Doping Effects in Cluster‐Mediated Bond Activation

Abstract

Gas-phase investigations of judiciously doped oxide clusters permit to address fundamental challenges related to, for example, the low-temperature oxidation of CO or the selective conversion of hydrocarbons. Modifying the size and composition of a free cluster in a controlled way enables the modification of local charge effects and of spin states, and spectroscopic studies in combination with computational work help to identify the active site of a catalyst and to unravel mechanistic details. Also, the interplay of the support material with the reactive part of a composite catalyst cluster can be addressed. Examples will be presented demonstrating how and why the gas-phase reactivities of heteronuclear clusters, in comparison with their homonuclear counterparts, toward small, generally rather inert molecules can be increased, decreased, or not significantly affected.

Thermal hydrogen-atom transfer from methane: A mechanistic exercise

“…In addition to clarifying mechanistic aspects of HAT by oxo species, systems are presented which indicate how the reactivity of cluster oxides can be 'tuned' by modifying the charge and spin states of a reacting system by judicious 'doping' of the clusters [71]. Further, these gas-phase studies permit to identify the active sites of a metal oxide, and the role of the support material can be disentangled from the active component in composite catalysts.…”

“…The question, which will be discussed next, deals with 'doping' effects and it will be shown that the controlled modification of a cluster oxide affects dramatically the local charge and spin distribution of the active site (for a recent review on this topic, see Ref. [71]). …”

Unexpected Mechanistic Variants in the Thermal Gas-Phase Activation of Methane

“…12 As shown computationally, intracomplex spin transfer in these systems is energetically rather disfavored, 8a,10c,13 and one may wonder how to alleviate the problem. One way to modify crucial properties, such as the spin density around a reaction center, is by judicious "doping", 14 •+ the spin is equally distributed over the two bridging oxygen atoms of the cluster, resulting in a barrier for HAT too high in energy to be accessible at ambient conditions. Thus, HAT is observed only with substrates that have a weaker C−H bond, e.g., propane or butane.…”

Die Chemie von [AuO]+/CH4 in der Gasphase: Selektive Sauerstoffatom‐Übertragung auf, statt Wasserstoffatom‐Abstraktion von Methan

“…[1] Die direkte Erzeugung von Methanol oder Formaldehyd durch C-O-Kupplung wurde in vielen Gasphasenstudien zur Methanaktivierung [2] erfolgreich realisiert. [1] Die direkte Erzeugung von Methanol oder Formaldehyd durch C-O-Kupplung wurde in vielen Gasphasenstudien zur Methanaktivierung [2] erfolgreich realisiert.…”