Celebrating 75 years of the Eley-Rideal mechanism

A selction of the attendees and speakers from the event on Wednesday 13th including speakers

In 1940 and 1941, Dan Eley and Eric Rideal published a series of important papers on the interchange of hydrogen on the surface of tungsten. At the time, mechanisms had already been proposed separately by Langmuir (1921) and Hinshelwood (1926) to explain how molecules chemisorbed on to neighbouring surface sites might undergo a bimolecular reaction to release a new species into the gas phase. What differentiated the Eley-Rideal mechanism from this earlier work, was the proposal that reactivity took place between a chemisorbed molecule/atom and a molecule that was loosely bound to the surface via weak van der Waals interactions. How the rate of reaction depended on the pressures of the reactants was used to distinguish between the two mechanisms.

In the years immediately following publication of their papers, the number of citations Eley and Rideal received would suggest that the mechanism was of significant interest to the wider surface science/catalysis community. However, despite being adopted by many physical chemistry text books as one of the classic processes in surface chemistry, there followed an extended period, during which time the papers received only modest attention. This situation has changed markedly in past four to five years where there has been a notable increase in the number of citations to all three papers, suggesting renewed interest in the mechanism. Two areas of research appear to be primarily responsible - the first of these is associated with application of the E-R mechanism to reactions involving atoms heavier than hydrogen, and at the meeting Prof. Aart Kleijn will describe his recent experimental work on the reactivity of nitrogen and oxygen atoms on a ruthenium surface. Complementing this study will be a theoretical analysis by Dr Maite Alducin, who will present results from molecular dynamics simulations on the formation of molecular nitrogen on a silver surface. A second recent application of the E-R mechanism comes from a comparatively new area of research - interstellar surface chemistry, where mechanisms are being investigated for the formation of molecular hydrogen on cold dust grains, which are thought to occupy regions of the interstellar medium. Prof. Stephen Price will describe the results of experiments on atom recombination on the surface of graphite, and this work will be placed in the context of the Eley-Rideal mechanism through quantum mechanical calculations described by Dr Anthony Meijer.

There does appear to be a slight mis-match between the original premise of the Eley-Rideal mechanism, which has one of the reactants held in place by weak van der Waals forces, and mechanisms adopted to interpret some of these more recent experiments. The latter now include a reaction pathway where a reactant species enters from the gas phase and reacts with a chemisorbed molecule without first becoming attached to the surface. On this theme, our final speaker of the meeting, Prof. Roel Prins, will offer fresh insight into the Eley-Rideal mechanism and will also show how it can be adapted to interpret a wide range of liquid and solid phase chemical and catalytic processes.

On Wednesday 13th, the School of Chemistry held an event to celebrate the Eley-Rideal Mechanism. The event was attended by Rod Eley, Dan Eley's son and some of his past students and former colleagues. Guest speakers included Professor Aart Kleijn (China), Dr Maite Alducin (Spain), Professor Stephen Price (UCL) and Dr Anthony Meijer (Sheffield).