On the role of thermal activation in selective photochemistry: mechanistic insight into the oxidation of propene on the V₄O₁₁⁻cluster

Abstract

An experimental methodology for a mechanistic analysis of gas phase chemical reactions is presented in the context of structure-reactivity relationships of metal oxide clusters relevant to photocatalysis. The spectroscopic approach is demonstrated with the investigation of the photoinduced oxygenation of propene on the V(4)O(11)(-) cluster, where the thermal activation and subsequent photoreaction are deduced with the information from (i) the temperature dependency of the aggregation kinetics in the propene-seeded helium atmosphere of an ion-trap reactor; (ii) the fluence dependency in the yield of different product channels of the photoreaction and (iii) the intensity dependency in the fragmentation of neutral reaction products that are probed via in situ multi-photon ionization. For the thermal reaction, selective hydrogen abstraction from the allylic position of propene accompanied by the linkage to the cluster at the dioxo moiety is postulated as the mechanism in the aggregation of propene on the V(4)O(11)(-) cluster. In accordance with an insightful neutralization-reionization study (Schröder et al., J. Mass. Spectrom., 2010, 301, 84), the subsequent photoinduced reaction is defined by an allylic oxidation in the formation of acrolein from the initial allyloxy radical photoproduct. The relevance of the observed selectivity is discussed in view of the electronic structure and bond motifs offered by high valence oxide systems such as the V(4)O(11)(-) cluster.

A nine-atom rhodium–aluminum oxide cluster oxidizes five carbon monoxide molecules

“…1a ). Additional experimental techniques such as multiphoton ionization 28 29 employing pulsed lasers are required to observe the neutral CO 2 molecules. However, N 2 experiment in Fig.…”

Thermal Methane Conversion to Syngas Mediated by Rh1-Doped Aluminum Oxide Cluster Cations RhAl3O4+

“…The intensity ratios of RhAl 3 O 3 H 4 + to RhAl 3 O 4 CH 2 + in Figure b and c are the same (0.28 ± 0.02) within the experimental uncertainties (±10%) so both of them can be due to the primary reactions: The assignments of the products in Figure b were further confirmed in the isotopic labeling experiment with CD 4 (Figure d). It is noticeable that the adopted experimental setup was not able to identify the neutral products H 2 and CO. Additional experimental techniques such as multiphoton ionization with pulsed lasers are required to observe these neutral molecules …”

Size and shape effects on the stability, electronic structure, and Raman spectroscopy of (SrO)n nanoclusters

“…The size‐selective fabrication and experimental characterization of metal oxide nanoclusters in the gas phase is a challenging and expensive task [1, 2]. Gas‐phase metal oxide clusters characterization has used mass spectroscopy to establish a connection between the clusters composition and the reactivity of the related systems with simple molecules (see References [1–6] and references therein). Spectroscopy techniques such as UV/VIS photodissociation and photoionization can also bring important information about the stability and composition of gas‐phase clusters [1, 2, 7–9].…”