Cooperative effects in the oxidation of CO by palladium oxide cations

Abstract

Cooperative reactivity plays an important role in the oxidation of CO to CO(2) by palladium oxide cations and offers insight into factors which influence catalysis. Comprehensive studies including guided-ion-beam mass spectrometry and theoretical investigations reveal the reaction products and profiles of PdO(2)(+) and PdO(3)(+) with CO through oxygen radical centers and dioxygen complexes bound to the Pd atom. O radical centers are more reactive than the dioxygen complexes, and experimental evidence of both direct and cooperative CO oxidation with the adsorption of two CO molecules are observed. The binding of multiple electron withdrawing CO molecules is found to increase the barrier heights for reactivity due to decreased binding of the secondary CO molecule, however, reactivity is enhanced by the increase in kinetic energy available to hurdle the barrier. We examine the effect of oxygen sites, cooperative ligands, and spin including two-state reactivity.

Compositions and Isomer Separation of Palladium Oxide Cluster Cations Studied by Ion Mobility Mass Spectrometry

“…In the gas phase, a number of experimental and theoretical investigations have been carried out so far on palladium oxide cluster ions, Pd n O m + . − Experimentally, mass spectrometric studies have been performed for the cluster cations leading to the determination of compositions and size distributions. , In such studies, Miyajima and Mafuné investigated thermal dissociation of the Pd n O m + cluster ions formed by laser desorption/ionization of palladium metal . Lang et al determined the compositions of the cluster ions produced by the sputtering technique .…”

“…They revealed that a variety of compositions were observed, including bare metallic clusters and various metal–oxygen combinations, such as Pd 2 O 1–4 + , Pd 3 O 0–6 + , Pd 4 O 0–7 + , Pd 5 O 1–7 + , and Pd 6 O 3–6 + . To comprehend the formation process and structures of palladium oxide clusters, theoretical studies on structures of small cluster species were examined. − Castleman et al and Das et al reported theoretical calculations for small clusters like PdO m + ( m = 2–3) and Pd n O 2 + ( n = 4–6) where the ground-state structures were found to have molecular oxygen. Bernhardt, Landman, Lang, and their co-workers performed first-principles density functional theory simulations on Pd n O m + with n = 2–8 .…”

Ligand-Mediated Reactivity in CO Oxidation of Niobium–Nickel Monoxide Carbonyl Complexes: The Crucial Roles of the Multiple Adsorption of CO Molecules

“…As one of important prototypical reactions, carbon monoxide (CO) oxidation has drawn significant attention in heterogeneous catalysis. − Extensive condensed-phase research efforts have been devoted to the exploration of the active site and reaction mechanism of the CO oxidation catalysts. − Gas-phase spectroscopic studies of metal oxide clusters under isolated and controllable conditions provide an alternative route to molecular-level understanding of the catalytic mechanisms. − Recently, the reactions of CO with various heteronuclear transition metal (TM) oxide clusters oxide species − were widely investigated to understand many facets of the TM oxide clusters, such as the composition of clusters, charge state, , the support, and the active atomic oxygen species. − The investigation of structure–reactivity relationship in the gas phase has revealed the more competitive reactivity of the peripheral oxygen than the bridging oxygen . However, the role of coadsorbed CO molecules has rarely been taken into account during CO oxidation. − …”

Effect of O2 and CO Exposure on the Photoelectron Spectroscopy of Size-Selected Pdn Clusters Supported on TiO2(110)

“…This phenomenon has been observed previously in supported and gas phase clusters. 76,77 The reduced binding with increasing O coverage is less pronounced as the first two O atom bind with 4.70 and 4.61 eV, while the third and fourth O atoms bind with energies of 4.44 and 3.62 eV.…”