Adsorption and conductivity studies in oxychlorination catalysis. Part 5.—Temperature-programmed desorption

Abstract

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 (E_d) of 73 kJ mol^–1. Another chemisorptive site has a value of 57 kJ mol^–1 for E_d 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 E_d(85, 94 and 97 kJ mol^–1). An assumed value of 10¹³ s^–1 for the pre-exponential factor A_d is appropriate in Redhead's method of analysis; the kinetics are consistent with unimolecular decomposition.