Plasma catalysis is an emerging process electrification technology for industry decarbonization. Plasma-catalytic dry reforming of methane (DRM) relies on the mutual effects of the plasma and the catalyst leading to the higher chemical conversion efficiency. The effects of catalyst surfaces on the plasma are predicted to play a major role, yet they remain unexplored. Here, a 1D plasma fluid model combined with 0D surface kinetics is developed to reveal how the surface reactions on platinum (Pt) catalyst affect the redistribution of the gas-phase particles. Two contrasting models with and without the surface kinetics as well as the Spearman rank correlation coefficients are used to quantify the effect of the key species (H, CH, CH2) on the CO generation. Advancing the common knowledge that Pt catalyst can influence the plasma chemistry directly by changing the surface loss/production of particles, this study reveals that the catalyst can also affect the spatial distributions of active species, thereby influencing the plasma chemistry in an indirect way. This result goes beyond the existing state-of-the-art which commonly relies on over-simplified 0D models which cannot resolve the spatial distribution. Further analysis indicates that the species spatial redistribution is driven by the dynamic catalyst surface adsorption-desorption processes. This work enables the previously elusive account of active species redistribution and may open new opportunities for plasma-catalytic sustainable chemical processes.

In the application of atmospheric pressure plasma jet, the influence of ambient gas cannot be ignored, especially in some specific scenarios which are highly sensitive to ambient species. Coaxial double-tube plasma jet device is a promising method for controlling the chemical properties of jet effluent by restraining the mutual diffusion between jet effluent and ambient gas. In this paper, the discharge characteristics and chemical properties of coaxial double-tube helium atmospheric pressure plasma jet at different flow rates of shielding gas are researched numerically, and the model is validated by experimental optical images. The results illustrate that the discharge is enhanced at the high flow rate, while it shows the weaker discharge behavior at the low flow rate as well as that without shielding gas. With the increase of shielded gas flow rate, the species density increases in the discharge space, which can be attributed to the wider main discharge channel caused by the increase of shielding gas flow rate. In addition, the analysis shows the great difference in the ions fluxes affected by the flow rate of the SG between the contour lines of different helium mole fractions. This study further reveals that different discharge positions have a great influence on the generation of nitrogen and oxygen species, thus deepening the influence of shielding gas flow rate on discharge behavior, and may provide new opportunities for the further application of plasma jet.

The effect of ambient air as an unavoidable problem for atmospheric pressure plasma jet (APPJ) applications has attracted a lot of interest, especially when the specific scenarios are highly sensitive to ambient species such as the biomedical process. The coaxial double-tube device is a promising method for controlling the ambient species into the jet effluent and thus the chemical properties of the jet effluent. In this work, the discharge characteristics and plasma chemistry of the coaxial double-tube helium APPJ at different shielding gas (SG) flow rates are studied numerically. An experiment on optical images of the discharge is conducted to illustratively validate the variation of the (main) discharge channel widths in the model as the SG flow rate varies. The results illustrate that the discharge is enhanced at the high flow rate, while it shows the weaker discharge behavior at the low flow rate as well as that without SG. The analysis of the dielectric plate surface indicates that the species fluxes to the dielectric plate significantly increase with the increases in the flow rate, which can be attributed to the wider (main) discharge channel. Moreover, to further explore the impact of the SG on the effluent chemistry, the ions fluxes on the surfaces of the main discharge channel and the discharge channel are distinguished and discussed. The analysis shows the great difference in the ions fluxes affected by the flow rate between the two discharge channels. In summary, advancing the knowledge that the flow rate of the SG has an impact on the discharge behavior, this study further reveals that different discharge positions greatly influence the production of nitrogen/oxygen species. This work enables the previously elusive account of the effect of SG and may open new opportunities for the further application of coaxial double-tube APPJ.