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 ZrO2 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 m2 /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.

The reduction behaviour of cobalt (Co) and undoped nickel oxide (NiO) under different atmospheres (hydrogen (H2) + nitrogen (20%, v/v) and carbon monoxide (CO) + nitrogen (40%, v/v)) have been investigated by temperature programmed reduction (TPR). The phases formed of partially and completely reduced samples were characterized by X-ray diffraction spectroscopy (XRD). TPR results indicate that the reduction of Co doped and undoped nickel oxide in both reductants proceed in one step reduction (NiO → Ni) without intermediate. TPR results also suggested that the addition Co metal into NiO, give different intensity to the peak. The reduction process of Co and undoped NiO accelerated almost completely reduced at T = 700 °C when H2 was used as a reductant. Meanwhile, XRD analysis indicated that NiO without Co composed better crystallite phases of NiO with higher intensity. © 2020 Trans Tech Publications Ltd, Switzerland.

This study was carry out to investigate the effect of 3% rhodium on the reduction behaviour of iron oxide by (10%, v/v) carbon monoxide in nitrogen as a reductant. The Rh/Fe2O3 samples were prepared by impregnation method and the reduction behavior of Rh/Fe2O3 and pure Fe2O3 were investigated by using temperature programmed reduction (TPR). The prepared samples and the reduced phases were characterized by X-ray diffraction spectroscopy (XRD). The results indicate that Rh/Fe2O3 give a better reducibility compared to Fe2O3 with a complete reduction at 650 �C, which is 250 �C lower than Fe2O3. The TPR results indicate that the reduction of Fe2O3 proceed in three steps reduction (Fe2O3 ? Fe3O4 ? FeO ? Fe) with Fe3O4 and FeO as intermediate states while for Rh/Fe2O3 as the TPR result showed the overlapping of second and third peak (Fe3O4 ? FeO and FeO ? Fe) at higher temperature. Addition of Rh may possibly reduce the formation of stable FeO that stable at higher temperature by accelerates the direct reduction of Fe3O4? Fe so the reduction process of Fe2O3 become faster. The XRD pattern shows the diffraction peaks of Rh/Fe2O3 is more intense with improved crystallinity for the characteristic peaks of Fe2O3 compared to pure Fe2O3. No visible sign of rhodium particles peaks in the XRD spectrum that indicates the Rh particles loaded onto the iron oxide are well dispersed. The well dispersed Rh onto the iron oxide and the ability to reduce the sintering effect to the iron oxide also has been confirmed by FESEM. The study shows that addition of Rh gives a better reducibility of iron oxide is also due to the ability of Rh to interact with CO as confirmed by the thermodynamic data with higher surface area compared to Fe2O3. � 2017, Malaysian Society of Analytical Sciences. All rights reserved.

The purposes of this study are to reduce Fe2O3 using hydrogen (H2) and carbon monoxide (CO) gases at a high temperature zone (500 °C–900 °C) by focusing on the influence of reduction gas concentrations. Reduction behavior of hematite (Fe2O3) at high temperature was examined using temperature programmed reduction (TPR) under non-isothermal conditions with the presence of 10% H2/N2, 20% H2/N2, 10% CO/N2, 20% CO/N2 and 40% CO/N2. The TPRCO results indicated that the first and second reduction peaks of Fe2O3 at a temperature below 660 °C appeared rapidly when compared to TPRH2. However, TPRH2 exhibited a better reduction in which Fe2O3 entirely reduced to Fe at temperature 800 °C (20% H2) without any remaining of wustite (FeO) whereas a temperature above 900 °C is needed for a complete reduction in 10% H2/N2, 10% and 20% CO/N2. Furthermore, the reduction of hematite could be improved when increasing CO and H2 concentrations since reduction profiles were shifted to a lower temperature. Thermodynamic calculation has shown that enthalpy change of reaction (ΔHr) for all phases transformation in CO atmosphere is significantly lower than in H2. This disclosed that CO is the best reductant as it is a more exothermic, more spontaneous reaction and able to initiate the reduction at a much lower temperature than H2 atmosphere. Nevertheless, the reduction of hematite using CO completed at a temperature slightly higher compared to H2. It is due to the presence of an additional carburization reaction which is a phase transformation of wustite to iron carbide (FeO → Fe3C). Carburization started at the end of the second stage reduction at 600 °C and 630 °C under 20% and 40% CO, respectively. Therefore, reduction by CO encouraged the formation of carbide, slower the reduction and completed at high temperature. XRD analysis disclosed the formation of austenite during the final stage of a reduction under further exposure with high CO concentration. Overall, less energy consumption needed during the first and second stages of reduction by CO, the formation of iron carbide and austenite were enhanced with the presence of higher CO concentration. Meanwhile, H2 has stimulated the formation of pure metallic iron (Fe), completed the reduction faster, considered as the strongest reducing agent than CO and these are effective at a higher temperature. Proposed iron phase transformation under different reducing agent concentrations are as followed: (a) 10% H2, 20% H2 and 10% C; Fe2O3 → Fe3O4 → FeO → Fe, (b) 20% CO; Fe2O3 → Fe3O4 → FeO → Fe3C → Fe and (c) 40% CO; Fe2O3 → Fe3O4 → FeO → Fe3C → Fe → F,C (austenite). © 2020 Hydrogen Energy Publications LLC

The aims of this study are to produce Fe3O4 from Fe2O3 using hydrogen (H2) and carbon monoxide (CO) gases by focusing on the influence of these gases on reduction of Fe2O3 to Fe3O4 at low temperature (below 500 °C). Low reduction temperature behavior was investigated by using temperature programmed reduction (TPR) with the presence of 20% H2/N2, 10% CO/N2, 20% CO/N2 and 40% CO/N2. The TPR results indicated that the first reduction peak of Fe2O3 at low temperature appeared faster in CO atmosphere compared to H2. Furthermore, reducibility of first stage reduction could be improved when increasing CO concentration and reduction rate were followed the sequence as: 40% CO > 20% CO > 10% CO > 10% H2. All reduction peaks were shifted to higher temperature when the CO concentration was reduced. Although, initial reduction by H2 occurred slower (first peak appeared at higher temperature, 465 °C) compared to CO, however, it showed better reduction with Fe2O3 fully reduced to Fe at temperature below 800 °C. Meanwhile, complete reduction happened at temperature above 800 °C in 10% and 20% CO/N2. Thermodynamic calculation revealed that CO acts as a better reducer than H2 as the enthalpy change of reaction (ΔHr) is more exothermic than H2 and the change in Gibbs free energy (ΔG) at 500 °C is directed to more spontaneous reaction in converting Fe2O3 to Fe3O4. Therefore, formation of magnetite at low temperature was thermodynamically more favorable in CO compared to H2 atmosphere. XRD analysis explained the formation of smaller crystallite size of magnetite by H2 whereas reduction of CO concentration from 40, 20 to 10% enhanced the growth of highly crystalline magnetite (31.3, 35.5 and 39.9 nm respectively). All reductants were successfully transformed Fe2O3 → Fe3O4 at the first reduction peak except for 10% CO/N2 as there was a weak crystalline peak due to remaining unreduced Fe2O3. Overall, less energy consumption needed in reducing Fe2O3 to Fe3O4 by CO. This proved that CO was enhanced the formation of magnetite, encouraged formation of highly crystalline magnetite in more concentrated CO, considered better reducing agent than H2 and these are valid at lower temperature.

The physical and chemical behaviour of bulk tungsten oxide (WO3) and Ni doped tungsten oxide (15% Ni/WO3) were examined by performing a temperature-programmed reduction (TPR) technique. The chemical composition, morphology, and surface composition of both samples before and after reduced were analysed by X-ray diffraction (XRD), scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) analysis. The XRD pattern of calcined Ni doped tungsten oxide powder comprised of WO3 and nickel tungstate (NiWO4) phases. The reduction behaviour was investigated by a non-isothermal reduction up to 900 °C achieved under (10 and 20% v/v) hydrogen in nitrogen (H2 in N2) and (20 and 40% v/v) carbon monoxide in nitrogen (CO in N2) atmospheres. The H2-TPR were indicated the reduction of bulk WO3 and 15% NiWO3 proceed in three steps (WO3 → WO2 → WO2 + W) and (WO3 → WO2 → W + Ni4W) respectively under 20% H2. Whereas, the reduction of 15% WO3 under 40% CO involves of two following stages: (i) low temperature (<800 °C) transformation of WO3 → WO2.72 → WO2 and, (ii) high temperature (>800 °C) transformation of WO2 → W → WC. Furthermore, NiWO4 alloy phase was transformed according to the sequence NiWO4 → Ni + WO2.72 → Ni + WO2 → Ni + W → Ni4W + W at temperature >700 °C and >800 °C in H2 and CO atmospheres, respectively. It can be concluded that the reduction behaviour of WO3 is matched with the thermodynamic data. In addition, the reduction under H2 is more favourable and have better reducibility compared to the CO gas. It is due to the small molecule size and molecule mass of H2 that encourages the diffusion of H2 molecule into the internal surface of the catalyst compared to CO. Moreover, Ni additive had improved the WO3 reducibility and enhancing the CO adsorption and promotes the formation of tungsten carbide (WC) by carburisation reaction. Besides, the formation of Ni during the reduction of 15% Ni/WO3 under CO reductant catalysed the Boudouard reaction to occur, which disproportionated the carbon monoxide to carbon dioxide and carbon (CO → CO2 + C). © 2020 Hydrogen Energy Publications LLC

Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO3) 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 MoO3 catalyst was attained with different reductant types and concentration (10% H2/N2, 10% and 20% CO/N2 (%, 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 (H2-TPR) results showed the reduction progression of three-stage reduction of MoO3 (Mo6+ → Mo5+ → Mo4+ → Mo0) with Mo5+ and Mo4+. XRD analysis confirmed the formation of Mo4O11 phase as an intermediate phase followed by MoO2 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 MoO2 layer which led to the growth of Mo phase. Meanwhile, the reduction of MoO3 catalyst in 10% carbon monoxide (CO) showed the formation of unstable intermediate phase of Mo9O26 at the early stage of reduction. Furthermore, by increasing 20% CO led to the carburization of MoO2 phase, resulted in the formation of Mo2C 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 MoO3 catalyst compared to carbon monoxide reductant. Hence, the reduction of MoO3 in carbon monoxide atmosphere promoted the formation of Mo2C which was in agreement with the thermodynamic assessment. © 2020 Hydrogen Energy Publications LLC