Plasma-assisted reduction of carbon dioxide in the gas phase

Abstract

The reduction of carbon dioxide by hydrogen, which constitutes the reverse water-gas shift reaction, is an active area of research because of its connection with the production of methanol and other fuels. Representative references are given, that have been reported in the catalysis literature where most of this research is described. In contrast with this, studies dealing with the plasma-assisted reduction of carbon dioxide, as a subset of the subject, are rather limited. A variety of products such as diamond, oxalic acid or fuel species have been obtained depending on the conditions. The present study was undertaken to explore the possibility of obtaining formic acid through the plasma-assisted reduction of carbon dioxide given the precedent that even a more complex molecule such as oxalic has been obtained. The production of formic acid was not anticipated to take place cleanly given the mechanistic complexity of such a process. The study was conducted nevertheless to seek an alternative to an electrochemical pathway to reduce carbon dioxide that has obvious shortcomings because of the requirement to dissolve the gas in a solvent, in addition to the limited concentration of reactant and products that might be obtained. Formic acid in the form of formate is a component of a cycle conceived to trap tritium from contaminated ground water that uses carbon dioxide from a selective oxidation step and hydrogen/tritium from the electrochemical reduction of the contaminated water. The electrochemical oxidation of formate is catalyzed by means of terpyridine bipyridine oxo ruthenium (IV), a complex that shows remarkable isotope effects so that tritiated formate is selectively enriched and may be separated by ion exchange.