DESORPTION OF ORGANIC ADSORBATES FROM CARBON I

Tracer experiments using Carbon-14 labeled acetone establish that chemisorption corresponding to ≤23% of the theoretical monolayer, occurs when acetone vapor is adsorbed on carbon black at 24-140°C. Up to 90% of this strongly adsorbed acetone can be removed unchanged by linear programmed temperature desorption at ≤550°C. Assuming first order kinetics, acetone desorption thermograms (rate of desorption vs. temperature) can be consistently resolved into four separate peaks with maxima at 140, 180, 230, and 280°C. Activation energies for resolved peaks range from 11 to 17 kcal/mole with Arrhenius frequency factors of 104-106 min-1. It is proposed that chemisorbed molecules are present in a mobile adsorbed phase and must undergo a loss of translational entropy prior to desorption. The amount and stability of chemisorbed acetone is determined by the size and perfection of graphitic basal planes on the surface of the carbon substrate. © 1969.