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‘Salted’ catalysts facilitate renewable energy storage

test plant

The catalysts modified with molten salt are examined at the test plant used for catalytic steam reformation of methanol. (Image: FAU)

FAU researchers develop new catalyst technology for generating hydrogen from methanol

Wind and solar power plants often generate more energy than is needed. That is why it is important to store this energy in such a way that it can be made usable again without difficulty or delay. Storing hydrogen in the form of methanol is seen as a promising method. However, this requires a powerful reaction accelerator in order to recover the hydrogen when power is needed. Researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have now developed platinum catalysts with a special coating from molten alkaline salts. These ‘salted’ catalysts significantly accelerate the release of hydrogen from methanol and selectivity is increased drastically. The researchers have published their results in the renowned journal Angewandte Chemie (Int. Ed. 2013, 52(19), 5028-5032).

The fluctuations in the energy quantity produced is a key issue in the use of renewable sources of energy: power is only generated while the sun is shining or the wind is blowing. It is difficult to anticipate when a large quantity of energy will be available. One solution for this problem is to store generated power in the form of methanol-based hydrogen: the generated power is first used to split the water into hydrogen and oxygen in a simple chemical reaction known as electrolysis. In the second step, the hydrogen is made to react with carbon dioxide, resulting in methanol and water. The liquid methanol – an alcohol – can be stored in tanks. At a later point, the hydrogen can be released again and, for instance, used in fuel cells.

The process of releasing the hydrogen from methanol is called steam reforming. This step is essentially a reversal of the reaction that produced the methanol. The gas may only contain a very small amount of carbon monoxide, however, as larger quantities of this gas are poison to the catalyst of the downstream fuel cell. To ensure that the breakdown of methanol is feasible in small, decentralised plants, the catalyst should work effectively at the lowest possible temperature.

The teams led by Prof. Dr. Peter Wasserscheid and Prof. Dr. Jörg Libuda at FAU have now developed such an improved catalyst. It consists of platinum nanoparticles on a medium of aluminium oxide. What makes it so special: the surface is coated with a thin layer of an alkaline salt.

Liquid salts do not evaporate under the chosen reaction conditions, meaning that they remain on the catalyst’s surface during steam reforming and permanently activate the active metal centres. The salt coating means that hydrogen can be removed from the reaction zone quickly once formed and more methanol can be converted more rapidly. Furthermore, the salt is hygroscopic, meaning it attracts water and makes it available at the active points of the catalyst when it is needed for the reaction. The alkaline ions strengthen the bond between the intermediate carbon monoxide and the catalyst, increasing the probability of a further reaction to carbon dioxide. Compared to uncoated material, the coated catalyst shows much more catalytic activity and significantly improved selectivity. Selectivity of carbon dioxide and hydrogen under comparable conditions is increased from 60 to more than 99 percent thanks to the salt coating.

The scientists

Prof. Dr. Peter Wasserscheid is Chair of Chemical Reaction Engineering at FAU. He is speaker of the Research Area ‘Catalytic Materials’ of the Erlangen Cluster of Excellence and is working on an Advanced Investigator Grant from the European Research Council on the subject ‘Dehydration catalysis with salt-coated catalysts’.

Prof. Dr. Jörg Libuda is a professor of Physical Chemistry at FAU. He leads several sub-projects of the Erlangen Cluster of Excellence ‘Engineering of Advanced Materials’ as well as other projects and networks at the national and European level. The focus of his scientific work are model studies and spectroscopic examinations of catalysts and materials relevant to power generation.

Further information:

Prof. Dr. Peter Wasserscheid
Phone: +49 (0)9131 85 27420
wasserscheid@crt.cbi.uni-erlangen.de

Prof. Dr. Jörg Libuda
Tel. +49 (0)9131 85 27308
joerg.libuda@fau.de

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