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

Abstract

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 (ΔEC–Cl) is greater than the desorption energy (ΔEdes). Systematically increasing the alkyl chain length increases ΔEdes until it is greater than ΔEC–Cl. The value of ΔEC–Cl was estimated by determining ΔEdes of the smallest alkyl chloride to dissociate during heating, i.e., the smallest alkyl chloride with ΔEC–Cl≤ΔEdes. 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 that ΔEC–Cl>ΔEdes for CH3(CH2)2Cl and ΔEC–Cl<ΔEdes for CH3(CH2)3Cl. The estimated range for the value of ΔEC–Cl is 60–64 kJ/mol and is consistent with the value of ΔEC–Cl estimated from previous studies of the dechlorination of fluorinated 1,1-dichloroethanes on the Pd(111) surface.