(693f) Stability and Reactivity of Encapsulated Monomeric and Dimeric Pt Clusters in Chabazite Framework

Supported Pt atoms are excellent catalysts for small alkane dehydrogenation. Single atom catalysts and low nuclearity clusters are viable options as they show high activity and are atom efficient. The challenge, however, lies in stabilizing Pt atoms on supports as they tend to sinter and lose catalytic activity at high temperatures. Recently, it has been shown that encapsulating Pt clusters in microporous materials such as zeolites enhances the stability of these catalysts¹. Incorporating heteroatoms such as Sn into the framework promotes homogenous dispersion of Pt clusters in the zeolite by serving as anchoring points². We aim to use computational methods to understand the catalyst stability and activity.

In this work, we first used Density-Functional Theory (DFT) to investigate all possible stable monomeric and dimeric Pt(0) species in CHA and Sn-CHA in the presence and absence of defects, namely silanol clusters and Al(III)-introduced Brønsted acid sites. For the defect-free CHA, single Pt atoms are stabilized by weakening an Si-O bond at the intersection of a 6- and 4-membered ring. In the presence of both silanol clusters and Brønsted acid sites, Pt single atoms are stabilized by weakening the -OH bond. In Sn-CHA, Pt atoms are stabilized by coordinating with the framework Sn in the absence of defects, whereas the defects stabilized Pt over framework Sn. Using insights from these DFT studies, we performed free energy ab initio molecular dynamics (AIMD) simulations to investigate the kinetic stability of these sites and understand the effect of entropy at 900K on the relative stability of several electronically comparable sites. Lastly, we evaluated the catalytic activity of these sites towards small alkane dehydrogenation on the most stable sites, guided by DFT and AIMD.

1. Moliner, M. et al., ACS Catalysis 2018, 8 (10), 9520-9528.
2. Xu, Z. et al., ACS Catalysis 2020, 10 (1), 818-828.