Chemical adsorption (or chemisorption) measurement techniques, which also include reactions, are useful for evaluating physical and chemical properties of materials that are critical for process / reaction performance.
Such properties can include the (reduction) temperature at which metals become catalytically active, amount of surface metal or active species available for reaction, strength of specific types of active sites, or ability of materials to perform after reduction/oxidation cycles.
In static adsorption, generally two adsorption ‘isotherms’ (quantity of gas adsorbed as a function of pressure at constant temperature) are collected at sub-atmospheric pressures: the first representing total adsorption, the second representing reversible adsorption, and the difference between the two representing the irreversible adsorption (i.e. ‘chemisorption’).
This technique provides information on the quantity of adsorption sites, from which subsequent calculations may be done. When the active surface area analysis is performed at one specific temperature, it is called isothermal chemisorption.
In dynamic chemisorption, the identity, quantity, and strength of active sites can be quantified by adsorption, desorption, or reaction under isothermal or temperature-programmed conditions Dynamic chemisorption utilize pulse chemisorption in a dynamic flow system to titrate the active surface.
For the dynamic system, depending on the experiment, a lower concentration of active gas may be in contact with the sample for only a few seconds. Depending on the sample, equilibration and access of the active gas to the adsorption sites of interest may be faster in the static system.
Temperature Controlled Programmed Lab Services
Temperature-programmed analyses are used to study chemisorption bonds under controlled conditions of varying thermal energy.
TPD- Temperature Programmed Desorption TPD is used to study the desorption of physical and chemically bound species on the surface of a material. the temperature of the sample is increased until the thermal energy is sufficient to break the chemisorption bond. By monitoring the temperatures at which molecules are liberated and determining the volume of gas desorbed at each temperature, the strength and number of adsorption sites can be determined.
TPR- Temperature Programmed Reduction TPR (reduction) is used to measure the quantity of reducible species in the sample. This analysis is typically used to evaluate metal-supported catalyst. while
TPO- Temperature Programmed Oxidation TPO (oxidation) is used to quantify the oxidizable sites contained within a material. More commonly,
TPO is used in applications such as the study of the kinetics of coking, evaluation of catalyst carbon burn-off, determination of the different forms of carbonaceous deposits present on the catalysts after a CO decomposition reaction or, stated more generally, measurements of oxygen consumption and product yields.
Available Chemisorption Tests:
Volumetric Chemisorption analysis
Dynamic or pulse Chemisorption analysis
Pulse Chemisorption using liquid vapors
Temperature-Programmed Reduction (TPR)
Temperature-Programmed Desorption (TPD)
Temperature-Programmed Oxidation (TPO)
Mass Spectrometry analysis*
Other Chemisorption Experiments:
Heat of Desorption, first order Kinetics
Isosteric Heat of Adsorption
* Must be combined with Temperature Program study or TGA