Session: 05-04: Methane Emissions Control

Paper Number: 110161

110161 - Increasing Si/al Molar Ratio to Improve Low Temperature Ch4 Oxidation Over Pd/lta 

Natural gas vehicles (NGVs) have decreased greenhouse gas emissions compared to gasoline and diesel vehicles.  The majority of natural gas emissions occur at the NGV exhaust due to unburnt methane (CH₄), the main component of natural gas, leaving the tailpipe [1].  CH₄ is 25 times more potent than CO₂ in impact on global warming and can be treated with CH₄ oxidation catalysts (MOCs).  Conventional MOCs consist of Pd/γ-Al₂O₃ that deactivates in the presence of H­_­2O.  Small-pore zeolites with optimized Si/Al molar ratio to tune their hydrophobicity, are a promising alternative to Pd/γ-Al₂O₃ [2].  Herein, small-pore Linde Type A (LTA) zeolites were synthesized with Si/Al molar ratios of 30, 69, and ∞ [3].  The synthesized LTA zeolites and commercial γ-Al₂O₃ were loaded with 1 wt.% Pd and their CH₄ oxidation performance was evaluated in a packed bed micro-reactor, loaded with 100 mg catalyst pellets (250-500 μm) at 333 sccm (WHSV = 199.8 L g_cat^-1h^-1).  The catalysts were initially pretreated at 600 ^oC/20 min (20% O₂/Ar) followed by catalytic evaluation under three consecutive CH₄ oxidation cycles (1500 ppm CH_4­, 5% O₂/Ar) from 100 to 600 ^oC (5 ^oC/min) in the absence and presence of 5% H₂O.  Increasing the Si/Al molar ratio of Pd/LTA from 30 to 69 led to an increase in CH₄ oxidation performance under both dry and wet conditions.  Specifically, Pd/LTA (69) achieved 90% CH₄ conversion at the lower temperature (T₉₀ = 360 ^oC) compared to Pd/LTA (30) (446 ^oC), Pd/LTA (∞) (414 ^oC), and Pd/γ-Al₂O₃ (366 ^oC) under dry conditions.  Pd/LTA (69) and Pd/LTA (∞) achieved lower T₉₀’s at 451 and 444 ^oC, respectively, in the presence of H₂O compared to Pd/γ-Al₂O₃ (484 ^oC) and Pd/LTA (30) that did not reach 90% CH₄ conversion up to 600 ^oC.  The apparent activation energy (E_app) and CH₄, O₂, H₂O reaction orders for Pd/LTA (∞) and Pd/γ-Al₂O₃ were evaluated under dry and wet conditions.  The results of this study indicate that Si/Al > 30 for Pd/LTA is required to achieve low temperature CH₄ oxidation performance that surpasses that of Pd/γ-Al₂O₃ under both dry and wet conditions.

References:

[1] D. Jiang, K. Khivantsev, Y. Wang, Acs. Catal., 10 (2020) 14304-14314.

[2] H.-Y. Chen, J. Lu, J.M. Fedeyko, A. Raj, Appl. Catal. A: Gen., (2022) 118534.

[3] B.W. Boal, J.E. Schmidt, M.A. Deimund, M.W. Deem, L.M. Henling, S.K. Brand, S.I. Zones, M.E. Davis, Chem. Mater., 27 (2015) 7774-7779.

Presenting Author: Tala Mon University at Buffalo

Presenting Author Biography: Tala’s undergraduate focused on the design of a methane recovery plant from landfill gases and the manufacturing of non-egg-based platform for influenza vaccine using SF9 insect cells. For his Master’s thesis, he explored the silencing effects of master regulatory transcription factor Foxa1/2 in human liver cancer cells and analyzed the spatial components of liver bud growth. Tala’s PhD is centered around reducing methane emissions in the exhaust gas of natural gas vehicles using zeolite supported palladium catalysts.