メタン雰囲気下におけるx-Al_2O_3に担持したPdOの結晶構造に及ぼすCeO_2添加の影響

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The effect of CeO_2 additions into a PdO catalyst supported on x-Al_2O_3 has been investigated. Changes in crystal structure have been examined in a methane atmosphere, in relation to catalytic activity for methane oxidation. The mass ratio Al_2O_3/PdO of the catalysts was kept constant at a value of 9, whereas the atomic ratio R = Pd/Ce was set to 0, 1, 2 and 5. The PdO-CeO_2/x-Al_2O_3 catalyst with R = 1 showed the best catalytic activity in methane oxidation. When the catalyst was heated at 300℃, Pd metal appeared under the O_2-deficient atmosphere, whereas PdO was reformed when the reduced catalyst was heated at 300℃ in an atmosphere with an O_2-excess. Line broadening of X-ray diffraction patterns was detected for both the (110) plane of PdO and the (200) plane of the Pd formed after heating, suggesting that stacking faults were introduced into these planes by the loss of oxygens in the PdO/Pd lattice during the reaction with methane. As the (110) planes in PdO correspond to the (200) planes of the fee Pd metal formed during reaction, in terms of the array of the constituent metal only, methane oxidation would easily proceed by way of these oxygen-deficient lattice planes.
社団法人日本セラミックス協会の論文
2004-03-01