Platinum Inhibits Low‐Temperature Dry Lean Methane Combustion through Palladium Reduction in Pd−Pt/Al2O3: An In Situ X‐ray Absorption Study

NSERCPeer ReviewedPalladium–platinum bimetallic catalysts supported on alumina with palladium/platinum molar ratios ranging from 0.25 to 4 are studied in dry lean methane combustion in the temperature range of 200 to 500 °C. Platinum addition decreases the catalyst activity, which cannot be explained by the decrease in dispersion or the structure sensitivity of the reaction. In situ X‐ray absorption near‐edge structure and extended X‐ray absorption fine structure spectroscopy measurements have been conducted for monometallic Pd, Pt, and 2:1 Pd−Pt catalysts. Monometallic palladium is fully oxidized in the full temperature range, whereas platinum addition promotes palladium reduction, even in a reactive oxidizing environment. The Pd/PdO weight ratio in bimetallic Pd−Pt 2:1 catalysts decreases from 98/2 to 10/90 in the 200–500 °C temperature range under the reaction conditions. Thus, platinum promotes the formation of the reduced palladium phase with a significantly lower activity than that of oxidized palladium. The study sheds light on the effect of platinum on the state of the active palladium surface under low‐temperature dry lean methane combustion conditions, which is important for methane‐emission control devices

Beitrag zur Berechnung rechteckiger Rahmen und Rahmenträger

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Comparative investigation of a Pd/Al₂O₃ catalyst system with TEM and STEM

Pd-only catalysts are attractive for automotive applications because of the low cost and wide availability of Pd compared with that of Pt and Rh. Analytical electron microscopy may be used to investigate the dispersion, which is a very important parameter in catalyst characterization, of the Pd particles on γ-Al2O3 supports. It was of interest to compare how two different techniques, TEM and STEM, might be used for the Pd-particle size determination in a model catalyst. The model system of 1wt%Pd/γ-Al2O3 used in the present study was prepared by the incipient wetness technique from a palladium nitrate solution. It was then dried at 120°C and calcined at 400°C, followed by steam aging at 600 °C for 24 hours. The TEM used was a JEOL 2000FX operated at 200 kV whereas the STEM used was a VG Microscopes HB-501UX operated in the Z-contrast mode at 100 kV.</jats:p