In-Situ Observations of Non-Classical Crystal Growth of Au Nanoparticles on Hematite

A significant research gap exists regarding the comprehensive investigation of crystallization mechanisms and facet-dependent stability of atomically precise metal clusters on metal oxide nanoparticles. To address this gap, our study focuses on a detailed examination of the sintering process of gold (Au) on facet-controlled hematite (α-Fe₂O₃) {104} and {001} nanoparticles through in-situ TEM observation. Our findings reveal the existence of three distinct crystal growth pathways of Au on hematite nanoparticles: Ostwald ripening, particle coalescence, and disordered intermediate-phase-mediated growth, where particle coalescence plays a dominant role in the sintering process. Furthermore, analysis of Au crystal growth kinetics on different hematite facets highlights the important influence of interfacial structure on the process, where hematite {001} stabilizes Au nanoparticles and suppresses their sintering more effectively than {104} facets. First-principles density functional theory calculations and atomistic molecular dynamics simulations with enhanced sampling provide valuable support for the crystal growth pathway selection of Au nanoparticles on hematite. Our research significantly contributes to the understanding of metal crystallization on hematite surfaces and offers essential guidelines for selecting hematite supports for heterogeneous catalysts.