Effect of Cu on Ni Catalyst for the Thermal Decomposition of Methane A Molecular Dynamics Investigation

investigated via ab initio DMol 3 molecular dynamics simulation. Initial simulation used the Local Density Approximation (LDA) with the Perdew-Wang 1992 (PWC) specific local exchange correlation functional, Gaussian double zeta plus polarization function basis set (DNP) at gamma (1x1x1) k-point calculation and orbital cut-off of 3.4 A, with additional parameters: T = 1300K, time step = 2.5 fs, simulation time of 0.25 ps, with canonical NVT (constant amount (N), volume (V) and temperature) thermodynamic ensemble and Generalized Gradient Moment (GGM) thermostat. Results demonstrate the capacity of Ni for carbon deposition, whereas the addition of Cu resulted in the following: promoted the disjoining of the H atoms from the C atom allowing the C atom to form more bonds with the metal surface; accelerated the initial catenation of the CH4 atom (Ni = 12.5 fs; Ni-Cu = 10.0 fs); and delayed the initial deposition of C atom on the metal surface (Ni = 30.0 fs; Ni-Cu = 37.5 fs). Examination of the decomposition mechanism revealed the initial formation of a metal-H bond between one of the H atoms of the CH4 molecule and one of the metal atoms, followed by the re-formation of a transition bond between the C atom and the H atom bonded to the metal. This brings the C atom towards the metal surface for deposition after which the transition C-H bond is broken. This implied role of hydrogen in the deposition of carbon agrees with experimental results in literature.