Revealing Sintering Kinetics of MoS 2 -Supported Metal Nanocatalysts in Atmospheric Gas Environments via Operando Transmission Electron Microscopy.

The decoration of two-dimensional (2D) substrates with nanoparticles (NPs) serve as heterostructures for various catalysis applications. Deep understanding of catalyst degradation mechanisms during service conditions is crucial to improve the catalyst durability. Herein, we studied the sintering behavior of Pt and bimetallic Au-core Pt-shell (Au@Pt core-shell) NPs on MoS ₂ supports at high temperatures under vacuum, nitrogen (N ₂ ), hydrogen (H ₂ ), and air environments by in situ gas-cell transmission electron microscopy (TEM). The key observations are summarized as effect of environment: while particle migration and coalescence (PMC) was the main mechanism that led to Pt and Au@Pt NPs degradation under vacuum, N ₂ , and H ₂ environments, the degradation of MoS ₂ substrate was prominent under exposure to air at high temperatures. Pt NPs were less stable in H ₂ environment when compared with the Pt NPs under vacuum or N ₂ , due to Pt-H interactions that weakened the adhesion of Pt on MoS ₂ . Effect of NP composition: under H ₂ , the stability of Au@Pt NPs was higher in comparison to Pt NPs. This is because H ₂ promotes the alloying of Pt-Au, thus reducing the number of Pt at the surface (reducing H ₂ interactions) and increasing Pt atoms in contact with MoS ₂ . Effect of NP size: The alloying effect promoted by H ₂ was more pronounced in small size Au@Pt NPs resulting in their higher sintering resistance in comparison to large size Au@Pt NPs and similar size Pt NPs. The present work provides key insights into the parameters affecting the catalyst degradation mechanisms on 2D supports.