Generation of Oxygen Radical Centers in Binary Neutral Metal Oxide Clusters for Catalytic Oxidation Reactions

Sr2Fe1.575Mo0.5O6-δ Promotes the Conversion of Methane to Ethylene and Ethane

Oxidative coupling of methane can produce various valuable products, such as ethane and ethylene, and solid oxide electrolysis cells (SOECs) can electrolyze CH₄ to produce C₂H₄ and C₂H₆. In this work, Sr₂Fe_1.575Mo_0.5O_6-δ electrode materials were prepared by impregnation and in situ precipitation, and Sr₂Fe_1.5Mo_0.5O_6-δ was taken as a reference to study the role of metal-oxide interfaces in the catalytic process. When the Fe/Sr₂Fe_1.575Mo_0.5O_6-δ interface is well constructed, the selectivity for C₂ can reach 78.18% at 850 °C with a potential of 1.2 V, and the conversion rate of CH₄ is 11.61%. These results further prove that a well-constructed metal-oxide interface significantly improves the catalytic activity and facilitates the reaction.

Generation of Hydroxyl Radicals in the Reaction of Dihydrogen with AuNbO4+ Cluster Cations

A molecular-level insight into the nature of reactive oxygen species involved in dihydrogen (H₂ ) dissociation is of great importance to understand gold catalysis. In this study, laser ablation generated and mass-selected AuNbO₄⁺ oxide cluster cations could dissociate H₂ in an ion-trap reactor. The reaction has been characterized by time-of-flight mass spectrometric experiments and density functional calculations. The lowest energy isomer of AuNbO₄⁺ contains two lattice oxygen (O^2- ) and one superoxide (O₂^.- ) species. The gold atom anchors the H₂ molecule in the first step and then delivers one hydrogen atom to the O^2- ion in H₂ dissociation. At the same time, O₂^.- is reduced into a peroxide unit that can accept the second hydrogen atom of H₂ with the generation of a hydroxyl radical as the main product. In this study, the important roles of the O₂^.- unit in the dissociation of H₂ have been identified.

The reactivity of stoichiometric tungsten oxide clusters towards carbon monoxide: the effects of cluster sizes and charge states

Density functional theory (DFT) calculations are employed to investigate the reactivity of tungsten oxide clusters towards carbon monoxide. Extensive structural searches show that all the ground-state structures of (WO3)n(+) (n = 1-4) contain an oxygen radical center with a lengthened W-O bond which is highly active in the oxidation of carbon monoxide. Energy profiles are calculated to determine the reaction mechanisms and evaluate the effect of cluster sizes. The monomer WO3(+) has the highest reactivity among the stoichiometric clusters of different sizes (WO3)n(+) (n = 1-4). The reaction mechanisms for CO with mono-nuclear stoichiometric tungsten oxide clusters with different charges (WO3(-/0/+)) are also studied to clarify the influence of charge states. Our calculated results show that the ability to oxidize CO gets weaker from WO3(+) to WO3(-) as the negative charge accumulates progressively.

Boron substitution in aluminum cluster anions: magic clusters and reactivity with oxygen

We have studied the size-selective reactivity of AlnBm(-) clusters m = 1,2 with O2 to investigate the effect of congener substitution in energetic aluminum clusters. Mixed-metal clusters offer an additional strategy for tuning the electronic and geometric structure of clusters and by substituting an atom with a congener; we may investigate the effect of structural changes in clusters with similar electronic structures. Using a fast-flow tube mass spectrometer, we formed aluminum boride cluster anions and exposed them to molecular oxygen. We found multiple stable species with Al12B(-) and Al11B2(-) being highly resistant to reactivity with oxygen. These clusters behave in a similar manner as Al13(-), which has previously been found to be stable in oxygen because of its icosahedral geometry and its filled electronic shell. Al13(-) and Al12B(-) have icosahedral structures, while Al11B2(-) forms a distorted icosahedron. All three of these clusters have filled electronic shells, and Al12B(-) has a larger HOMO-LUMO gap due to its compact geometry. Other cluster sizes are investigated, and the structures of the AlnB(-) series are found to have endohedrally doped B atoms, as do many of the AlnB2(-) clusters. The primary etching products are found to be a loss of two Al2O molecules, with boron likely to remain in the cluster.