In this mechanism, proposed in 1938 by D. D. Eley and E. K. Rideal, only one of the molecules adsorbs and the other one reacts with it directly from the gas phase, without adsorbing ("nonthermal surface reaction"):
: A(g) + S(s) ⇌ AS(s)
: AS(s) + B(g) → Products
Constants are  and  and rate equation is . Applying steady state approximation to AS and proceeding as before (considering the reaction the limiting step once more) we get . The order is one with respect to B. There are two possibilities, depending on the concentration of reactant A:
:* At low concentrations of A, , and the order is one with respect to A.
:* At high concentrations of A, , and the order is zero with respect to A.
The following reactions follow an Eley–Rideal mechanism:
* CH + ½ O (adsorbed) → (CHCH)O The dissociative adsorption of oxygen is also possible, which leads to secondary products carbon dioxide and water.
* CO + H (ads.) → HO + CO
* 2 NH + 1½ O (ads.) → N + 3HO on a platinum catalyst
* CH + H (ads.) → CH on nickel or iron catalysts