Eley–Rideal, the Other Mechanism

Abstract

In 2016, it was 100 years ago that Langmuir formulated the famous Langmuir equation θ = KP/(1 + KP) for the adsorption of molecules on surfaces, which is used in the description of catalytic reactions between two chemisorbed molecules. Also in 2016, it was 75 years ago that Eley and Rideal studied the mechanism of the reaction between a chemisorbed molecule and a physisorbed molecule. However, they studied a very special case of adsorption, whereas the more general interaction of a chemisorbed molecule and a molecule colliding with it from the gas phase had already been proposed by Langmuir in addition to the reaction between two chemisorbed molecules. Therefore, the reaction between a chemisorbed molecule and a gaseous colliding molecule should be called Langmuir–Rideal reaction rather than Eley–Rideal reaction, as it is often called in surface science, catalysis and astronomy. The mechanism that Eley and Rideal really studied some 75 years ago is important in heterogeneous as well as homogeneous catalysis in the liquid-phase and is related to outer-sphere reactions.