Kinetic and Mechanistic Study of CO and Hydrocarbon Oxidation, and NOx Oxidation and Reduction over Pt-Pd Catalysts



Journal Title

Journal ISSN

Volume Title



Increasing vehicle fuel economy is crucial for lowering greenhouse gas emissions. One approach being evaluated is the application of low temperature combustion (LTC) engines, which are more fuel efficient than standard diesel engines. However, current diesel oxidation catalysts (DOCs) are not able to reduce the higher CO and hydrocarbon (HC) levels present in LTC exhaust to the required amount needed to meet environmental regulations.
This dissertation focuses on understanding bimetallic Pt-Pd catalysts with the aim to design catalysts so LTC engines can meet emissions regulations. A series of studies was conducted with Pt:Pd catalysts of varying mole ratio, including bench scale reactor temperature programmed oxidation (TPO) experiments to evaluate catalyst performance and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to evaluate surface species during reaction.
In the first study, CO and C3H6 oxidation were characterized. In terms of CO oxidation, the relationship between Pt:Pd ratio and CO oxidation light-off temperatures was related to dicarbonyl species forming on the Pt catalyst leading to CO inhibition, and carbonate species deactivation dominated at high Pd ratios. For propylene oxidation, the Pd-rich catalysts performed poorly, and partial oxidation products deactivated these catalysts. The second study investigated how water addition, a prevalent exhaust component, affects these trends and surface species.
In the third study, spatially resolved Fourier transform infrared spectroscopy (Spaci-FTIR) was used to measure gas-phase concentration profiles during CO and C3H6 oxidation reactions over a Pt monolith supported catalyst. Near the catalyst front, due to surface species accumulation on the catalyst surface identified by DRIFTS, two inflection points in the light-off curves were observed and were correlated to accumulation of surface species during reaction.
The final study includes larger HCs, such as dodecane, and investigates how both homogeneous and heterogeneous hydrocarbon oxidation can occur under LTC exhaust conditions. This has implications in the future of catalyst testing for these emission conditions, as well as for the design of these catalysts. Collectively these studies can be used in order to design DOCs to lower light-off temperatures and take advantage of homogeneous hydrocarbon oxidation reactions for downstream catalysts.



Oxidation catalysts, Spatially resolved reactions, Hydrocarbon oxidation, Bimetallic Pt:Pd catalysts, CO oxidation, Homogeneity, Heterogeneity, Reaction coupling


Portions of this document appear in: Hazlett, Melanie J., Melanie Moses-Debusk, James E. Parks II, Lawrence F. Allard, and William S. Epling. "Kinetic and mechanistic study of bimetallic Pt-Pd/Al2O3 catalysts for CO and C3H6 oxidation." Applied Catalysis B: Environmental 202 (2017): 404-417. And in: Hazlett, Melanie J., and William S. Epling. "Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model oxidation catalyst." Catalysis Today 267 (2016): 157-166. And in: Hazlett, Melanie J., and William S. Epling. "COUPLED HOMOGENEOUS AND HETEROGENEOUS HYDROCARBON OXIDATION IN LOW TEMPERATURE COMBUSTION EXHAUST." Emission Control Science and Technology.