Oxyiodination catalyst

A process for preparation of mono and diiodo benzene, naphthalene or diphenyl by iodinating a fluoro, chloro, bromo, iodo, hydroxy, or cyclo substituted benzene, naphthalene or diphenyl, which comprises reacting, at a temperature in the range of 100.degree. to 500.degree. C., a source of iodine with the substituted benzene, naphthalene or diphenyl in the presence of molecular oxygen over a zeolite catalyst with a pore size of 6 angstroms or greater and greater than ten percent of the exchangeable cations being alkali, alkaline earth or rare earth metal cations, wherein said catalyst contains an amount of a modifier effective to substantially prevent deactivation of said catalyst by alkyl substituted aromatic compounds, said modifier being selected from the group consisting of hydrogen, copper, zinc, cadmium, silver, and mercury ions or salts thereof.