Selective CO oxidation in a hydrogen-rich stream over Au/γ-Al₂O₃ catalysts

The selective oxidation of CO in a stream rich in H₂ was investigated over a series of Au/γ-Al₂O₃ catalysts. It was found that the presence of Mg citrate in the preparation solution had a significant effect on the properties of the catalyst. Catalysts prepared without citrate contained larger Au particles, were less active catalytically, and were less selective for CO oxidation. Although the experimental uncertainties were large, there appeared to be an optimal average Au particle size of about 5-10 nm for best activity and selectivity. At 100°C, about 50% selectivity was obtained over the more selective catalysts, which depended only weakly on either O₂ or CO conversion.