Recurring Competitive Reactions: Desorption of Methane and Molecular Hydrogen From Cu(001)

Abstract

Methane and molecular hydrogen desorption from a methyl and hydrogen exposed Cu(001) surface is investigated. Both gaseous products are observed nearly simultaneously within two temperature regimes separated by more than 100 K. The lower temperature desorption, at ∼325 K, is believed to result from two processes which compete for adsorbed atomic hydrogen: methyl reduction and associative hydrogen desorption. The higher-temperature competitive desorption is initiated after the onset of thermal decomposition of remaining methyl species, at ∼420 K. Kinetic simulations of the two presumed competing reactions are used to show observable and comparable methane and hydrogen evolution can occur in two temperature regimes, only with a precise balance of kinetic parameters, but fail to accurately reproduce the observed small differences in CH(4) and H(2) peak desorption temperatures. It is concluded that either the utilized desorption kinetics are inaccurate at low H((a)) coverages or rapid desorption, or the same reactions are not competitive at higher temperatures and an alternative active mechanism for product evolution must exist.

Controlled Growth of Single‐Crystal Graphene Films

“…Therefore, this phenomenon also indicates that dehydrogenation is involved in the overall graphene growth process, as confirmed by isotope‐labeling experiments . In addition, desorption of active carbon species from Cu surface is non‐negligible and the gas phase compositions might also influence the nucleation behaviors of graphene …”

“…[30] In addition, desorption of active carbon species from Cu surface is non-negligible and the gas phase compositions might also influence the nucleation behaviors of graphene. [36,45,46] The formation energy of carbon clusters on Cu(111) surfaces can be described by Equation (1)…”

Theoretical Insights on the C2Hy Formation Mechanism During CH4 Dissociation on Cu(100) Surface

“…C 2 H y Formation Reaction and the Activated Second-order CH x+1 + CH z−1 Reaction. According to the speculations in the previous experimental study, 29 there are two possible reactions between CH x species, that is, C 2 H y formation, reaction 1, and the activated second-order CH x−1 + CH z−1 , reaction 2, as follows:…”

“…Motivated by this idea, a systematic study on the possible reaction mechanism for C 2 H y formation on Cu(100) surface has been conducted in this work by employing the density functional theory (DFT). Meanwhile, the activated second-order CH x +1 + CH z –1 reactions based on the experiment are also considered in this study.…”

“…It is known that the hydrocarbon molecule dissociation, the diffusion of C atoms or clusters on the catalyst surface, the formation of the nucleation graphene islands, and the growth of graphene islands are the main four steps for graphene CVD growth. 22−28 It is obvious that the first dissociation process is the precondition for the graphene growth and the decom- 29 are also considered in this study.…”