Monitoring by in situ neutron diffraction of simultaneous dehydration and Ni2+ mobility in partially exchanged NaY zeolites

Abstract

Powder neutron diffraction is used to follow structural changes occurring during heat and vacuum assisted dehydration of 3 wt% nickel exchanged NaY. The structures determined from Rietveld refinement confirm the nickel ion displacement from the supercages and sodalite cages towards hexagonal prisms upon water removal. Not only this mobility but also its relationship with the dehydration level is demonstrated, owing to real time quantification of dehydration through changes in the intensity of the incoherent neutron scattering signal. Comparison with TGA data proves that this signal is fully attributable to water molecules adsorbed in the zeolite. STEM/EDX and in situ heating TEM studies provide complementary information on homogeneous Ni distribution (initial state) and on reductive sintering in vacuum at a high temperature.