Journals Proceedings

Abstract

This study focuses on the catalytic decomposition of CH4 for the production of carbon nanotubes (CNTs). The decomposition of a single CH4 molecule on Ni/γ- Al2O3 catalyst surface with and without Cu was observed via ab initio calculations. The structural model was based on the transformation of metallic Ni and Cu into Ni-Cu alloy on γ- Al2O3 from experimental data. Structural relaxation and decomposition simulations were performed using Materials Studio 2016 DMol3 with the Local Density Approximation – Vosko-Wilk-Nusair (LDA-VWM) exchange correlation functional, Gaussian double zeta plus polarization function basis set (DNP) at 2x2x1 k-point calculation and orbital cut-off of 3.5 Å, with simulation parameters: T = 1300K, time step = 1.9 fs (78.5 a.u.), simulation time of 0.38 ps, with canonical NVT (constant amount (N), volume (V) and temperature (T)) thermodynamic ensemble and Generalized Gaussian Moment (GGM) thermostat. Simulation data suggest lower C deposition at 1:1 Ni-Cu. Simulation data also suggest a weak Ni – γ-Al2O3 interaction characterized by the ―lifting‖ of the Ni matrix and Ni-Cu alloy off of the γ-Al2O3 during CH4 decomposition. The addition of Cu did not significantly alter the crystal size and structure of the Ni/γ-Al2O3 matrix. These results agree respectively with experimental findings: decreased CNT content with at 1:1 Ni-Cu content; CNT growth was found to follow the tip-growth model; and there was no significant correlation between the diameter of the CNT produced and Cu content in the catalyst. These findings demonstrate that the catalytic decomposition of CH4 for the production of CNTs is environmentally promising via the modification of the metallic composition of the catalyst.