Temperature effects on adsorption and diffusion dynamics of CH3CH2(ads) and H3C–C≡C(ads) on Ag(111) surface and their self-coupling reactions: Ab initio molecular dynamics approach

Abstract

Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C-C(β)≡C(α) (ads)) and ethyl (H3C(β)-C(α)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C-C(β)≡C(α)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of -C(β)≡C(α)- stretching are gradually merged into one peak as a result of the dominant motion of the stand-up -C-C(β)≡C(α)- axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(β)-C(α)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(β)-C(α)H2(ads) adsorbed on the Ag(111) surface has been observed. These calculated IR spectra are in a good agreement with experimental reflection absorption infrared spectroscopy results. Furthermore, the dynamics behaviors of H3C-C(β)≡C(α)(ads) and I coadsorbed on the Ag(111) surface point out the less diffusive ability of H3C-C(β)≡C(α)(ads) due to the increasing s-character of Cα leading to the stronger Ag-Cα bond in comparison with that of H3C(β)-C(α)H2(ads) and I coadsorbed on the same surface. Finally, these DFTMD simulation results allow us to predict the energetically more favourable reaction pathways for self-coupling of both H3C-C(β)≡C(α)(ads) and H3C(β)-C(α)H2(ads) adsorbed on the Ag(111) surface to form 2,4-hexadiyne (H3C-C≡C-C≡C-CH3(g)) and butane (CH3-CH2-CH2-CH3(g)), respectively. The calculated reaction energy barriers for both H3C-C≡C-C≡C-CH3(g) (1.34 eV) and CH3-CH2-CH2-CH3(g) (0.60 eV) are further employed with the Redhead analysis to estimate the desorption temperatures approximately at 510 K and 230 K, respectively, which are in a good agreement with the experimental low-coverage temperature programmed reaction spectroscopy measurements.

Complex Reaction Network Thermodynamic and Kinetic Autoconstruction Based on Ab Initio Statistical Mechanics: A Case Study of O2 Activation on Ag4 Clusters

“…Furthermore, free energy calculations in a reaction network within the TST framework depend on the harmonic oscillator (HO) approximation, which is inaccurate at high temperatures because it neglects the translational and rotational motions of weak interactions between molecules and substrates. − In the meantime, at high temperatures, the reaction pathway will most probably not follow the MEP, based on the transition state (active complex) hypothesis. On the other hand, there is a decent amount of work on using molecular dynamics methods in catalysis and surface reactions, ,− providing more accurate descriptions of the free energy and reaction pathways at finite temperatures than HO-TST methods.…”