CH4 dehydrogenation on Cu(111), Cu@Cu(111), Rh@Cu(111) and RhCu(111) surfaces: A comparison studies of catalytic activity

摘要

In the CVD growth of graphene, the reaction barriers of the dehydrogenation for hydrocarbon molecules directly decide the graphene CVD growth temperature. In this study, density functional theory method has been employed to comparatively probe into CH4 dehydrogenation on four types of Cu( 1 1 1) surface, including the flat Cu( 1 1 1) surface (labeled as Cu(1 1 1)) and the Cu( 1 1 1) surface with one surface Cu atom substituted by one Rh atom (labeled as RhCu(1 11)), as well as the Cu(1 1 1) surface with one Cu or Rh adatom (labeled as Cu@Cu( 1 1 1) and Rh@Cu(1 1 1), respectively). Our results show that the highest barrier of the whole CH4 dehydrogenation process is remarkably reduced from 448.7 and 418.4 kJ mol(-1) on the flat Cu(1 1 1) and Cu@Cu(1 1 1) surfaces to 258.9 kJ mol(-1) on RhCu( 1 1 1) surface, and to 180.0 kJ mol(-1) on Rh@Cu(1 1 1) surface, indicating that the adsorbed or substituted Rh atom on Cu catalyst can exhibit better catalytic activity for CH4 complete dehydrogenation; meanwhile, since the differences for the highest barrier between Cu@Cu(1 1 1) and Cu( 1 1 1) surfaces are smaller, the catalytic behaviors of Cu@Cu(1 1 1) surface are very close to the flat Cu(1 1 1) surface, suggesting that the morphology of Cu substrate does not obviously affect the dehydrogenation of CH4, which accords with the reported experimental observations. As a result, the adsorbed or substituted Rh atom on Cu catalyst exhibit a better catalytic activity for CH4 dehydrogenation compared to the pure Cu catalyst, especially on Rh-adsorbed Cu catalyst, we can conclude that the potential of synthesizing high-quality graphene with the help of Rh on Cu foils may be carried out at relatively low temperatures. Meanwhile, the adsorbed Rh atom is the reaction active center, namely, the CVD growth can be controlled by manipulating the graphene nucleation position. (C) 2015 Elsevier B.V. All rights reserved.