Turning diamond into methane

Experiments demonstrate a high reactivity between carbon and hydrogen at conditions comparable with those in the Earth’s upper mantle.

Turning diamond – the finest gem – into methane – one of the worst greenhouse gases, more than 25 times potent than CO2 at trapping heat in the atmosphere – may not sound a brilliant idea. However, an international collaboration between scientists from the University of Edinburgh, the University of Bologna, the Centre National de la Recherche Scientifique (France), HPSTAR (China) and the Institute of Solid State Physics (Chinese Academy of Sciences) discovered that diamond and hydrogen can react yielding to methane, in what may play a key role in cycling carbon in the deep Earth.

The researchers observed that methane was produced by diamond-hydrogen interactions in seconds at conditions of pressure and temperature analogous to those at 70 km deep.  Although the possibility for diamond to form from methane in the Earth’s mantle was known, the opposite reaction was not included in the inventory of processes regulating the deep carbon cycle.

Dr Peña-Alvarez from the University of Edinburgh's Centre for Science at Extreme Conditions commented on the experiment:

To experimentally reproduce deep Earth conditions, we used an experimental apparatus called a diamond-anvil cell, where the flat surfaces of two diamonds are pushed against each other. We noticed that when the cell is loaded with pure hydrogen and heated, the diamonds readily react to form methane and longer-chain hydrocarbons.

Professor Vitale Brovarone from the University of Bologna and the Centre National de la Recherche Scientifique, reported:

This discovery provides a new tile of the deep carbon cycle, which accounts for about 90% of the total carbon on Earth. The genesis of methane from diamond and hydrogen also demonstrates that hydrocarbons unrelated to biological activities can form in deep Earth and may act as source of energy for shallower geological reservoirs.

The collaboration includes former School of Physics and Astronomy PhD students Dr Philip Dalladay-Simpson, who is currently based at HPSTAR, China and Dr Mary-Ellen Donnelly who is currently based at Oak Ridge Spallation Source, United States of America.