Nature 495, 85–89 (2013)

The problems associated with the storage and transport of hydrogen prevent the widespread adoption of hydrogen-based fuel cells. One proposed solution is to use a carrier liquid from which hydrogen can be generated as and when it is needed. Methanol has been proposed as one such carrier; however, hydrogen is typically generated from methanol by reforming with steam — a process that requires temperatures in excess of 200 °C and pressures of 25–50 bar. These conditions limit the efficiency of the process and make it unsuitable as the hydrogen source for portable fuel cells.

Now, a team led by Matthias Beller at the University of Rostock in Germany have developed an efficient homogeneous catalyst that dehydrogenates methanol at low temperature. The active catalyst is formed from an octahedral ruthenium complex by removing a labile chloride ligand and converts methanol to three H2 molecules and carbon dioxide. In a series of steps, the alcohol is first oxidized to formaldehyde, then formic acid, before finally being converted to carbon dioxide. One equivalent of hydrogen gas is liberated at each stage representing the complete conversion of all available hydrogen in methanol. The additional hydrogen atoms required are supplied by water or a hydroxide base and the catalytic process is capable of generating H2 at temperatures as low as 72 °C.

Catalysts with a metal-on-metal-oxide-support structure have been used for methanol reforming before, however, this is the first organometallic dehydrogenation catalyst defined at a molecular level that can liberate more than one molecule of hydrogen for each molecule of methanol converted. The catalyst is tolerant of a range of methanol–water mixtures, is stable for over 350,000 catalytic cycles and retains high activity over several weeks. The process produced hydrogen and carbon dioxide with only very low levels of CO and CH4, which is important if the H2 is to be subsequently used in a fuel cell.