Reactivity of Ce-ZrO2 (doped with La-, Gd-, Nb-, and Sm-) toward partial oxidation of liquefied petroleum gas: Its application for sequential partial oxidation/steam reforming

Ce-ZrO₂ was found to have useful partial oxidation activity under moderate temperatures. It converted liquefied petroleum gas (LPG) to H₂, CH₄, CO and CO₂ with small amounts of C₂H₆ and C₂H₄ formations depending on the operating temperature and provided significantly greater resistance toward carbon deposition compared to conventional Ni/Al₂O₃. The doping of La, Sm and Gd over Ce-ZrO₂ considerably improved catalytic reactivity, whereas Nb-doping reduced its reactivity. It was found that the impact of doping element is strongly related to the degrees of oxygen storage capacity (OSC) and/or lattice oxygen (O_O^x) of materials. Among all catalysts, La-doped Ce-ZrO₂ was observed to have highest OSC value and was the most active catalyst. Above 850 °C with inlet LPG/O₂ molar ratio of 1.0/1.0, the main products from the reaction over La-doped Ce-ZrO₂ were H₂, CH₄, CO, and CO₂.     

Hydrogen production by catalytic partial oxidation of methane and propane on Ni and Pt catalysts

In recent years the catalytic partial oxidation has been taken into consideration as a suitable process for hydrogen production, because of its exothermic nature which makes the process less energy and capital cost intensive with respect to steam reforming. In this paper the behaviour of three different catalyst typologies, two based on Ni–_Al2O3${\mathrm{Al}}_2{\mathrm{O}}_3$ (different in active phase composition) and one constituted by Pt supported on _CeO2${\mathrm{CeO}}_2$, is studied for partial oxidation of propane (as representative of liquefied petroleum gas). For comparison the same catalysts have been tested also in methane partial oxidation.     

Preparation and characterization of CuOAl2O3 catalyst for dimethyl ether production via methanol dehydration

In the present study, a CuOAl₂O₃ catalyst with CuAl₂O₄ spinel structure was prepared by a co-precipitation method and used for dimethyl ether (DME) production via methanol dehydration at 50 bar and different reaction temperatures (150, 250, and 350 °C). Upon XPS analysis of the copper and aluminum species in the fresh and used CuOAl₂O₃ catalyst, CuAl₂O₄ was found to be the dominant species with more than 50% of total composition. Three reductive reactions and temperatures for the formation of CuH (102.3 °C), the interaction between Cu²⁺ and Al atoms (356.6 °C), and the reduction of CuO (520.1 °C) were analyzed by H₂-TPR. Furthermore, the copper oxidation state in the fresh and used catalyst was Cu(II), as determined by the XANES spectra. The fine structural parameters revealed that the coordination number of Cu changed from 2.75 to 2.44 during the catalytic reaction, and that the CuO bond distance increased from 1.94 to 1.98 Å due to strengthened Cu²⁺Al interactions. On-line FTIR spectra revealed that the optimum temperature for the formations of HCOOH (by-product) and DME (product) were 150 and 250 °C, respectively. The catalytic reactions in the duration of DME synthesis were found that included methanol decomposition, methanol/formic acid formations, and methanol dehydration occurring at CuO, Cu, and Al₂O₃/CuAl₂O₄ active sites, respectively. The highest methanol conversion (67.3%) and DME yield (40.6%) were obtained at 250 °C and 50 bar, as demonstrated by the catalyst performance. In addition, optimum DME formation (equilibrium constant 1.76 × 10^?2 L mol^?1 h^?1 and activation energy 5.14 kJ mol^?1) occurred at 250 °C, as determined from the linear regression of the second order model with a high R² value (0.98). The exothermal and non-spontaneous nature of DME formation at high temperature was evaluated through thermodynamic calculations of the reaction enthalpy, entropy, and Gibbs energy.     

Hydrogen-rich gas production for solid oxide fuel cell (SOFC) via partial oxidation of butanol: Thermodynamic analysis

Butanol partial oxidation for hydrogen-rich gas production has been studied by Gibbs free energy minimization method. The optimum conditions for hydrogen-rich gas production are identified: reaction temperatures between 1115 and 1200 K and oxygen-to-butanol molar ratios between 1.6 and 1.7 at 1 atm. Under the optimal conditions, complete conversion of butanol, 93.07%–96.56% yield of hydrogen and 94.02%–97.55% yield of carbon monoxide could be achieved in the absence of coke formation. The butanol partial oxidation with O₂ is suitable for providing hydrogen-rich fuels for Solid Oxide Fuel Cell (SOFC). Higher pressures have a negative effect, but inert gases have a positive effect, on the hydrogen yield. Coke tends to form at lower temperatures and lower oxygen-to-butanol molar ratios.     

Effective hydrogen production from partial oxidation of propane over composite Ni/Al2O3SiC catalyst

In this work, hydrogen production from partial oxidation (POX) of propane over composite Ni/Al₂O₃SiC catalyst was investigated. In order to utilize the high thermal conductivity and chemical stability of SiC, the composite Al₂O₃SiC support of the catalyst was synthesized by precipitation technique, then Ni component was loaded using impregnation method. The as-prepared samples were characterized by X-ray diffraction, BET, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. As observed, stacking porous structures were appeared after calcination process by doping SiC with certain ratios. According to the stiochiometric ratio, a C₃H₈O₂ (1:1.5) gas mixture was used to study the catalytic activity for hydrogen production from POX of propane. From the results, local overheat of the catalyst bed generated by the exothermic reactions was relieved by doping SiC and Ni/Al₂O₃SiC (30 wt%) catalyst performed a higher hydrogen production. Aggregation and carbon deposition of Ni/Al₂O₃SiC (30 wt%) catalyst were reduced compared to Ni/Al₂O₃ from the observation of SEM and TEM with H₂ production up to around 236 μmol/g_cat·s and kept stable for 26 h at 600 °C. By means of TGA, non-isothermal oxidative decarburizations of the spent catalysts were studied. It was found that less carbon deposit and lower activation energy for oxidative decarburization were found by doping SiC to Ni/Al₂O₃.     

Reducing the operation temperature of a solid oxide fuel cell using a conventional nickel-based cermet anode on dimethyl ether fuel through internal partial oxidation

Dimethyl ether (DME)-oxygen mixture as the fuel of an anode-supported SOFC with a conventional nickel-cermet anode for operating at reduced temperatures is systematically investigated. The results of the catalytic tests indicate that sintered Ni-YSZ has high activity for DME partial oxidation, and DME conversion exceeds 90% at temperatures higher than 700 °C. Maximum methane selectivity is reached at 700 °C. Cell performance is observed between 600 and 800 °C. Peak power densities of approximately 400 and 1400 mW cm⁻² at 600 and 800 °C, respectively, are reached for the cell operating on DME-O₂ mixture. These values are comparable to those obtained using hydrogen as a fuel, and cell performance is reasonably stable at 700 °C for a test period of 340 min. SEM results demonstrate that the cell maintains good geometric integrity without any delimitation of respective layer after the stability test, and EDX results show that carbon deposition occurrs only at the outer surface of the anode. O₂-TPO analysis shows that carbon deposition over the Ni-YSZ operating on DME is greatly suppressed in the presence of oxygen. Internal partial oxidation may be a practical way to achieve high cell performance at intermediate-temperatures for SOFCs operating on DME fuel.     

Effect of ruthenium addition on molybdenum catalysts for syngas production via catalytic partial oxidation of methane in a monolithic reactor

Hydrogen is mainly produced from hydrocarbon resources. Natural gas, mostly composed of methane, is widely used for hydrogen production. As a valuable feedstock for ‘Fischer–Tropsch’ (FT) process and ‘Gas to Liquids’ (GTL) technology, syngas production from catalytic partial oxidation of methane (CPOM) is gaining prominence especially owing to its more desirable H₂/CO ratio; relatively less energy consumption, and lower investment, compared to steam reforming processes (SMR), the leading technology.In the present study, effect of ruthenium (Ru) addition on molybdenum (Mo) catalysts for syngas production from methane (CH₄) via partial oxidation in a monolithic reactor was investigated. Mo based catalysts supported on Nickel (Ni) and Cobalt (Co) metal oxides and Ni-Co bimetallic oxides and their Ru added versions were developed, characterized, and tested for performance in a monolithic type reactor system. Catalyst activity was investigated in terms of H₂ and CO selectivity, CH₄ conversion; and CO₂ emission and it is concluded that addition of Ru over the structure led to increase in catalytic activity and reduction in carbon deposition over the catalyst surface.     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

SOFC anodes for direct oxidation of hydrogen and methane fuels containing H2S

Single cell solid oxide fuel cells using Ni-YSZ and Co-YSZ anodes were tested in H₂, CH₄, H₂S/H₂ and H₂S/CH₄ fuel mixtures. Their performance was found to quickly degrade in dry CH₄ due to carbon deposition and lifting of the anode from the electrolyte. In contrast, hydrogen or methane containing H₂S showed an increase in exchange current densities when compared to H₂,M/YSZ/LSM,air systems (M = Ni or Co) despite having less optimal anode microstructure. Conversion from metal to metal-sulfide in the presence of H₂S produced large, dense metal-sulfide particles surrounded by YSZ, thus decreasing the triple-phase boundary. Furthermore, CoS-based anodes showed phase segregation and densification toward the electrolyte. Despite this, long-term testing at η_a = 0.5 V of the H₂S/CH₄,CoS-YSZ/YSZ/LSM,air system showed no signs of degradation of the anode over a 6-day period. Only after removal of H₂S from the H₂S/CH₄ stream did the CoS-anode reduce back to Co, signifying H₂S is required to maintain the metal-sulfide active anode.     

Synthesis of NiO/MgO/ZrO2 catalyst for syngas production from partial oxidation and dry reforming of biogas

This work focuses on a facile NiO/MgO/ZrO₂ synthesis protocol for syngas production via partial oxidation and dry reforming of biogas. Herein, performance of the developed catalysts with different amounts of MgO (0–40 %wt. of support) and NiO (10–50 %wt.) on %CH₄ conversion, %CO₂ conversion, H₂/CO ratio, and carbon formation are studied. The results reveal the presence of monoclinic ZrO₂ and tetragonal ZrO₂ phases with 50%NiO/ZrO₂ catalyst synthesized by surface modification technique using carbon derived from urea. Addition of MgO in the catalyst shows ability to stabilize tetragonal ZrO₂ phase as well as enhance basic surface of the catalyst. These properties render the adsorption of CO₂ molecules on the surface, which subsequently are reduced by carbon, leading to CO production. Appropriated amount of NiO and MgO, which is 30 %wt. NiO and 20 %wt. MgO (relative to ZrO₂) can produce syngas having quality (H₂/CO molar ratio) of ca. 2.     

Thermodynamic and catalytic properties of Cu- and Pd- oxides over mixed γ–χ–Al2O3 for methanol dehydration toward dimethyl ether

The development of catalytic systems to generate alternative energies capable of replacing diesel is a great challenge. Methanol dehydration (2CH₃OH → CH₃OCH₃ + H₂O) is one of the most suitable catalytic reactions to produce dimethyl ether (DME). In DME synthesis, CuO/γ–Al₂O₃ based-materials showed to be catalytically active at high pressures, but these lack high performance under atmospheric conditions. In this work, we synthesized CuO/γ–χ–Al₂O₃, PdO/γ–χ–Al₂O₃, and CuOPdO/γ–χ–Al₂O₃ by a facile impregnation method for methanol dehydration at atmospheric pressure. Catalytic results showed that the CuOPdO/γ–χ–Al₂O₃ sample performed the highest activity. All catalysts reached selectivity of 100% toward DME, regardless of the reaction temperature. Remarkably, the bimetallic catalyst containing low loadings of copper and palladium retained stability during 48 h of reaction at 275 °C, and after its regeneration they showed a similar trend. The activation energies (E_a) for the methanol dehydration using the catalyst that performed the highest catalytic activity CuOPdO/γ–χ–Al₂O₃ compared with the material with the lowest catalytic activity γ–χ–Al₂O₃ were obtained. The activation energy values of the γ–χ–Al₂O₃ and CuOPdO/γ–χ–Al₂O₃ catalysts were 112.57 kJ/mol and 45.73 kJ/mol, respectively.     

Experimental and numerical study of detailed reaction mechanism optimization for syngas (H2 + CO) production by non-catalytic partial oxidation of methane in a flow reactor

The National Institute of Standards and Technology (NIST) detailed reaction mechanism of methane combustion was optimized based on a flow reactor experiment to obtain syngas (H₂ + CO). The experimental methane partial oxidation was conducted with pre-mixed gas in a flow reactor. Specifically, 0.2% methane and 0.1% oxygen were diluted with 99.7% argon, restraining the exothermic effect. The experiment was conducted from 1223 K to 1523 K under pressure. Through a comparison of the experimental results with calculated values, the NIST mechanism was selected as a starting point. Rate coefficients of O + OH = O₂ + H, CH₃ + O₂ = CH₃O + O, and C₂H₂ + O₂ = HCCO + OH were replaced with results from other studies. The replaced rate coefficient for CH₃ + O₂ = CH₃O + O was again optimized, within its reported uncertainty of 3.16, based on the experimental results of this study. The revised value of the rate coefficient for CH₃ + O₂ = CH₃O + O was k₃₇ = 7.92 × 10¹³ × e^{(−31400/RT)}. The optimized mechanism showed better performance in predicting the results of other studies, as well as this study. The optimization reduced the RMS error for the results of this study from 6.7 to 1.18.     

Catalytic partial oxidation of methane and isotopic oxygen exchange reactions over O labeled Rh/Gadolinium doped ceria

¹⁸O labeled catalysts, Rh/(Ce_0.91Gd_0.09)O_2−x (Rh/GDC10) and Rh/γ-Al₂O₃ (Rh/ALU) were used to study the catalytic partial oxidation of methane (CPOM) and oxygen isotopic exchange reactions. During the CPOM tests, higher C¹⁸O than C¹⁶O concentrations were observed over ¹⁸O labeled Rh/GDC10 than Rh/ALU, which is explained by the higher oxygen storage capacity and oxygen mobility of the former catalyst. Similarly, Rh/GDC10 showed higher oxygen exchange rates than Rh/ALU during the isotopic exchange experiments. The oxygen exchange between the gas phase and the solid is limited by the oxygen mobility in/on the catalyst. This catalytic behavior is due to the fact that ceria has two stable oxidation states, Ce³⁺ and Ce⁴⁺ and the addition of Gd³⁺ to ceria lattice enhanced the oxygen mobility by the creation of oxygen vacancies. These higher oxygen exchange rates also correlate to higher concentrations of C¹⁸O than C¹⁶O during the CPOM experiments. Pulse experiments suggest that the reaction mechanism for the CPOM on Rh/GDC10 occurred through a mixed (direct and indirect) mechanism. The direct mechanism assumes that H₂ and CO are primary reaction products formed in the oxidation zone at the catalyst entrance. Thus, CO formed from the reaction between lattice oxygen in Rh/GDC10 and adsorbed atomic carbon. CO₂ is formed through an indirect mechanism, where CH₄ reacts with O₂ to form CO₂ and H₂O. CO forms through the reactions between 1) CO₂ and CH₄ and 2) CH₄ and H₂O.     

Partial oxidation of methane over CeO2 loaded hydrotalcite (MgNiAl) catalyst for the production of hydrogen rich syngas (H2, CO)

In this work, partial oxidation of methane (POM) was investigated using Mg-Ni-Al (MNA) hydrotalcite promoted CeO₂ catalyst in a fixed bed reactor. MNA hydrotalcite was synthesized using the co-precipitation process, while CeO₂ was incorporated via the wetness impregnation technique. The CeO₂@MNA samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) technique. The catalytic activity of CeO₂ promoted MNA (CeO₂@MNA) for POM reaction was evaluated for various CeO₂ loading kept the feed ratio CH₄/O₂ = 2 at 850 °C. The catalyst containing 10 wt% cerium loading (10%CeO₂@MNA) showed 94% CH₄ conversion with H₂/CO ratio above 2.0, that is more suitable for FT synthesis. The performance of catalyst is attributed to highly crystalline stable CeO₂@MNA with better Ce-MNA interactions withstand for 35 h time on stream. Furthermore, the spent catalyst was examined by TGA, SEM-EDS, and XRD to evaluate the carbon formation and structural changes during the span of reaction time.     

Hydrogen production by catalytic partial oxidation of methane over staged Pd/Rh coated monoliths: Spatially resolved concentration and temperature profiles

The catalytic partial oxidation (CPOX) of methane is studied over staged palladium/alumina and rhodium/alumina coated monoliths by an in-situ sampling technique to resolve the axial species concentration and temperature profiles. A molar C/O ratio of unity, which is stoichiometric for the formation of synthesis gas (CO/H₂), and short residence times are chosen for this autothermal process. The profiles of the staged monoliths are compared with profiles of single-sliced palladium/alumina and rhodium/alumina coated monoliths. The investigations clearly show two zones inside the catalytic channel. In the staged catalyst with the Pd stage being on the upstream side as well as in the single-sliced Pd catalyst, hydrogen is not formed before oxygen is almost completely consumed, i.e. a total oxidation zone is observed in front of a steam reforming zone. In the Rh catalyst, in the first 2 mm zone, total oxidation and steam reforming occur as prevalent reactions followed by a reforming zone with steam reforming as dominating reaction. The observations are interpreted in terms of the indirect and direct route towards hydrogen formation in CPOX of methane.     

Syngas production by integrating CO2 partial gasification of pine sawdust and methane pyrolysis over the gasification residue

The aim of this work was to study syngas production by integrating CO₂ partial gasification (for CO production) of pine sawdust (PS) and methane pyrolysis (for H₂ production) over the gasification residue. Effect of the gasification conditions (including CO₂ flow rate, reaction temperature, mass ratio of PS:Ni and reaction time) was investigated on properties of the gasification residue. Besides CO-rich gas released from the gasification process with CO₂ conversion up to about 92%, the gasification residue could serve as robust catalyst for H₂ production by methane pyrolysis. Thanks to the nickel crystallites formed with high reduction degree and high dispersion on the surface after the gasification process, the gasification residue was competent for high and stable methane conversion (about 91%) at 850 °C. In addition to the flexible syngas output (in theory, with an arbitrary ratio of H₂/CO), valuable filamentous carbons can be achieved by regulating the process parameters.     

Improvement of splitting performance of Ce0.75Zr0.25O2 material: Tuning bulk and surface properties by hydrothermal synthesis

Thermochemical cycles received renewed interest as CO₂ and H₂O energy-upgrading processes using solar energy as source. The two-step cycles, based on self-reduction in a solar reactor at high temperature (above 1300–1400 °C) and re-oxidation by CO₂ and/or H₂O flow, are the most interesting due to their simplicity and high theoretical solar-to-fuel efficiency. In the two-step cycle, ceria has been recognized as the benchmark material but it suffers from high reduction temperature, low re-oxidation kinetics as well as low stability, thus hindering practical application. In this work, the redox properties of two Ce_0.75Zr_0.25O₂ materials prepared by hydrothermal synthesis were compared with those of a co-precipitated sample with the same nominal composition used as reference. Samples were characterized by X-Ray Diffraction (XRD), N₂ physisorption, Scanning Elecron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and Electron Paramagnetic Resonance (EPR); their self-reducibility and CO₂ splitting activity were tested in a Thermogravimetric (TG) balance, while H₂O splitting properties were studied in an ad-hoc fixed bed reactor on H₂ pre-reduced samples. Characterization results and activity tests agreed that the Ce³⁺ fraction both on the surface and in the bulk of ceria-zirconia can be increased by hydrothermal synthesis, thus providing improved redox properties and higher splitting activity with respect to the co-precipitated sample. So, hydrothermal synthesis, providing a controlled nucleation and growth of crystallites, appears as a promising route for the preparation of ceria-based materials with tuned oxygen vacancies.     

Direct dimethyl-ether proton exchange membrane fuel cells and the use of heteropolyacids in the anode catalyst layer for enhanced dimethyl ether oxidation

In this study, polarization and impedance experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. The DME flow rate, backpressure, and water flow rate were optimized. Three heteropolyacids, phosphomolybdic acid, H₃PMo₁₂O₄₀. (HPMo), phosphotungstic acid, H₃PW₁₂O₄₀, (HPW), and silicotungstic acid, H₄SiW₁₂O₄₀, (HSiW) were incorporated into the anode catalyst layer in combination with Pt/C. Both HPW-Pt and HSiW-Pt showed higher overall performance than the Pt control. Anodic polarizations were also performed, at 30 psig, Tafel slopes of 67 mV dec⁻¹, 72 mV dec⁻¹, and 79 mV dec⁻¹ were found for HPW-Pt, HSiW-Pt and the Pt control, respectively. At 0 psig, the Tafel slopes were 56 mV dec⁻¹, 58 mV dec⁻¹, and 65 mV dec⁻¹ for HPW-Pt, HSiW-Pt and the Pt control. The trends in the Tafel slope values are in agreement with the polarization data and the electrochemical impedance spectroscopy results. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control. When the maximum power density obtained using the HPW-Pt MEA is normalized by the mass of Pt used, the optimal result, 78 mW mg⁻¹ Pt, the highest observed at 30 psig and 100 °C to date.     

Low-temperature catalytic partial oxidation of hydrocarbons (C1–C10) for hydrogen production

The catalytic partial oxidation of hydrocarbons to provide hydrogen for fuel cells, mobile or stationary, requires high temperatures (900°C), multireactors and incurs the highest incremental costs for the gasoline fuel processor. New experimental data between 500°C and 600°C, supported by equilibrium calculations, show that hydrogen with low carbon monoxide concentrations can be produced from liquid and gaseous hydrocarbons, thus simplifying the reactor chain. Low sulphur refinery feeds (C₄–C₆, C₄–C₁₀), simulated natural gas (C₁–C₃) and single compounds are used and safety procedures discussed. Results from laboratory reactors with 1 wt% rhodium on mixed oxide catalysts show that hydrogen rates of 43,000 lH₂/h/l reactor (power density 129 kWth/l reactor) are produced with RON=95 feeds. However, the cost and availability of rhodium limit the catalyst rhodium content to 0.1 wt% when 31,100 lH₂/h/l reactor were measured. Optimisation and reactor scale-up for heat management is in progress.     

Partial oxidation of methane over Rh/supported-ceria catalysts: Effect of catalyst reducibility and redox cycles

Partial oxidation of methane (POM) was studied over Rh/(Ce_0.56Zr_0.44)O_2−x, Rh/(Ce_0.91Gd_0.09)O_2−x, Rh/(Ce_0.71Gd_0.29)O_2−x and Rh/(Ce_0.88La_0.12)O_2−x. The effect of catalyst reducibility and redox cycles was investigated. It was found that the type of doped-ceria support and its reducibility played an important role in catalyst activity. It was also observed that redox cycles had a positive influence on H₂ production, which was enhanced as the number of redox cycle increased. Results of carbon formation are discussed as a function of ionic conductivity. Temperature programmed reduction (TPR) profiles, BET surface area, ionic conductivity and XRD patterns were determined to characterize catalysts. Catalytic tests revealed that of the materials tested, Rh/(Ce_0.56Zr_0.44)O_2−x was the most active material for the production of syngas, which correlates with its TPR profile. It was observed that doping CeO₂ with Zr, rather than with La or Gd caused an enhanced reducibility of Rh/supported-ceria catalysts.