Reactions Of Ch2=Chbr And Ch3chbr2 On Cu(100) And O/Cu(100)

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 (similar to 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, H-2, 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.