Comparison of conventional and solid-state ion exchange procedures for the incorporation of lanthanum in H-beta zeolite

Lanthanum-exchanged beta zeolites have been prepared by a solid-state ion-exchange procedure which consists of calcining in static conditions a mechanical mixture of LaCl3.7H(2)O and H-beta zeolite. The exchanged samples have been characterized at various steps of their preparation by XRD, BET, FTIR, TEM, EDS and chemical analyses. The results have been compared to those obtained on samples exchanged in solution. In the case of conventional ion exchange in solution, the incorporation of La into the zeolitic pores is strongly limited due to the steric hindrance caused by the large hydration sphere of the La3+ ions. As a consequence, strongly heterogeneous samples contaminated by La-rich crystalline particles are obtained even at rather low La contents or after repeating the exchange several times. In contrast, the yield for lanthanum incorporation reaches values as high as 100% when the solid-state exchange procedure is used. Moreover, the samples are highly homogeneous and no loss of crystallinity is observed in spite of the very simple conditions used (calcination in static). The exchange by La species of protons initially present in the H-beta parent sample is confirmed by FTIR spectra of OH groups, which also reveal that part of the incorporated La species interact with the silanol groups. (C) 1998 Elsevier Science B.V. All rights reserved.