Spherically shaped Co3O4 particles were synthesized by one-pot solvothermal treatment of Co(NO3)2 in n-octanol that is free of structure-directing agents or pore formers. Au nanoparticles (2-4 nm) dispersed on the Co3O4 substrates were fabricated using deposition-precipitation method. The as-synthesized Co3O4 (without calcination) and the corresponding Au-containing catalyst achieved complete CO oxidation at 90°C and 80°C, respectively. Upon calcination, the condensed Co3O4 formed on which uniform dispersion of small-sized flat Au entities (3.0 ± 0.6 nm) with large Au-Co3O4 interfaces was established, showing complete CO oxidation at 110°C. These two types of catalysts were found to be extremely durable even when operated in a period beyond 70 h under certain conditions. The calcined Co3O4-based Au catalyst can outperform Au/d-Co3O4 in both activity and stability when subjected to a pre-reaction at 350°C for 5 h. The yolk-shell type Co3O4@SiO2 catalysts synthesized by controllable acid-etching of Co3O4 cores demonstrated an optimal Co3O4 core-SiO2 shell interaction and a suitable Co3O4 core particle size for CO oxidation. Both Co3O4 substrates and Au/Co3O4 systems were found to encounter substantial activity enhancement by in situ pretreatment. The pretreatment resulted in (i) transformation of AuOx to Au0, (ii) higher fraction of surface Co3+, and (iii) suitably lower concentration of surface oxygen adspecies, accounting for the enhanced activities.
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