DFT Study of Selective α-Fluoride Elimination of Adsorbed CF_3(ads) on Both Ag(111) and Cu(111) Surfaces

Abstract

Total-energy calculations based on (1) density functional theory (DFT) in connection with ultrasoft pseudopotential (USP) and generalized gradient spin-polarized approximation (GGSA), (2) the partial structural constraint path minimization (PSCPM) method, and (3) an analysis tool of the partial density of states (PDOS) have been used to investigate the possible energetic profile for the selective activation of C-F bonds, that is, the single R-fluoride elimination of adsorbed CF 3(ads) on both Cu(111) and Ag(111) surfaces leading to adsorbed CF 2(ads) and F (ads) on both surfaces. Following our proposed most possible reaction pathway, namely, the diffusion of the hcp-hollow site of CF 3(ads) toward the top site accompanied by the single R-fluoride elimination to form the fcc-hollow site of F (ads) , our calculated energy barrier on the Ag(111) surface is significantly larger than (∼0.462 eV) that on the Cu(111) surface. We attribute this unusual high-energy barrier for the single R-fluoride elimination of adsorbed CF 3(ads) to forming a productlike distorted transition-state structure on the Ag(111) surface, that is, the larger stretching of a C-F bond and the larger distortion of bond lengths of Ag-Ag on the Ag(111) surface, in comparison with a less energy barrier to forming a reactant-like distorted transition-state structure on the Cu(111) surface, that is, smaller stretching of a C-F bond and smaller distortion of bond lengths of Cu-Cu on the Cu(111) surface. Consequently, the single R-fluoride elimination of adsorbed CF 3(ads) to form adsorbed CF 2(ads) and F (ads) leading to the formation of CD 2 CF 2(g) , CD 2 dCD 2(g) , and CF 2 d CF 2(g) through coupling reactions with CD 2(ads) coadsorbed on the Ag(111) surface will be suppressed by the methylene (CD 2 ) insertion into the Ag-CF 3(ads) bond with CD 2(ads) coadsorbed on the Ag(111) surface to initially form adsorbed Ag-CD 2 CF 3(ads) and to continually form CD 2 dCF 2(g) through the β-fluoride elimination on the same surface. Finally, our calculated surface electronic states, that is, PDOS, of both Cu(111) and Ag(111) surfaces and our calculated bonding nature, that is, PDOS, of both carbon and fluorine within adsorbed CF 3(ads) on the same surfaces at their different transition-state structures, that is, reactant-like on Cu(111) versus productlike on Ag(111), are investigated to obtain further insight into the effect of both surface electronic states and C-F bond strength on their different reactivity for the single R-fluoride elimination of adsorbed CF 3(ads) on both surfaces.

Theoretical Study of the Stability of Carbene Intermediates Formed During the Hydrodechlorination Reaction of the CF x Cl4−x Family on the Pd(110) Surface

“…Very recently, Lin et al [71] have shown by theoretical calculations that CF 3 species can dissociate on Cu(111) and Ag(111) surfaces with relatively low activation energies; 20 and 64 kJ/mol, respectively. This may indicate that this fragment would dissociate to CF 2 on Pd catalyst with a similar low activation energy.…”

Temperature dependence of vibrational modes of CH3CC(ads) and I(ads) coadsorbed on Ag(111): Ab initio molecular dynamics approach

“…Next, the second most stable CH 3 AC (b) BC (a) (bridge)-I(bridge) (ads) on the Ag(111) surface will rupture the CAI bond, which is accompanied by the diffusion of both CH 3 AC (b) BC (a) (bridge) (ads) and I(bridge) (ads) into the nearest hollow sites, particularly the CH 3 AC (b) BC (a) (fcc) (ads) ---I(fcc) (ads) site, as shown in Figure 2b. The partial structural constraint path minimization method [20] is used to establish both energetically more favorable reaction pathways as shown in Figure 3. The details of the calculated structures are reported in Figures 5a-5f, and their comparisons with calculated IR spectra are shown in Figure 4a; these results lead to the assignment of individual IR active peaks, which will be illustrated and discussed below.…”

“…The vacuum region is set to be $ 16 Å . [20] For the Brillouin-zone integration, we use a 3 Â 3 Â 1 k-point grid that is determined by Monkhorst-Pack special points. All of the calculations are performed by a spin-polarized scheme.…”