Hydrogen economy, along with methanol economy, has emerged over the years as a promising strategy to combat recent global warming and climate change. Hydrogen (H2) is an ideal fuel due to its high energy density by weight and clean combustion; however, low volumetric density and explosive and inflammable nature of H2 necessitate the use of proper— safe and efficient— storage and carrier system for its practical use as a fuel. Methanol can be a convenient source of H2 because of its high H2 content and easy production and handling. Herein, we have developed a reversible hydrogen storage system based on amine reforming of methanol (dehydrogenative coupling of amine and methanol) in the presence of well-defined Ru-pincer catalysts. The traditional steam reforming is performed at high temperatures of 240-260 °C in the presence of heterogeneous catalysts. Recently, the use of homogeneous Ru and Fe catalysts have enabled aqueous methanol reforming at much lower temperatures (70-90 °C). However, both steam and aqueous methanol reforming involve the emission of CO2 gas into the atmosphere, which subsequently needs to be recaptured in order to obtain a "carbon neutral cycle". Whereas in amine reforming of methanol, the carbon is trapped as liquid formamide or urea product and as a result stays back in the reactor vessel. Interestingly, reduction of these formamide or urea products back to the amine and methanol can be achieved by a mere H2 pressure swing. A theoretical H2 storage capacity of 6.4 wt% can be obtained when ethylenediamine and methanol are used as the coupling partners. When proper combination of amine substrate and catalyst is used, both dehydrogenation and hydrogenation reaction proceed with high yields (90% and &gt;99% respectively). H2 is generated without any concomitant CO formation such that the gas can be directly fed to an H2 fuel cell without any purification. NMR mechanistic study suggests the in-situ formation of several Ru monohydride complexes. To the best of our knowledge, reversible reforming of methanol, that is dehydrogenation and subsequent hydrogenation in the same pot, is demonstrated for the first time in this study.

Efficient reversible hydrogen carrier system based on amine reforming of methanol

253rd National Meeting (2017)

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