Direct observation of noble metal nanoparticles transforming to thermally stable single atoms

Abstract

Single noble metal atoms and ultrafine metal clusters catalysts tend to sinter into aggregated particles at elevated temperatures, driven by the decrease of metal surface free energy. Herein, we report an unexpected phenomenon that noble metal nanoparticles (Pd, Pt, Au-NPs) can be transformed to thermally stable single atoms (Pd, Pt, Au-SAs) above 900 °C in an inert atmosphere. The atomic dispersion of metal single atoms was confirmed by aberration-corrected scanning transmission electron microscopy and X-ray absorption fine structures. The dynamic process was recorded by in situ environmental transmission electron microscopy, which showed competing sintering and atomization processes during NP-to-SA conversion. Further, density functional theory calculations revealed that high-temperature NP-to-SA conversion was driven by the formation of the more thermodynamically stable Pd-N structure when mobile Pd atoms were captured on the defects of nitrogen-doped carbon. The thermally stable single atoms (Pd-SAs) exhibited even better activity and selectivity than nanoparticles (Pd-NPs) for semi-hydrogenation of acetylene.

Densely Populated Single Atom Catalysts

“…With the development of advanced instruments and characterization techniques, researchers are able to gain deeper insight into the structure of single atoms in the SACs, including its chemical environment and spatial structure. In this section, we would review the specific technologies for analyzing the structure of SACs.…”

In Situ Thermal Atomization To Convert Supported Nickel Nanoparticles into Surface‐Bound Nickel Single‐Atom Catalysts

“…[1] It is urgent to search for the efficient ways to decrease the CO 2 accumulation in air.R ecently,e lectroreduction of CO 2 has been regarded as ap romising approach to decrease CO 2 as well as convert it into the other useful raw materials,such as CO,C H 4 ,C 2 H 4 ,H COOH. [7] As illustrated in Figure 1a,weselect aNCsupport with an average diameter of 200 nm obtained by as imple pyrolysis treatment of ZIF-8 ( Figure S1 in the Supporting Information) as as upport. [3] However,t he main problem is that most of the synthetic methods for single-atoms catalysts are based on the bottomup strategy,i nw hich the metal ions are adsorbed on the defect-containing matrix and then reduced to form single atoms in the whole support.…”

“…[5] TheNiNPs could break surface CÀCb onds.A tt he same time,w hen Ni NPs diffuse within the N-doped carbon matrix, the Ni atoms can be bound to the N-rich defects.A sar esult, Ni NPs are gradually eroded and finally transformed into an atomic dispersion. [7] As illustrated in Figure 1a,weselect aNCsupport with an average diameter of 200 nm obtained by as imple pyrolysis treatment of ZIF-8 ( Figure S1 in the Supporting Information) as as upport. [7] As illustrated in Figure 1a,weselect aNCsupport with an average diameter of 200 nm obtained by as imple pyrolysis treatment of ZIF-8 ( Figure S1 in the Supporting Information) as as upport.…”

In Situ Transmission Electron Microscopy on Energy‐Related Catalysis

“…Transformation from Metal Noble Particles to Thermally Stable Single Atoms (SAs) : In general, single metallic atoms or metal clusters tend to agglomerate during thermal heating processes, showing ripening characters in order to reduce surface energies. By contrast, the work by Wei et al illustrated an inverse phenomenon, noble metal NPs transforming into stable SAs above 900 °C in an inert atmosphere. By using in situ environmental TEM, they directly probed the dynamic processes, the competition between thermal sintering and atomization.…”

“…c) Average diameter and number of particles versus pyrolyzing time at 1000 °C. Reproduced with permission . Copyright 2017, Springer Nature.…”