Low-temperature, atmospheric pressure reverse water-gas shift reaction in dielectric barrier plasma discharge, with outlook to use in relevant industrial processes

Plasma discharges offer a direct way to convert electrical to chemical energy and to store volatile renewable energy sources. Converting CO2 in this way can contribute to reducing the greenhouse effect, and provide additional opportunity for chemical processing, e.g., on-site or on a small scale. The CO2 hydrogenation to CO via the reverse water-gas shift reaction (RWGS) generates synthesis gas for use as feedstock to different fuels and chemicals. The RWGS reaction carried out in a Dielectric Barrier Discharge (DBD) plasma reactor benefits from operation at ambient pressure and mild temperature, as compared to the harsher conditions of conventional RWGS processing. To develop that with outlook to real-life uses, e.g., toward methanol synthesis, key performances need to be achieved; that is, i.a., a threshold CO2 conversion, a high CO selectivity at low impurity (low CH4 selectivity), and a high (H2 − CO2)/(CO + CO2) ratio (favourable for high reaction rates) as well as tolerable energy efficiency. Central plasma process parameters for this are the feed gas ratio, residence time, and uniformly distributed microdischarges. The optimisation of an individual key performance can be adverse to the other so that the process exploration is a task. This gives room to introduce new plasma operation types, and the burst mode was applied for the first time to the RWGS reaction in the present work. By this fast (millisecond) periodic switching on and off the plasma, the process temperature can be reduced as well as a better microdischarge distribution can be achieved. The residence time is not only set by the flow rate, as commonly done, but also by taking the discharge gap as an additional parameter of freedom, which also impacts the reducing distribution. As a result of relevant process conditions, at CO selectivity of 98%, 337 mmol/kWh is obtained as the energy efficiency of CO formation. Whereas the best CO2 conversion of 50% and the (H2 − CO2)/(CO + CO2) ratio of 2 were obtained at respective optimum process parameters.