Low Temperature Aqueous-Phase Methanol Dehydrogenation to Hydrogen and Carbon Dioxide

摘要

Renewable energies like wind and sun light contribute progressively to a sufficient and sustainable energy supply. However, due to its fluctuating occurrence, the storage of electric energy becomes increasingly important. In this respect, approaches for the interconversion of electric and chemical energy earned more attention. A special focus is laid onto carbon dioxide based hydrogen storage in liquid organic materials. Such a material is methanol which possesses a high hydrogen content of 12.6%. While the methanol synthesis from CO_2 and H_2 is on the way to become reality, further improvements for the dehydrogenation of methanol at milder conditions are still a prerequisite to enable this storage option. We present the efficient low temperature aqueous-phase methanol dehydrogenation process employing molecularly-defined metal complexes. Besides Ru(Ⅱ) also noble metal free Fe(Ⅱ) HPNP pincer complexes are able to catalyze this reaction at temperatures between 65-95°C and ambient pressure. Excellent catalyst turnover frequencies of up to 4.700 h~1 and turnover numbers to ＞ 350.000 have been achieved. By application of a bi-catalytic system containing a second ruthenium complex to accelerate especially the cleavage of formic acid cleavage, generated as intermediate, it was possible to perform a base-free dehydrogenation of methanol as well.