Temperature-Programmed Reactions of Aromatic Compounds on Au(111) and on a Model Gold Catalyst

Aromatic compounds are often employed as solvents and probe molecules in gold-mediated catalytic processes, and therefore, their interaction with gold surfaces is relevant to improve the design of catalysts and processes. Herein, we compare the interaction of various aromatic molecules (benzene, toluene, phenylacetylene, phenol, o-benzenediol, benzyl alcohol, benzaldehyde, and benzenethiol) with clean and oxygen-covered Au(111) surfaces through temperature-programmed reaction/mass spectrometry. While the clean surface is important from a fundamental point of view, the oxygen-covered Au surface is a model of a working heterogeneous gold catalyst. Condensation experiments demonstrate that, with respect to benzene, the functionalities increase significantly the adsorption energies, opening pathways for decomposition and surface poisoning. Over the O/Au surface, there is a clear trend in Bri nsted reactivity, following the order benzenethiol > phenylacetylene > benzenediol > benzyl alcohol > phenol > benzaldehyde > toluene, benzene. This trend has been confirmed by performing displacement reactions of the type B + AH = BH + A, where B is a dehydrogenated species and AH is a molecule with a sufficient acidity to regenerate the original molecule BH. Finally, based on the structure of the B species, we find as potential pathways (a) further dehydrogenation (e.g., benzyl alcohol to benzaldehyde), (b) coupling (e.g., benzenethiol to dibenzene disulfide), or (c) surface decomposition (e.g., phenol to residual carbon). Since the extent to which each of these reactions take place is related to the molecular structure of the aromatic molecule, this study provides relevant information for designing catalytic routes for aromatic molecules.

Automated summary

This study compares the interaction of aromatic compounds with gold surfaces and finds that the introduction of functional groups significantly increases the adsorption energy, affecting the pathways for decomposition and poisoning reactions. Furthermore, the molecular structure of the aromatic molecule determines the extent to which further dehydrogenation, coupling, or surface decomposition reactions occur.