Chemical adsorption, also known as chemisorption, is the process that results from a chemical bond between adsorbate molecules and particular surface locations on a material. These locations are known as active sites.
This article will outline the process of chemisorption and its relationship to catalysis.
An Overview of Catalysis
Catalysis refers to the process in which a reaction is altered by the presence of a non-consumable substance called a catalyst. Catalytic agents may decrease/increase the rate of reaction, decrease the required temperature for the reaction, or alter the selectivity of the reaction.
Why is Adsorption So Important in Catalysis
Adsorption is a key step in heterogeneous catalysis because, through adsorption, a gas phase molecule (adsorbate) can bind to solid surface atoms (adsorbent) before reacting to form more desirable products. In catalysis, the reactants are the adsorbate and the catalyst is the adsorbent. Two types of adsorptions are physical adsorption (physisorption) and chemical adsorption (chemisorption). Physisorption is weakly bound with a low enthalpy of adsorption (typically 20 kJ/mol) and chemisorption is stronger bound (typically 200 kJ/mol).
Chemisorption occurs when a molecule moves close enough to surface atoms so that their electron clouds overlap. The adsorbate and adsorbent share electrons, leading to the formation of chemical bonds.
In physisorption, molecules are attracted to the surface atoms due to van der Waals forces. No chemical bonds are formed between the adsorbent and adsorbate and their electronic states are not altered.
In molecular adsorption, the adsorbate stays intact such as in alkene binding using platinum. Dissociation adsorption involves more than one bond-breaking concomitantly. The barrier to dissociation impacts the rate of adsorption with an example being binding H2 to a metal catalyst.
Benefits of Chemisorption
Chemisorption methods with probe molecules such as CO, H2 and NH3 are well suited to the evaluation of chemical and physical properties of materials that are crucial for reaction/process performance. Chemisorption is often used to quantify the number of active sites available to create catalysis in chemical reactions.
Chemisorption measurements are used for catalysis characterization in a range of industries such as petroleum refining, biofuel production, plastic production, environmental studies, and many more.
Quadrupole mass spectrometers are powerful tools for catalysis research. Hiden Analytical offers a wide range of quadrupole mass spectrometer systems suitable for your catalysis research needs and beyond.