An Atomic-Scale Study On Sintering Behaviors Of Metal Nanocatalysts On Surfaces Of Two-Dimensional Carbon Materials Via In Situ Transmission Electron Microscopy

Supported metal nanocatalysts have found their wide applications in modern chemical engineering,organic synthesis,environmental protection.etc.These catalysts are generally metal nanoparticles dispersed on supporting materials,designing for maintaining the high catalytic activities of small metal nanoparticles while decreasing their using amount and increasing their dispersity.However,thermal-induced sintering of small metal nanoparticles into larger ones of nanocatalysts acts as the major challenge during their preparations and applications,which greatly reduces the atomic utilization of metal catalysts and then severely decreases productivity.Therefore,understanding and thus relieving the thermal-induced sintering of supported nanocatalysts is a research focus to propel their practical applications.Recently,many experimental evidences have described the central role of metal-support interaction(MSI)in determining the sintering resistance of metal nanocatalysts,and theoretical calculations have proven that strong/weak MSI can impact the sintering resistance of metal NPs via different sintering kinetics.But,so far,there is still a lack of efficient description on the relationship between MSI and sintering resistance,and the underlying nexus for MSI-sintering mechanism is almost elusive for the community.In situ transmission electron microscopy(TEM),with its rapid technical advances and high spatiotemporal resolution,enables us the capability to examine nanoscale“processing” dynamics in simulated environments.Herein,we used two kinds of twodimensional(2D)carbon materials(graphene and hydrogen-substituted graphyne(Hs GY))as supports,and studied the sintering evolution of metal nanoparticles on the supports by in situ TEM and theoretical simulations methods.The key research contents are as follows:By using in situ TEM,we show a direct observation concerning the sintering of metal nanocatalysts on 2D carbon graphene and Hs GY supports.It is suggested that the significant sintering resistance of supported nanoparticles on Hs GY originates from the Ostwald ripening(OR)mechanism due to strong MSI,whereas graphene has only weak MSI with nanoparticles and hence the dominant mechanism of sintering is particle migration and coalescence(PMC).To fully reveal the relationship between MSI and sintering mechanism,we further analyzed the sintering behavior of Pd nanocatalysts supported on Hs GY and graphene from the perspectives of thermodynamics and kinetics with density functional theory(DFT)calculations and molecular dynamics(MD)simulations.Combined with our electron energy loss spectroscopy(EELS)analysis on the catalyst,we found that the stronger incomplete charge transfer interaction(ICTI)between metal NPs and Hs GY controls the sintering mechanism in OR regime and leads to remarkable sintering resistance.Finally,we also observed the sintering process of Pt and Au nanoparticles on Hs GY with in situ TEM,and also found their excellent sintering resistance.In summary,our experimental and theoretical results directly reveal the relationship between "thermal stability-sintering mechanism-ICTI/MSI" for supported catalysts,and may pave a new avenue toward the design of anti-sintering highperformance nanocatalysts.