2022 Volume 65 Issue 2 Pages 58-66
In methods for removing odorous and harmful substances from the exhaust gas of chemical industry plants and living environments by selective catalytic oxidation, it is necessary to lower the reaction temperature from the viewpoint of saving energy. Supported gold nanoparticle catalysts that can catalytically remove CO and NH3 at room temperature have been developed. Nb2O5 and Ta2O5 are classified as acidic oxide, and the surface of the oxides is negatively charged due to their low isoelectric point. The widely used deposition precipitation method using HAuCl4 precursor has been difficult to deposit gold nanoparticles because the gold precursors existing as anions do not interact with each other. The colloidal sol immobilization method was applied to deposit gold on Nb2O5 and Ta2O5 and we successfully prepared Au/Nb2O5 and Au/Ta2O5 with average gold particle sizes of ca. 2.7 nm. These Au/Nb2O5 and Au/Ta2O5 catalysts showed 100 % conversion for CO oxidation (1 % CO in air, SV = 20,000 mL h−1 gcat−1) at room temperature. The Au/Nb2O5 catalyst showed 20 % conversion with 100 % selectivity to N2 for NH3 selective catalytic oxidation (50 ppm NH3 in air, SV = 40,000 mL h−1 gcat−1) at room temperature. The catalytic activity depended on the crystal structure of the support, and Brönsted acid sites on the support surface were important for obtaining high selectivity to N2 in the case of selective catalytic oxidation of NH3. The synergy of oxidation ability of gold nanoparticles and acid sites of the support will expand the possibilities in the field of catalyst reactions.
