Role of surface coverage of alumina with Pt nanoparticles deposited by laser electrodispersion in catalytic CO oxidation

Highlights: • Size-selected Pt nanoparticles were deposited on alumina by laser electrodispersion. • Electronic state and catalytic behavior of Pt particles depend on surface coverage. • Pt⁰/Pt²⁺ ratio in reaction mixture changes with Pt loading and surface coverage. This work elucidates the role of surface coverage of alumina with Pt nanoparticles on the catalyst efficiency in CO oxidation. Size-selected Pt nanoparticles were deposited on the outer surface of alumina pellets by the laser electrodispersion technique. The alumina surface coverage with Pt varied from 0.04 to 3.5 nanoparticle layers and affected the Pt electronic state and catalyst efficiency. Even in the multilayer coatings nanoplatinum particles remained isolated. The catalysts were tested in CO oxidation at CO/O₂ ratios of 0.2, 1 and 2 in the temperature-programmed and pulse reaction modes. At CO/O₂ = 0.2 the temperature of 50% CO conversion increased with decreasing the surface coverage with Pt particles. At CO/O₂ = 2 the decrease in the surface coverage enhanced the catalyst activity. Pt⁰ dominates only in multilayer catalysts, however, approximately half of platinum remained non-oxidized even at such a low metal loading as 0.01 wt%. The change in the electronic state of platinum under the thermal treatment in the reaction mixture affected the catalyst efficiency. The oxidation state of Pt depended on the metal loading, reaction temperature, CO/O₂ ratio in the reaction mixture, mode of its feeding and surface coverage with Pt nanoparticles that influenced the interparticle and particle – support interactions.