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The Langmuir adsorption model deviates significantly in many cases, primarily because it fails to account for the surface roughness of the adsorbent. Rough inhomogeneous surfaces have multiple site types available for adsorption, with some parameters varying from site to site, such as the heat of adsorption.
The Langmuir model of adsorption [2] assumes . The maximum coverage is one adsorbate molecule per substrate site. Independent and equivalent adsorption sites. This model is the simplest useful approximation that still retains the dependence of the adsorption rate on the coverage, and in the simplest case, precursor states are not considered.
The model appears to have been first proposed for carbon monoxide on silica-supported platinum by Brandt et al. (1993). [46] A similar, but independent model was developed by King and co-workers [47] [48] [49] to describe hydrogen adsorption on silica-supported alkali promoted ruthenium, silver-ruthenium and copper-ruthenium bimetallic catalysts.
The following reactions follow an Langmuir–Rideal mechanism: [4] C 2 H 4 + 1 / 2 O 2 (adsorbed) → (CH 2 CH 2)O The dissociative adsorption of oxygen is also possible, which leads to secondary products carbon dioxide and water. CO 2 + H 2 (ads.) → H 2 O + CO; 2 NH 3 + 1 + 1 / 2 O 2 (ads.) → N 2 + 3H 2 O on a platinum catalyst
The Hertz–Knudsen equation describes the non-dissociative adsorption of a gas molecule on a surface by expressing the variation of the number of molecules impacting on the surfaces per unit of time as a function of the pressure of the gas and other parameters which characterise both the gas phase molecule and the surface: [1] [2]
The langmuir (symbol: L) is a unit of exposure (or dosage) to a surface (e.g. of a crystal) and is used in ultra-high vacuum (UHV) surface physics to study the adsorption of gases. It is a practical unit, and is not dimensionally homogeneous, and so is used only in this field. It is named after American physicist Irving Langmuir.
Specifically, it was through the models of Overton, Langmuir, Gorter and Grendel, and Davson and Danielli, that it was deduced that membranes have lipids, proteins, and a bilayer. The advent of the electron microscope, the findings of J. David Robertson , the proposal of Singer and Nicolson , and additional work of Unwin and Henderson all ...
BET model of multilayer adsorption, that is, a random distribution of sites covered by one, two, three, etc., adsorbate molecules. The concept of the theory is an extension of the Langmuir theory, which is a theory for monolayer molecular adsorption, to multilayer adsorption with the following hypotheses: