Methanol Steam reforming for the production of high-purity hydrogen
A hydrogen-based energy infrastructure provides an ideal solution to our energy-related environmental problems. Besides the low cost of methanol, its good availability, high energy density, easy and safe handling and storage grant methanol a high potential as hydrogen storage molecule. The release of hydrogen for use in fuel cells is preferably carried out by the heterogeneously catalysed steam reforming of methanol:
CH3OH(g) + H2O(g) → 3 H2 + CO2 H°298K = 49.4 kJmol-1
Usually Cu-based catalysts are used, where, in addition to CO2, CO is also formed with a concentration of 500 to 2000 ppm. However, a CO concentration in H2 fuel below 20 ppm already leads to a significant drop in performance of the proton exchange membrane fuel cell (PEMFC). In addition, Cu-based catalysts suffer from deactivation above 300 °C due to sintering. In alternative systems such as Pd/ZnO, a reaction occurs between the support material and metal particles under reducing conditions forming intermetallic compounds (e.g. ZnPd, ZnPd2 or Zn3Pd2) resulting in very complex systems.
To gain a better understanding of the processes, we examine unsupported, well characterised intermetallic compounds concerning their catalytic properties in methanol steam reforming. Till now, the intermetallic compounds ZnPd and ZnNi (as a cheaper alternative) have been characterised in terms of their behaviour. ZnPd shows an extremely strong selectivity dependence on the composition (see. Fig. 1). From the in situ XPS study results, this behaviour can be attributed to the change in the oxidation properties of ZnPd with the composition. It is here demonstrated for the first time that a combination of intermetallic surface and ZnO is required for excellent catalytic properties.1,2
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Figure 1: the dependence of CO2 selectivity in the methanol steam reforming on the atomic composition of ZnPd. |
- M. Friedrich, D. Teschner, A. Knop-Gericke, M. Armbrüster, J. Catal. 285, 2012, 41. doi:10.1016/j.jcat.2011.09.013
- M. Friedrich, D. Teschner, A. Knop-Gericke, M. Armbrüster, J. Phys. Chem. C 116, 2012, 14930. doi:10.1021/jp303174h
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