Negative thermal expansion and cationic migration in zeolite Y used in FCC catalysts

The influence of extra-framework cations on the intrinsic negative thermal expansion (NTE) of calcined ultra-stable and lanthanum-exchanged zeolites Y was analysed. High-temperature thermal behaviour, cationic migration and dealumination were examined by in situ high temperature X-ray powder diffraction and thermogravimetric (TG) analyses. We analysed protonated ultrastable zeolite Y and zeolite Y containing 13% La2O₃ (LaY), and investigated how the presence of La³⁺ influences thermal behaviour of zeolite Y. Uncalcined LaY was also analysed to observe the La³⁺ migration before calcination. Mass loss up to 990℃ was accompanied by TG analyses. X-ray powder diffraction data were analysed by Rietveld method. Our data show that lanthanum migration from supercages to sodalitic cavities is not reversible. However, some La³⁺ migration occurs above 400℃ and we observe emptying of site I', migration to site I and to some extent to site II'. Furthermore, we examined the dealumination process as well. Both samples show two distinct thermal behaviours, positive or near-zero thermal expansion up to 500℃ and NTE above this temperature. Together with intrinsic NTE in faujasite type zeolites, the dealumination process is largely responsible for NTE at high temperatures. (author)