Search results
Results from the WOW.Com Content Network
gas molecules only interact with adjacent layers; and; the Langmuir theory can be applied to each layer. the enthalpy of adsorption for the first layer is constant and greater than the second (and higher). the enthalpy of adsorption for the second (and higher) layers is the same as the enthalpy of liquefaction. The resulting BET equation is
Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbent surface. Examples include macroscopic phenomena that can be very obvious, like corrosion [clarification needed], and subtler effects associated with heterogeneous catalysis, where the catalyst and reactants are in different pha
Thus, the use of alternative probe molecules can often result in different obtained numerical values for surface area, rendering comparison problematic. The model also ignores adsorbate–adsorbate interactions. Experimentally, there is clear evidence for adsorbate–adsorbate interactions in heat of adsorption data.
The key assumption used in deriving the BET equation that the successive heats of adsorption for all layers except the first are equal to the heat of condensation of the adsorbate. The Langmuir isotherm is usually better for chemisorption, and the BET isotherm works better for physisorption for non-microporous surfaces.
Vapor-solid reactions: formation of an inactive surface layer and/or formation of a volatile compound that exits the reactor. [22] This results in a loss of surface area and/or catalyst material. Solid-state transformation : solid-state diffusion of catalyst support atoms to the surface followed by a reaction that forms an inactive phase.
In chemisorption, molecules are adsorbed on the surface by valence bonds and only form monolayer adsorption. A direct transition from physisorption to chemisorption has been observed by attaching a CO molecule to the tip of an atomic force microscope and measuring its interaction with a single iron atom. [ 12 ]
In geology, a bed is a layer of sediment, sedimentary rock, or volcanic rock "bounded above and below by more or less well-defined bedding surfaces". [1] A bedding surface is three-dimensional surface , planar or curved, that visibly separates each successive bed (of the same or different lithology ) from the preceding or following bed.
Surface reconstruction refers to the process by which atoms at the surface of a crystal assume a different structure than that of the bulk. Surface reconstructions are important in that they help in the understanding of surface chemistry for various materials, especially in the case where another material is adsorbed onto the surface.