Abstract
Polymer electrolyte membrane fuel cells (PEMFCs) for household applications utilize H2 produced from natural gas via steam reforming followed by a water gas shift (WGS) unit. The H2-rich gas contains CO2 and small amounts of CO, which is a poison for PEMFCs. Today, CO is mostly converted by addition of O2 and preferential oxidation, but H2 is then also partly oxidized. An alternative is selective CO methanation, studied in this work. CO2 methanation is then a highly unwanted reaction, consuming additional H2. The kinetics of CO methanation in CO2/H2 rich gases were studied with a home-made Ru catalyst in a fixed bed reactor at 1 bar and 160–240 °C. Both CO and CO2 methanation can be well described by a Langmuir Hinshelwood approach. The rate of CO2 methanation is slow compared to CO. CO2 is directly converted to methane, i.e., the indirect route via reverse water gas shift (WGS) and subsequent CO methanation could be excluded by the experimental data and in combination with kinetic considerations. Pore diffusion may affect the CO conversion (>200 °C). The kinetic equations were applied to model an adiabatic fixed bed methanation reactor of a fuel cell appliance.
Highlights
In recent years, the interest in proton-exchange membrane fuel cells (PEMFCs), known as polymer electrolyte membrane fuel cells, for stationary applications such as households or office buildings has increased [1]
The kinetics of CO methanation in CO2 /H2 rich gases were studied with a home-made Ru catalyst in a fixed bed reactor at 1 bar and 160–240 ◦ C
CO2 is directly converted to methane, i.e., the indirect route via reverse water gas shift (WGS) and subsequent CO methanation could be excluded by the experimental data and in combination with kinetic considerations
Summary
The interest in proton-exchange membrane fuel cells (PEMFCs), known as polymer electrolyte membrane fuel cells, for stationary applications such as households or office buildings has increased [1]. The development of a catalyst with high activity and selectivity for CO methanation at low temperatures, optimally at temperatures of the off-gas of the WGS unit of around 200 ◦ C, is important. Ruthenium catalysts show these characteristics for selective CO methanation [13,14,15,16,17,18]. Based on own screening experiments with a variety of Co and Ru catalysts with regard to activity and selectivity for selective CO methanation [19], a 2 wt% Ru/γ-Al2 O3 catalyst was selected as most suitable for this application This Ru catalyst was prepared and applied for the investigation of the CO methanation reaction under varying reaction conditions, starting from gas mixtures containing only. An adiabatic fixed reactor was simulated to determine the amount of a methanation catalyst needed for a typical household fuel cell system
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