Kinetic interactions between hydrogen and carbon monoxide oxidation over platinum

The heterogeneous chemistry coupling of H₂ and CO over platinum was investigated experimentally and numerically for H₂/CO/O₂/N₂ mixtures with overall lean equivalence ratios φ = 0.13–0.26, H₂:CO molar ratios 1:5–3:1, and a pressure of 5 bar. Experiments were performed in an optically accessible channel-flow reactor at surface temperatures 510–827 K and involved in situ Raman measurements of major gas-phase species concentrations and thermocouple measurements of surface temperatures. Emphasis was placed on the low temperature range 510–600 K, whereby H₂ inhibited the CO oxidation, and which was of particular relevance to gas turbine idling and part-load operation. Comparisons of measurements with 2-D simulations attested the aptness of the employed kinetic scheme, not only for H₂/CO fuel mixtures but also for pure CO. Measured and predicted transition temperatures below which H₂ inhibited CO oxidation agreed well with each other, showing a main dependence on the overall equivalence ratio (550 ± 5 K at φ = 0.13 and 600 ± 5 K at φ = 0.26) and a weaker dependence on the H₂:CO ratio. Furthermore, this inhibition was non-monotonically dependent on the H₂:CO ratio, becoming higher at a value of 1:1. The inhibiting kinetic effect of H₂ was an outcome of the competition between H₂ and CO/O₂ for surface adsorption and, most importantly, of the competition between the adsorbed H(s) and CO(s) for surface-deficient O(s). Finally, transient simulations in practical catalytic channels revealed the interplay between kinetic and thermal effects. While at φ = 0.13 the H₂/CO reactive mixture exothermicity was insufficient to overtake the kinetic inhibition, at φ = 0.26 catalytic ignition could still be achieved at temperatures well-below the transition temperature. The effect of H₂:CO molar ratio on the light-off times was quite strong, suggesting care when designing syngas catalytic rectors with varying compositions.     

Metal oxide hydrogen,oxygen, and carbon monoxide sensors for hydrogen setups and cells

Use of hydrogen, oxygen, and carbon oxide semiconductor sensors made of metal oxides allows controlling electronically the content of these gases in operation of many hydrogen setups, cells and devices. Present review-paper gives a general idea of achievements in this field.     

Kinetic interplay between hydrogen and carbon monoxide in syngas-fueled catalytic micro-combustors

The combined oxidation of hydrogen and carbon monoxide over platinum in micro-combustors at catalytic surface temperatures below 600 K was studied numerically, using a two-dimensional computational fluid dynamics (CFD) model with detailed heterogeneous and homogeneous reaction mechanisms and multicomponent transport. Simulations were performed at different surface temperatures and feed compositions to study the kinetic interplay between hydrogen and carbon monoxide. A sensitivity analysis of the heterogeneous reaction mechanism was performed to identify the rate-controlling steps. Finally, possible mechanisms for the observed behavior were discussed. It was shown that there is significant kinetic interplay between hydrogen and carbon monoxide. Carbon monoxide significantly inhibits the catalytic oxidation of hydrogen. In contrast, the presence of hydrogen was found to promote the catalytic oxidation of carbon monoxide, with the largest effect shown for the small addition of hydrogen, then this effect progressively decreases with the further increase of hydrogen concentration. Accordingly, the apparent reaction order with respect to hydrogen changes from positive to negative, then to zero. The promoting effect of hydrogen can be attributed to the carboxyl pathway, which is crucial to describe the process.     

Periodically regenerating diesel particulate filter with a hydrogen/carbon monoxide mixture addition

This investigation analyses the effect of introducing a H₂/CO mixture, upstream of a diesel particulate filter (DPF), in an attempt to support the regeneration process. The introduction of the mixture was achieved via various periodic strategies in an attempt to reduce the volume of mixture required while still maintaining proficient regeneration qualities. In addition to this, the effect of space velocity and engine load on the regeneration process was also investigated. The experimental data showed that the mixture addition supported the regeneration process by increasing the filter temperature via an exothermic reaction. The most beneficial spraying strategy introduced the mixture to the DPF every 20 s, with each injection event lasting for a period of 10 s. This strategy required 50% less mixture volume than the constant spray strategy but still induced similar regeneration capabilities. In addition to this, it was noted that a decrease in space velocity reduced the rate of temperature increase but improved the peak filter temperature resulting in increased regeneration proficiency. It was also noted that a reduction in engine load reduced the mean filter temperature but overall had minimal effect on the regeneration process.     

Hydrogen production from ethanol with low carbon monoxide generation in a one-pot reaction with iron oxides as catalysts

Bulk γ-Fe₂O₃ (maghemite) and Fe₃O₄ (magnetite) were synthesized with Fe(III) hydroxyacetate as an intermediate during the preparation step. The fresh and used catalysts were characterized by X-ray diffraction, N₂ adsorption at 77 K, Mössbauer spectroscopy at 298 K, diffuse-reflectance spectroscopy, and thermogravimetric analysis. The solids were used as catalysts in the ethanol hydrotreatment within the range of 673–758 K. The catalysts showed a satisfactory selectivity for H₂ and an especially low CO production. These activities and selectivities were analyzed in conjunction with the structural properties of the oxides. Magnetite seemed to be a more appropriate catalyst than maghemite since the latter was converted into magnetite at reaction temperatures higher than 713 K because of the reducing atmosphere.     

Studies on influence of hydrogen and carbon monoxide concentration on reduction progression behavior of molybdenum oxide catalyst

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.     

Design of fuel cell systems laboratory for hydrogen,carbon monoxide and hydrocarbon safety

As research and development efforts in the area of fuel cells and hydrogen based energy accelerate, a large number of accidents have occurred in research laboratories. In this context, a design methodology for a simple, scaleable, modular and human-independent system for hydrogen, carbon monoxide and hydrocarbon safety in research laboratories is valuable. We have designed, developed and operationalized such a system in a pre-existing generic laboratory space. In this paper, we provide details of the mechanical, electrical and control aspects of this laboratory. We use CFD analysis to design a ventilation system, and to locate gas detectors for optimum detection time. The gas detectors, actuators, a real-time controller and other electrical components are part of a safety monitoring system that continuously gathers information, processes this information and takes appropriate action to safeguard personnel and equipment in real time. This fully operational safety laboratory is now a University-level research hub for all fuel cell (and other energy related) research activities, and is also one of a kind in the region. We also expect that the experience gained in this endeavor will be useful to other researchers in building a safe workplace.     

Fuel-cell grade hydrogen production by coupling steam reforming of ethanol and carbon monoxide removal

Challenges of coupling steam reforming of ethanol (SRE) and carbon monoxide (CO) removal to continuous fuel-cell grade hydrogen (H₂) production were assessed. A SRE reactor, based on a previous optimized RhPt/CeO₂SiO₂ catalyst, was coupled to a CO removal reactor, based on AuCu/CeO₂ catalysts with different Au:Cu weight ratios. Fuel-cell grade H₂ was achieved with a Au_1.0Cu_1.0/CeO₂ catalyst at 210 °C on the CO removal reactor. AuCu/CeO₂ catalysts characterization suggests that Au favors CO conversion by the formation of possible Au⁰-CO_ad species, and Cu improves CO₂ yield by promoting oxygen vacancies on CeO₂. However, operando DRIFTS by 95 h showed that Au_1.0Cu_1.0/CeO₂ catalyst is susceptible to deactivation by the diminish on the CO_ad species and oxygen vacancies, and the formation of carbonate species. These results allowed us to propose a cyclic reduction treatment to prevent catalyst deactivation of Au_1.0Cu_1.0/CeO₂ (95 h of time-on-stream) while producing fuel-cell grade H₂.     

Engine knock and combustion characteristics of a spark ignition engine operating with varying hydrogen and carbon monoxide proportions

Varying proportions of hydrogen and carbon monoxide (synthesis gas) have been investigated as a spark ignition (SI) engine fuel in this paper. It is important to understand how various synthesis gas compositions effect important SI combustion fundamentals, such as knock and burn duration, because in synthesis gas production applications, the compositions can vary significantly depending on the feedstock and production method.A single cylinder cooperative fuels research (CFR) engine was used to investigate the knock and combustion characteristics of three blends of synthesis gas (H₂/CO ratio); 1) 100/0, 2) 75/25, and 3) 50/50, by volume. These blends were tested at three compression ratios (6:1, 8:1, and 10:1), and three equivalence ratios (0.6, 0.7, and 0.8).It was revealed that the knock limited compression ratio (KLCR) of a H₂/CO mixture increases with increasing CO fraction, for a given spark timing. For a given equivalence ratio and spark timing, a 50%/50% H₂/CO mixture produced a KLCR of 8:1 compared to a 100% H₂ condition, which produced a KLCR of 6:1. The burn duration and ignition lag is also increased with increasing CO fraction. The results from this work are important for those considering using synthesis gas as a fuel in SI engines. It reveals that although CO is a slow burning fuel, higher CO fractions in synthesis gas can be beneficial, because of its increased resistance to knock, which gives it the potential of producing higher indicated efficiencies through the utilization of an engine with a higher compression ratio.     

Studies on reduction of chromium doped iron oxide catalyst using hydrogen and various concentration of carbon monoxide

Chemical reduction behaviour of 3% chromium doped (Cr–Fe₂O₃) and undoped iron oxides (Fe₂O₃) were investigated by using temperature programmed reduction (TPR). The reduced phases were characterized by X-ray diffraction spectroscopy (XRD). The reduction processes were achieved with 10% H₂ in nitrogen (%, v/v), 10% and 20% of carbon monoxide (CO) in nitrogen (%, v/v). In hydrogen atmosphere, the TPR results indicate that the reduction of Cr–Fe₂O₃ and Fe₂O₃ proceed in three steps (Fe₂O₃ → Fe₃O₄ → FeO → Fe) with Fe₃O₄ and FeO as intermediate states. A complete reduction to metallic iron for both samples occurred at 900 °C. As for CO reductant, the profiles show the reduction of Fe₂O₃ also proceeded in three steps with a complete reduction occurs at 900 °C in 10% CO with no sign of carbide formation. Nevertheless, a 20% CO was able to reduce the completely at lower temperature at 700 °C and there is a formation of iron carbide at 500 °C but the carbide disappeared as the reduction temperature increase. Meanwhile in 10% CO atmosphere, Cr–Fe₂O₃ shows a better reducibility compared to Fe₂O₃ with a complete reduction at 700 °C, which is 200 °C lower than Fe₂O₃. A Cr dopant in the Fe₂O₃ can lead to formation of various forms of iron carbides such as F₂C, Fe₅C₂, Fe₂₃C₆ and Fe₃C as the CO concentration was increased to 20%. The transformation profile of iron phases during carburization follows the following forms, Fe₂O₃ → Fe₃O₄ → iron carbides (Fe_xC). The XRD pattern shows the diffraction peaks of Cr–Fe₂O₃ are more intense with improved crystallinity for the characteristic peaks of Fe₂O₃ compare to undoped Fe₂O₃. No visible sign of chromium particles peaks in the XRD spectrum that indicates the Cr particles loaded onto the iron oxide are well dispersed. The uniform dispersion with no sign of sintering effects of the Cr dopant on the Fe₂O₃ was confirmed by FESEM. The study shows that Cr dopant gives a better reducibility of iron oxide but promotes the formation of carbides in an excess CO concentration.     

Development of a polyaniline nanofiber-based carbon monoxide sensor for hydrogen fuel cell application

The sensing of carbon monoxide (CO) impurity contained in hydrogen fuel is a challenging work in the field of low temperature proton exchange membrane fuel cell (PEMFC). In the present work a chemiresistive gas sensor based on polyaniline (PANI) nanofibers was developed to detect CO in hydrogen. The sensor was fabricated by a template-free electrochemical polymerization of aniline on an interdigitated electrode. The most distinctive feature of the fabricated sensor was the formation of a horizontally oriented, monolayered PANI nanofiber network on the insulating gap area. The gas sensing character of the PANI nanosensor was evaluated by measuring the change in electrical resistance when gas atmosphere was changed from pure hydrogen to mixtures of CO in hydrogen. The results demonstrated that the PANI nanosensor had an excellent responding ability on CO in hydrogen with a concentration as low as 1 ppm. The influences of parameters, such as nanostructure, doping level, dopants, and CO concentrations, on the sensing characters of the nanosensor were discussed. The responding mechanism was attributed to the different binding sites of CO and H₂ with PANI: H₂ with the protonated amine nitrogen atoms and CO with the unprotonated amine nitrogen atoms. In view of its novel sensing mechanism and high sensing performance, the fabricated sensor is very promising to be applied as a new type of CO sensor to prevent the catalysis poisoning of PEMFC.     

Preferential catalytic oxidation of carbon monoxide in presence of hydrogen over bimetallic AuPt supported on zeolite catalysts

A series of AuPt/A zeolite and Pt/A zeolite catalysts prepared by incipient wetness impregnation are investigated for the preferential oxidation (PROX) of carbon monoxide in the presence of hydrogen over the temperature range of 50–310 °C under atmospheric pressure. The results indicate that when a small amount of gold is added to the Pt/A zeolite catalyst, the CO selectivity is improved at low temperatures, and 1% AuPt/A zeolite (at a weight ratio of Au:Pt = 1:2) gives the best performance, which provides a high CO conversion in combination with a high CO selectivity. In more realistic simulated reformate gases containing 10% CO₂ and 10% H₂O, there is not much difference between those in the presence and the absence of CO₂ and H₂O. Transmission electron microscopic and X-ray diffraction studies show that the two metals, Au and Pt, appear to be severely phase separated, which is confirmed by energy dispersive investigations.     

Understanding on the effect of morphology towards the hydrogen and carbon monoxide sensing characteristics of tin oxide sensing elements

Though the gas sensing properties of atmospheric plasma sprayed tungsten oxide, zinc oxide, titanium oxide, tin oxide and copper oxide coatings were well investigated, reports comparing sensing characteristics of plasma sprayed sensor thick film coating with its bulk counterpart are hardly found in the literature. This work attempts to compare hydrogen and carbon monoxide sensing characteristics, namely gas response, response time, recovery time of plasma sprayed tin dioxide thick film with tin dioxide bulk sensor. Gas response in the presence of hydrogen gas (23–81%) was superior to that of carbon monoxide gas (19–79%). An attempt was made to understand plausible reason behind superior hydrogen gas response. Thus, gas response as a function of temperature was simulated using a gas diffusion equation for hydrogen and carbon monoxide gases. Estimated parameters, namely, activation energy of transduction and first order kinetics were correlated with sensor microstructure and experimental gas response values. For hydrogen sensing, shorter response time (30–138 s) and recovery time (118–161 s) of thick film as compared to response time (64–234 s) and recovery time (183–196 s) of bulk sensor was correlated with microstructure of sensory elements. It was observed that tin dioxide thick film, owing to its porous morphology with small-sized particulates exhibited superior hydrogen gas response, short response time and recovery time as compared to its bulk counterpart.     

Characterisation of the electrochemical water gas shift reactor (EWGSR) operated with hydrogen and carbon monoxide rich feed gas

Water gas shift units are used to raise the H₂ yield of reforming processes by converting CO to CO₂ and additional H₂. Additional subsequent processes are required to separate H₂ from the product gas stream to obtain pure H₂. This study investigates a novel electrochemical membrane reactor, where the water gas shift reaction occurs electrochemically. The reactor is operated at 393 K and 403 K with electrical energy to enable hydrogen purification in terms of electrochemical pumping, as well as a simultaneous electrochemical CO oxidation to increase the yield of purified H₂. The experimental results show the influence of several operation parameters upon its operation characteristics (e.g. cell voltage, electrochemical CO oxidation, the energy demand, etc.). The process yielded high overall exergy efficiencies of, e.g. 78.3%, whereas the anodic outlet stream contributed with 35%-units, and the purified hydrogen with 43.3%-units.     

Catalytic reduction of nitrogen oxide by carbon monoxide,methane and hydrogen over transition metals supported on BEA zeolites

Different metals were impregnated onto BEA zeolites supports by ion-exchanging method to prepare catalysts for NO reduction. Activities of the prepared catalysts were then examed in a fixed bed reactor for NO reduction by CO, H₂, and CH₄. Experimental results indicated that Cu-BEA shows high catalytic activity for NO reduction by CO and H₂ at 300 °C–500 °C, while Co-BEA shows high catalytic activity of NO reduction by CH₄ at 400 °C–500 °C. Activities of all the catalysts increase as the temperature rises. Then characterization of H₂-TPR, XED, XPS and BET were conducted used to investigate the physical and chemical properties of these BEA catalysts. In-situ Fourier transform-infrared spectroscopy was also used to study the mechanism of the reaction of NO reduction by CO, CH₄ and H₂. The reason of different activities over different BEA catalysts was then carefully explored.     

Influence of hydrogen and carbon monoxide on reduction behavior of iron oxide at high temperature: Effect on reduction gas concentrations

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 TPR_CO results indicated that the first and second reduction peaks of Fe₂O₃ at a temperature below 660 °C appeared rapidly when compared to TPR_H2. However, TPR_H2 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).     

Hydrogenation of carbon monoxide over cobalt nanoparticles supported on carbon nanotubes

This paper describes a catalytic reaction of hydrogen and carbon monoxide (Fischer-Tropsch synthesis (FTS)) over carbon nanotubes (CNTs) supported cobalt nanoparticles. We have investigated the effect of calcination of the catalysts on FTS performance using X-ray diffraction (XRD), H₂ chemisorption, temperature programmed reduction (TPR), temperature programmed oxidation (TPO), and transmission electron microscopy (TEM) techniques. With the increase of outer diameter of CNTs, specific surface area of the catalyst decreases while Co particle size increased accompanying with a decrease in CO conversion. The FTS performance is similar for samples calcined in N₂ or air at temperature below 550 °C. Over 550 °C, the results are much different in that the Co/CNTs can keep its activity due to the unchanged CNTs structure in N₂ while the Co/CNTs almost lose activity owing to the loss of CNTs structure and sintering of cobalt oxide clusters in air.     

High-pressure hydrogen/carbon monoxide syngas turbulent burning velocities measured at constant turbulent Reynolds numbers

Using a double-chamber explosion facility, we measure high-pressure turbulent burning velocities (S_T) of lean syngas (35%H₂/65%CO) spherical flames at constant turbulent Reynolds numbers (Re_T ≡ u′L_I/ν) varying from 6700 to 14,200, where the root-mean-square turbulent fluctuation velocity (u′) and the integral length scale (L_I) are adjusted in proportion to the decreasing kinematic viscosity of reactants (ν) at elevated pressure (p) up to 1.2 MPa. Results show that, contrary to popular scenario for turbulent flames, at constant Re_T, S_T decreases similarly as laminar burning velocities (S_L) with increasing p in minus exponential manners. Moreover, at constant p, S_T/S_L increases noticeably with increasing Re_T. It is found that the present very scattering S_T/S_L data at different p and Re_T can be nicely merged onto a relation of S_T/u′ = 0.49Da^0.25, where Da is the turbulent Damköhler number and values of S_T/u′ tends to level-off when Da > 160 and p > 0.7 MPa.     

Effect of hydrogen additive on methane decomposition to hydrogen and carbon over activated carbon catalyst

The effect of H₂ addition on CH₄ decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H₂ to CH₄ changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H₂ flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H₂, and when the H₂ flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H₂ to CH₄ and the catalyst deactivation is restrained. Filamentous carbon is obtained when H₂ is introduced into CH₄ reaction gas compared with the agglomerate carbon without H₂ addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition.     

Physical and chemical behaviour of tungsten oxide in the presence of nickel additive under hydrogen and carbon monoxide atmospheres

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 → WO_2.72 → WO₂ and, (ii) high temperature (>800 °C) transformation of WO₂ → W → WC. Furthermore, NiWO₄ alloy phase was transformed according to the sequence NiWO₄ → Ni + WO_2.72 → 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).