In-situ studies of gas phase composition and anode surface temperature through a model DIR-SOFC steam–methane reformer at 973.15 K

A comparative study into the effects of total volume flow rate, methane ‘residency time’, methane volume flow rate, and steam-to-carbon ratio on the steam–methane reforming process was performed in a model Direct Internal Reforming SOFC (DIR-SOFC) reformer operating in steady state at a nominal temperature of 973 K. The spatial distributions of major gas species (CH₄, H₂O, CO, CO₂, and H₂) over the reformer surface were measured in-situ using Vibrational Raman Spectroscopy. Surface temperature measurements were recorded using IR thermometry. The effects of varying the intake mole fractions of methane and water were considered. The results of this work have demonstrated a strong positive correlation between the intake mole fraction of methane and the rate of the steam–methane reformation reaction. A weak negative correlation between the intake mole fraction of water and the rate of the reformation reaction was also shown.     

Application of heat flux as a control variable in small-scale packed-bed steam reforming

In steam reformation, high thermal resistance and poor heat transfer of the packed catalyst bed can create time-lag between the moment when the heat is applied and the corresponding rise in temperature. Thus, problems arise from the dynamic requirements of the system, which can create a time-lag in the reactor's performance and also induce temperature oscillations resulting in a degrading catalyst. Lag compensation is necessary if one uses temperature feedback control to maintain the reactor temperature. A better solution is to recognize that heat flux is more suitable as a control variable, since available heat is what sustains the chemical reaction inside the reactor. Thus, controlling heat flux can directly influence the reaction and the resultant temperature inside the reactor. A heat flux controller is implemented for two small-scale, packed-bed, steam reformers. A standard temperature feedback controller is also implemented. The two systems are compared in their transient response. Temperature and reformate gas concentrations are measured to evaluate the performance of the two controller topologies. The heat flux based controller significantly outperforms the temperature feedback controller in both geometries tested.     

Development of Ni catalysts for gas production from biomass gasification. Reactivity in steam- and dry-reforming

Biomass gasification can be optimised in a fluidised bed by the use of metallic nickel as active phase grafted on olivine. Natural olivine ((Mg, Fe)₂SiO₄) has been chosen as catalyst support because of its activity in biomass steam gasification and tar cracking, its high attrition resistance.

After impregnation of nickel oxide on olivine and calcination at 900, 1100 or 1400°C, different interactions between the precursor and the support have been revealed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy coupled to energy dispersive X-ray spectroscopy. Temperature programmed reduction has completed this study and permitted to control the reducibility of the catalysts. The most promising catalyst determined after these different characterisation studies contained 2.8 wt.% of Ni and was calcined at 1100°C. It exhibited strong nickel–olivine interaction but the grafted nickel oxide particles stayed reducible under catalytic test conditions.

Already at 750°C, this catalyst presented a high activity in dry-reforming (95% methane conversion) and steam-reforming (88% methane conversion) and yield in syngas (80% and 75% CO yield, respectively). An excess of water content in steam-reforming inhibited the catalytic activation which could be retrieved by addition of a reducer like H₂.

No sintering of nickel particles and very little carbon deposition has been observed on this catalytic system by characterisation studies after catalytic tests. This can explain its very good ageing behaviour (at least 260 h at 800°C) and justifies its use in a fluidised bed pilot plant.     

Catalytic steam reforming of methane using Rh supported on Sr-substituted hexaaluminate

This paper reports the synthesis, characterization, and performance of steam-reforming catalysts based upon dispersed Rh particles on Sr-substituted hexaaluminate supports. As confirmed by electron microscopy and X-ray diffraction, the Sr-substituted hexaaluminate provides a plate-like support structure that resists sintering and occlusion of the Rh. The hexaaluminate is synthesized using an alumoxane process, with the cation substitution accomplished by exchange with metal acetylacetonates. The Rh is dispersed using impregnation with metal-nitrate salts. A stagnation-flow reactor is used to measure catalytic activity. In these experiments, the catalyst is applied to a flat surface that is held at a fixed temperature. Reactive gases (methane, steam, and diluent) impinge on the catalytic stagnation surface. Microprobe mass spectrometry is used to measure gas-phase species profiles in the boundary layer normal to the catalyst surface. The experiments are interpreted using a chemically reacting flow model, including an elementary heterogeneous chemical reaction mechanism. Results confirm that the Rh on Sr-substituted hexaaluminate is a highly stable and active reforming catalyst.     

A multi-membrane reformer for the direct production of hydrogen via a steam-reforming reaction of methane

We designed and prepared a multi-membrane reformer (MMR) for the direct production of hydrogen via a steam-reforming (SR) reaction of methane. The MMR consisted of two single modules containing coin-shaped nickel metal catalysts and Pd-based membrane. The SR reaction was performed in the MMR for relatively high-pressure operation ranges (P₂ = ∼21 bar) without sweep gas and the methane conversion and hydrogen production rate were observed under various experimental conditions. It was found that the high-performance of the Pd-based membrane and the porous metal catalyst and their configuration in the MMR guaranteed a high rate of hydrogen production. For instance, the methane conversion, the rate of hydrogen separation and the hydrogen purity were 75%, 30.6 L/h and 99.95%, respectively, under the experimental conditions of 540 °C, S/C = 3.0 and del-P = 20 bar. The design and performance of MMR show potential advantages, such as the simple preparation of a compact membrane reformer able to operate in relatively high-pressure ranges and easy enlargement of the hydrogen production capacity by stacking the modules, which is possible due to the disk-type shape of the metal catalyst and the membrane.