Carbon–Chlorine Bond Dissociation on the Pd(111) Surface

Dissociation of the C–Cl bonds in straight chain alkyl chlorides (CH3(CH2)nCl, n= 0–5) adsorbed on the Pd(111) surface has been investigated using temperature programmed desorption (TPD) and X-ray photoemission spectroscopy (XPS). Short chain alkyl chlorides adsorbed on the Pd(111) surface at low temperatures desorb during heating because the intrinsic activation energy for C–Cl bond cleavage (1EC–Cl) is greater than the desorption energy (1Edes). Systematically increasing the alkyl chain length increases 1Edes until it is greater than 1EC–Cl. The value of 1EC–Cl was estimated by determining 1Edes of the smallest alkyl chloride to dissociate during heating, i.e., the smallest alkyl chloride with 1EC–Cl≤1Edes. The TPD and XPS studies showed that while adsorbed CH3(CH2)2Cl desorbs from the Pd(111) surface during heating, CH3(CH2)3Cl is the shortest alkyl chloride to dissociate. This implies that1EC–Cl>1Edes for CH3(CH2)2Cl and1EC–Cl<1Edes for CH3(CH2)3Cl. The estimated range for the value of 1EC–Cl is 60–64 kJ/mol and is consistent with the value of 1EC–Cl estimated from previous studies of the dechlorination of fluorinated 1,1-dichloroethanes on the Pd(111) surface. c © 2000 Academic Press