Key points from this module:
- Higher temperatures result in lower adsorption coverages for a given pressure.
- An adsorption isotherm is a plot of amount adsorbed (or fraction of the amount adsorption) versus gas-phase pressure at equilibrium at one temperature.
- Molecules with higher heats of adsorption have higher surface coverages.
- At sufficiently low pressures for adsorption that obey a Langmuir isotherm, surface coverage is linearly proportional to pressure.
- At sufficiently high pressures, surfaces become saturated so that increasing the pressure does not increase the surface coverage.
- Langmuir isotherms assume all sites on a surface are uniform.
- At adsorption equilibrium, the rates of adsorption and desorption are equal.
- The adsorbent is the solid on which an adsorbate adsorbs.
From studying this module, you should now be able to:
- Know the meanings of adsorption, adsorbent, and adsorbate.
- Calculate the amount of adsorbent needed to decrease the amount of adsorbate in the gas phase to a fraction of its initial value, given constants for a Langmuir isotherm at the temperature of interest.
- Given at least two measurements for the amount adsorbed and its equilibrium pressure, determine Langmuir isotherm parameters.
- Given adsorption measurements (amount adsorbed and equilibrium pressure) at two or more temperatures, determine the heat of adsorption.
See also: Langmuir-Hinshelwood Kinetics
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder