EleyRidealtyp

EleyRidealtyp is a term used in surface chemistry and catalysis to denote reactions that follow the Eley–Rideal mechanism. In this mechanism, a gas-phase reactant collides with a chemisorbed species on a solid surface and reacts to form products that desorb, without the gas-phase reactant first binding to the surface. This contrasts with Langmuir–Hinshelwood-type processes, where both reactants are adsorbed, diffuse on the surface, and then react.

Within an EleyRideal type step, the reaction rate is often described as proportional to the flux of the gas-phase reactant and to the surface coverage of the adsorbed species. A common form is r = k_ER · P_A · θ_B, where P_A is the partial pressure (or concentration) of the gas-phase reactant A, θ_B is the coverage of the adsorbed species B, and k_ER is a temperature- and surface-dependent rate constant. The mechanism can become relevant when adsorption of the gas-phase reactant is weak or when the impingement rate is high, enabling direct reactions without prior adsorption.

Historical context and scope: the mechanism was proposed by D. Eley and W. Rideal in 1938 to explain certain catalytic gas reactions on metal surfaces. In many real systems, multiple pathways coexist, and the EleyRideal typology is used to categorize steps within broader kinetic models that include Langmuir–Hinshelwood steps as well as mixed mechanisms.

See also: Eley–Rideal mechanism; Langmuir–Hinshelwood mechanism; heterogeneous catalysis.