Gas-phase catalytic oxidation of CO by Au(2-)

Charge-dependent trends in structures and vibrational frequencies of [CO-Au-O2](q) (q = -1, 0, +1) complexes: evidence for cooperative interactions

Charge-dependent trends in the structures, vibrational frequencies, and binding energies of binary [AuCO](q) and [AuO(2)](q) and ternary [O(2)AuCO](q) complexes (q = -1,0,+1), have been investigated using density functional theory calculations. Three different geometrical motifs, given descriptive names of "separated", "pre-reactive", and "long-range", are identified for the ternary complexes. For the binary systems, the general trend is that the complexes become more diffuse as the charge becomes more negative, having longer intermolecular bond distances and weaker binding energies. The trends shown by the ternary complexes are more complicated, and are different for the various geometrical motifs. However, a general trend is that there is a cooperative interaction involving both the CO and O(2) with the Au center, which becomes more pronounced as the negative charge on the complexes increases from cationic to neutral to anionic. This cooperative interaction leads to increased electron density on the O(2) moiety, as is reflected in the bond-lengths and vibrational frequencies. Furthermore, it is found that for the pre-reactive complexes, the role of the Au center is to stabilize the formation of a conjugated π-system between the CO and O(2) molecules.

Interaction of carbon monoxide with Au(111) modified by ion bombardment: a surface spectroscopy study under elevated pressure

Gold based model systems exhibiting the structural versatility of nanoparticle ensembles and being accessible for surface spectroscopic investigations are expected to provide new information about the adsorption of carbon monoxide, a key process influencing the CO oxidation activity of this noble metal in nanoparticulate form. Accordingly, in the present work the interaction of CO is studied with an ion bombardment modified Au(111) surface by means of a combination of photoelectron spectroscopy (XPS and UPS), sum frequency generation vibrational spectroscopy (SFG), and scanning tunneling microscopy (STM). While no adsorption was found on intact Au(111), data collected on the ion bombarded surface at cryogenic temperatures indicated the presence of stable CO adsorbates below 190 K. A quantitative evaluation of the C 1s XPS spectra and the surface morphology explored by STM revealed that the step edge sites created by ion bombardment are responsible for CO adsorption. The identification of the CO binding sites was confirmed by density functional theory (DFT) calculations. Annealing experiments up to room temperature showed that at temperatures above 190 K unstable adsorbates are formed on the surface under dynamic exposure conditions that disappeared immediately when gaseous CO was removed from the system. Spectroscopic data as well as STM records revealed that prolonged CO exposure at higher pressures of up to 1 mbar around room temperature facilitates massive atomic movements on the roughened surface, leading to its strong reordering toward the structure of the intact Au(111) surface, accompanied by the loss of the CO binding capacity.

Kick: constraining a stochastic search procedure with molecular fragments

An extension of the Kick program developed by Bera et al. (J Phys Chem A 2006, 110, 4287) is described in which chemically sensible molecular fragments are used in an automated stochastic search algorithm. This results in a vastly reduced region of the potential energy surface which can be explored very quickly. We present use of this modified algorithm to the search for low-lying isomers, and we present candidates for the global energy minimum, for a range of chemical systems. We highlight the usefulness of this procedure for exploring reactions of molecules with transition metal clusters and to the microsolvation of a small dipeptide.

Theory and simulation in heterogeneous gold catalysis

This critical review covers the application of quantum chemistry to the burgeoning area of the heterogeneous oxidation by Au. We focus on the most established reaction, the oxidation of CO at low temperature. The review begins with an overview of the methods available comparing the treatment of the electron-electron interaction and relativistic effects. The structure of Au particles and their interaction with oxide reviews is then discussed in detail. Calculations of the adsorption and reaction of CO and O2 are then considered and results from isolated and supported Au clusters compared (155 references).