Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation

Abstract

The drive to develop maximal atom‐efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever‐increasing interest in single‐atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8–10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less‐electronegative row 4 elements (Fe, Co, Ni) ranged from −1.40 to −1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between −2.20 and −2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d‐shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.

Synergistic Effects in the Activity of Nano‐Transition‐Metal Clusters Pt12M (M=Ir, Ru or Rh) for NO Dissociation

“…The reactivity index was calculated using a Fermi weighted density of states approximation as this method has already been shown to give very satisfactory results for catalytic systems. [8] The introduction of a weight function, defined as the derivative of the Fermi-Dirac distribution function for a given nominal electron temperature (kBT) allows to scale the contributions of successive energy levels to the overall reactivity. 3.…”

“…Based on the optimal nominal electron temperature of 0.15 eV for the naked clusters in vacuum, we ultimately computed the local Fermi softness (s_F^-) -describing a potential charge transfer process from the catalytic cluster towards the reagent of interest (NO)as a tool to predict the strength of the adsorption of a nitrogen oxide molecule. [8] The Pt 12 Ru 0.86 0.81 choice for this local index -obtained as an integrated product between the Fermi-Dirac weight function and contributions only occurring from the metallic cluster (local density of states) -over an energy range whose upper limit is the Fermi level, is justified by the assumption that nitrogen oxide will mainly interact with the transition metal complex rather than with the amorphous silica zeolite. Overall, an increase in softness relative to the vacuum situation is observed in Table 4, which may suggest that the chosen silica pore is a less suitable choice for clusters aiming at strong interaction with a hard molecule such as NO.…”

“…[7] Secondly, single atom catalysis has been investigated, whereby single transition-metal atoms are positioned onto the supporting oxide. [8] However, many challenges remain related to the lifespan activity of these materials due to undesired mobility of the metal atoms over the oxide surface as well as their segregation into the bulk. [9,10] Finally, the aggregation of nanoclusters on oxides after thermal activation has been shown to provide important catalytic performance.…”

Proposal of a Fermi–Dirac-Derived Reactivity Descriptor: Beyond the Frontier MO Model

“…On an ending note, during the course of this article redaction, a publication was released, dealing with the application of C-DFT descriptors in the solid state, noticeably Fukui functions and local softness . These descriptors were evaluated through different formulations, noticeably relying on the Fermi–Dirac population scheme.…”

“…On an ending note, during the course of this article redaction, a publication was released, dealing with the application of C-DFT descriptors in the solid state, noticeably Fukui functions and local softness. 50 These descriptors were evaluated through different formulations, noticeably relying on the Fermi−Dirac population scheme. Difficulties were met in the computation and interpretation of the electrophilic response, related to the large difference in levels of density between the conduction and valence bands.…”