Making molecular hydrogen for industrial chemical and petroleum processes is costly. The typical approach mixes water and carbon monoxide (a by-product of fossil-fuel processing) at thermodynamic equilibrium in an industrial-sized reactor heated to about 800 °C. Besides producing about 50 million tons of H2 each year, the method yields carbon dioxide, which engineers must then remove through an expensive separation process. Now Ian Metcalfe of Newcastle University and his colleagues have reported an alternative process. The reactor that Metcalfe devised exploits an approach known as chemical looping, which bypasses the need to mix the reactants.

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