Large natural gas engines, such as those used for power generation and maritime transportation, generate less CO2 than coal or petroleum, but the global warming impact of uncombusted methane (CH4) emitted in the exhaust far exceeds CO2 and must be abated by using catalytic aftertreatment devices.
Although metal oxide-supported Pd catalysts are active for CH4 oxidation, they require temperatures above 500 ºC and high Pd loadings to convert CH4 in the presence of combustion products such as H2O, CO2, SO2. Such demanding operating conditions lead to fast and irreversible catalyst deactivation, hindering widespread commercial implementation.
Zeolites are promising support materials to overcome these challenges due to their hydrothermal stability, resistance to dealumination in the presence of steam, and unique ability to confine active metals to prevent thermal sintering.
Our recent work demonstrates that small- and medium-pore zeolites, such as CHA and MFI, respectively, with very high Si/Al ratios (50-∞) can stabilize reactive Pd nanoparticles, either through encapsulation or metal-support anchoring, and increase CH4 oxidation rates at low temperatures in the presence of H2O.
CH4 oxidation performance after simulated aging at 650 ºC for 1 h under wet-lean conditions (0.15% CH4, 5% O2, 5% H2O, bal. Ar) reveals that 1 wt.% Pd/CHA catalysts with Si/Al > 33 attain > 90% CH4 at temperatures below 400 ºC compared to 500 ºC for a conventional 1 wt.% Pd/Al2O3 catalyst. Furthermore, steady state CH4 turnover frequencies over Pd-based CHA and MFI catalysts are up to 4× greater than 1 wt.% Pd/Al2O3, suggest that these high-silica zeolites contain Pd sites that more easily activate CH4 by inhibiting the accumulation of inactive hydroxyl species on the Pd surface in the presence of H2O while facilitating O2 adsorption and transport to oxidize adsorbed CH4¬. Increasing the zeolite Si/Al ratio leads to greater hydrophobicity and improved catalyst durability in presence of H2O during CH4 oxidation under lean-burn conditions by decreasing the mobility of active Pd species and reducing the inhibiting effect of H2O on catalytic turnovers.
Viktor J. Cybulskis was born in South Bend, IN and received his B.S. in chemical engineering from Purdue University in 2005. He worked in the petrochemical industry on the Texas Gulf Coast for six years and then returned to Purdue and received his Ph.D. in 2016 under the direction of Fabio Ribeiro and W. Nicholas Delgass. After completing a postdoc with Mark Davis at Caltech, Viktor joined Syracuse University in 2018 as an assistant professor.
Cybulskis’ research focuses on understanding the molecular details of heterogeneously catalyzed reactions and designing reactive micro-environments to enable new pathways for selective chemical transformations. He received the ACS PRF Doctoral New Investigator Award (2022) and was selected as a finalist for the Beckman Young Investigator Award (2023). He currently serves as Secretary of AIChE’s Licensing and Professional Development Committee and is regularly involved in session organization and chairing at national meetings for AIChE, ACS, and NAM. In his free time, he enjoys the outdoors, reading, watching sports, and spending time with his family.