Structural stability and uniformity of magnetic Pt nanoparticles in NaY zeolite.

Based on first-principles calculations, the structural stability and magnetic variety of Pt nanoparticles encapsulated in a NaY zeolite are investigated. Among 50 stable isomers in the gas phase, due to geometrical constraints, only about 1/3 of those clusters can be inserted in the zeolite pores. Severe structural rearrangements occur depending on whether the solid angle at the Pt vertex bound to the super-cage is larger than 2 sr (i.e., icosahedron). The most relevant example is the structural instability of the icosahedron and, when including van der Waals dispersion forces the opening of the gas phase global minimum moves towards a new L-shaped cubic wire, otherwise unstable. The total magnetisation of the encapsulated Pt decreases due to the stabilisation of less coordinated isomers, with the majority of clusters characterised by a total magnetisation of 2μ, while the majority of free clusters exhibit a threefold value. This analysis allows the understanding of the magnetic behaviour observed in recent experiments through the variety of the isomers which can be accommodated in the zeolite pore.