A theoretical study on the mechanism of small carbon clusters growth in low-temperature plasma

Abstract

Abstract Understanding the interaction between small alkane radical ions and methane could lead to more efficient ways of hydrogen production, which is an essential component in the field of green energy. It can contribute to developing new plasma processing methods for natural gas utilization or for its conversion into other useful products. In this study, using first-principles calculations we analyzed interactions between small alkane radical ions and methane molecules, which result in growth of carbon clusters and production of hydrogen in methane plasma. Our observations revealed that anion-methane interactions initiate from C-H bond rupture in CH4, with the lowest activation barrier seen in negative ions undergoing a hydrogen transfer reaction. Positive alkane ion radicals demonstrated a different initial step in the clustering process where CH3 and H transfer reactions occur simultaneously. The total reaction between positive ethyl ion and methane has low activation energy in accordance with experimental studies. Also, estimated rate constants are in reasonable agreement with experimental values for a wide range of temperatures. Our calculations showed that both negative and positive ethyl ions readily react with methane, forming hydrogen molecules and C3 ion radicals. However, the continued growth of these radicals encounters increasing activation barriers, suggesting a slowdown in the carbon ion clusterization rate and hydrogen production for larger clusters. These findings are crucial for carbon nanoparticle generation and hydrogen production using the plasma catalysis process.