Hollow γ-Al_2O_3 microspheres as highly “active” supports for Au nanoparticle catalysts in CO oxidation

摘要

Consisted of closely packed nanoflakes, γ-Al_2O_3 hollow microspheres with ca. 4–6 μm in diameter, and 500–700 nm in shell thickness have been hydrothermally synthesized through utilizing Al(NO_3)_3·9H_2O as precursor, urea as precipitant agent and sulfate K_2SO_4, (NH_4)_2SO_4, or KAl(SO_4)_2·12H_2O as additive, followed by a calcination step. The samples were further characterized by thermogravimetric analysis, scanning electron microscope, x-ray powder diffraction, nitrogen adsorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO etc. The morphology of alumina products was strongly dependent on the presence of SO_4~(2-). Then via a deposition–precipitation method, 3 wt.% Au nanoparticles supported on γ-Al_2O_3 hollow microspheres exhibit excellent performance with a complete CO conversion at 0 °C (T_(100%)=0 °C) and 50 % conversion at 125 °C (T_(50%)=-25 °C). The good catalytic activity is associated with the special hollow microsphere structures assembled by nanoflakes of γ-Al_2O_3 support. The DRIFTS confirms the presence of Auδ+ and Au0 on the surface of γ-Al2_O_3 hollow microspheres. As a contrast, Au catalyst prepared using alumina support with undefined morphology shows low activity under the same catalytic test conditions (T_(100%)=190 °C, T_(50%)=80 °C).