Abstract Iodobenzene decomposes on Pd(111) and forms benzene, iodine, adsorbed carbon, and hydrogen. At low initial iodobenzene exposures no iodobenzene desorbs, benzene desorbs at 500 K, and hydrogen desorbs between 500 and 700 K, indicative of decomposition of some of the benzene. At high initial exposures iodobenzene desorbs at about 200 K and benzene desorbs at about 160 K; however, no hydrogen desorbs. Iodine desorbs from Pd(111) around 1000 K. Adsorbed iodine atoms passivate the Pd(111) surface toward the decomposition of iodobenzene and the dehydrogenation of benzene. Experiments with perdeuterated iodobenzene show that the benzene forms from reaction of phenyl with sub-surface hydrogen by 143 K.