Interactions of plasma species on nickel catalysts: A reactive molecular dynamics study on the influence of temperature and surface structure

Methane reforming by plasma catalysis is a complex process that is far from understood. It requires a multidisciplinary approach which ideally takes into account all effects from the plasma on the catalyst, and vice versa. In this contribution, we focus on the interactions of CH_x (x={1,2,3}) radicals that are created in the plasma with several nickel catalyst surfaces. To this end, we perform reactive molecular dynamics simulations, based on the ReaxFF potential, in a wide temperature range of 400-1600K. First, we focus on the H₂ formation as a function of temperature and surface structure. We observe that substantial H₂ formation is obtained at 1400K and above, while the role of the surface structure seems limited. Indeed, in the initial stage, the type of nickel surface influences the C-H bond breaking efficiency of adsorbed radicals; however, the continuous carbon diffusion into the surface gradually diminishes the surface crystallinity and therefore reduces the effect of surface structure on the H₂ formation probability. Furthermore, we have also investigated to what extent the species adsorbed on the catalyst surface can participate in surface reactions more in general, for the various surface structures and as a function of temperature. These results are part of the ongoing research on the methane reforming by plasma catalysis, a highly interesting yet complex alternative to conventional reforming processes.