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The sluggish reaction kinetics in the cathode usually leads to considerable cathode polarization resistance, hindering the development of proton conducting solid oxide fuel cells (H-SOFCs) operated at intermediate temperatures (400–650 °C). To address this problem, for the first time, a novel hybrid catalyst consisting of PrNi0.5Mn0.5O3 and PrOx is impregnated in the (La0.60Sr0.40)0.95Co0.20Fe0.80O3-δ (LSCF) cathode of H-SOFCs, resulting in significant enhancement of the cathode reaction kinetics. Single cells with impregnated LSCF cathode and BaZr0.8Y0.2O3 (BZY) electrolyte yield a maximum power density (MPD) of 0.198 W cm−2 at 600 °C, more than doubled of that with blank LSCF cathode (0.083 W cm−2). ECR and EIS studies reveal that the hybrid catalyst can substantially accelerate the oxygen-ion transfer and oxygen dissociation-absorption processes in the cathode, resulting in significantly lower polarization resistance and higher MPD. In addition, the hybrid catalyst possesses good chemical and microstructural stability at 600 °C. Consequently, the single cells with impregnated LSCF cathode show excellent durability. This study shows that the impregnation of this novel hybrid catalyst in the cathode could be a promising approach to improve the performance and stability of H-SOFCs.

A miniature methanol reformer system has been designed and built to technology readiness level exceeding a laboratory prototype. It is intended to feed fuel cells with electric power up to 100 W and contains a complete setup of the technological elements: catalytic reforming and PROX reactors, a combustor, evaporators, actuation and sensing elements, and a control unit. The system is engineered not only for performance and quality of the reformate, but also for its lightweight and compact design, seamless integration of elements, low internal electric consumption, and safety. In the paper, the design of the system is presented by focussing on its miniaturisation, integration, and process control.

Analysis of a fuel processor based on methanol steam reforming has been carried out to produce fuel cell grade H2. Six reactor configurations namely FBR1 (fixed bed reactor), MR1 (H2 selective membrane reactor with one reaction tube), MR2 (H2 selective membrane reactor with two reaction tubes), FBR2 (FBR1 + preferential CO oxidation (PROX) reactor), MR3 (MR1 + PROX), and MR4 (MR2 + PROX) are evaluated by simulation to identify the suitable processing scheme. The yield of H2 is significantly affected by H2 selective membrane, residence time, temperature, and pressure conditions at complete methanol conversion. The enhancement in residence time in MR2 by using two identical reaction tubes provides H2 yield of 2.96 with 91.25 mol% recovery at steam/methanol ratio of 1.5, pressure of 2 bar and 560 K temperature. The exit retentate gases from MR2 are further treated in PROX reactor of MR4 to reduce CO concentration to 4.1 ppm to ensure the safe discharge to the environment. The risk of carbon deposition on reforming catalyst is highly reduced in MR4, and MR4 reactor configuration generates 7.4 NL min−1 of CO free H2 from 0.12 mol min−1 of methanol which can provide 470 W PEMFC feedstock requirement. Hence, process scheme in MR4 provides a compact and innovative fuel cell grade H2 generating unit.

Since hydrogen is produced by reforming of hydrocarbon it contains carbon monoxide (CO). In order to make hydrogen suitable for proton exchange membrane fuel cell application there is need to reduce concentration of CO less than 100 ppm. Water–Gas-Shift reactions subsequent to reforming lower CO concentration in H 2 to about 1–1.5% by volume. Preferential oxidation of CO (PROX–CO) using a catalyst is therefore important for further cleaning up of CO from H 2 . The catalyst in this study is platinum supported over lanthanum ferrite–ceria (Pt/LaFeO 3 –CeO 2 ) exhibits excellent activity of 99.8% and selectivity of 95.7% at a relatively lower temperature of 100 °C with an equivalence ratio of 3 for PROX–CO. The concentration of CO is reduced from 1% v/v in feed to ca. 30 ppm in product gas with relatively lower loss of hydrogen is the most significant achievement in this study. The catalyst is selective towards CO oxidation as the hydrogen loss is relatively low (ca. 3.8%) and there is no methane formation. The improvement in catalytic activity and selectivity is attributed to the strong metal support interaction and open morphology of catalyst. The results obtained in this study reveal the excellent catalytic activity by using LaFeO 3 –CeO 2 as support for Pt catalyst.

A coking-resistant catalyst prepared using a novel catalyst support is characterized and its performance on reforming of natural gas for fuel cell system applications is investigated. Two key issues, i.e., the stability of catalyst under the reforming environment and deposition of carbon on the catalyst surfaces leading to deactivation, have to be resolved. The reforming operations are performed using a modified external autothermal reforming (ATR) approach. Desulfurized natural gas is used as a feedstock to avoid catalyst poisoning and air is exploited as an oxidant. It is found that the reforming catalyst is able to remain stable and free from pulverization at the desired operating conditions when α-Al 2 O 3 is employed as a catalyst support in place of the commonly used γ-Al 2 O 3 counterpart. In addition, the ceria (CeO 2 )-assisted Pt catalyst coated on the α-Al 2 O 3 support, i.e., Pt/CeO 2 /α-Al 2 O 3 , is able to significantly eliminate the coking problem with a CH 4 conversion rate >99% and a generated H 2 concentration ∼62% at 1073 K. A reaction mechanism is proposed to elucidate the coking-resistance of the catalyst, which also accounts for the stability of the catalyst. The reforming catalyst has been tested continuously for 2400 h and is still able to maintain a good operating condition.

We adapt a general-purpose optimization-based parameter estimation technique previously described in the literature [1] to evaluate the suitability of a number of common kinetic models for the representation of key performance characteristics (conversion and selectivity) of catalysts used for the preferential oxidation of CO in the presence of H 2 . We find that, for process engineering applications, there is no clear practical advantage to using mechanistically based kinetic models (e.g. Langmuir–Hinshelwood) unless the precise chemical mechanism is known. Empirical rate models are found generally to provide equivalent or better simulations of key performance variables for a diverse group of catalyst formulations. Furthermore, we demonstrate that the water–gas-shift (WGS) reaction is relevant within PROX reaction systems under conditons containing high fractions of CO 2 and H 2 , confirming the expectations of Choi and Stenger (2004) [2] . Finally, we attempt to identify any emergent trends in kinetic parameters among catalysts sharing similar active metal or metal oxide components. Unfortunately, apart from confirming that the activation barrier for CO oxidation is generally less than the barrier for H 2 oxidation (an expected relationship for PROX catalysts), no such trends are found.

Catalysts based on inverse CeO2/CuO configurations employed for preferential oxidation of CO in a H2-rich stream have been explored with respect to optimization of preparation parameters like calcination temperature and atmosphere. For this purpose, the catalysts precursors prepared by microemulsion have been characterized by TG-DTA, DRIFTS and XRD in order to select most adequate conditions. Selected specimens were further analysed by SBET measurements as well as with respect to catalytic and redox properties by activity measurements and H2-TPR tests. Activity differences are explained on the basis of textural, chemical and structural characteristics of the catalysts as a function of variations in the mentioned preparation parameters, with optimum properties being achieved for the specimen calcined under air at 500 °C.

The application of the catalytic system CuO/CeO2 supported on Zr doped SBA-15 mesoporous silica to the preferential oxidation of CO on hydrogen streams (CO-PROX) suitable to be used to feed PEM fuel cells, has been studied. A loading of 20% (wt.) Ce and 6% (wt.) Cu was found optimal for the CO-PROX reaction. The influence of the presence of CO2 and H2O in the gas feed was also studied in order to simulate the real operation conditions of a PEMFC feed stream generated by alcohol steam reforming. The catalysts were characterized by XRD, adsorption–desorption of N2 at −196 ◦ C, TEM, –H2-TPR and XPS. The system reducibility was found modified by the incorporation of zirconium in the support, with improvement of both the conversion and selectivity of the catalytic system, compared to the same material without Zr. © 2010 Elsevier B.V. All rights reserved.

Recent advances in anode electrocatalysts for low-temperature PEM fuel cells are increasing tolerance for CO in the H 2 -rich anode stream. This study explores the impact of potential improvements in CO-tolerant electrocatalysts on the system efficiency of low-temperature Nafion-based PEM fuel cell systems operating in conjunction with a hydrocarbon autothermal reformer and a preferential CO oxidation (PROx) reactor for CO clean-up. The incomplete H 2 clean-up by PROx reactors with partial CO removal can present conditions where CO-tolerant anode electrocatalysts significantly improve overall system efficiency. Empirical fuel cell performance models were based upon voltage–current characteristics from single-cell MEA tests at varying CO concentrations with new Pt–Mo alloy reformate-tolerant electrocatalysts tested in conjunction with this study. A system-level model for a liquid-fueled PEM fuel cell system with a 5 kW full power output is used to study the trade-offs between the improved performance with decreased CO concentration and the increased penalties from the air supply to the PROx reactor and associated reduction in H 2 partial pressures to the anode. As CO tolerance is increased over current state-of-the-art Pt alloy catalysts, system efficiencies improve due primarily to higher fuel cell voltages and to a lesser extent to reductions in parasitic loads. Furthermore, increasing CO tolerance of anode electrocatalysts allows for the potential for reduced system costs with minimal efficiency penalty by reducing PROx reactor size through reduced CO conversion requirements.

This work analyzes the CO-PrOx reactor design as a component of the CO clean-up system of the ethanol processor for H2 production applied to PEM fuel cells. The operating conditions of the processor require compact and lightweight pieces of equipment and efficient operation at different conditions. An egg-shell catalyst type of Pt/Al2O3 is considered. One-dimensional heterogeneous catalytic reactor model accounting for interfacial gradients is used to optimize the PrOx reactor. Different reactor components are added gradually to illustrate how the system dimensions and configuration change after optimization. The optimization problem determines the optimal reactor length, reactor diameter, catalyst particle diameter, inlet reactants temperature and insulating material thickness that minimize the total system volume. On these model-based results, the final reactor design is mainly governed by the presence of hemispherical heads (distributor and collector). Different inlet CO compositions and power generation targets are analyzed. According to the inlet CO level, more than one catalytic stage is required to meet design goals and fulfill process constraints. The model-based reactor optimization of the pseudo-adiabatic operation allows obtaining both designs for reducing volumes and optimal operating conditions that allows conventional reactor technology. Afterwards, simulation runs based on a rigorous one-dimensional heterogeneous catalytic reactor model accounting for intra-particle gradients are performed using data obtained from model-based optimization results. The aim of these simulations is to verify feasibility of the optimal design obtained from the proposed one-dimensional heterogeneous catalytic reactor model without intra-particle gradients, which is intended to approximate an egg-shell catalyst behavior. The present work reflects clearly the advantages of applying mathematical programming techniques to optimize both design and operation conditions of the PrOx reactor. Fil: Oliva, Diego Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo y Diseño. Universidad Tecnológica Nacional. Facultad Regional Santa Fe. Instituto de Desarrollo y Diseño; Argentina Fil: Francesconi, Javier Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo y Diseño. Universidad Tecnológica Nacional. Facultad Regional Santa Fe. Instituto de Desarrollo y Diseño; Argentina Fil: Mussati, Miguel Ceferino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo y Diseño. Universidad Tecnológica Nacional. Facultad Regional Santa Fe. Instituto de Desarrollo y Diseño; Argentina Fil: Aguirre, Pio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo y Diseño. Universidad Tecnológica Nacional. Facultad Regional Santa Fe. Instituto de Desarrollo y Diseño; Argentina

The catalytic activities of low-temperature CO oxidation and preferential CO oxidation (PROX) in rich-H2 stream over the Pt/SiO2 and rare earth oxides modified Pt/SiO2 catalysts have been investigated. The addition of rare earth oxide additives to the Pt/SiO2 catalyst can promote the catalytic performance remarkably. The catalytic activities for PROX are dependent on the basicities of these oxides. The higher basic strength leads to higher activity. For Pt–CeO2/SiO2, the catalytic activity depends strongly on the content of CeO2 and on the mole ratio of CO/O2. XRD and H2-temperature-programmed reduction (TPR) results show that the additives not only improve the dispersion of metallic Pt on the support surface, but also increase the reducibility of PtOx in Pt–CeO2/SiO2. The formation of the Pt–Ce alloy decreases the electron back-donation from the Pt 5d orbital to the 2σ* orbital of CO, and consequently suppresses CO–Pt bonding, resulting in the lowered CO coverage.

An experimental investigation is performed into the cleanup of CO in hydrogen for proton exchange membrane fuel cell (PEMFC) using Pt/Al 2 O 3 and Ru/Al 2 O 3 catalysts. Additionally, the effects of adding the transition metals Co and Fe to a Ru/Al 2 O 3 catalyst are examined. The results show that as the level of Pt addition is increased, the maximum CO conversion rate is achieved at a lower temperature. With Ru/Al 2 O 3 catalysts, the CO conversion rate increases significantly with increasing Ru addition at temperatures lower than 80 °C For both catalysts, the methane yield increases with increasing temperature and increasing noble metal addition. At temperatures in the range of 100–140 °C, the CO conversion rate and methane yield of the Pt- and Ru-based preferential oxidation (PROX) reactions are both insensitive to the density of the honeycomb carrier. The CO conversion rate is significantly improved by the addition of Fe at temperatures lower than 160 °C and by the addition of Co at temperatures higher than 200 °C. Of the two metals, Fe results in a greater reduction of the methane yield at high temperatures. Finally, both catalysts achieve a stable cleanup performance over the course of a 12-h stability test and suppress the CO concentration to an acceptable level for PEMFC applications.

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% CO 2 and 10% H 2 O, there is not much difference between those in the presence and the absence of CO 2 and H 2 O. 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.

A fuel cell made with silicon is operated with hydrogen supplied by a reformer and a preferential oxidation (PrOx) reactor those are also made with silicon. The performance and durability of the fuel cell is analyzed and tested, then compared with the results obtained with pure hydrogen. Three components of the system are made using silicon technologies and micro electro-mechanical system (MEMS) technology. The commercial Cu-ZnO-Al 2 O 3 catalyst for the reformer and the Pt-Al 2 O 3 catalyst for the PrOx reactor are coated by means of a fill-and-dry method. A conventional membrane electrode assembly composed of a 0.375 mg cm −2 PtRu/C catalyst for the anode, a 0.4 mg cm −2 Pt/C catalyst for the cathode, and a Nafion™ 112 membrane is introduced to the fuel cell. The reformer gives a 27 cm 3 min −1 gas production rate with 3177 ppm CO concentration at a 1 cm 3 h −1 methanol feed rate and the PrOx reactor shows almost 100% CO conversion under the experimental conditions. Fuel cells operated with this fuel-processing system produce 230 mW cm −2 at 0.6 V, which is similar to that obtained with pure hydrogen.

We have investigated the relationship between the catalyst preparation and the catalytic activity of Pt–Au/CeO2, Pt/CeO2 and Au/CeO2 catalysts for preferential oxidation (PROX) of CO in simulated reformed gas. The prepared catalysts were characterized by XRD, XRF, BET, SEM, TEM and TPR techniques. The catalytic activity tests were carried out in the temperature range of 50–190 °C under atmospheric pressure. The results indicated that all single-step sol–gel catalysts exhibited the maximum CO conversion. The amount of metal loading and the ratios of Pt–Au catalysts had an important effect on the catalytic activity. In addition, the blockage of catalytic active sites by adsorbed H2O and CO2 in the feed stream decreased the activity of the Pt–Au/CeO2 catalysts. This catalyst exhibited good stability.

KIER has been developing a novel fuel processing system to provide hydrogen rich gas to residential PEMFCs system. For the effective design of a compact hydrogen production system, each unit process for steam reforming and water gas shift, has a steam generator and internal heat exchangers which are thermally and physically integrated into a single packaged hardware system. The newly designed fuel processor (prototype II) showed a thermal efficiency of 78% as a HHV basis with methane conversion of 89%. The preferential oxidation unit with two staged cascade reactors, reduces, the CO concentration to below 10 ppm without complicated temperature control hardware, which is the prerequisite CO limit for the PEMFC stack. After we achieve the initial performance of the fuel processor, partial load operation was carried out to test the performance and reliability of the fuel processor at various loads. The stability of the fuel processor was also demonstrated for three successive days with a stable composition of product gas and thermal efficiency. The CO concentration remained below 10 ppm during the test period and confirmed the stable performance of the two-stage PrOx reactors.

In order to supply pure hydrogen to proton exchange membrane (PEM) fuel cells and avoid CO poisoning, selective CO oxidation in H2 was studied over Ce-Pt/γ-Al2O3. Adding the Ce promoted the CO conversion and selectivity of Pt/γ-Al2O3 with changing loading weights of Pt and Ce, oxygen concentration, residence time, and the composition of gases (H2O, CO2, and N2). At 250 °C, adding H2O to the feed gas enhanced the CO conversion due to the water–gas shift reaction. While, adding CO2 to the feed gas suppressed the CO conversion due to the reversible water–gas shift reaction. In situ BET and XRD tests showed that well-dispersed metallic Pt particles (−2 nm) existed on the Ce oxide over the alumina support, which helps to supply oxygen to the Pt for a high activity of CO oxidation and selectivity.

The rapid development of the polymer electrolyte fuel cell (PEFC) technology in recent years has stimulated research in all areas of fuel processing catalysis for hydrogen generation. A new precious metal catalyst with an improved precious metal utilisation, which allows the low temperature reforming (550–650 °C) of hydrocarbons, was developed. The low temperature reforming results in low carbon monoxide concentrations, in the range of 2–5 vol.%, making it possible to omit the shift units before the preferential oxidation unit (PROX). For the PROX unit a selective catalyst was developed to oxidize the carbon monoxide down to a level acceptable for PEFCs. To demonstrate the “shift-less” fuel processing concept, a test unit was built containing a gasoline reformer and a PROX unit. At GHSV of 3319–19795 h −1 and T = 595–645 °C complete conversion of C 2+ was achieved. First, a dual fixed-bed reactor configuration with staged air supply was tested for the PROX. With this configuration hot spots over 280 °C occurred, which made a selective conversion of carbon monoxide impossible. The hot-spot problem was drastically reduced by using an annulus reactor achieving >99.93% carbon monoxide conversion due to the better heat dissipation. The hydrogen conversion in the PROX unit was high at around 27%. This value may be improved by better temperature control of the PROX reactor. Reformate gas with hydrogen concentrations up to 51 vol.% could be produced from sulphur-free gasoline (RON = 95). Reformate gas with 32% H 2 and 2 polymer electrolyte fuel cell. A stable cell voltage of 680 mV was obtained at a current density of 500 mA cm −2 for operation with pure O 2 as oxidant. Changing the oxidant to air led to a cell voltage decline of 120 mV.

The effects of magnesium on platinum catalyst used for the preferential oxidation of carbon monoxide for polymer electrolyte membrane fuel cell applications are investigated. The CO conversion and selectivity on Pt–Mg/Al2O3 for a H2-rich stream are 93.1 and 62.0%, respectively, but only 70.2 and 46.89% on Pt/Al2O3. The superior activity of Pt–Mg/Al2O3 for the preferential oxidation of CO is due to an increase in the hydroxyl groups that results from an increase in basicity with the addition of Mg, as well as to an increase in the electron density on the surface of the Pt catalyst. Moreover, the content of hydroxyl groups on the Pt catalysts is promoted by water vapour.

The CO removal with preferential CO oxidation (PROX) over an industrial 0.5% Ru/Al2O3 catalyst from simulated reformates was examined and evaluated through considering its simultaneously involved oxidation and methanation reactions. It was found that the CO removal was fully due to the preferential oxidation of CO until 383 K. Over this temperature, the simultaneous CO methanation was started to make a contribution, which compensated for the decrease in the removal due to the decreased selectivity of PROX at higher temperatures. This consequently kept the effluent CO content as well as the overall selectivity estimated as the ratio of the removed CO amount over the sum of the consumed O-2 and formed CH4 amounts from apparently increasing with raising reaction temperature from 383 to 443 K when the CO2 methanation was yet not fully started. At these temperatures the tested catalyst enabled the initial CO content of up to 1.0 vol. % to be removed to several tens of ppm at an overall selectivity of about 0.4 from simulated reformates containing 70 vol. % H-2, 30 vol. % CO2 and with steam of up to 0.45 (volume) of dry gas. Varying space velocity in less than 9000 h(-1) did not much change the stated overall selectivity. From the viewpoint of CO removal the article thus concluded that the methanation activity of the tested Ru/Al2O3 greatly extended its working temperatures for PROX, demonstrating actually a feasible way to formulate PROX catalysts that enable broad windows of suitable working temperatures. (c) 2005 Elsevier B.V. All rights reserved.

Recent advances in the development of short contact time (SCT) reactor design approaches allow reformers capable of overcoming current barriers of cost, size, weight, complexity and efficiency associated with conventional reactor design approaches. PCI has developed an SCT based approach using a patented substrate (trademarked Microlith ® ) and proprietary coating technology [1] . The high heat and mass transport properties of the substrate have been shown to significantly reduce reactor size while improving performance. Resistance to coking, especially at low H 2 O:C ratios, has also been observed with these reactors. This paper summarizes the results of auto thermal reforming (ATR) of an iso -octane-based liquid fuel. In addition Microlith-based water gas shift (WGS) and preferential CO oxidation (PROX) reactors were also examined for fuel processing applications. Surprisingly, selectivity advantages for these kinetically controlled reactions were observed [2] . Examples described here include low methanation selectivity in WGS applications and large operating windows for PROX at very high space velocities. A complete reformer system with Microlith ATR, WGS and PROX reactors has been identified. Sensitivity of system size with regard to steam:carbon ratios, and the resulting implications for reactor/heat exchanger sizes were documented and a compact system identified.

The selective oxidation of CO in the presence of excess H2 was investigated over a ceria-promoted Cu–alumina catalyst. This catalyst shows nearly exclusive oxidation of CO versus H2 with an O2 concentration in stoichiometric proportion to CO, making it possible to purify a fuel cell feed stream with a minimum loss of energy content associated with H2. The effect of the presence of CO2 and H2O in the feed on the activity and selectivity of the catalyst, and the long-term stability were also investigated. The catalysts were characterized by X-ray diffraction (XRD), CO chemisorption and temperature-programmed reduction (TPR). Copper is better dispersed on the ceria-promoted alumina support in comparison to alumina alone. CuO is the active phase for selective CO oxidation. Oxygen vacancies supplied and enhanced by ceria are responsible for improved activity.

Steady-state models are developed to describe an experimental methane fuel processor that is intended to provide hydrogen for a fuel cell system for power generation (2–3 kW). First-principle reactor models are constructed to describe a series of reactions, i.e., steam and autothermal reforming (SR/ATR), high- and low-temperature water–gas shift (HTS/LTS) reactions and preferential oxidation (PROX) reactions, at different sectors of the reactor system for methane reforming as well as gas cleaning. The pre-exponential factors of the rate constants are adjusted to fit the experimental data and the resultant reactor model provides a reasonably good description of steady-state behaviour. Next, sensitivity analyses are performed to locate the optimum operating point of the fuel processor. The objective function of the optimization is fuel processor efficiency. The dominating optimization variables include: the ratios of water and oxygen to the hydrocarbon feed to the autothermal reforming reactor and the inlet temperature of the reactor. The results indicate that further improvement in fuel processor efficiency can be made with a reliable process model.

The University of Duisburg-Essen and the Center for Fuel Cell Technology (ZBT Duisburg GmbH) have developed a compact multi-fuel steam reformer suitable for natural gas, propane and butane. Fuel processor prototypes based on this concept were built up in the power range from 2.5 to 12.5 kW thermal hydrogen power for different applications and different industrial partners. The fuel processor concept contains all the necessary elements, a prereformer step, a primary reformer, water gas shift reactors, a steam generator, internal heat exchangers, in order to achieve an optimised heat integration and an external burner for heat supply as well as a preferential oxidation step (PrOx) as CO purification. One of the built fuel processors is designed to deliver a thermal hydrogen power output of 2.5 kW according to a PEM fuel cell stack providing about 1 kW electrical power and achieves a thermal efficiency of about 75% (LHV basis after PrOx), while the CO content of the product gas is below 20 ppm. This steam reformer has been combined with a 1 kW PEM fuel cell. Recirculating the anodic offgas results in a significant efficiency increase for the fuel processor. The gross efficiency of the combined system was already clearly above 30% during the first tests. Further improvements are currently investigated and developed at the ZBT.

An integrated ethanol fuelled proton exchange membrane fuel cell (PEMFC) power system was investigated following a second law exergy analysis. The system was assumed to have the typical design for automobile applications and was comprised of a vaporizer/mixer, a steam reformer, a CO-shift reactor, a CO-remover (PROX) reactor, a PEMFC and a burner. The exergy analysis was applied for different PEMFC power and voltage outputs assuming the ethanol steam reforming at about 600 K and the CO-shift reaction at about 400 K. A detailed parametric analysis of the plant is presented and operation guidelines are suggested for effective performance. In every case, the exergy analysis method is proved to allow an accurate allocation of the deficiencies of the subsystems of the plant and serves as a unique tool for essential technical improvements.

Various catalysts containing different catalytic materials, supports, and additives were tested for the preferential oxidation (PROX) of carbon monoxide from a hydrogen-rich gas stream. The results were analyzed based on three reactions involved in the PROX: oxidation of carbon monoxide, H 2 –O 2 reaction, and methanation. The PROX reactions were performed in two reaction systems, one for catalyst screening and kinetic study and the other for simulation of the catalytic performance under real reaction conditions. The performances of PROX on different catalysts, varying active components, supports, and additives, were ranked in terms of carbon monoxide conversion and hydrogen consumption. Base metal added platinum catalysts exhibited excellent ability for the carbon monoxide removal. TPR results indicated that a new active species was formed resulting in the enhancement of catalytic activity. PtCo/Al 2 O 3 was tested with a simulated steam-reformed fuel for confirmation of its high activity. The effect of operating conditions was analyzed on the PtCo/Al 2 O 3 , and the optimum conditions for PROX were obtained.

Our recent studies of CO preferential oxidation (PrOx) identified systematic differences between the characteristic curves of CO conversion for a microchannel reactor with thin-film wall catalyst and conventional mini packed-bed lab reactors (m-PBR's). Strong evidence has suggested that the reverse water-gas-shift (r-WGS) side reaction activated by temperature gradients in m-PBR's is the source of these differences. In the present work, a quasi-3D tubular non-isothermal reactor model based on the finite difference method was constructed to quantitatively study the effect of heat transport resistance on PrOx reaction behavior. First, the kinetic expressions for the three principal reactions involved were formed based on the combination of experimental data and literature reports and their parameters were evaluated with a non-linear regression method. Based on the resulting kinetic model and an energy balance derived for PrOx, the finite difference method was then adopted for the quasi-3D model. This model was then used to simulate both the microreactor and m-PBR's and to gain insights into their different conversion behavior. Simulation showed that the temperature gradients in m-PBR's favor the reverse water-gas-shift (r-WGS) reaction, thus causing a much narrower range of permissible operating temperature compared to the microreactor. Accordingly, the extremely efficient heat removal of the microchannel/thin-film catalyst system eliminates temperature gradients and efficiently prevents the onset of the r-WGS reaction.

A performance model for a reformer, consisting of the catalytic partial oxidation (CPO), high- and low-temperature water-gas shift (HTWGS and LTWGS), and preferential oxidation (PROX) reactors, has been formulated. The model predicts the composition and temperature of the hydrogen-rich reformed fuel-gas mixture needed for the fuel cell applications. The mathematical model equations, based on the principles of classical thermodynamics and chemical kinetics, were implemented into a computer program. The resulting software was employed to calculate the chemical species molar flow rates and the gas mixture stream temperature for the steady-state operation of the reformer. Typical computed results, such as the gas mixture temperature at the CPO reactor exit and the profiles of the fractional conversion of carbon monoxide, temperature, and mole fractions of the chemical species as a function of the catalyst weight in the HTWGS, LTWGS, and PROX reactors, are here presented at the carbon-to-oxygen atom ratio (C/O) of 1 for the feed mixture of n-decane (fuel) and dry air (oxidant).

Ceria-supported Au catalysts for selective oxidation of CO under simulated fuel processing conditions for polymer electrolyte membrane fuel cell (PEMFC) application were investigated. Fresh and used catalysts were characterized by X-ray diffraction, X-ray fluorescence and transmission electron microscopy (TEM). The influence of catalyst heat treatment, reaction temperature, gas composition and space velocity on CO conversion and CO 2 selectivity has been evaluated. Air calcination at 500 °C resulted in the establishment of adequate interfacial metal oxide properties which are essential to promote the selective CO oxidation. CO conversion close to 100% was obtained at 120 °C, whereas CO 2 selectivities not higher than 40% were obtained in the entire temperature range investigated (80–120 °C). The presence of CO 2 in the inlet stream negatively affected both CO conversion and CO 2 selectivity. Both calcined and uncalcined Au/CeO 2 catalysts resulted to be very stable, as demonstrated by 120 h endurance tests. TEM investigation of the used catalysts revealed that a surface Au particles reconstruction occurred during reaction.

Natural gas fuel processors have been developed for 500 W and 1 kW class residential polymer electrolyte fuel cell (PEFC) systems. These fuel processors contain all the elements—desulfurizers, steam reformers, CO shift converters, CO preferential oxidation (PROX) reactors, steam generators, burners and heat exchangers—in one package. For the PROX reactor, a single-stage PROX process using a novel PROX catalyst was adopted. In the 1 kW class fuel processor, thermal efficiency of 83% at HHV was achieved at nominal output assuming a H 2 utilization rate in the cell stack of 76%. CO concentration below 1 ppm in the product gas was achieved even under the condition of [O 2 ]/[CO]=1.5 at the PROX reactor. The long-term durability of the fuel processor was demonstrated with almost no deterioration in thermal efficiency and CO concentration for 10,000 h, 1000 times start and stop cycles, 25,000 cycles of load change.

The University of Duisburg–Essen has developed a compact multi-fuel steam reformer suitable for natural gas, propane and butane. This steam reformer was combined with a polymer electrolyte membrane fuel cell (PEM FC) and a system test of the process chain was performed. The fuel processor comprises a prereformer step, a primary reformer, water gas shift reactors, a steam generator, internal heat exchangers in order to achieve an optimised heat integration and an external burner for heat supply as well as a preferential oxidation step (PROX) as CO purification. The fuel processor is designed to deliver a thermal hydrogen power output from 500 W to 2.5 kW. The PEM fuel cell stack provides about 1 kW electrical power. In the following paper experimental results of measurements of the single components PEM fuel cell and fuel processor as well as results of the coupling of both to form a process chain are presented.

The kinetics of CO preferential oxidation (PROX) was studied to evaluate various rate expressions and to simulate the performance the CO oxidation step of a methanol fuel processor for fuel cell applications. The reaction was carried out in a micro reactor testing unit using a commercial Engelhard Selectoxo (Pt–Fe/γ-alumina) catalyst and three self-prepared catalysts. Temperature was varied between 100 and 300 °C, and a of range feed rates and compositions were tested. A reaction model in which three reactions (CO oxidation, H2 oxidation and the water gas shift reaction) occur simultaneously was chosen to predict the reactor performance. Using non-linear least squares, empirical power-law type rate expressions were found to fit the experimental data. It was critical to include all three reactions to determine good fitting results. In particular, the reverse water gas shift reaction had an important role when fitting the experimental data precisely and explained the selectivity decrease at higher reaction temperatures. Using this three reaction model, several simulation studies for a commercial PROX reactor were performed. In these simulations, the effect of O2/CO ratio, the effect of water addition, and various non-isothermal modes of operation were evaluated. The results of the simulation were compared with corresponding experimental data and shows good agreement.

The selective oxidation of carbon monoxide in a hydrogen-rich stream is an important reaction in fuel cell technology. Fuel cells that use hydrogen produced from a combustion source contain small amounts of CO that must be removed to extremely low levels (

Innovative recent research has suggested that gold-based catalysts are potentially capable of being effectively employed in fuel cells and related hydrogen fuel processing. The justification for developing the gold catalyst technologies described, is not only based on their promising technical performance, but also the relatively low stable price and greater availability of gold compared with the platinum group metals. The employment of gold catalysts could therefore produce a welcome reduction in the capital cost of fuel cell installations. The most likely first use for gold catalysts is for the removal of carbon monoxide impurities from the hydrogen feedstock streams used for fuel cells. Such hydrogen is usually obtained from reforming reactions (from hydrocarbons or methanol) either from free-standing plant or from an on-board reformer in a vehicle in the case of transport applications. Absence of carbon monoxide would enable fuel cells to run at lower temperatures and with improved efficiency. Effectiveness of gold catalysts in this application has already been demonstrated. Preferential oxidation (PROX) of carbon monoxide in hydrogen-rich reformer gas is best effected by a gold catalyst (Au/α-Fe 2 O 3 ) which is significantly more active at lower temperatures than the commercial PROX catalyst, i.e. Pt/γ-Al 2 O 3 currently used for this purpose. Supported gold catalysts are also very active in the water gas shift reaction used for producing hydrogen from carbon monoxide and water. Research has shown that gold supported on iron oxide (Au/α-Fe 2 O 3 ) catalyst is more active at lower temperatures than both the α-Fe 2 O 3 support and the mixed copper/zinc oxide (CuO/ZnO) catalyst currently used commercially. Preparation of gold on iron oxide and gold on titania (Au/Fe 2 O 3 and Au/TiO 2 ) by deposition–precipitation produces more active catalysts than by conventional co-precipitation. Other applications for gold in fuel cells are described and include its use as a corrosion resistant material and the incorporation of gold catalysts to provide useful improvements in electrode conductivity.

A preferential oxidation (PROX) reactor for a 10-kWe polymer electrolyte membrane fuel cell (PEMFC) system is developed. Pt-Ru/Al 2 O 3 catalyst powder, with a size of 300–600 μm is applied for the PROX reaction. To minimize pressure drop and to avoid hot spots in the catalyst bed, the reactor is designed as a dual-staged, multi-tube system. The performance of the 10-kWe PROX unit is evaluated by feeding simulated gasoline reformate which contains 1.2 wt.% carbon monoxide (CO). The CO concentration of the treated reformate is lower than 20 ppm in the steady-state and is under 30 ppm at 65% load change. Hydrogen loss in the steady-state is about 1.5% and the pressure drop across the reactor is 4 psi. Start-up characteristics of the 10-kWe PROX system are also investigated. It takes 3 min to reduce the CO concentration to below 20 ppm. Several controllable factors are found to shorten the start-up time.

We present in-situ IR (DRIFTS) measurements on CO adsorption and preferential CO oxidation (PROX) in H 2 -rich gas on Pt/γ-Al 2 O 3 and Au/α-Fe 2 O 3 catalysts at their envisaged operating temperatures of 200°C and 80°C, respectively, which in combination with kinetic data show that the underlying reason for the very different PROX reaction kinetics on these two catalysts is the difference in steady-state CO coverage. Whereas on the platinum catalyst this is always near saturation under reaction conditions, causing a negative reaction order (−0.4) and a p CO -independent selectivity, the amount of adsorbed CO on the gold particles (indicated by an IR band at ∼2110 cm −1 ) strongly depends on the CO partial pressure. From the position of the IR band of CO adsorbed on Au/α-Fe 2 O 3 , the steady-state coverages on the Au surface are shown to be significantly below saturation, with an upper limit of approximately θ CO =0.2. Low reactant surface concentrations on Au explain the positive reaction order with respect to p CO (+0.55 at 80°C) as well as the observed decoupling of the CO and H 2 oxidation rates, which results in a loss of selectivity with decreasing p CO .

Natural gas and methanol are the most economical fuels for residential fuel cell power generators as well as for mobile PEM-fuel cells. However, they have to be reformed with steam into hydrogen, which is to be cleaned from CO by shift-reaction and by partial oxidation to a level of no more than 30 ppm CO. This level is set by the Pt/Ru–C-anode of the PEMFC. A higher partial oxidation reaction rate for CO than those of Pt/Ru–C can be achieved in an oxidic Au–catalyst system. In the Fe 2 O 3 –Au system, a reaction rate of 2·10 −3 mol CO/s g Au at 1000 ppm CO and 5% “air bleed” at 80°C is achieved. This high rate allows to construct a catalyst-sheet for each cell within a PEMFC-stack. Practical and theoretical current/voltage characteristics of PEMFCs with catalyst-sheet are presented at 1000 ppm CO in hydrogen with 5% “air bleed”. This gives the possibility of simplifying the gas processor of the plant.