To improve the catalytic activity of Co3O4 for CO oxidation, we synthesized a series of Co3O4 catalysts (x%La-Co3O4) with different La doping amounts using the deposition–precipitation method and investigated their catalytic activities and water resistance. The results indicated that the trace doping of La (i.e., 1.0–3.0 atom%) significantly improved the catalytic activity of Co3O4 for CO oxidation. The main reason was that the doped La increased the content of Co3+ in Co3O4, which was the main active Co species for CO oxidation. In addition, doping with La improved the water resistance and catalytic stability of Co3O4 under wet conditions. Pure Co3O4 was dramatically deactivated within a short period (the CO conversion decreased by 80% in 1 h), while 2%La-Co3O4 maintained a CO conversion of over 75% within 15 h. The improved water resistance of 2%La-Co3O4 was mainly due to the reduced hydroxyl content on the Co3O4 surface, which increased the surface hydrophobicity of Co3O4. This work is expected to provide a strategy for the preparation of water-resistant and highly active Co3O4 catalysts for CO oxidation.
