Size‐Dependent Binding Energies of Methane to Small Gold Clusters

Abstract

The reactions of small gold cluster cations Au(x)(+) (x=2-6) with CH(4) were studied by joint gas-phase kinetics and first-principles density functional theory calculations. The experimentally obtained temperature-dependent low pressure rate constants were analyzed by employing the Lindemann energy transfer model for association reactions in conjunction with statistical RRKM theory. In this way cluster-size-dependent binding energies of methane to the gold cluster cations were determined from the experimental data for two different transition-state models. The experimental binding energies obtained by employing a "loose" transition-state model are in good agreement with the theoretical values at the optimal adsorption geometries, while a "tight" transition-state model clearly gives a lower limit for the binding energies. Additionally, Kohn-Sham molecular orbitals of Au(x)-CH(4)(+) are presented to gain detailed insight into the cluster-methane bonding mechanism.

Catalysis with Supported Size-selected Pt Clusters

“…Thus, only the performance and mode of operation of this type of source (with Pt clusters as example) is described. Other concepts for cluster generation and an overview over existing sources are available in the literature [157,17,88,151,215,189,216,11,217,14].…”

Size- and Structure-specificity in Catalysis by Gold Clusters

“…reproduced by combining gas-phase kinetics and first-principle density functional theory calculations. 16,17 For O 2 , gold cluster anions exhibit a dramatic evenodd atom reactivity variation with only the even atom (odd electron) cluster anions exhibiting evidence of reactivity, whereas for the cations only ten atom monovalent cations exhibit evidence of reactivity. While odd-sized Au n ¹ clusters, which are not reactive to molecular oxygen, form weakly bound van der Waals complexes, even-sized Au n ¹ clusters form superoxo (OO ¹ ) to chemisorbed hydroperoxo (OOH) species leading to much higher reactivity.…”

Selective C−H Bond Cleavage in Methane by Small Gold Clusters

“…The Ar‐tagged complexes exhibit better resolved features, which are considered below. Similar to the Au 3 + case, the calculated minimum‐energy isomeric structures of Au 2 CH 4 + and Au 4 CH 4 + contain a nondissociated methane molecule ( 2‐a and 4‐a ) while the hydrido methyl complexes ( 2‐b and 4‐b ) are higher in energy by 0.05 eV and 0.35 eV, respectively. In addition, for Au 4 CH 4 + a second hydrido methyl complex isomer (structure 4‐c ) has been found theoretically, which is 0.53 eV higher in energy with respect to the lowest energy isomer.…”

“…The IR‐MPD spectrum of a specific gold cluster–methane complex is recorded by monitoring the ratio of its mass signal with ( I ) and without ( I 0 ) laser light while varying the laser wavelength. A complicating factor is that either methane or its dissociation products are typically rather strongly bound to the gold clusters, thus requiring the absorption of a large number of photons to enable dissociation. This complication is circumvented in two complementary ways.…”