Chemical Reduction Behavior of Zirconia Doped to Nickel at Different Temperature in Carbon Monoxide Atmosphere

Abstract

The reduction behavior of nickel oxide (NiO) and zirconia (Zr) doped NiO (Zr/NiO) was investigated using temperature programmed reduction (TPR) using carbon monoxide (CO) as a reductant and then characterized using X-ray diffraction (XRD), nitrogen absorption isotherm using BET technique and FESEM-EDX. The reduction characteristics of NiO to Ni were examined up to temperature 700 °C and continued with isothermal reduction by 40 vol. % CO in nitrogen. The studies show that the TPR profile of doped NiO slightly shifts to a higher temperature as compared to the undoped NiO which begins at 387 °C and maximum at 461 °C. The interaction between ZrO 2 with Ni leads to this slightly increase by 21 to 56 °C of the reduction temperature. Analysis using XRD confirmed, the increasing percentage of Zr from 5 to 15% speed up the reducibility of NiO to Ni at temperature 550 °C. At this temperature, undoped NiO and 5% Zr/NiO still show some crystallinity present of NiO, but 15% Zr/NiO shows no NiO in crystalline form. Based on the results of physical properties, the surface area for 5% Zr/NiO and 15% Zr/NiO was slightly increased from 6.6 to 16.7 m 2 /g compared to undoped NiO and for FESEM-EDX, the particles size also increased after doped with Zr on to NiO where 5% Zr/NiO particles were 110 ± 5 nm and 15% Zr/NiO 140 ± 2 nm. This confirmed that the addition of Zr to NiO has a remarkable chemical effect on complete reduction NiO to Ni at low reduction temperature (550 °C). This might be due to the formation of intermetallic between Zr/NiO which have new chemical and physical properties.

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

“…However, the addition of zirconia would delay the reduction progress of MoO3 catalyst which was confirmed by detection of the remaining intermediate phase Mo4O11 in XRD diffractogram as compared to pure MoO3 catalyst. According the Gibbs, free energy changed the combination of MoO3 with ZrO2 and was able to increase the reduction temperature due to zirconia oxide difficulty to reduce [17]. Referring to the characterisation in XRD analysis, it confirmed that MoO3 catalyst can be reduced to MoO2 phase in CO atmosphere by involving two reduction stages, namely Mo 6+ → Mo 5+ and Mo 5+ → Mo 4+ [8].…”

“…This result was contrary with the desirable properties in zirconia addition for doping to enhance the reduction process. It suggested that there were some changes in the solid surface properties that particularly interrupted the reduction process [17]. It may due to the stable structure of alloy ZrMo2O8 (JCPDS 38-1466), which promoted a strong modification to the behaviour of the catalyst.…”