Converting carbon dioxide to methane using iron and sunlight

A combined team of researchers from Université Paris Diderot in France and Universidad Nacional de Córdoba in Argentina has discovered a reaction process that can be used to convert carbon dioxide to methane. In their paper published in the journal Nature, the team describes their technique, how well it worked, and their ideas for improving it. As human endeavours continue to introduce carbon dioxide into the atmosphere, leading to global warming, scientists around the world seek alternative ways to reduce both the amount of the gas emitted into the air and the amount that is already there. In this new effort, the researchers have developed a chemical process that involves doing both at the same time—by converting carbon dioxide into methane, which can be burned to use as a greener energy source. The technique involves irradiating a carbon dioxide solution of acetonitrile, which has a single electron to donate, a photosensitiser and a catalyst that has an iron tetraphenylporphyrin compound that has been functionalized with tetraphenylporphyrin groups. Irradiation by sunlight continues for several hours. The process leads to the creation of methane, carbon monoxide and hydrogen. The researchers acknowledge that the process is grossly inefficient because the product produced is actually 82 percent carbon monoxide. It is also very slow, producing just 12 grams of methane per hour. But the team believes it can be made much more efficient using a revised two-step procedure. This is because they noticed that what was actually occurring was a conversion of initial ingredients to a mostly carbon monoxide product, some of which was then converted to methane. The researchers note that they also used pure carbon dioxide for their tests, from a canister. An improved process would have to include first pulling the gas from the air, while also keeping out impurities. The team also has plans to better understand what actually occurs during the reactions—they know the iron binds to the carbon dioxide during the first part of the process, but it is still not clear how hydrogenation of the molecule occurs.

Phys.org, 20 July 2017 ; http://phys.org