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Dynamics of the reversible inhibition during methane oxidation on bimetallic Pd‐Pt catalysts studied by modulation‐excitation XAS and DRIFTS

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Water and NO reversibly inhibit catalytic methane oxidation to CO 2 over Pd/Al 2 O 3 and Pd-Pt/Al 2 O 3 at temperatures near 50% conversion. Modulation-excitation X-ray absorption spectroscopy (ME-XAS) was used to characterize the interaction of the inhibitors with the Pd and Pt components. Simulated X-ray absorption near-edge structure (XANES) spectra of Pd and Pt with various surface species were used to verify the findings of ME-XAS measurements. Diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) allowed to correlate methane oxidation with surface formate species. An interaction of water with active Pd sites and water coverage of the Al 2 O 3 support caused a drastic drop in formate production, correlated with the observed inhibition. In a similar manner, nitrite groups formed from gas-phase NO inhibited the production of formates. At higher tem­pe­ra­tures, the inhibition was reversed into a promoting effect by surface nit­rates formed from NO that oxidized gas-phase methane. This ap­proach is not only interesting for emission control but in general for ca­ta­lysts where dynamic structural changes occur.

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