Phenol deoxygenation mechanisms on Fe(110) and Pd(111)

The catalytic deoxygenation of phenolic compounds has become a major area of interest in recent years because they are produced during the pyrolysis of lignin and are present in biofuels. Our previous work showed that a PdFe bimetallic catalyst was catalytically active for the deoxygenation of phenolics. To better understand and control the catalytic deoxygenation reaction of phenolics, the detailed surface reaction mechanisms are needed for phenol, a key intermediate in phenolic deoxygeantion. Here, we have examined five distinct reaction mechanisms for the deoxygenation of phenol on the Fe(110) and Pd(111) surfaces so as to identify the most likely deoxygenation mechanism on these surfaces. Our results show that the elementary phenol deoxygenation reaction step for each mechanism was highly endothermic on Pd(111), whereas the same mechanisms are exothermic on Fe(110). On the basis of the reaction energy studies, detailed mechanistic studies were performed on the Fe(110) surface, and it was found that the most energetically and kinetically favorable reaction mechanism occurs via the direct cleavage of the C-O bond.