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

Abstract

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 NH 3-TPD, D 2/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 LaPO 4 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 D 2/OH isotopic exchange, than the acidity of modified ZSM-5, evaluated from NH 3-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.