Hollow γ-Al2O3 microspheres as highly “active” supports for Au nanoparticle catalysts in CO oxidation

Abstract

Consisted of closely packed nanoflakes, γ-Al₂O₃ hollow microspheres with ca. 4–6?μm in diameter, and 500–700?nm in shell thickness have been hydrothermally synthesized through utilizing Al(NO₃)₃·9H₂O as precursor, urea as precipitant agent and sulfate K₂SO₄, (NH₄)₂SO₄, or KAl(SO₄)₂·12H₂O 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 SO₄ ^2?. Then via a deposition–precipitation method, 3?wt.% Au nanoparticles supported on γ-Al₂O₃ hollow microspheres exhibit excellent performance with a complete CO conversion at 0?°C (T _100%?=?0?°C) and 50?% conversion at ?25?°C (T _50%?=??25?°C). The good catalytic activity is associated with the special hollow microsphere structures assembled by nanoflakes of γ-Al₂O₃ support. The DRIFTS confirms the presence of Au^δ+ and Au⁰ on the surface of γ-Al₂O₃ 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).