How Fast Do Microhydrated Al Clusters React: A Theoretical Study

Abstract

The dynamics of the first step of the reaction of small Al m clusters m = {3,13} with up to four water molecules has been studied. The first stage in the reaction, which may ultimately result in the production of H2, is the generation of a HAl m OH·(H2O) n−1 species, which can take place through transition states of the relay type, in which the water molecules may play different catalytic roles; namely, they can be involved directly in a Grotthuss-like mechanism by forming a relay bridge, or they may lower the saddle point energy by interacting with the molecules of the relay bridge. Rate coefficients have been computed with the inclusion of tunneling effects. The results indicate that the optimal configuration (the one giving the highest values of the rate coefficient for 50 K < T < 500 K) in the case of the Al3·(H2O) n system involves three water molecules in the relay bridge. In the case of the Al13 cluster, the two-water system is the most efficient. It is remarkable that Al3 delivers much higher rates than Al13 or a single Al atom. It is argued that Al13 and Al have, somehow, a similar behavior from the point of view of the rates, the Gibbs activation energies, and the tunneling transmission coefficients, which gives some dynamically based support to viewing the Al13 cluster as a kind of “superatom”.

Hydrogen migration dynamics in hydrated Al clusters: The Al17(−)·H2O system as an example

“…A study of the Al 3 · (H 2 O) 2 system showed that the BHandHLYP functional is also quite consistent with basis set changes. 78 Although not the ideal functional for naked clusters, it still has the property of not missing local minima, even when they are shallow kinks on the potential energy surface. Finally it is not likely to underestimate the depth of any stationary point of the potential surface with respect to the reactants Al 17 (−) + H 2 O, something which could result in too low rates.…”

“…[40][41][42][43][44][45][46] It includes also a number of theoretical studies on the structural aspects of Al clusters, [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] and about their interaction [65][66][67][68][69][70][71][72] and reaction [73][74][75][76][77][78][79] with simple molecules.…”

On reactivity of superatom Be8C with nucleophiles to produce hydrogen

“…Based on previous study of the Be n C clusters [30], the economical B3PW91 functional [30][31][32][33] was adopted, along with the 6-311++G(d, p) basis set, to obtain the optimized structures in this work. Harmonic vibrational frequency analysis was performed at the same level to ensure that the optimized structures correspond to transition states or true minima on the potential energy surfaces.…”

Single‐point Attack of Two H2O Molecules towards a Lewis Acid Site on the GaAl12 Clusters for Hydrogen Evolution

“…Moreover, the primary surface‐bound H 2 O can bring new active sites for the O−H bond activation and adsorption of the second hydroxyl compound . An H 2 molecule can be released from the Al cluster only when the adsorption sites for the second water can result in two Al−H bonds or an Al−H and O−H bond at an adjacent position so that an H 2 can be released ,,. This principle is actually analygous to the Langmuir‐Hinshelwood (LH) mechanism as implemented in surface catalysis .…”

“…It is worth mentioning that the 13‐atom clusters have been used as models to simulate the chemical activity of nanoparticles, for instance, the catalytic activity toward CO oxidation was evaluated on Ag 13 . Also there is a previous study around the reactivity of H 2 O with Al 13 showing feasible O−H bond dissociation at the adsorption of four H 2 O molecules . To fully demonstrate the HER mechanisms, we searched the active sites and reaction paths for water adsorption and O−H bond dissociation on Al 13 and Al 12 Ga 1 with a comparison to Ga 13 clusters.…”