Reaction pathways of cis- and trans-2-butene on Mo(110) and C/Mo(110):: selective activation of α and β C-H bonds

The reaction pathways of cis- and trans-2-butene on clean Mo(110) and carbide-modified Mo(110) surfaces have been studied using a combination of temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The vibrational data reveal that the decomposition pathways of cis- and trans-2-butene are different on clean Mo(110). In the case of cis-2-butene, the olefinic alpha(C-H) bonds are cleaved at 80 K to produce surface hydrogen and 2-butyne. In contrast, the initial decomposition of trans-2-butene also involves beta(C-H) bond scission, such that at least one of the methyl groups of the molecule is converted to a CH2, group at temperatures below 150 K. On carbide-modified Mo(110), the initial decomposition step for bath cis- and trans-2-butene involves alpha(C-H) bond cleavage to form 2-butyne. This difference in reactivity of Mo(110) and carbide-modified Mo(110) towards the 2-butenes provides experimental evidence that the formation of the carbide overlayer enhances the selective activation of alpha(C-H) bonds. (C) 1998 Published by Elsevier Science B.V. All rights reserved.