Comparison of the Chemistry of ClCH₂CH(CH₃)OH and ClCH₂CH₂CH₂OH on Cu(100) and O/Cu(100)

Abstract

Thermal reactions of bifunctional 1-chloro-2-propanol and 3-chloro-1-propanol on Cu(100) and oxygen-precovered Cu(100) are presented in this article. X-ray photoelectron spectroscopy, reflection–absorption infrared spectroscopy and temperature-programmed reaction/desorption have been employed to investigate the decomposition process of 1-chloro-2-propanol on Cu(100). The competitive dissociation of the functional C–Cl and CO–H at 265 K results in the formation of ClCH2CH(CH3)O– and −CH2CH(CH3)O– surface intermediates at a 2:1 concentration ratio. This ratio decreases to ∼0.6:1 at 300 K. The −CH2CH(CH3)O– oxametallacycle is theoretically predicted to be bonded on the Cu(100) surface, with both the O and CH2 at bridge sites. This surface intermediate decomposes mainly at 300 K producing CH3C(O)CH3 and CH3CH═CH2 in addition to H2 and CO. Preadsorbed oxygen atoms can stabilize the oxametallacycle and increases its reaction temperature to ∼350 K. Moreover, propene formation is promoted relative to acetone. In the reaction of 3-chloro-1-propanol on Cu(100), a low-temperature (159 K) formation channel of ClCH2CH═CH2 is observed. Other products presumably from −CH2CH2CH2O– reaction, including CH2═CHCHO, CH3CH2CHO, C2H4, CO, and H2, evolve at a temperature higher than ∼300 K. No propene from C–O dissociation is formed. Preadsorption of oxygen causes the evolution of these products to be shifted to ∼400 K, with additional CH3CH2CH2OH and a small amount of CH3CH═CH2. The theoretical calculation indicates that −CH2CH2CH2O– is bonded via the 3CH2 and O at atop and bridge sites, respectively, and has an energy slightly higher than that of −CH2CH(CH3)O–, by 3.4 kcal·mol–1.