Room-Temperature Methane Activation Mediated by Free Tantalum Cluster Cations: Size-by-Size Reactivity.

The energetics of small cationic tantalum clusters and their gas-phase adsorption and dehydrogenation reaction pathways with methane are investigated with ion-trap experiments and spin-density-functional-theory calculations. Ta clusters are exposed to methane under multicollision conditions in a cryogenic ring electrode ion-trap. The cluster size affects the reaction efficiency and the number of consecutively dehydrogenated methane molecules.

Catalytic Non-Oxidative Coupling of Methane on TaO.

Mass-selected TaO cluster ions catalyze the transformation of methane in a gas-phase ion trap experiment via nonoxidative coupling into ethane and H, which is a prospective reaction for the generation of valuable chemicals on an industrial scale. Systematic variation of the reaction conditions and the isotopic labeling of methane by deuterium allow for an unambiguous identification of a catalytic cycle. Comparison with the proposed catalytic cycle for tantalum-doped silica catalysts reveals surprising similarities as the mechanism of the C-C coupling step, but also peculiar differences like the mechanism of the eventual formation of molecular hydrogen and ethane.

An efficient laser vaporization source for chemically modified metal clusters characterized by thermodynamics and kinetics.

A laser vaporization cluster source that has a room for cluster aggregation and a reactor volume, each equipped with a pulsed valve, is presented for the efficient gas-phase production of chemically modified metal clusters. The performance of the cluster source is evaluated through the production of Ta and Ta oxide cluster cations, TaO (y ≥ 0). It is demonstrated that the cluster source produces TaO over a wide mass range, the metal-to-oxygen ratio of which can easily be controlled by changing the pulse duration that influences the amount of reactant O introduced into the cluster source.