Mechanisms of Complete Dissociation of CO₂ on Iron Clusters

Abstract

Dissociation of CO 2 on iron clusters was studied by using semilocal density functional theory and basis sets of triple-zeta quality. Fe 2 , Fe 4 , and Fe 16 clusters were selected as the representative host clusters. When searching for isomers of Fe n CO 2 , n = 2, 4 and 16 corresponding to carbon dioxide attachment to the host clusters, its reduction to O and CO, and to the complete dissociation, it was found that the total spin magnetic moments of the lowest energy states of the isomers are often quenched with respect to those of initial reagents Fe n + CO 2 . Dissociation pathways of the Fe 2 + CO 2 , Fe 4 + CO 2 , and Fe 16 + CO 2 reactions contain several transition states separated by the local minima states; therefore, a natural question is where do the spin flips occur? Since lifetimes of magnetically excited states were shown to be of the order of 100 fs, the search for the CO 2 dissociation pathways was performed under the assumption that magnetic deexcitation may occur at the intermediate local minima. Two dissociation pathways were obtained for each Fe n + CO 2 reaction using the gradient-based methods. It was found that the Fe 2 + CO 2 reaction is endothermic with respect to both reduction and complete dissociation of CO 2 , whereas the Fe 4 + CO 2 and Fe 16 + CO 2 reactions are exothermic to both reduction and complete dissociation of carbon dioxide. The CO 2 reduction was found to be more favorable than its complete dissociation in the Fe 4 case.

Reaction Dynamics of CO2 Hydrogenation on Iron Catalysts Using ReaxFF Molecular Dynamics Simulation

“…The low-energy structures obtained for Fe 4 and Fe 16 as shown in Figure 1 agree with the low-energy clusters obtained from DFT calculations. 19 The Fe 256 cluster is also shown as an example of a larger cluster. The dimensions of the simulation boxes containing the Fe 4 and Fe 16 clusters were 25.0 × 25.0 × 25.0 Å 3 and those containing the Fe 256 cluster were 30.0 × 30.0 × 30.0 Å 3 , and they were periodic in all directions.…”

Observation of inserted oxocarbonyl species in the tantalum cation-mediated activation of carbon dioxide dictated by two-state reactivity

“…[14][15][16][17][18] Apart from experimental investigations, there are also a considerable amount of theoretical studies focusing on transition metal-mediated reactions with CO 2 in an effort to elucidate salient features of mechanisms and kinetics. [19][20][21][22][23] Taking the electronic structure of CO 2 into consideration, the most commonly adopted method of effective activation concerns electron density donation to the antibonding π* orbital, leading to a negatively charged CO 2 moiety and further enabling overall reduction of bond strength along with bending distortion from its initial linear geometry. 2 The changes in the charge distribution and geometric structures give rise to vibrational frequency shifts regarding the asymmetric stretching mode of the CO 2 molecule.…”

“…14–18 Apart from experimental investigations, there are also a considerable amount of theoretical studies focusing on transition metal-mediated reactions with CO 2 in an effort to elucidate salient features of mechanisms and kinetics. 19–23…”

Nitrogen Reduction to Ammonia on a Fe16 Nanocluster: A Computational Study of Catalysis

“…That study also found that both N atoms and N 2 dimers prefer cluster surface sites and do not penetrate inside the cluster. The same cluster was also recently tested as a catalyst for reactions of the CO 2 dissociation into separated atoms C and two O atoms on the surface of the cluster. Computationally, studying reactions of small molecules on small 3d-transition metal clusters makes it possible to use all-electron basis sets which can yield more precise descriptionscompared to plane wave methods that incorporate effective core potentialsof relevant electronic effects including the dependence of ground state energies on spin multiplicity which, the results of the present study show, play an important role in reaction energetics. It is now possible to synthesize size-selected subnanometer clusters of metals and metal oxides . Therefore, the catalytic activity of ultrasmall nanoparticles is now amenable to be studied in detail in the laboratory. …”

“…That study also found that both N atoms and N 2 dimers prefer cluster surface sites and do not penetrate inside the cluster. The same cluster was also recently tested as a catalyst for reactions of the CO 2 dissociation into separated atoms C and two O atoms on the surface of the cluster.…”