Adsorption and conductivity studies in oxychlorination catalysis. Part 5.—Temperature-programmed desorption
The desorption of ethylene, 1,2-dichloroethane (EDC), carbon dioxide and other adsorbates from CuCl2 has been studied using temperature-programmed desorption (t.p.d.). A chemisorptive centre corresponding to an ethylene concentration of 5 × 10–9 mol m–2 has an energy of activation for desorption (Ed) of 73 kJ mol–1. Another chemisorptive site has a value of 57 kJ mol–1 for Ed when the ethylene coverage is 10–6–10–7 mol m–2. These magnitudes are closely related to previously reported heats of chemisorption, suggesting adsorption to be only weakly activated.
EDC is shown to desorb readily whereas CO2 has three distinct values of Ed(85, 94 and 97 kJ mol–1). An assumed value of 1013 s–1 for the pre-exponential factor Ad is appropriate in Redhead's method of analysis; the kinetics are consistent with unimolecular decomposition.