Effects of particle size, composition, and support on catalytic activity of AuAg nanoparticles prepared in reverse block copolymer micelles as nanoreactors

Block copolymer (BCP) micelles formed by polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) were used as nanoreactors for preparing stable bimetallic AuAg nanoparticles (NPs) with finely tunable composition and diameters. Micelles loaded with NPs were then deposited onto TiO2 and Al2O3 in order to investigate the catalytic properties of the NPs with respect to CO oxidation. The polymer matrix could be removed by thermal treatment at 400 °C under H2 or O2. Different parameters, such as support, particle size, and metal composition were varied independently, so that their influence on the catalytic activity for CO oxidation could be separated. The atomic Au/Ag ratio was varied from 1:2 to 2:1, and the highest activity was obtained for an Au/Ag ratio of 1, showing synergy effects of both metals for catalyzing CO oxidation. Using nanosized TiO2 as support and an Au/Ag ratio of 1, the nanoparticle diameter was varied between ∼3 and ∼20 nm which led to a variation of activity by a factor of ∼7 (in a continuous flow reactor at 70 °C) with the smallest particles showing the highest turnover frequencies (TOFs). In comparison, regular TiO2 as catalyst carrier showed significantly lower performance than nanostructured TiO2 while no activity was found on non-reducible γ-Al2O3. Independently, all three parameters (metal particle size, Au/Ag atomic ratio, and the support) showed significant effects on the catalytic activity.

Graphical abstractSupported bimetallic AuAg nanoparticles, homogeneous in size and composition, can be prepared using block copolymer micelles as nanoreactors, depositing the particle-loaded micelles, and removing the polymer by thermally induced depolymerization. Independent variation of particle size, composition, and support allowed for separating effects of these parameters on the catalytic activity for CO oxidation.Figure optionsDownload full-size imageDownload high-quality image (184 K)Download as PowerPoint slideHighlights► Supported AuAg nanoparticles, homogeneous in composition and size, were prepared. ► Particle size, composition, and support were controlled and varied independently. ► The PS-PVP nanoreactor shell could be completely removed from the support. ► Particles with Au/Ag = 1:1 on nanosized TiO2 show highest activity for CO oxidation. ► Both oxide support and Ag take on key roles in activating molecular oxygen.