Low temperature carbon monoxide oxidation over gold nanoparticles supported on sodium titanate nanotubes

Small gold particles having sizes of 1.0-2.0 nm were deposited on the surface of the sodium trititanate (Na₂Ti₃O₇) nanotube by the ion exchange method. This nanotube-supported gold catalyst was able to oxidize CO at the sub-ambient temperature. In a pulse reactor, the gold catalyst could achieve a T_50% of 218 K using 1.0 vol.% CO/He gas pulses (0.34 μmol CO/pulse). In the Au loadings of 0.39-2.53 wt.%, the activity of the gold catalyst increased with the gold loading. Calcination of nanotube support at higher than 383 K prior to the gold deposition produced a catalyst with a lower activity. Regarding the effect of calcining the gold particles on the activity (with NaTNT support calcined at 673 K), the catalyst with gold particles heated at 383 K only exhibited the best CO oxidation activity. XPS indicated that there are three gold species with different oxidation state, Au⁰, Au⁺¹ and Au^δ-, in the calcined gold catalysts. As calcination temperature increased, the Au⁰ concentration increased at the consumption of Au⁺¹ species, while the Au^δ- concentration remained relatively constant. This fact strongly suggested that Au⁺¹ species must play an important role in the activity in the sub-ambient temperature region.