Coprecipitation of Au clusters and alumina sol in supercritical CO2—the facile way to stabilize gold nanoparticles within oxide matrix

A novel method for the synthesis of catalytically active composites based on gold clusters incorporated into an alumina matrix was proposed. The method combines sol–gel and supercritical fluid technologies. The composites were synthesized by precipitating of gold clusters and alumina sol mixture in the supercritical antisolvent (SAS) carbon dioxide medium. Gold clusters were synthesized in the colloidal solution of alumina sol in situ (one-pot synthesis) via controlled reduction of AuIII using PPh3 as a stabilizer for the first time. It was shown that this method allows us to stabilize gold clusters with sizes less than 2 nm in the alumina matrix with a developed specific surface area (SBET = 441 m2/g) and a narrow pore size distribution. The obtained composite does not contain stabilizer, which may poison the catalyst. The developed approach makes possible to synthesize catalytically active composites with a certain amount of gold cluster and oxide matrix of different nature.