Christopher P. Thurgood

Deactivation of Cu/ZnO/Al2O3 catalyst: evolution of site concentrations with time

The reforming of methanol is acknowledged as a convenient means to generate hydrogen for a PEFC due to the low temperature (<280 °C) at which the reaction occurs and the low CO content of the reformate. However, the catalyst is prone to deactivation in the upper range of its operating temperatures. This paper presents a method of analysis in which relative changes in site concentrations are deduced from a series of long-duration rate measurements. The sites involved in the reforming reaction are shown to evolve independently of each other. In particular, concentration of sites for hydrogen adsorption decline at a greater rate than those responsible for the adsorption of oxygenated species. A key process in the deactivation of the catalyst is the decrease in its capacity to adsorb and dissociate hydrogen.

Improved performance of a catalytic plate reactor coated with distributed layers of reforming and combustion catalysts for hydrogen production

Performance of a catalytic plate reactor coated with different patterns of distributed layers of reforming and combustion catalysts is investigated for the endothermic methane steam reforming (MSR) coupled with the exothermic methane combustion to produce hydrogen. To simulate MSR, an experimentally validated surface microkinetic model for a nickel-based catalyst is implemented in reforming flow channels. Required thermal energy to the MSR sites is supplied by catalytic and gas-phase methane combustion (MC) carried out in the neighbouring parallel flow channels. To simulate combustion reactions, a reduced surface microkinetic model for the catalytic MC and power rate model for the gas-phase MC are implemented in combustion flow channels. The study considers two-dimensional domains for the coating layers of reforming and combustion catalysts and identifies the internal-diffusion limitations for the reforming-catalyst coating thicker than 50 μm and for the combustion-catalyst coating thicker than 5 μm. Results obtained for different patterns of distributed coatings of reforming and combustion-catalysts are evaluated against the results obtained for conventional continuous coating layers by comparing temperature distribution, conversion, yield, selectivity, H2/CO ratio, efficiency, effectiveness-factor and plate-thickness. The study finds that by optimizing the distributed coating layers of the combustion-catalyst not only improves the utilization of both the catalysts and hydrogen production by 5% but also reduces the maximum plate temperature and axial thermal gradients along with 74% less combustion-catalyst compared to the continuous coating design. The study also finds that optimized distributed coating layers of both reforming and combustion catalysts predicts the similar methane conversion and hydrogen production as with the continuous coating layers for the same inlet molar feed rate but with 28% less reforming-catalyst and 74% less combustion-catalyst. Further, the study reports that the influence of distributed coatings of reforming and combustion catalysts is more pronounced in improving the performance of a catalytic plate reactor designed with relatively thick plate.

Simulation of a 25 kW Steam-Methanol Fuel Processor/PEM Fuel Cell System

The transition to a hydrogen economy will require an intermediate energy carrier until a sufficient hydrogen infrastructure can be implemented. A likely near-term candidate is the on-board or on-site production of hydrogen from steam-methanol reforming. The low tolerance of PEM fuel cell anode electrocatalyst, to the carbon monoxide produced during reforming, necessitates a hydrogen purification or carbon monoxide clean-up sub-system. Considerable advantages can be gained from the use of a steam-methanol reformer with a palladium-silver alloy membrane, hydrogen purification unit. In the present work we have examined such a system. A simulation comprised of a Polymer Electrolyte Membrane Fuel Cell electrochemical model, a membrane permeation model and a commercially available thermodynamics calculation package was constructed. The case investigated in this work is of a 25 kW nominal DC power generating system. A maximum efficiency of 40% was achieved at reformer and membrane unit conditions of 200°C and 300 psia with 97% conversion of the inlet methanol. The effects of variation in temperature and pressure where also investigated. It was found that the reformer and membrane unit pressure had the most significant effect on overall system efficiency. The system efficiency increases with pressure reaching a maximum at the upper limit of the operating region, 300 psia.Copyright