Irreversible Catalyst Deactivation Mechanisms of PdO/γ-Al₂O₃ Catalysts for Lean Methane Oxidation

Journal Article · Wed Oct 09 00:00:00 EDT 2024 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.4c03690· OSTI ID:2475726

Chen, Hai-Ying ^[1]; Lugo-Jose, Yuliana ^[2]; Fedeyko, Joseph M. ^[2]; Toops, Todd J. ^[1]; Fidler, Jacqueline ^[3]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
2. Johnson Matthey Inc., Wayne, PA (United States)
3. CONSOL Energy Inc., Canonsburg, PA (United States)

PdO/γ-Al₂O₃ catalysts suffer from gradual and irreversible catalyst deactivation under lean CH₄ oxidation conditions, especially in a wet feed. Here, time-resolved CO chemisorption DRIFTS measurements are conducted systematically on a series of PdO/γ-Al₂O₃ catalysts to probe the surface reactivity of PdO nanoparticles after various in situ pretreatments. At 80 °C, CO barely adsorbs on fully oxidized PdO surfaces but interacts with coordinatively unsaturated Pd sites, causing gradual reduction of the PdO surfaces. This results in the formation of characteristic IR bands on various metallic Pd⁰ sites. By monitoring and comparing the formation kinetics of these IR bands on samples before and after CH₄ oxidation, we theorize that the irreversible catalyst deactivation during CH₄ oxidation is caused by PdO surface reconstruction, in which coordinatively unsaturated Pd sites gradually become fully coordinated by oxygen. Effectively, the surface reconstruction leads to the formation of a passivation layer on the PdO nanoparticles, which hinders their ability in activating CH₄, and hence the subsequent oxidation reaction. Temperature-programmed reduction with CO as the reductant (CO-TPR) reveals that the passivation layer formed during CH₄ oxidation is significant enough to increase the reduction temperature of PdO nanoparticles of the 3.0% PdO/γ-Al₂O₃ samples, although such an effect is less obvious for the 0.4% PdO/γ-Al₂O₃ samples. On the other hand, it is also discovered that the passivation layer is not completely inert. Under certain reaction conditions, with some being relatively mild, such as low-temperature CO oxidation in a net lean atmosphere and in the presence of H₂O, the passivation layer can undergo structure change which results in regeneration or even activation of CH₄ oxidation activity of an already deactivated catalyst. Additionally, it is discovered that the fully coordinated Pd–O surface is a metastable phase under CH₄ oxidation conditions. In the presence of H₂O and at ambient temperatures, surfaces with coordinatively unsaturated Pd sites are thermodynamically more favorable.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Advanced Research Projects Agency - Energy (ARPA-E)
• Grant/Contract Number: AC05-00OR22725; AR0001532
• OSTI ID: 2475726
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 20 Vol. 14; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CO Chemisorption
Catalyst Deactivation
DRIFTS Spectrum
Methane Oxidation
PdO/γ-Al2O3
Surface Reconstruction