Determination of the Evolution of Heterogeneous Single Metal Atoms and Nanoclusters under Reaction Conditions: Which Are the Working Catalytic Sites?

Abstract

Identification of active sites in heterogeneous metal catalysts is critical for understanding the reaction mechanism at the molecular level and for designing more efficient catalysts. Because of their structural flexibility, subnanometric metal catalysts, including single atoms and clusters with a few atoms, can exhibit dynamic structural evolution when interacting with substrate molecules, making it difficult to determine the catalytically active sites. In this work, Pt catalysts containing selected types of Pt entities (from single atoms to clusters and nanoparticles) have been prepared, and their evolution has been followed, while they were reacting in a variety of heterogeneous catalytic reactions, including selective hydrogenation reactions, CO oxidation, dehydrogenation of propane, and photocatalytic H2 evolution reaction. By in situ X-ray absorption spectroscopy, in situ IR spectroscopy, and high-resolution electron microscopy techniques, we will show that some characterization techniques carried out in an inadequate way can introduce confusion on the interpretation of coordination environment of highly dispersed Pt species. Finally, the combination of catalytic reactivity and in situ characterization techniques shows that, depending on the catalyst–reactant interaction and metal–support interaction, singly dispersed metal atoms can rapidly evolve into metal clusters or nanoparticles, being the working active sites for those abovementioned heterogeneous reactions.

One-Step High-Temperature-Synthesized Single-Atom Platinum Catalyst for Efficient Selective Hydrogenation

“…The stability of SACs is a critical issue for their practical applications [15][16][17]. It was reported that the presence of subnanometer clusters in SACs can affect the overall thermal stability [18][19][20][21][22][23]. Tremendous efforts are made to improve the thermal stability by enhancing the metal-support interactions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

Insights into the Mechanism of n-Hexane Reforming over a Single-Site Platinum Catalyst

“…N or O), has opened up a new research frontier in the catalysis field. [1][2][3][4] Many catalytic reactions have been explored, such as methane selectively oxidation to methanol and acetic acid using Rh SSCs, [5] CO oxidation and hydrogen generation from methanol using Pt SSCs, [6][7][8] etc. The reduction of particle size to single-atom level always achieves the maximum utilization of expensive noble metals, along with enhancement of activity, stability or selectivity.…”

High-loading and thermally stable Pt1/MgAl1.2Fe0.8O4 single-atom catalysts for high-temperature applications

“…Considering that no Pt loss was detected after calcination at high temperatures (Table S1), the possibility that the disappearance of CO adsorption might stem from volatilization of Pt can be excluded. Thus the result of no adsorption of CO should be related to the cationic nature of Pt [40] and may suggest a strong interaction between Pt and Fe. The different interactions between Pt and Fe were further studied by H 2 -TPR.…”