Issue 48, 2022

Adsorption and keto–enol-tautomerisation of butanal on Pd(111)

Abstract

Microscopic-level understanding of the interaction of hydrocarbons with transition metal surfaces is an important prerequisite for rational design of new materials with improved catalytic properties. In this report, we present a mechanistic study on the keto–enol tautomerisation of butanal on Pd(111), which was theoretically predicted to play a crucial role in low-barrier hydrogenation of carbonyl compounds. These processes were addressed by a combination of reflection-absorption infrared spectroscopy, molecular beam techniques and theoretical calculations at the density functional theory level. Spectroscopic information obtained on Pd(111) suggests that butanal forms three different aldehyde species, which we indicate as A1–A3 as well as their enol counterpart E1. The electronically strongest perturbed and strongest binding species A1 is most likely related to the η2(C,O) adsorption configuration, in which both C and O atoms are involved in the bonding with the underlying metal. The species A2 weakly binds and is less electronically perturbed and can be associated with the η1(O) adsorption configuration. The third type of aldehyde species A3, which is nearly unperturbed and is found only at low temperatures, results from the formation of the butanal multilayer. Importantly, the enol form of butanal was observed on the surface, which gives rise to a new characteristic band at 1104 cm−1 related to the stretching vibration of the C–O single bond (ν(C–O)). With increasing temperature, the multi-layer related species A3 disappears from the surface above 136 K. The population of aldehyde species A1 and the enol species E1 noticeably increases with increasing temperature, while the band related to the aldehyde species A2 becomes strongly attenuated and finally completely disappears above 120 K. These observations suggest that species E1 and A1 are formed in an activated process and – in view of the strongly anti-correlated population of the species E1 and A2 – it can be concluded that enol species E1 is most likely formed from the weakly bound aldehyde species A2 (η1(O)). Finally, we discuss the possible routes to enol stabilization via intermolecular bonding and provide the possible structure of the enol-containing stabilized complex, which is compatible with all spectroscopic observations. The obtained results provide important insights into the process of keto–enol tautomerisation of simple carbonyl compounds.

Graphical abstract: Adsorption and keto–enol-tautomerisation of butanal on Pd(111)

Supplementary files

Article information

Article type
Paper
Submitted
21 9 2022
Accepted
14 11 2022
First published
30 11 2022

Phys. Chem. Chem. Phys., 2022,24, 29480-29494

Adsorption and keto–enol-tautomerisation of butanal on Pd(111)

J. Wulfes, A. Baumann, T. Melchert, C. Schröder and S. Schauermann, Phys. Chem. Chem. Phys., 2022, 24, 29480 DOI: 10.1039/D2CP04398J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements