Remarkable Structural Effect on the Gold–Hydrogen Analogy in Hydrogen-Doped Gold Cluster

Abstract

In accordance with the well established gold–hydrogen analogy, a hydrogen atom mimics the properties of a gold atom in gold clusters. In a recent study it has been demonstrated that the properties of a hydrogen atom doped small gold cluster (Au7H) are not in conformity with the aforementioned analogy. In this paper we study the properties of the Au7H cluster exhaustively to re-examine the validity of the gold–hydrogen analogy in the context of adsorption of CO and O2 molecules on pristine gold and hydrogen atom doped gold clusters. For this purpose we first determine the most stable structure of the Au7H cluster by using an ab initio density functional theory based method with generalized gradient approximation (GGA) and Meta-GGA exchange-correlation functionals. We carry out geometry optimization by considering various planar and three-dimensional isomers of the Au7H cluster as initial geometries. We find that the lowest energy structure of Au7H is a planar one with C 2v symmetry, and it is very close to the structure of the Au8 cluster with D 4h symmetry. Furthermore, to examine the validity of the gold–hydrogen analogy we carry out a detailed investigation of the adsorption of CO and O2 molecules on the most stable as well as various other low energy isomers of the Au7H cluster. We find that the adsorption energies and the extent of activation of CO and O2 molecules on the most stable planar isomer of Au7H are almost the same as those on the parent Au8 cluster with D 4h symmetry proving the validity of the gold–hydrogen analogy. On the other hand, for the high energy three-dimensional isomers of the Au7H cluster obtained from the pristine Au8 cluster with T d symmetry, we find a significant enhancement in adsorption energy as well as the extent of activation of CO and O2 molecules as compared to those for the corresponding pristine cluster. Therefore, the high reactivity of the 3D isomer of the Au7H cluster may be attributed to its existence in a state which is higher in energy than its most stable planar isomer.

Gold–Hydrogen Analogy in Small–Sized Hydrogen–Doped Gold Clusters Revisited

“…We can further note from this figure that the most stable geometry of each of the clusters of interest is two‐dimensional (2D) in nature, that is, planar. We wish to point out here that the most stable structures of Au n clusters obtained in this work match quite well with the structures reported in various theoretical and experimental studies [28,44,58–63] …”

“…To understand the binding and activation of CO and O 2 molecules onto Au n −1 H and Au n ( n =2–10) clusters, we adsorb a CO or an O 2 molecule onto all the non‐equivalent sites of the most stable geometries of these clusters. It has been observed by many researchers that CO prefers to sit on an Au atom, whereas O 2 molecule prefers to get adsorbed on a single Au atom or the bridge position between two Au atoms [25,27,28,62,67] . Keeping this in mind we adsorb the CO and O 2 molecules at both the Au vertex and bridge positions of the clusters.…”

“…Besides the atoms from the above‐mentioned groups, the effect of doping gold clusters with a hydrogen atom on their electronic structure and chemical reactivity towards CO and O 2 molecules have also been investigated both experimentally [19–21] and theoretically [22–28] . According to an experimental study by Lauher and Wald, [29] the gold derivatives could potentially be used as alternatives for cluster hydrides in which it is difficult to locate the hydrogen by X‐ray diffraction.…”

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis

“…Hence, incorporation of a H atom in Au clusters does not change the geometric and electronic structure appreciably. [ 120 ] Tsukuda and co‐workers synthesized several hydride‐adduct Au clusters by further addition of NaBH 4 to the existing clusters. [ 53 , 56 , 121 ] The inclusion of hydride from BH 4 − was confirmed by isotope labeling with NaBD 4 .…”

“…[ 96 ] Theoretical calculations revealed enhanced reactivity and catalytic activity of H‐doped Au clusters. [ 120 , 122 ] The hydrogen loss pathways in Au clusters open up the possibility of studying the mechanism of gold‐catalyzed hydrogen‐related reactions such as hydrogen evolution and hydrogenation reactions.…”