Influence of Zr Additive on the Chemical Reduction Behaviour of MoO3 in Carbon Monoxide Atmosphere

Abstract

Temperature-programmed reduction (TPR) was used to observe the chemical reduction behaviour of molybdenum trioxide (MoO3) and zirconia (Zr)-doped MoO3 catalyst by using carbon monoxide (CO) as the reductant. The characterisation of catalysts was performed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM) analyses. The reduction performance were examined up to 700°C and reduction was continued for 60 min at 700°C in a stream of 20 vol. % CO in nitrogen. The TPR profile showed that the doped MoO­3 catalyst was slightly moved to a higher temperature (580°C) as compared to the undoped MoO3 catalyst, which began at around 550°C. The interaction between zirconia and molybdenum ions in doped MoO3 catalyst led to an increase in the reduction temperature. According to characterisation of the reduction products by using XRD, it revealed that the reduction behaviour of pure MoO3 to MoO2 by CO reductant involved two reduction stages with the formation of Mo4O11 as the intermediate product. Meanwhile, MoO3 catalyst doped with zirconia caused a delay in the reduction process and was proven by the presence of Mo4O11 species at the end of reactions. Physical analysis by using BET showed a slight increase in surface area of 3% Zr-MoO3 from 6.85 m2/g to 7.24 m2/g. As for TEM analysis, black tiny spots located around MoO3 particles revealed that the zirconia was successfully intercalated into MoO3 particles. This confirmed that formation of intermetallic between Zr-MoO3 catalyst will give new chemical and physical properties which has a remarkable chemical effect by disturbing the reduction progression of MoO3 catalyst.