CH3CH2OH, CD3CD2OD, and CF3CH2OH Decomposition on ZnO(1(1)over-bar00)

Abstract

The decomposition of CH3CH2OH, CD3CD2OD, and CF3CH2OH on Zn (1 (1) over bar 00) was studied using temperature programmed reaction spectroscopy. CH3CH=O (CD3CD=O, CF3CH=O), CH2=CH2 (CD2=CD2, CF2=CH2), H2O (D2O) and H-2 (D-2) were formed in all cases. The CH3CH2OH decomposition mechanism includes the formation of two intermediate species on the surface: CH3CH2- bonded to surface lattice O atoms decomposes to form CH2=CH2 while CH3CH2O- bonded to surface Zn atoms decomposes to form CH3CH=O. A significant isotope effect observed for the formation of CH2=CH2 versus CD2=CD2 suggests that C-H(D) bond breaking at the beta-carbon is the rate-limiting step in CH3CH2- (CD3CD2-) decomposition. Decomposition of CF3CH2OH leaves F-atoms on the surface as a result of beta-fluoride elimination in CF3CH2-. A significant F substituent effect in desorption of CF3CH=O versus CH3CH=O indicates that the CF3 group increases the barrier to the beta-hydride elimination step yielding CF3CH=O and suggests that the transition state is cationic, C delta+ center dot center dot center dot H delta+.