Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO
3) catalyst. The composition and morphology of the reduced phases were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). The reduction progression of MoO
3 catalyst was attained with different reductant types and concentration (10% H
2/N
2, 10% and 20% CO/N
2 (%, v/v)). Two different modes of reduction process were applied. The first approach of reduction involved non-isothermal mode reduction up to 700 °C, while the second approach of reduction involved the isothermal mode reduction for 60 min at 700 °C. Hydrogen temperature programmed reduction (H
2-TPR) results showed the reduction progression of three-stage reduction of MoO
3 (Mo
6+ → Mo
5+ → Mo
4+ → Mo
0) with Mo
5+ and Mo
4+. XRD analysis confirmed the formation of Mo
4O
11 phase as an intermediate phase followed by MoO
2 phase. After 60 min of isothermal reduction, peaks of metallic molybdenum (Mo) appeared. Whereas, FESEM analysis showed porous crater-like structure on the surface cracks of MoO
2 layer which led to the growth of Mo phase. Meanwhile, the reduction of MoO
3 catalyst in 10% carbon monoxide (CO) showed the formation of unstable intermediate phase of Mo
9O
26 at the early stage of reduction. Furthermore, by increasing 20% CO led to the carburization of MoO
2 phase, resulted in the formation of Mo
2C rather than the formation of metallic Mo, as confirmed by XPS analysis. Therefore, the presented study shows that hydrogen gave better reducibility due to smaller molecular size, which contributed to high diffusion rate and achieved deeper penetration into the MoO
3 catalyst compared to carbon monoxide reductant. Hence, the reduction of MoO
3 in carbon monoxide atmosphere promoted the formation of Mo
2C which was in agreement with the thermodynamic assessment.
相似文献