Effect of Hydrazine Pretreatment on the Activity, Stability and Active Sites of Cobalt Species for Preferential Oxidation (PROX) of CO in H2-Rich Stream

The as-prepared (Co 3O 4) and hydrazine-treated (Co 3O 4(H)) cobalt catalysts were prepared using the precipitation method and evaluated at a temperature range of 40–220 °C for preferential oxidation (PROX) of CO in excess hydrogen. An improved surface reducibility with smaller crystallite size was noted on hydrazine-treated cobalt species (i.e., Co 3O 4(H) catalyst), which indicates some surface transformation. This finding correlates with the surface roughness formation (as depicted by scanning electron microscope (SEM) and transmission electron microscope (TEM) data), which was further confirmed by an increase in the Brunauer–Emmett–Teller (BET) surface area. The mesoporous structure of the Co 3O 4(H) catalyst remained intact, as compared to that of the Co 3O 4 catalyst. Interestingly, the in situ treatment of the standalone Co 3O 4(H) catalyst decreased the maximum CO conversion temperature (T 100%) from 160 °C (over Co 3O 4) to 100 °C, with good selectivity. The Co 3O 4(H) catalyst showed good stability, with approximately 85% CO conversion at 100 °C for 21 h, as compared to a faster deactivation of the Co 3O 4 catalyst. However, the Co 3O 4(H) catalyst was unstable in both CO 2 and the moisture environment. Based on the evaluation of spent hydrazine-treated (CoO(H)) cobalt catalyst, the high PROX activity is associated with the formation of Co 3+ species as confirmed by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and temperature-programmed reduction (TPR) data. View Full-Tex