Direct methane-methanol and benzene-phenol conversions on Fe-ZSM-5 zeolite: Theoretical predictions on the reaction pathways and energetics

The reaction pathways and the energetics for the direct methane-methanol an d benzene-phenol conversions that occur on the surface of Fe-ZSM-5 zeolite are analyzed from B3LYP DFT computations. We propose a reasonable model for "alpha-oxygen", a surface oxygen species responsible For the catalytic rea ctivities of Fe-ZSM-5 zeolite. Our model involves an iron-ore species on th e AlO4 surface site of the zeolite as a catalytic active center and as a so urce of oxygen. The essential features of the reaction pathways for the met hane-methanol and benzene-phenol conversions are identical, especially in b onding characters, In the initial stages of each reaction, methane or benze ne comes into contact with the active iron site of the "alpha-oxygen" model , leading to the reactant (methane or benzene) complex. After the initial c omplex is formed, each reaction takes place in a two-step concerted manner, via neither radical species nor ionic intermediates. The concerted reactio n pathway for the methane (benzene) hydroxylation involves an H atom abstra ction and a methyl (phenyl) migration at the iron active center. From compu ted energetics for the reaction pathways, we predict that the benzene hydro xylation should be energetically more favorable than the methane hydroxylat ion.