Particle Hopping and Coalescence of Supported Au Nanoparticles in Harsh Reactive Environments.

Sintering of supported metal nanoparticles (NPs) is a general and important phenomenon in materials and catalysis science. A consensus view is that it takes place either via the Ostwald ripening (OR) or particle migration and coalescence (PMC) mechanism through the substrate, but how sintering occurs under high gas pressure and high temperature has not been addressed. Here, we perform millisecond-scale environmental kinetic Monte Carlo (EKMC) simulations combined with density functional theory (DFT) calculations to reveal a unique through-space sintering mechanism, particle hopping and coalescence (PHC). Under high CO pressure and high temperature, the coalescence of Au NPs takes place through NP hopping up from the anatase TiO2(101) substrate and mass transfer via the gas phase. When the sintered floating NP reaches a critical size, it spontaneously redeposits onto the substrate. This process is driven by the preference of interfacial Au atoms of small NPs to interact with CO rather than the substrate at a high CO chemical potential. The PHC mechanism implies that NP sintering and intersubstrate catalyst transfer may occur easier than expected during reactions and provides a distinct perspective to understand catalyst thermal deactivation under harsh operando conditions.