Reaction of Aluminum Cluster Cations with a Mixture of O₂ and H₂O Gases: Formation of Hydrated-Alumina Clusters

Abstract

We present reactions of size-selected free aluminum cluster cations, Al N + (N = 1−14), exposed to a mixture of water and oxygen gases. It is featured that chemical species assignable to Al 2 O 6 H 7 + and Al 2 O 7 H 9 + were commonly produced as prominent reaction products from all of the sizes, except N = 1. These product ions were found to be produced via the formation of Al 2 O 3 + in the initial stage of reactions with O 2 and H 2 O, which was followed by successive hydrogenation and hydration. This reaction pathway was identified by examining reactivity of each intermediate product step by step. Structures of the product ions were analyzed by collision-induced dissociation experiments and DFT calculations; for example, coexistence of isomers, Al 2 O 5 H 5 (H 2 O) + and Al 2 O 4 H 3 (H 2 O) 2 + , with one and two intact H 2 O molecules, respectively, was suggested for Al 2 O 6 H 7 + . The chemical compositions of the ions produced in the present reactions are expressed nominally as Al 2 O 3 (H 2 O) n H + , which is similar, except for the proton, to that of hydrated alumina, that is, forms of bulk aluminum abundant naturally. The present finding gives molecular-level insights into formation processes of aluminum minerals in a natural environment.

Adsorption and Subsequent Reaction of a Water Molecule on Silicate and Silica Cluster Anions

“…Ion–molecule reactions of ions consisting of Si, O, Mg, and Fe with gas molecules, for example, H 2 O, H 2 , and CO, might contribute to chemistry in the interstellar environment such as molecular evolution and delivery of water to the Earth. In this regard, we have reported the formation of clusters with mineral compositions and reaction of silicon-oxide cluster anions, Si n O m – , with a CO molecule because gas-phase clusters provide good models of free radicals and ions. Agglomeration of silicon-oxide clusters has been investigated to understand the growth process of silicate and silica particles in space. , Reactions of silicate and silica clusters with H 2 O, however, have not been reported; here we examine clusters consisting of Si, O, and Mg as silicate clusters and silicon-oxide clusters (Si n O m – with m / n ≈ 2) as silica clusters.…”

Reaction Sites of CO on Size-Selected Silicon Oxide Cluster Anions: A Model Study of Chemistry in the Interstellar Environment

“…11 To study chemical processes in interstellar space, sizeselected gas-phase clusters provide good models of free radicals with mineral composition. In this regard, we have reported formation of clusters with hydrated-alumina composition through successive oxidation, 12 hydration, and hydroxylation of aluminum cluster cations: 13 hydrated alumina is one of the abundant minerals in the Earth and space. More important are silicates because of their prominent abundance among minerals.…”

Al Valence Controls the Coordination and Stability of Cationic Aluminum–Oxygen Clusters in Reactions of Aln+ with Oxygen

“…However, if aluminum cation clusters are considered, the products can be investigated more directly. Besides, there are numerous studies illustrating the stability and reactivity of size-dependent Al clusters. − However, despite the importance of aluminum oxide, the question remains whether there exist Al n O m + compositions with unique stability. , …”