DFT Study of Pt Particle Growth inside β-Zeolite Cages

Abstract

The preferred location and the corresponding energetics of zeolite-embedded single metal atoms and small metal particles are hot topics within active site optimization and catalyst tuning, even as part of bifunctional materials design. In this context, periodic density functional theory was used to provide insights on the interactions of a platinum atom with the microporous cages of a purely silicious β-zeolite (BEA) framework. Cluster growth was subsequently addressed, up to Pt3@BEA systems, following a one-by-one platinum atom addition; platinum migration between cages was taken into account as well. An unbiased approach was employed, which allowed a wide panorama of structures being considered in addition to a thorough analysis in terms of energetics, cluster geometries, and cavity distortions. Calculations revealed that the optimal interaction geometry for a single platinum atom is realized where two strong Pt-O bonds in almost linear arrangement can form, regardless of the cavity involved. This can cause distortions or even breaking of the zeolite structure, a factor which however is not decisive in determining the energetics of systems with two and three platinum atoms. Platinum migration is associated with energy barriers ranging from 100 to 200 kJ mol-1, depending on the cages. Up to the dimensions considered here, preference for clustering is observed, being the embedded Pt3 systems in almost all cases energetically favored with respect to isolated atoms within the BEA framework.