Oxidation of Nitric Oxide on Gas-Phase Cerium Oxide Clusters via Reactant Adsorption and Product Desorption Processes

Abstract

The reactivity of cerium oxide cluster cations, CenO2n+x(+) (n = 2-9, x = -1 to +2), with NO was investigated using gas-phase temperature-programmed desorption (TPD) combined with mass spectrometry. Target clusters were prepared in the gas phase via the laser ablation of a cerium oxide rod in the presence of oxygen, which was diluted using helium as a carrier gas. NO adsorbed onto stoichiometric and oxygen-rich clusters of CenO2n+x(+) (x = 0-2), forming CenO2n+x(NO)(+) (x = 0-2) species. Gas-phase TPD was measured for the NO-adsorbed clusters, revealing that CenO2n(NO)(+) released NO2 at 600-900 K, forming CenO2n-1(+). Therefore, the overall reaction was the oxidation of NO by the CenO2n(+) clusters, which was explained in terms of a Langmuir-Hinshelwood type reaction. An activation barrier existed between the initial complex (CenO2n(NO)(+)) and the final oxidation products (CenO2n-1(+) + NO2). To determine the nature of the intermediates and the activation barrier, TPD was also performed on CenO2n-1(NO2)(+), which had been prepared through the adsorption of NO2 on CenO2n-1(+) for comparison. The activation barrier was associated with the release of NO2 from the intermediate complex (CenO2n-1(+)-NO2 → CenO2n-1(+) + NO2) rather than the structural rearrangement that formed NO2 in the other intermediate complex (CenO2n(+)-NO → CenO2n-1(+)-NO2).

Ce in the +4 oxidation state: Anion photoelectron spectroscopy and photodissociation of small CexOyHz− molecules

“…21 In addition to this work, Aubriet et al have studied cerium oxyhydroxide cluster formation with mass spectrometry and density functional theory modeling. 22 Beyond water, the reactivity of cerium oxides with carbon and nitrogen oxides, [23][24][25][26][27][28] sulfur dioxide, 29 molecular oxygen, 30 and hydrocarbons 31,32 has also been investigated.…”

Reaction Kinetics of Nitric Oxide on Size-Selected Silver Cluster Cations

“…As for other transition-metal clusters, gas-phase reactions with NO were reported for Co n + , − Ni n – , Cu n ±/0 , , Nb n ± , Rh n ± , , V n O m , Ta n O m , Cu n O m ± , , Ce n O m + , and Cu n Al + . Dissociative adsorption of NO on cobalt cluster cations, Co n + , , is followed by a release of N 2 to produce an O 2 adduct. , Sequential adsorption of NO and a release of N 2 have also been reported for Rh n ± . , NO molecules adsorbed on Cu n ±/0 do not exhibit a reaction between them, , whereas their reactivity is altered by oxidation or by doping of Al; oxidation of NO to NO 2 was reported for Cu n O m + , while a release of N 2 was observed for Cu n O 2 – and Cu n Al + . , It was also reported that NO is reduced to N 2 O by Cu nanoclusters on an Al 2 O 3 film .…”

“…For Ni n – and Nb n – , on the other hand, the production of NO 2 – and NO 3 – via an electron transfer from the cluster was observed as well as a release of N 2 , forming oxidized cluster anions. , For Nb n + , the formation of Nb n N 2 O + and Nb n NO 2 + was observed . As for oxide clusters of V, Ta, and Ce, NO adsorption is the only reaction channel for V n O m + and Ta n O m + , whereas NO is oxidized to NO 2 by Ce n O m + , forming Ce n O m –1 + . NO thus shows a rich variety of reactions depending on the catalysts.…”

“…, 50,51 Nb n ± , 52 Rh n ± , 53,54 V n O m , 55 Ta n O m , 55 Cu n O m ± , 51,56 Ce n O m + , 57 and Cu n Al + . 58 Dissociative adsorption of NO on cobalt cluster cations, Co n + , 44,46 is followed by a release of N 2 to produce an O 2 adduct.…”

“…49,52 . 57 NO thus shows a rich variety of reactions depending on the catalysts. In addition to these reaction experiments, IR multiphoton dissociation spectroscopy was reported for Au n NO + and Rh n TaNO + .…”