Modular Pd/Zeolite Composites Demonstrating the Key Role of Support Hydrophobic/Hydrophilic Character in Methane Catalytic Combustion

Journal Article · Thu Apr 11 00:00:00 EDT 2019 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.9b00596· OSTI ID:1532473

Losch, Pit ^[1]; Huang, Weixin  ^[2]; Vozniuk, Olena ^[3]; Goodman, Emmett D. ^[2]; Schmidt, Wolfgang ^[3]; Cargnello, Matteo  ^[2]

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1. Stanford Univ., CA (United States). Dept. of Chemical Engineering and SUNCAT Center for Interface Science and Catalysis; Max-Planck-Inst. für Kohlenforschung, Mülheim (Germany)
2. Stanford Univ., CA (United States). Dept. of Chemical Engineering and SUNCAT Center for Interface Science and Catalysis
3. Max-Planck-Inst. für Kohlenforschung, Mülheim (Germany)

Complete catalytic oxidation of methane in the presence of steam at low temperatures (T < 400 °C) is a crucial reaction for emission control, yet it presents profound challenges. The activation of the strong C–H bond of methane at low temperature is difficult, and the water present in any realistic application poisons the active surface and promotes sintering of Pd particles during the reaction. Finding materials that can deliver high reaction rates while being more resistant to the presence of water is imperative for advancing several technological applications of natural gas-based systems. However, methods to fairly compare the activity of Pd catalysts (the most active metal for methane combustion) are needed in order to perform useful structure–property relationship studies. Here in this paper, we report a method to study how zeolite hydrophobicity affects the activity of Pd nanoparticles in the reaction, which led to a significant improvement in the water resistance. Mesoporous zeolites were synthesized starting from commercially available microporous zeolites. In this way, a variety of hierarchically porous zeolites, with different hydrophobic/hydrophilic character, were prepared. Preformed colloidal Pd nanoparticles could be deposited within mesostructured zeolites. This approach enabled the systematic study of key parameters such as zeolite framework, Al content, and the Pd loading while maintaining the same Pd particle size and structure for all the samples. Detailed catalytic studies revealed an optimum hydrophobic/hydrophilic character, and a promising steam-resistant catalyst, namely, 3.2 nm Pd particles supported on mesoporous zeolite beta or USY with a Si/Al ratio of 40, emerged from this multiparametric study with a T₅₀ of 355 °C and T₉₀ of 375 °C (where T₅₀ and T₉₀ are temperature values at which the samples reach 50% and 90% methane conversion, respectively) in steam-containing reaction conditions. Finally, we verified that the designed catalysts were stable by in-depth postcatalysis characterization and operando diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) analyses confirming that water adsorbs less strongly on the active PdO surface due to interaction with the zeolite acid sites. This method can be of general use to study how zeolite supports affect the reactivity of supported metals in several catalytic applications.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-76SF00515; DGE-1656518
• OSTI ID: 1532473
• Journal Information: ACS Catalysis, Vol. 9, Issue 6; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
42 ENGINEERING
C−H activation
emissions control
colloidal nanoparticles
hierarchical porosity
mesoporous zeolite