Temperature-Induced Structural Changes in Acidic L-Zeolite: An In Situ Synchrotron Time-Resolved Powder Diffraction Study

Zeolite L (K6Na3Al9Si27O72 & BULL;21H(2)O, the synthetic counterpartofthe mineral perlialite) has important catalytic properties, the efficiencyof which derives from the high acidity due to the presence of Bronstedsites (BAS), enhanced by the synergistic activity with Lewis sites(LAS) with increasing temperature. In this work, we carried out adetailed structural characterization of the acid form of this zeolite(H-LTL) by in situ time-resolved synchrotron X-raydiffraction from room temperature up to 800 & DEG;C on a powderedsample in order to obtain the structural response to heating. Despitethe fact that the crystallinity is maintained when the maximum temperatureis reached, thermal pathways show significant distortions of channelaperture as well as differences in host-guest interactions.The distortion of the T2 polyhedron and the progressive widening ofthe O3-T2-O5 angle suggest the formation of a Lewisacid site from the progressive conversion of BAS on O5 at 550 & DEG;Cduring heating. The in situ synchrotron X-ray diffractiondata provided reliable evidence of the high thermal stability of theacidic L-zeolite and the adaptable behavior of the framework duringthe evolution of the BAS to LAS.