CO₂ activation and dissociation on the low miller index surfaces of pure and Ni-coated iron metal: a DFT study

Abstract

We have used spin polarized density functional theory calculations to perform extensive mechanistic studies of CO2 dissociation into CO and O on the clean Fe (100), (110) and (111) surfaces and on the same surfaces coated by a monolayer of nickel. CO2 chemisorbs on all three bare facets and binds more strongly to the stepped (111) surface than on the open flat (100) and close-packed (110) surfaces, with adsorption energies of -88.7 kJmol -1 , -70.8 kJmol -1 and -116.8 kJmol -1 on the (100), (110) and (111) (110) and (111) facets respectively. We have also investigated the thermodynamics and activation energies for CO2 dissociation into CO and O on the bare and Ni-deposited surfaces.Generally, we found that the dissociative adsorption states are thermodynamically preferred over molecular adsorption, with the dissociation most favoured thermodynamically on the closepacked (110) facet. The trends in activation energy barriers were observed to follow that of the trends in surface work functions; consequently, the increased surface work functions observed on the Ni-deposited surfaces resulted in increased dissociation barriers and vice versa. These results suggest that measures to lower the surface work function will kinetically promote the dissociation of CO2 to CO and O, although the instability of the activated CO2 on the Ni-covered 2 surfaces will probably result in CO2 desorption from the nickel-doped iron surfaces, as is also seen on the Fe(110) surface. Graphical abstract Introduction

Two‐dimensional CoOOH as a Highly Sensitive and Selective H2S, HCN and HF Gas Sensor: A Computational Investigation

“…The obtained vibrational frequencies for the adsorbed H 2 S, HCN and HF gas molecules were lower than that of the isolated gas-phase molecule, which shows that the asymmetric and symmetric stretches were shifted to a lower vibrational frequency. The significant shifts in the vibrational modes show that the H 2 S, HCN and HF gas molecules are activated [66]. Moreover, the computed vibrational frequencies agreed with experimental results [67,68].…”

A DFT investigation of the mechanisms of CO2 and CO methanation on Fe (111)

“…CO 2 adsorption on Fe (111) is seen to require an energy barrier of − 4.6 kJ mol −1 [38]. In this study, hydrogenation of the Fe (111) surface is also seen to be barrier less and dissociative; hence, atomic hydrogen co-adsorption is explored in each elementary step via the Langmuir-Hinshelwood-type reaction.…”

“…Each slab is made up of the 36 atoms whereby there are 6 layers and 6 atoms in each layer. In all calculations, the top 3 layers and adsorbate are allowed to relax and bottom 3 layers fixed to mimic the bulk material as employed in earlier computations [37,38]. The Climbing Image Nudged Elastic Band (CI-NEB) method was used to determine all transition-state structures along the reaction coordinate.…”

Mechanisms of CO2 reduction into CO and formic acid on Fe (100): a DFT study

“…The preferred CO 2 adsorption site on the clean Fe (100) surface has been reported to be the hollow site [24]. At the hollow site, we considered CO 2 binding through the carbon and the two oxygen atoms in the 3 possible configurations (see Fig.…”

“…DFT investigations of the rWGS reaction mechanism on nickel (211) indicated the redox path to be favoured both kinetically and thermodynamically [21]. Despite earlier DFT calculations [22][23][24] have reported the spontaneous formation of anionic CO 2 δ− species on all the low-Miller indices of iron surfaces, to the best of our knowledge, no systematic theoretical study has been conducted to understand the mechanism of the rWGS reaction on iron. In the present study, the catalytic CO 2 hydrogenation intermediates and reaction barriers leading to carbon monoxide and formic acid production on iron (100) have been studied.…”