1-Butene cracking to propene over P/HZSM-5: Effect of lanthanum

HZSM-5 zeolite was modified using diammonium hydrogen phosphate and then lanthanum nitrate by impregnation. The surface structure and properties of P–La co-modified ZSM-5 were studied by the techniques of NH3-TPD, D2/OH isotopic exchange and solid state MAS NMR. In addition to modifying Brønsted acid sites (BAS) in HZSM-5, La additive also interacted with phosphorus species previously bonded to zeolitic hydroxyls or condensed in zeolite. Phosphorus species in zeolite surface were labile to form LaPO4 entity when La was introduced to P/HZSM-5. Hence, some BAS were released which were previously bonded by phosphate. The 1-butene cracking was more dependent on the hydroxyl density, from the measurement of D2/OH isotopic exchange, than the acidity of modified ZSM-5, evaluated from NH3-TPD measurement. For the steamed catalysts, the highest activity was observed on the ZSM-5 co-modified by P and La, in which the number of P atoms surpassed that of lanthanum. Furthermore, the introduced lanthanum stabilized P species in the zeolite from leaching in steam at high temperatures.