In situ XAFS analysis of deactivation mechanism of combustion catalysts for gas sensors

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The deactivation mechanism of Pd/・-alumina catalysts for gas sensor by hexamethyldisiloxane (HMDSO) exposure has been investigated. The chemical state and local structure of Pd in the catalysts has been characterized under the reduction and oxidation conditions after HMDSO exposure by in situ X-ray absorption fine structure (XAFS) measurement. The Pd/・-alumina catalyst after HMDSO exposure hardly changed the chemical state of Pd even under the O2/N2atmosphere though it oxidized easily under the O2/N2atmosphere at the temperature of 300℃. This result shows thatthe Pd of the catalyst existed as the metal under the oxidizingcondition after the HMDSO exposure. It suggests that the contact between Pd site and gases was inhibited by the adsorption of the substance derived from HMDSO on the catalytic surface.