Séminaire LRS | Eleni A. Kyriakidou "High silica small pore zeolites for low temperature CH4 oxidation application"

Natural gas has garnered attention as a cleaner alternative fuel for vehicles compared to gasoline or diesel. The main component of natural gas is methane (CH₄) and is 25 times more potent than CO₂ in impact to global warming over a 100-year period. The conventional solution for CH₄ remediation is its catalytic oxidation using Pd/Al₂O₃ catalysts.
However, Pd/Al₂O₃ catalysts suffer from low conversions and deactivation through Pd sintering in typical exhausts of natural gas vehicles containing high amounts of H₂O (5–10%) at low temperatures (<400°C). A promising supportalternative is zeolites that can act as molecular sieve through size limiting pores to restrict Pd sintering in the presence of H₂O. Specifically, Pd supported on small-pore zeolites achieved higher CH4 oxidation performance compared to zeolites with larger pores. Moreover, the hydrophobicity of zeolites can be increased by increasing the Si content to prevent H₂O inhibition. Herein, small-pore LTA and CHA zeolites were synthesized with Si/Al molar ratios > 1 loaded with 1 wt.% Pd and their CH₄ oxidation performance was compared with that of 1 wt.% Pd/Al₂O₃, the state- of-the-art catalyst for CH₄ oxidation. The results indicated that an improved CH₄ oxidation performance in the presence of H₂O can be achieved by increasing the hydrophobicity of Pd/zeolite catalysts. The impact of the zeolite Si/Al molar ratio, hydrothermal durability and sulphur tolerance on the low-temperature oxidation activity, and H₂O exposure on Pd speciation at ambient temperure (25°C) and moisture (3.1% H₂O), will be discussed