Influence of ionic conductivity and dielectric constant of the catalyst on DBD plasma-assisted CO2 hydrogenation into methanol

Abstract

Dielectric barrier discharge (DBD) plasma technology is a promising method for producing methanol from CO2 hydrogenation as the reaction can be run at atmospheric pressure and temperatures below 100 °C. The choice of the catalyst is crucial and has to be made not only according to its activity and selectivity towards the desired product, but its effect on plasma properties. In this work, the influence of several important catalytic properties of DBD plasma such as the dielectric constant of the catalyst and ionic conductivity is studied. The effects of the catalyst support and the addition of promoters on CO2 hydrogenation under DBD plasma are also studied. To this end, Cu and Cu–ZnO catalysts supported on γ-Al2O3 and a template-free seedless ZSM-5 (Si/Al molar ratio of 23) were prepared to study their catalytic performance on CO2 hydrogenation into methanol under DBD plasma. These catalysts were fully characterized by XRD, SEM, N2 physisorption, temperature programmed reduction and in situ FTIR CO adsorption. The relative complex permittivity of the catalysts was measured and the ionic conductivity was estimated using a modified Debye model. In this paper, the role of the ionic conductivity of the catalyst was identified as a crucial parameter in plasma-assisted CO2 hydrogenation. It was found that the lower the value of the ionic conductivity, the better the CO2 conversion. Indeed, high ionic conductivity reduces the density of the plasma and decreases the dissociation of CO2. The highest CO2 conversion value (34.0%) was observed for the nonconductive alumina support, whereas the highest methanol yield (0.5%) was observed for the zeolite-supported Cu–ZnO catalyst.