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Languages : en
Pages : 13
Book Description
We have demonstrated in this work (1) that methane is readily activated at mild conditions (100°C, 1 torr) over a relatively noble metal, Pd. This was observed using a stepped and kinked Pd(679) crystal (1), and other crystal faces are now being investigated to establish whether the cracking of the C-H bond of methane on Pd is structure sensitive or structure insensitive. Oxygen chemisorption is extremely structure sensitive: weakly bonded, highly reactive oxygen overlayers form on Pd(100) surface (2), while strongly bonded, moderately reactive oxygen overlayers form on Pd(111) and Pd(679). Reaction of the weakly bonded oxygen with surface carbide gives rise to CO2 over clean Pd(100) but to CO over halogen-doped Pd(100) (3--5). The effect of halogens is primarily ensemble-controlling, or oxygen-supply restricting, but long range influence of surface Cl on the strength of the Pd-O bond has also been observed (3). Because the overall chemistry of methane activation with the subsequent oxidation gives rise to the very important oxidative reforming CH4 + 1/2 O2 -->{sub Pd/Cl} CO + 2 H2, Pd/Cl we plan to continue our study of this reaction in detail over Pd(100) (completed), Pd(111) (initiated), Pd(311) (initiated), Pd(110) (to be initiated), and Pd(679) (completed), without and with the halogen modifiers.