Double-Oxygen-Atom Transfer in Reactions of CemO2m+ (m=2-6) with C2H2

Role of H2O Adsorption in CO Oxidation over Cerium-Oxide Cluster Anions (CeO2)nO- (n = 1-4)

Water (H2O) is ubiquitous in the environment and inevitably participates in many surface reactions, including CO oxidation. Acquiring a fundamental understanding of the roles of H2O molecules in CO oxidation poses a challenging but pivotal task in real-life catalysis. Herein, benefiting from state-of-the-art mass-spectrometric experiments and quantum chemical calculations, we identified that the dissociation of a H2O molecule on each of the cerium oxide cluster anions (CeO2)nO- (n = 1-4) at room temperature can create a new atomic oxygen radical (O•-) that then oxidizes a CO molecule. The size-dependent reactivity of H2O-mediated CO oxidation on (CeO2)nO- clusters was rationalized by the orbital compositions (O2p) and energies of the lowest unoccupied molecular orbitals of active O•- radicals modified by H2O dissociation. Our findings not only provide new insights into H2O-mediated CO oxidation but also demonstrate the importance of H2O in modulating the reactivity of the O•- radicals.

Geometrical Structures of Gas-Phase Cerium Oxide Cluster Cations after Reaction with Nitric Oxide Studied by Ion Mobility Mass Spectrometry

Cerium oxide cluster cations were reacted with nitric oxide molecules and then measured by ion mobility mass spectrometry (IMMS). Ce_nO_2n+1N⁺ species appeared as products of the reaction Ce_nO_2n⁺ + NO → Ce_nO_2n+1N⁺, and their collision cross sections (CCSs) with helium were obtained by IMMS. The experimental CCSs of Ce_nO_2n+1N⁺ were 2-6 Ų larger than those of Ce_nO_2n⁺ for n = 4-10. Geometrical structures of Ce₄O₉N⁺ and Ce₅O₁₁N⁺ were assigned by comparing experimental CCSs with theoretically calculated CCSs of candidate structures. The suggested structures showed that the adsorbed NO molecule is oxidized by the Ce_nO_2n⁺ cluster into a nitrite (NO₂^-) or nitrate (NO₃^-). The Ce_nO_2n+1N⁺ species are regarded as intermediates of the NO oxidation reaction Ce_nO_2n⁺ + NO → Ce_nO_2n-1⁺ + NO₂, and therefore, the present results are helpful for understanding redox reactions involving gas-phase Ce_nO_2n⁺ cluster ions.

Photodissociation of Cerium Oxide Nanocluster Cations

Cerium oxide cluster cations, CexOy(+), are produced via laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. The mass spectrum displays a strongly preferred oxide stoichiometry for each cluster with a specific number of metal atoms x, with x ≤ y. Specifically, the most prominent clusters correspond to the formula CeO(CeO2)n(+). The cluster cations are mass selected and photodissociated with a Nd:YAG laser at either 532 or 355 nm. The prominent clusters dissociate to produce smaller species also having a similar CeO(CeO2)n(+) formula, always with apparent leaving groups of (CeO2). The production of CeO(CeO2)n(+) from the dissociation of many cluster sizes establishes the relative stability of these clusters. Furthermore, the consistent loss of neutral CeO2 shows that the smallest neutral clusters adopt the same oxidation state (IV) as the most common form of bulk cerium oxide. Clusters with higher oxygen content than the CeO(CeO2)n(+) masses are present with much lower abundance. These species dissociate by the loss of O2, leaving surviving clusters with the CeO(CeO2)n(+) formula. Density functional theory calculations on these clusters suggest structures composed of stable CeO(CeO2)n(+) cores with excess oxygen bound to the surface as a superoxide unit (O2(-)).

Gas-phase reaction of CeVO5+ cluster ions with C2H4: the reactivity of cluster bonded peroxides

The reactivity of the peroxide unit with hydrocarbon molecules on transition metal oxide clusters with a closed-shell electronic structure has been identified for the first time.