The catalytic properties of the heterogeneous catalysts are mainly influenced by synergetic functions of interfaces between metal species and metal oxide supporting materials as catalytic active site in most catalytic reactions. These catalytic properties are known to be greatly affected by changes in the electronic properties of surface metal and metal oxide support through controlling the degree of metal reduction. Here, we report the catalytic properties of partially reduced cobalt catalyst (Co-CoOx), composed with sub-surface cobalt oxides covered with the metallic cobalt species by simple partial reduction of cobalt oxide catalyst. We reveal that the degree of metal reduction is controlled by adjusting the reduction temperature derived from the temperature-programmed reduction (TPR) pattern of cobalt oxide, and the interfaces between metal and sub-surface metal oxide are formed simultaneously, and the resulting interfaces play a crucial role in the catalytic reaction, which is investigated by a density functional theory (DFT) calculation of the Co/CoOx catalyst. We also performed the geometry optimization of bulk cobalt oxide in 5 model structures of Co3O4, CoO, Co/CoO(sub), Co/CoO(top), and Co metal with CO or H2 molecule to evaluate the adsorption configuration. Finally, we verified the catalytic performance by experiments with results that the partially reduced Co-CoOx catalyst exhibits a higher turnover rate of CO hydrogenation at lower temperatures than supported Ru catalyst, well-known superior precious metal catalyst, implicating that it is promising and cost-effective non-precious metal catalyst.

Sub-surface cobalt oxides covered with the metallic cobalt for selective CO hydrogenation

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