Toward Phase and Catalysis Control: Tracking the Formation of Intermetallic Nanoparticles at Atomic Scale

Abstract

Intermetallic nanoparticles (iNPs) have yielded enormous successes in catalytic applications by the formation of ordered phases. However, atomic-level understanding of the alloying mechanism, which plays a pivotal role in controlling intermetallic phases and tailoring their catalytic properties, is still elusive. In this study, we discovered a consecutive formation of ordered Pt3Sn and PtSn phases during the growth of Pt-Sn iNP inside a well-defined nano-reactor at elevated temperature by using in situ scanning transmission electron microscopy. We found that the surface-mediated diffusion of Sn controls overall dynamics of the reaction, while the unique coherent interfacial structure is determinative for the PtSn transformation. We then further controlled the phase selection of Pt-Sn iNPs and demonstrated their distinguishable catalytic behaviors. Our findings not only provide detailed experimental evidence on the alloying mechanism in intermetallic nanoscale systems but also pave the way for mechanistic control of synthesis and catalytic properties of iNPs. How do atoms rearrange in a solid-state reaction to form new structures, especially in catalytic systems with dramatic property difference? Understanding atomic dynamics is key to achieving controlled synthesis of catalysts and other materials. Using advanced electron microscopy, we directly monitor the rearrangement of atoms during a reaction between nanocrystalline Pt and SnO2 and observe consecutive formation of Pt3Sn and PtSn. This real-time imaging provides invaluable understanding of the alloying mechanisms in intermetallic nanoscale systems, which enables precise phase selection and thereby control of the catalytic properties, as we demonstrate for the semi-hydrogenation of acetylene. In pursuit of fully controlled synthesis of intermetallic nanoparticles, our results have made an important step forward in the structure manipulation to serve society with more efficient and affordable energy and chemistry. We have monitored the formation process of Pt-Sn intermetallic nanoparticles at atomic scale by using in situ aberration-corrected transmission electron microscopy. This provides direct imaging of the alloying mechanism in bimetallic nanoscale systems. The surface-mediated Sn diffusion and a coherent Pt3Sn/PtSn interface are responsible for overall reaction dynamics. These new insights allowed us to control the phases of these Pt-Sn iNPs and thereby tune catalysis of the acetylene semi-hydrogenation reaction.