A theoretical study of methyl chemisorption on Ni(111)

Abstract

Calculations including electron correlation have been performed for methyl adsorbed on nickel clusters mimicking the Ni(111) surface. The chemisorption energies are evaluated following a recently developed scheme, in which the cluster is prepared for bonding. In this way cluster dependent oscillations of the chemisorption energies are largely eliminated. By also using calculated vibrational frequencies of the adsorbed methyl an almost certain assignment of the preferred chemisorption site is obtained. Methyl is found to adsorb in the threefold hollow site with a chemisorption energy in the range 50–55 kcal/mol. The origin of the soft C–H frequencies observed experimentally is a charge transfer from the metal into the C–H antibonding orbitals. The only weak sign of a direct metal–carbon–hydrogen interaction in the calculations is that the C–H frequency is slightly lower for an eclipsed compared to a staggered orientation of methyl in the threefold hollow. The present results are compared to previous experimental and theoretical results for methyl adsorbed on metal surfaces.

A theoretical study of CH4 dissociation on pure and gold-alloyed Ni(111) surfaces

“…A softening of these modes during adsorption has been found. 6 It has been explained as due to charge donation from the surface Table II. into the methyl group, 14 or alternatively by a displacement of the methyl radical away from the hollow site that brings one H atom into a Ni atop position. 15 Thus we are left with 9 degrees of freedom of the H-CH 3 dimer, that may be decomposed into three translations, three rotations, and three orientations of the CH 3 radical relative to the C-H bond.…”

“…14,15 The carbon atom is located 1.56 Å above the surface. Again, this bond distance is somewhat lower than the result of 1.84 Å from CI cluster calculations.…”

“…Early work concentrated on the insertion of a single Ni atom into a C-H bond in methanestudies addressed the chemisorption of CH 3 on the Ni͑111͒ surface modeled by medium-sized clusters. 14,15 In recent years, Yang and Whitten treated the dissociative chemisorption of CH 4 on Ni͑111͒ in a large cluster model at the CI ͑configuration interaction͒ level. 16 They report a barrier of 71 kJ/mol for adsorption of CH 3 and H into separated threefold hollow sites.…”

The relationship between adsorption energies of methyl on metals and the metallic electronic properties: A first‐principles DFT study

“…[15][16][17][18][19][20][21][22][23][24][25][26] Yang and Whitten 15,26 have reported that the adsorption energy of CH 3 on the Ni(111) surface using the many-electron embedding theory and modeling the lattice as a 28-atom, three-layer cluster. Ab initio CI cluster calculation was performed by Schule and coworkers 16 on Ni(111) with distinct cluster sizes. The extended Hückel method was widely employed, such as the chemisorption studies of hydrocarbons by Gavin et al 17 on Ni(111), methyl adsorption on Pt(111) by Minot et al, 18 and the bonding and coupling of CH x on Co, Cr, and Ti by Hoffmann and coworks.…”

“…13,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] Among them, most studies were concentrated on Ni(111). [15][16][17][18][19][20][21][22][23][24][25][26] Yang and Whitten 15,26 have reported that the adsorption energy of CH 3 on the Ni(111) surface using the many-electron embedding theory and modeling the lattice as a 28-atom, three-layer cluster. Ab initio CI cluster calculation was performed by Schule and coworkers 16 on Ni(111) with distinct cluster sizes.…”