CHEMICAL GAS ADSORPTION

In chemical gas adsorption a reactive gas as hydrogen or carbon monoxide is used to obtain information on the active properties of the metal phase of a (supported) metal catalyst. The sample is first reduced in hydrogen and then evacuated to retrieve the active metal phase. In the volumetric method, known amounts of hydrogen (Pt, Ni, Rh, Ru) or CO (Pd, Pt) are dosed and subsequently adsorbed at different partial pressures, resulting in a chemisorption isotherm. This isotherm measurement is repeated after applying an evacuation step at the analysis temperature, to remove weakly adsorbed species (back-sorption method). The difference between the two isotherms represents the chemically bonded reactive gas and is used in the calculations.

The measurements are performed on a Quantachrome Autosorb-1C and the report consists of a graphic showing the two measured isotherms and its corresponding difference and a table giving information on specific metal surface area, metal dispersion, and average crystallite size.