Looking by grazing incidence small angle x-ray scattering at gold nanoparticles supported on rutile TiO2(110) during CO oxidation

The catalytic activity of oxide-supported gold nanoparticles depends crucially on their size. The present work describes a dedicated set-up in which particle size is determined by grazing incidence small angle x-ray scattering (GISAXS) and reactivity is analysed via a mass spectrometer. Catalytically active gold nanoparticles supported on TiO 2 (110) of size ranging between 2.4 and 5 nm were characterized during the CO oxidation at pressures in the range 0.1–100 mbar. The growth was found 3D and the particles were best modelled by a truncated sphere. The reaction rate per Au atom measured at 470 K was seen to increase in a monotone manner as the cluster size decreases, without reaching any maximum. Particles of size lower than 3 nm were stable under oxygen but sintering occurs when CO is added at 470K. That dimension coincides with the switch which was previously observed from nucleation-growth, with particles pinned on defects, to coalescence where particles become independent of defects.