Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

Abstract

Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO ₄ for SiO ₄ tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al–Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.

Abstract

Substitution of framework silicon for aluminium in zeolites affects Brønsted acidity and subsequently catalytic activity. Here, the authors use atom probe tomography to obtain quantitative insights into the spatial distribution of individual aluminium atoms, including their distribution and segregation.