(190a) Mechanisms Underlying Coke Formation over Ni-Based Catalysts for Dry Reforming of Methane: A First Principles Study

Nickel (Ni) catalysts have garnered significant attention for their potential in dry reforming of methane (DRM). However, their widespread application is hindered by rapid deactivation due to carbon deposition, a phenomenon known as coke. In this talk, we aim to elucidate the intricate mechanisms underlying coke formation over Ni-based catalysts, focusing specifically on the step edges. Based on first-principles simulations, we will first present the dynamic behavior of atomic carbon on the stepped Ni (755) surfaces and evaluate the variations in binding strength with varying carbon contents. Our calculations uncover a compelling driving force directing carbon transport toward the step edge, with subsurface diffusion identified as the primary limiting step. We observe a weakening in the carbon binding strength at the step edge as carbon accumulates, facilitating the formation of carbon dimer. Notably, subsurface carbon readily incorporates into the coke structure attached to the step, promoting coke growth. Additionally, we investigate the impact of adding small amounts of copper (Cu) into Ni catalysts, resulting in Ni−Cu catalysts, on their coking resistance. The presence of Cu atoms favorably covering the step edge of Ni−Cu catalysts impedes subsurface carbon transport to the step sites where carbon precipitation occurs. Our findings underscore the importance of precise control over Cu concentration and spatial distribution for optimizing catalyst design. The improved understanding offers valuable guidelines for the rational design of Ni-based catalysts with enhanced coking resistance, not only for DRM but also other reforming processes.