Ethylene Glycol Reforming to Generate Hydrogen for Reduction of Nitric Oxide under Lean Conditions over Supported Palladium Catalysts

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The recent tightening of permissible NOx release from diesel-powered engines has intensified the search for a catalytic system that can effectively remove NOx under challenging diesel exhaust conditions. Hydrogen-assisted selective catalytic reduction (H2-SCR) using supported palladium catalysts offers significant promise for lean NOx treatment due to its high activity at low temperatures. The origin of the superior activity of these supported Pd catalysts remains inconclusive. Practically, a source of H2 needs to be secured onboard the vehicle since the H2 concentration in the diesel exhaust is too low. In this thesis research, the feasibility of a coupled system consisting of an ethylene glycol (EG) reforming unit for H2 production followed by H2/CO-deNOx unit was evaluated. Na modified Pt/Al2O3 was studied for gas phase EG reforming at 230 °C to identify conditions to generate gaseous products suitable for NOx reduction downstream. Addition of oxygen (O2/EG above 0.9) to the reforming feed was found to prevent deactivation of Na/Pt/Al2O3 when EG concentration was 2.2%. H2 contribution from WGS was insignificant under our reforming conditions. Na modification of Pt/Al2O3 resulted in higher H2 and CO2 production, suggesting an enhancement in the WGS activity by Na. Pd/Ti-PILC catalysts were selected for this study due to their high activity and selectivity. Pd/Ti-PILC catalysts with Pd loading between 0.1 - 0.5 wt% were prepared and tested for NO reduction activity with H2-CO. The 0.1 wt% Pd/Ti-PILC was found to be most active and O2-H2 titration measurements indicate that this sample had a higher Pd dispersion compared to a Pd catalyst of a higher Pd loading. This suggests that the key parameter governing the activity of Pd supported catalysts for H2-CO SCR of NO is the Pd particle size. The 0.1 Pd/Ti-PILC catalyst showed a large reduction in its ability to adsorb H2. SCR of NO using H2 derived from EG reforming led to deactivation of Pd/Ti-PILC. The cause of deactivation was exposure to EG and can be circumvented by operating the reformer at an O2/EG of 2.0 to achieve complete EG conversion.

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  • 08/29/2018
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