Low-temperature CO oxidation on Au/Fe_xO_y catalysts

Supported gold catalyst has been reported to have high CO oxidation activity at low-temperature. The aim of this study was to develop a Au/Fe _xO_y catalyst that is active under ambient conditions, is low-cost, is resistant to moisture, and has high stability. Iron oxide was chosen because it is cheap and resistant to moisture. A method to prepare a Fe_xO_y support that has a higher surface area and abundant hydroxyl groups on the surface was developed. The Fe_xO_y was prepared with a very low feeding rate of FeCl₃ (10 mL/min), at a constant pH of 10, was dried at 120°C, and had a very high surface area with abundant hydroxyl groups. The surface area of Fe_xO_y was as high as 400 m²/g. It was used as a support for gold in low-temperature CO oxidation. Supported gold catalysts were prepared by deposition - precipitation (DP) using HAuCl₄ as the Au precursor under various pH values and calcined at various temperatures. The catalysts were characterized by atomic absorption spectroscopy, X-ray diffraction (XRD), N₂ sorption, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). XRD results showed that gold metal had a particle size under the detection limit, which was less than 4 nm. TEM images confirmed that the particle sizes of gold for all the catalysts were less than 4 nm. XPS spectra showed that Au is in metal state Au⁰. The method applied in this study leads to a fairly uniform dispersion of gold nanoparticles with diameter less than 4 nm and narrow size distribution. The catalytic activity of CO oxidation under ambient conditions was measured using a fixed bed continuous flow reactor. It demonstrated that pH value and calcination temperature play key roles in creating high catalytic performance for the Au/F_xO_y catalyst. The catalyst prepared by the DP method at pH 9 and calcined at 180°C gave the highest activity. In addition, this catalyst was very resistant to moisture. Full conversion was kept at ambient temperature with, a gas hourly space velocity of 40 000 h^-1 over 2000 h on stream.