Simulation and thermodynamic analysis of chemical looping reforming and CO2 enhanced chemical looping reforming

The production of hydrogen from methane via two chemical looping reforming (CLR) processes was simulated and thermodynamically analysed, one process being the conventional CLR process, the other being a CO₂ sorption enhanced process. The aim of the work was to identify suitable operating conditions for obtaining an optimum hydrogen gas purity and yield, whilst operating auto-thermally, at atmospheric pressure and with no carbon formation. In both simulations, the reactors were simulated using the Gibbs minimisation technique. NiO was used as the oxygen storing species, whilst CaO was used as the CO₂ adsorbent.     

Thermodynamic study of combining chemical looping combustion and combined reforming of propane

Existing energy generation technologies emit CO₂ gas and are posing a serious problem of global warming and climate change. The thermodynamic feasibility of a new process scheme combining chemical looping combustion (CLC) and combined reforming (CR) of propane (LPG) is studied in this paper. The study of CLC of propane with CaSO₄ as oxygen carrier shows thermodynamic feasibility in temperature range (400-782.95 °C) at 1 bar pressure. The CO₂ generated in the CLC can be used for combined reforming of propane in an autothermal way within the temperature range (400-1000 °C) at 1 bar pressure to generate syngas of ratio 3.0 (above 600 °C) which is extremely desirable for petrochemical manufacture. The process scheme generates (a) huge thermal energy in CLC that can be used for various processes, (b) pure N₂ and syngas rich streams can be used for petrochemical manufacture and (c) takes care of the expensive CO₂ separation from flue gas stream and CO₂ sequestration. The thermoneutral temperature (TNP) of 702.12 °C yielding maximum syngas of 5.98 mol per mole propane fed, of syngas ratio 1.73 with negligible methane and carbon formation was identified as the best condition for the CR reactor operation. The process can be used for different fuels and oxygen carriers.     

Multiphase CFD-based models for chemical looping combustion process: Fuel reactor modeling

Chemical looping combustion (CLC) is a flameless two-step fuel combustion that produces a pure CO₂ stream, ready for compression and sequestration. The process is composed of two interconnected fluidized bed reactors. The air reactor which is a conventional circulating fluidized bed and the fuel reactor which is a bubbling fluidized bed. The basic principle is to avoid the direct contact of air and fuel during the combustion by introducing a highly-reactive metal particle, referred to as oxygen carrier, to transport oxygen from the air to the fuel. In the process, the products from combustion are kept separated from the rest of the flue gases namely nitrogen and excess oxygen. This process eliminates the energy intensive step to separate the CO₂ from nitrogen-rich flue gas that reduce the thermal efficiency.Fundamental knowledge of multiphase reactive fluid dynamic behavior of the gas-solid flow is essential for the optimization and operation of a chemical looping combustor.Our recent thorough literature review shows that multiphase CFD-based models have not been adapted to chemical looping combustion processes in the open literature. In this study, we have developed the reaction kinetics model of the fuel reactor and implemented the kinetic model into a multiphase hydrodynamic model, MFIX, developed earlier at the National Energy Technology Laboratory. Simulated fuel reactor flows revealed high weight fraction of unburned methane fuel in the flue gas along with CO₂ and H₂O. This behavior implies high fuel loss at the exit of the reactor and indicates the necessity to increase the residence time, say by decreasing the fuel flow rate, or to recirculate the unburned methane after condensing and removing CO₂.     

In situ gasification and CO2 separation using chemical looping with a Cu-based oxygen carrier: Performance with bituminous coals

This paper is concerned with the chemical looping combustion of coal in a technique whereby the fuel is gasified in situ using CO₂ in the presence of a batch of supported copper oxide (the “oxygen carrier”) in a single reactor. As the metal oxide becomes depleted, the feed of fuel is discontinued, the inventory of fuel is reduced by further gasification and then the contents are re-oxidised by the admission of air to the reactor, to begin the cycle again. A catalyst support, impregnated with a saturated solution of copper and aluminium nitrates, acted as a durable oxygen carrier over numerous cycles of reduction and oxidation, using air as the oxidant. Two bituminous coals (Taldinskaya, Russia, and Illinois No. 5, USA) were investigated and compared with a lignite (Hambach, Germany). The lignite was highly reactive and was gasified completely by 15 mol% CO₂ in N₂ at 1203 K and 1 bar, so that there was no build up of char in the bed. The bituminous coals produced chars much less reactive than the lignite char, so that there was a steady accumulation of char in the bed with number of cycles, with the degree of accumulation being dependent on the reactivity of the char. Since the kinetics of gasification by CO₂ of the chars from either bituminous coal were slow, their rates were controlled by intrinsic chemical kinetics and were not affected by the ability of the oxygen carrier to alter the rates of external mass transfer when gasification is rapid. However, it is likely that rates of gasification in the presence of the carrier are still larger than in its absence, owing to the overall lower [CO] present in the bulk of the fluidised bed during chemical looping. At the temperature used, the carrier was cycling between Cu and Cu₂O, since CuO is only stable if the partial pressure of O₂ exceeds 0.03 bar at 1203 K. The CuO decomposes to Cu₂O and O₂ relatively rapidly at these temperatures, once the oxygen concentration is effectively zero. It was impossible to ascertain in our experiments whether the oxygen so generated, after the switching of the air for nitrogen before the start of the succeeding cycle of gasification, made any substantial difference to the reactivity of the char present in the bed. The rate of oxidation of the carrier was found to be much more rapid than the rate of oxidation of the inventory of char. This allows a preferential oxidation of the carrier and most likely accounts for why progressively less CO and CO₂ is produced during successive cycles with short periods of oxidation: the increasingly reduced carrier reacts more rapidly than the char. There was no obvious impact from the sulphur contained in the fuels, but longer-term testing is needed. No agglomeration between the carrier particles and the ash was observed, despite the high temperatures during oxidation.     

In situ gasification of a lignite coal and CO2 separation using chemical looping with a Cu-based oxygen carrier

Chemical looping combustion (CLC) has the inherent property of separating CO₂ from flue gases. This paper is concerned with the application of chemical looping to the combustion of a solid fossil fuel (a lignite and its char) in a technique whereby the fuel is gasified in situ using CO₂ in the presence of a batch of supported copper oxide (the “oxygen carrier”) in a single reactor. As the metal oxide becomes depleted, the feed of fuel is discontinued, the inventory of fuel is reduced by further gasification and then the contents are re-oxidised by the admission of air to the reactor, to begin the cycle again. The choice of oxides is restricted because it requires an oxide which is exothermic during reduction to balance the endothermic gasification reactions. Copper has such oxides, but a key question is whether or not it can withstand temperatures at which gasification rates are significant (∼1173 K), particularly from the point of view of avoiding sintering and deactivation of the carrier in its reduced form. It was found that an impregnated carrier, made by impregnating a θ-alumina catalyst support (BET area 157 m²/g) with a saturated solution of copper and aluminium nitrates, acted as a durable carrier over 20 cycles of reduction and oxidation, using both Hambach lignite coal, and its char, and with air as the oxidising agent. During the course of the experiments, the BET surface area of the support fell from ∼60 m²/g, just after preparation, to around 6 m²/g after 20 cycles. However, this fall did not appear to affect the overall capacity of the oxygen carrier to react with fuels and its effect on the kinetics of the reaction with CO did not influence the outcome of the experiments, since the overall performance of the looping scheme is dominated by the much slower kinetics of the gasification reaction. The apparent kinetics of the gasification are faster in the presence of the looping agent: this is because the bulk concentration of CO in the presence of the looping agent is lower, and partly because the destruction of CO in the vicinity of a gasifying particle enhances the rate of removal of CO by mass transfer (and increases the local concentration of CO₂). There was little evidence to suggest a direct reaction between carbonaceous and carrier solids, other than via a gaseous intermediate. However, the observation of finite rates of conversion in a bed of active carrier, fluidised by nitrogen, is a scientific curiosity, which we have not been able to explain satisfactorily. At 1173 K, as used here, rates of gasification of Hambach lignite, and its char, are significant. The CuO in the carrier decomposes at 1173 K to produce gas-phase O₂ and Cu₂O: both can react with CO produced by gasification, whilst the O₂ can react directly with the char.     

Hydrogen production via chemical looping dry reforming of methane: Process modeling and systems analysis

The present study presents and analyses a family of “chemical looping dry reforming” (CLDR) processes that produce inherently separated syngas (H₂ and CO) streams via a combination of methane cracking in a “cracker reactor” and the Boudouard reaction (i.e., conversion of the formed carbon with CO₂ to CO) in a “CO₂ reactor,” and then further maximize the H₂ yield via conversion of the produced CO via water-gas-shift. Remaining CO₂ emissions are minimized via CO₂ capture and sequestration. Four different configurations are evaluated which differ in how the heat required for the highly endothermic dry reforming reaction is supplied: (i) combustion of additional CH₄ feed (CLDR-CH₄); (ii) combustion of some of the CO produced in the CO₂ reactor (CLDR-CO); and combustion of some of the carbon produced in the cracker reactor with (iii) pure oxygen (CLDR-C-oxy); or (iv) with air (CLDR-C-air). Process models are developed to comparatively analyze the mass and energy balances of these configurations, and benchmark them against H₂-production via conventional dry reforming and steam reforming of methane. Our results show that CLDR-C-oxy is the most promising H₂-production pathway among the chemical looping and conventional technologies both in terms of chemical energy efficiency and in terms CO₂ emissions. Thus, the unique flexibility offered by the production of inherently separated syngas streams in CLDR enables overcoming the disadvantage of the strongly endothermic dry reforming reaction by combusting carbon internally in the reactor and thus achieving highly effective heat integration. Overall, the results support the technical viability and demonstrate the promise for strong process intensification of CLDR compared to conventional dry reforming and even steam reforming, the most widely used H₂-production pathway to-date.     

The calcium looping cycle for CO2 capture from power generation, cement manufacture and hydrogen production

Calcium looping is a CO₂ capture scheme using solid CaO-based sorbents to remove CO₂ from flue gases, e.g., from a power plant, producing a concentrated stream of CO₂ (∼95%) suitable for storage. The scheme exploits the reversible gas-solid reaction between CO₂ and CaO(s) to form CaCO₃(s). Calcium looping has a number of advantages compared to closer-to-market capture schemes, including: the use of circulating fluidised bed reactors—a mature technology at large scale; sorbent derived from cheap, abundant and environmentally benign limestone and dolomite precursors; and the relatively small efficiency penalty that it imposes on the power/industrial process (i.e., estimated at 6-8 percentage points, compared to 9.5-12.5 from amine-based post-combustion capture). A further advantage is the synergy with cement manufacture, which potentially allows for decarbonisation of both cement manufacture and power production. In addition, a number of advanced applications offer the potential for significant cost reductions in the production of hydrogen from fossil fuels coupled with CO₂ capture. The range of applications of calcium looping are discussed here, including the progress made towards demonstrating this technology as a viable post-combustion capture technology using small-pilot scale rigs, and the early progress towards a 2 MW scale demonstrator.     

Ca-based sorbent looping combustion for CO2 capture in pilot-scale dual fluidized beds

To demonstrate process feasibility of in situ CO₂ capture from combustion of fossil fuels using Ca-based sorbent looping technology, a flexible atmospheric dual fluidized bed combustion system has been constructed. Both reactors have an ID of 100 mm and can be operated at up to 1000 °C at atmospheric pressure. This paper presents preliminary results for a variety of operating conditions, including sorbent looping rate, flue gas stream volume, CaO/CO₂ ratio and combustion mode for supplying heat to the sorbent regenerator, including oxy-fuel combustion of biomass and coal with flue gas recirculation to achieve high-concentration CO₂ in the off-gas. It is the authors' belief that this study is the first demonstration of this technology using a pilot-scale dual fluidized bed system, with continuous sorbent looping for in situ CO₂ capture, albeit at atmospheric pressure. A multi-cycle test was conducted and a high CO₂ capture efficiency (> 90%) was achieved for the first several cycles, which decreased to a still acceptable level (> 75%) even after more than 25 cycles. The cyclic sorbent was sampled on-line and showed general agreement with the features observed using a lab-scale thermogravimetric analysis (TGA) apparatus. CO₂ capture efficiency decreased with increasing number of sorbent looping cycles as expected, and sorbent attrition was found to be another significant factor to be limiting sorbent performance.     

Development of Ni-Pd bimetallic catalysts for the utilization of carbon dioxide and methane by dry reforming

The present research deals with catalyst development for the utilization of CO₂ in dry reforming of methane with the aim of reaching highest yield of the main product synthesis gas (CO, H₂) at lowest possible temperatures. Therefore, Ni-Pd bimetallic supported catalysts were prepared by simple impregnation method using various carriers. The catalytic performance of the catalysts was investigated at 500, 600 and 700 °C under atmospheric pressure and a CH₄ to CO₂ feed ratio of 1. Fresh, spent and regenerated catalysts were characterized by N₂ adsorption for BET surface area determination, XRD, ICP, XPS and TEM. The catalytic activity of the studied Ni-Pd catalysts depends strongly on the support used and decreases in the following ranking: ZrO₂-La₂O₃, La₂O₃ > ZrO₂ > SiO₂ > Al₂O₃ > TiO₂. The bimetallic catalysts were more active than catalysts containing Ni or Pd alone. A Ni to Pd ratio = 4 at a metal loading of 7.5 wt% revealed the best results. Higher loading lead to increased formation of coke; partly in shape of carbon nanotubes (CNT) as identified by TEM. Furthermore, the effect of different calcination temperatures was studied; 600 °C was found to be most favorable. No effect on the catalytic activity was observed if a fresh catalyst was pre-reduced in H₂ prior to use or spent samples were regenerated by air treatment. Ni and Pd metal species are the active components under reaction conditions. Best conversions of CO₂ of 78% and CH₄ of 73% were obtained using a 7.5 wt% NiPd (80:20) ZrO₂-La₂O₃ supported catalyst at a reaction temperature of 700 °C. CO and H₂ yields of 57% and 59%, respectively, were obtained.     

Computational fluid dynamic simulations of chemical looping fuel reactors utilizing gaseous fuels

A computational fluid dynamic (CFD) model for the fuel reactor of chemical looping combustion technology has been developed, with special focus on accurately representing the heterogeneous chemical reactions. A continuum two-fluid model was used to describe both the gas and solid phases. Detailed sub-models to account for fluid–particle and particle–particle interaction forces were also incorporated. Two experimental cases were analyzed in this study (Son and Kim, 2006; Mattison et al., 2001). Simulations were carried out to test the capability of the CFD model to capture changes in outlet gas concentrations with changes in number of parameters such as superficial velocity, metal oxide concentration, reactor temperature, etc. For the experiments of Mattisson et al. (2001), detailed time varying outlet concentration values were compared, and it was found that CFD simulations provided a reasonable match with this data.     

Characteristics of the NiO/hexaaluminate for chemical looping combustion

Chemical looping combustion technology has drawn much attention due to advantages such as no NO_x formation and simple CO₂ separation. The thermally stable oxygen carrier in the redox cycle at 1,000–1,400 K is necessary for the chemical lopping combustion. The thermally stable hexaaluminate can be a good candidate for the support material of the oxygen carrier. In this work, NiO/hexaaluminate has been developed in order to apply for chemical looping combustion. From the X-ray diffraction patterns, it was found that most of Ni existed in the form of NiO and NiAl₂O₄ in the obtained sample. The NiO supported on NiAl₂O₄ showed good characteristics in the reduction and oxidation reaction. The present work suggested that NiO/hexaaluminate is a promising material as oxygen carrier for the chemical looping combustion.     

Syngas and a separate nitrogen/argon stream via chemical looping reforming - A 140 kW pilot plant study

A dual circulating fluidized bed pilot plant was operated in chemical looping reforming conditions at a scale of 140 kW fuel power with natural gas as fuel. A nickel-based oxygen carrier was used as bed material. The pilot plant is equipped with an adjustable cooling system. Three experimental campaigns have been carried out at 747 °C (1020 K), 798 °C (1071 K) and 903 °C (1176 K), respectively. In each campaign, the global stoichiometric air/fuel ratio was varied step-wise between 1.1 and the minimum value possible to keep the desired operating temperature when the cooling is finally switched off. The results show that the fuel reactor exhaust gas approaches thermodynamic equilibrium. The residual amount of methane left decreases with increasing fuel reactor temperature. Further, the oxygen in the air reactor can be completely absorbed by the solids as soon as the air reactor operating temperature is higher than 900 °C (1173 K). Even though no steam was added to the natural gas feed no carbon formation was found for global excess air ratios larger than 0.4.     

Sorbent-enhanced/membrane-assisted steam-methane reforming

Thermodynamic equilibrium and kinetic reactor models are used to simulate a fluidized bed membrane reactor with in situ or ex situ hydrogen and/or CO₂ removal for production of pure hydrogen by steam methane reforming. In the equilibrium model, the membranes and CO₂ removal are located in separate vessels downstream of the reformer. As the recycle ratio increases, the overall performance approaches that where membranes are located inside the reactor. Whether located in situ or ex situ, hydrogen removal by membranes and CO₂ capture by sorbents both enhance hydrogen production. In the kinetic reactor model, a circulating fluidized bed membrane reformer is coupled with a catalyst/sorbent regenerator. Sorbent enhancement combined with membranes could provide very high hydrogen yields. In addition, since carbonation is exothermic, with its heat of reaction similar in magnitude to the endothermic heat of reaction of the net reforming reactions, sorbent enhancement can provide much of the heat needed in the reformer. The overall heat needed for the process would then be provided in a separate calciner, acting as a sorbent regenerator. While the technology is promising, several practical issues need to be examined.     

Mechanistic investigation of chemical looping combustion of coal with Fe2O3 oxygen carrier

The reaction of three Chinese coals with Fe₂O₃ oxygen carrier (OC) was performed in a thermogravimetric analyzer (TGA), with special focuses on the effects of varying heating rate and coal rank on reactivity. Fourier transform infrared spectroscopy (FTIR) was used to in situ detect the emitted gases from TGA. Field scanning electron microscopy/energy-dispersive X-ray spectrometry (FSEM-EDX) was used to study the morphology and elemental compositions of the reaction residues collected from TGA and the related phase evaluation was further identified by X-ray diffraction (XRD). Through all these experiments, it was found that the pyrolysis of coal samples without Fe₂O₃ OC under N₂ atmosphere underwent the dehydration and the ensuing primary and secondary pyrolysis stages. The increasing heating rate shifted the characteristic temperature (T_m) of the primary pyrolysis to a higher temperature and favored a more rapid generation of volatile matters. When the three coals reacting with Fe₂O₃ OC, TGA results demonstrated even over 200 °C, the reaction still experienced the partial pyrolysis at the relatively low temperature and the ensuing two reactions of Fe₂O₃ with the pyrolysis products at the primary and secondary stages. The coal of low rank with high volatile content should be preferred for the full conversion of coal into CO₂. Furthermore, the activation energy of Fe₂O₃ OC reacting with PDS at its primary pyrolysis stage was the largest, more than 70 kJ/mol. Finally, SEM-EDX and further XRD analysis of the residues from the reaction of PDS with Fe₂O₃ OC indicated the reduced counterpart of Fe₂O₃ was Fe₃O₄, and some inert iron compounds such as Fe₂SiO₄ and FeAl₂O₄ were also generated, which might deteriorate the reactivity of Fe₂O₃ OC.     

Influence of calcination conditions on carrying capacity of CaO-based sorbent in CO2 looping cycles

This study examines the loss of sorbent activity caused by sintering under realistic CO₂ capture cycle conditions. The samples tested here included two limestones: Havelock limestone from Canada (New Brunswick) and a Polish (Upper Silesia) limestone (Katowice). Samples were prepared both in a thermogravimetric analyzer (TGA) and a tube furnace (TF). Two calcination conditions were employed: in N₂ at lower temperature; and in CO₂ at high temperature. The samples obtained were observed with a scanning electron microscope (SEM) and surface compositions of the resulting materials were analyzed by the energy dispersive X-ray (EDX) method. The quantitative influence of calcination conditions was examined by nitrogen adsorption/desorption tests, gas displacement pycnometry and powder displacement pycnometry; BET surface areas, BJH pore volume distributions, skeletal densities and envelope densities were determined. The SEM images showed noticeably larger CaO sub-grains were produced by calcination in CO₂ during numerous cycles than those seen with calcination in nitrogen. The EDX elemental analyses showed a strong influence of impurities on local melting at the sorbent particle surface, which became more pronounced at higher temperature. Results of BET/BJH testing clearly support these findings on the effect of calcination/cycling conditions on sorbent morphology. Envelope density measurements showed that particles displayed densification upon cycling and that particles calcined under CO₂ showed greater densification than those calcined under N₂. Interestingly, the Katowice limestone calcined/cycled at higher temperature in CO₂ showed an increase of activity for cycles involving calcination under N₂ in the TGA. These results clearly demonstrate that, in future development of CaO-based CO₂ looping cycle technology, more attention should be paid to loss of sorbent activity caused by realistic calcination conditions and the presence of impurities originating from fuel ash and/or limestone.     

Thermodynamic analysis of dry autothermal reforming of glycerol

Dry autothermal reforming of glycerol uses a combination of dry (CO₂) reforming and partial oxidation reactions to produce syngas rich product stream. Thermodynamic equilibrium data for dry autothermal reforming of glycerol was generated for temperature range 600-1000 K, 1 bar pressure, OCGR [feed O₂/C (C of glycerol only) ratio] 0.1 to 0.5 and CGR [feed CO₂/glycerol ratio] 1 to 5 and analyzed. The objective of the paper is to identify the thermodynamic domain of the process operation, study the variation of product distribution pattern and describe the optimum conditions to maximize yield of the desired product and minimize the undesired product formation. Higher OCGR and higher CGR yielded a syngas ratio (∼ 1), with lower carbon and methane formation, while lower CGR and lower OCGR yielded good hydrogen and total hydrogen, with low water and CO₂ production. The best thermoneutral condition for DATR of glycerol operation was seen at a temperature of 926.31 K at 1 bar pressure, OCGR = 0.3 and CGR = 1 that gave 2.67 mol of hydrogen, 4.8 mol of total hydrogen with negligible methane and carbon formations.     

Hydrogen production through chemical looping using NiO/NiAl2O4 as oxygen carrier

A new autothermal route to produce hydrogen from natural gas via chemical looping technology was investigated. Tests were conducted in a micro-fixed bed reactor loaded with 200 mg of NiO/NiAl₂O₄ as oxygen carrier. Methane reacts with a nickel oxide in the absence of molecular oxygen at 800 °C for a period of time as high as 10 min. The NiO is subsequently contacted with a synthetic air stream (21% O₂ in argon) to reconstitute the surface and combust carbon deposited on the surface. Methane conversion nears completion but to minimize combustion of the hydrogen produced, the oxidation state of the carrier was maintained below 30% (where 100% represents a fully oxidized surface). Co-feeding water together with methane resulted in stable hydrogen production. Although the carbon deposition increased with time during the reduction cycle, the production rate of hydrogen remained virtually constant. A new concept is also presented where hydrogen is obtained from methane with inherent CO₂ capture in an energy neutral 3-reactors CFB process. This process combines a methane combustion step where oxygen is provided via an oxygen carrier, a steam methane reforming step catalyzed by the reduced oxygen carrier and an oxidizing step where the O-carrier is reconstituted to its original state.     

Modelling of a fluidized bed carbonator reactor to capture CO2 from a combustion flue gas

In recent years several processes incorporating a carbonation-calcination loop in an interconnected fluidized bed reactor have been proposed as a way to capture CO₂ from flue gases. This paper is a first approximation to the modelling of a fluidized bed carbonator reactor. In this reactor the flue gas comes into contact with an active bed composed of particles with very different activities, depending on their residence time in the bed and in the carbonation-calcination loop. The model combines the residence time distribution functions with existing knowledge about sorbent deactivation rates and sorbent reactivity. The fluid dynamics of the solids (CSTR) and gases (PF) in the carbonator are based on simple assumptions. The carbonation rates are modelled defining a characteristic time for the transition between a fast reaction regime to a regime with a zero reaction rate. On the basis of these assumptions the model is able to predict the CO₂ capture efficiency for the flue gas depending on the operating and design conditions. Operating windows with high capture efficiencies are discussed, as well as those conditions where only modest capture efficiencies are possible.     

Carbon-free dry reforming of methane to syngas over NdCoO3 perovskite-type mixed metal oxide catalyst

CoNdO_x (Co/Nd = 1) is a highly promising catalyst for the carbon-free CO₂ reforming of methane. Influence of the Co/Nd ratio on the catalyst performance in the CO₂ reforming and also on the crystalline phases and reduction by temperature programmed reduction (TPR) of the CoNdO_x catalyst has also been investigated. The CoNdO_x (CoNd = 1.0) catalyst consisted of mainly NdCoO₃ perovskite-type mixed metal oxide and it showed not only a high resistance to carbon formation at different process conditions (viz. temperature = 750–900 °C and gas hourly space velocity (GHSV) = 10000–50000 cm³ g^–1 h^–1) but also high activity and selectivity in the CO₂ reforming process. The high resistance to carbon formation for this catalyst is attributed mostly to strong metal (Co°)–support (Nd₂O₃) interactions.