Thermochimica Acta, Vol.359, No.2, 131-141, 2000
Gas adsorption studied by pulse thermal analysis
The potential of pulse thermal analysis (PulseTA(R)) for measuring gas adsorption is studied. PulseTA(R) is based on the injection of a given amount of the adsorptive gas into a carrier gas stream and monitoring of changes in mass, enthalpy and gas composition, occurring as a result of adsorption-desorption phenomena. The method allows to study adsorption at atmospheric pressure and temperatures above 30 degrees C. Continuous monitoring of the concentrations of the pulsed probe molecules in the carrier gas provides the opportunity to investigate the dynamics of physisorption processes. The desorption rate of physisorbed species is shown to depend on carrier gas flow and thickness of the sample bed. An important advantage of PulseTA(R), compared to classical volumetric methods, is that pretreatment of the adsorbent, determination of the kind and amount of preadsorbed gases, as well as temperature programmed desorption can all be carried out in the same experimental set-up. The efficiency and reliability of PulseTA(R) for gas adsorption studies is demonstrated by comparing ammonia adsorption measurements on various solids with corresponding volumetric measurements. Solids used as adsorbents include zeolites ZSM-5 and mordenite, a titania-silica aerogel and a commercial nickel catalyst, integral heats of adsorption and the amount of chemisorbed ammonia were found to agree well with values reported in the literature.