Heterogeneous single-atom catalysts (SACs) have shown remarkable activity and selectivity. However, syntheses of stable SACs are challenging because of the high surface free energy of single metal atoms. In this study, we report that chelate fixating of the metal precursors with a chelating agent with a higher boiling point than reduction temperature produces high densities of SACs. Several parameters, including effects of electrostatic adsorption, anionic/cationic precursors, ionic strength, and incipient wetness conditions, were investigated. Single-atom catalysts with different loadings were synthesized on several supports, including carbon Volcan XC-72, TiO2, SiO2, and diamond. Herein, we showed that it is possible to produce almost entirely SACs at incipient wetness conditions. The XPS Pt 4f peak after reduction at 170°C showed that the catalyst contains almost entirely single-atom Pt on the surface of the support. The small Pt 4f peak at low Binding energy is recorded even lower than 71.2 eV that is expected for Pt clusters/nanoparticles. It is likely that some Pt atoms react with the carbon creating some carbide. A representative image shows a comparison between the strong electrostatic adsorption (SEA) method that produces ultrasmall and well-dispersed nanoparticles and equivalent single-atom catalysts on both VXC-72 and TiO2 supports. We shed some light on the synthesis process using UV-Visible spectroscopy and NMR spectroscopy to understand the synthesis steps and chelating process.

Chelate fixation to produce high densities of supported single-atom catalysts

ACS Fall 2021

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