Reactions of CH2CHBr and CH3CHBr2 on Cu(100) and O/Cu(100)

5 years ago

Reactions of CH2CHBr and CH3CHBr2 on Cu(100) and O/Cu(100)

Chao-Ming Chiang, Tai-You Chen, Che-Ming Yang, Hong-Ping Lin, Szu-Han Lee, Jong-Liang Lin

Temperature-programmed reaction/desorption (TPR/D) and reflection–absorption infrared spectroscopy (RAIRS) have been employed to study the reactions of CH₂═CHBr and CH₃CHBr₂ on Cu(100) and O/Cu(100). In the TPR/D study, CH₂═CH—CH═CH₂ is the sole product detected from the reaction of CH₂═CHBr adsorbed on Cu(100) and featured by complex, coverage-dependent thermal desorption profiles (∼220–380 K). The preadsorbed oxygen can modify the evolution behavior of 1,3-butadiene from the CH₂═CHBr reaction but has no influence on the main 1,3-butadiene formation at 265 K. Moreover, the surface oxygen participates in the CH₂═CHBr reaction, forming an intermediate of >C═C═O, as well as additional products of H₂O, C₂H₂, CO, and CO₂, presumably via H-abstraction. New reaction pathways, which are otherwise not observed in the TPR/D study, are opened when CH₂═CHBr impinges on Cu(100) at high temperatures. At 500 K, H₂, C₂H₂, and C₂H₄ are generated from the incident CH₂═CHBr molecules upon Cu(100). The reaction of adsorbed CH₃CHBr₂ on Cu(100) only forms CH₃CH═CHCH₃ in TPR/D experiments. This product can be generated at the surface temperature as low as 120 K. Preadsorbed oxygen on Cu(100) can increase the 2-butene formation to 190 K, the peak temperature. An additional product of CH₃CHO is also formed, but its amount is small. Apparently, preadsorbed oxygen on Cu(100) has different effects on the reaction pathways for the adsorbed CH₂═CHBr and CH₃CHBr₂.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b05397

DOI: 10.1021/acs.jpcc.7b05397