Session: Technical Posters

Paper Number: 110160

110160 - Thermally Stable Pd/ssz-13 Catalysts With Excellent Methane Oxidation Activity Under Lean Conditions 

Thermally Stable Pd/SSZ-13 Catalysts with Excellent Methane Oxidation Activity under Lean Conditions

Prateek Khatri¹, Tala Mon¹, Joshua Pacheco², Bjorn Moden², Eleni A. Kyriakidou^1*

¹Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA

²Zeolyst International, R&D Center, 280 Cedar Grove Rd., Conshohocken, PA 19428, USA

^*elenikyr@buffalo.edu

CH₄ emissions from the exhaust of natural gas vehicles (NGVs) have become an immediate environmental concern owing to its 25-fold higher potential for global warming than CO₂.  Thus, there is an immediate need for catalytic materials capable of reducing CH₄ emissions.  Pd/Al₂O₃, the state-of-the-art catalyst for CH₄ oxidation, deactivates in the presence of H₂O leading to a decrease in CH₄ oxidation performance.  In contrast, zeolite-supported Pd catalysts have a tuned hydrophobicity and possess a promising CH₄ oxidation activity.  Herein, 2 wt.% Pd/SSZ-13 catalysts with Si/Al molar ratios > 50 were synthesized, and their CH₄ oxidation activity before and after hydrothermal aging (HTA) was investigated under lean conditions.  Briefly, SSZ-13 zeolites with Si/Al molar ratios of > 50 were synthesized through a modified hydrothermal synthesis route [1] and their CH₄ oxidation performance was compared with a second series of SSZ-13 samples with Si/Al molar ratios of 65, 83, and 93.  2 wt.% Pd was added to all SSZ-13 samples via an ion exchange method, followed by drying (110 ⁰C/8 h) and calcination (500 ⁰C/2 h). The CH₄ oxidation performance was evaluated over 100 mg of catalyst (200-500 µm) at a total flow rate of 333 sccm (200 L gcat^-1h^-1).  The catalysts were initially pretreated using 11% H₂O, 6% CO₂, and 8.5% O₂, balance Ar at 600 ⁰C/20 min followed by evaluation under a feed containing 1500 ppm CH₄, 90 ppm NOx, 760 ppm CO, 8.5% O₂, 6% CO₂, 11% H₂O, balance Ar [2].  2 wt.% Pd/SSZ-13(75) (value in the parenthesis indicates Si/Al molar ratio) reached T_50,90’s (temperatures corresponding to 50 and 90% CH₄ conversion) at 379/443 ⁰C.  However, an increase in the Si/Al molar ratio led to an improvement in the CH₄ oxidation performance.  For instance, higher Si/Al molar ratio samples such as 2 wt.% Pd/SSZ-13(156) achieved T_50,90’s at lower temperatures of 364/427 ⁰C compared to 2 wt.% Pd/SSZ-13(75).  Since 2 wt.% Pd/SSZ-13(156) outperformed all studied catalysts, the effect of HTA on its CH₄ oxidation activity was also investigated.  2 wt.% Pd/SSZ-13(156) was hydrothermally aged (20% O₂, 10% H₂O, balance Ar) at 650 ⁰C/12 h followed by three consecutive CH₄ oxidation cycles.  The T_50,90’s achieved by HTA 2 wt.% Pd/SSZ-13(156) were at 385/473 ⁰C (1^st cycle), 386/474 ⁰C (2^nd cycle), and 387/474 ⁰C (3^rd cycle).  Thus 2 wt.% Pd/SSZ-13(156) exhibited excellent CH₄ oxidation activity.  The sulfur tolerance of Pd/SSZ-13(156) will also be reported.  

References

[1] Prodinger, S., Derewinski, M.A., Wang, Y., Washton, N.M., Walter, E.D., Szanyi. J., Gao, F., Wang, Y., and Peden, C.H. Appl. Catal. B: Environ. 201, 461-9 (2017).

[2] Rappé K.G., DiMaggio C., Pihl J.A., Theis J.R., Oh S.H., Fisher G.B., Parks J., Easterling V.G., Yang M., Stewart M.L., and Howden K.C. Emission Contr. Sci. Technol. 5, 183-214 (2019).

Presenting Author: Prateek Khatri University at Buffalo

Presenting Author Biography: Dr. Prateek Khatri
Postdoctoral Associate
Catalysts Design & Energy Applications Laboratory
Department of Chemical and Biological Engineering
University at Buffalo

Areas of Interest
CH4 oxidation, automotive catalysis, exhaust after-treatment, monolith reactors, NOx emissions, Dry reforming of methane

Education
Ph.D., Department of Chemical Engineering, Indian Institute of Technology Delhi
M. Tech., Indian Institute of Technology Varanasi