Dynamics of the Reversible Inhibition during Methane Oxidation on Bimetallic Pd‐Pt Catalysts Studied by Modulation‐Excitation XAS and DRIFTS
Alexey Boubnov, Andreas Gremminger, Maria Casapu, Olaf Deutschmann, Jan‐Dierk Grunwaldt
Abstract
Abstract 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.