIES

La2O3 catalysts have been characterized by adsorption and surface reac tions of pyridine and propan-2-ol using IR spectroscopy. The La2O3 cat alysts were obtained from two different precursors (lanthanum acetate La(CH3CO2)(3) . 1.5H(2)O (LaAc) and lanthanum acetoacetonate [La(acac) ]) with pretreatment at 800 degrees C. Both catalysts have the same cr ystal structure but are different in their microstructure and surface morphology. IR results indicate that at 25 degrees C, pyridine was irr eversibly adsorbed via coordination to Lewis sites of different acid s trengths. The acidity strength and type of Lewis acid for La(acac) is higher and different from that of LaAc. At 25 degrees C for LaAc, pyri dine cracking occurred with the formation of various surface species, i.e. LaAc is more basic than La(acac). IR results of gas and surface s pecies of propan-2-ol for both catalysts revealed that propan-2-ol is irreversibly adsorbed at 25 degrees C in the form of coordinated molec ules: terminal and bridge-bonded 2-propoxides. These coordinated molec ules are the initial surface intermediates for the dehydration reactio n below 250 degrees C. However, the bridged 2-propoxide species is the precursor for the dehydrogenation reaction (acetone formation). Quant itative analyses of the gas-phase results indicated that the highly cr ystalline, lower surface area and strongly basic LaAc catalyses propan -2-ol dehydrogenation, forming acetone, at 200 degrees C, with higher activity and selectivity for acetone formation than La(acac), which is itself more selective for the dehydration of propan-2-ol to propene. At >350 degrees C, the dehydrogenation product (acetone) was involved in a secondary surface reaction, presumably with the surface hydroxy g roups created from water vapour (dehydration product) giving CH4, CO2 and isobutylene.