Formation of Catalytically Active Nanoparticles under Thermolysis of Silver Chloroplatinate(II) and Chloroplatinate(IV).

The thermal behaviour of Ag 2 [PtCl 4 ] and Ag 2 [PtCl 6 ] complex salts in inert and reducing atmospheres has been studied. The thermolysis of compounds in a helium atmosphere is shown to occur in two stages. At the first stage, the complexes decompose in the temperature range of 350-500 °C with the formation of platinum and silver chloride and the release of chlorine gas. At the second stage, silver chloride is sublimated in the temperature range of 700-900 °C, while metallic platinum remains in the solid phase. In contrast to the thermolysis of Ag 2 [PtCl 6 ], the thermal decomposition of Ag 2 [PtCl 4 ] at 350 °C is accompanied by significant heat release, which is associated with disproportionation of the initial salt to Ag 2 [PtCl 6 ], silver chloride, and platinum metal. It is confirmed by DSC measurements, DFT calculations of a suggested reaction, and XRD. The thermolysis of Ag 2 [PtCl 4 ] and Ag 2 [PtCl 6 ] compounds is shown to occur in a hydrogen atmosphere in two poorly separable steps. The compounds are decomposed within 170-350 °C, and silver and platinum are reduced to a metallic state, while a metastable single-phase solid solution of Ag 0.67 Pt 0.33 is formed. The catalytic activity of the resulting nanoalloy Ag 0.67 Pt 0.33 is studied in the reaction of CO total (TOX) and preferential (PROX) oxidation. Ag 0.67 Pt 0.33 enhanced Pt nano-powder activity in CO TOX, but was not selective in CO PROX.