Mechanistic Study of CO and Propylene Oxidation on Bimetallic Pt=Pd/Al2O3 Catalysts for Low Temperature Combustion Exhaust

Melanie  Hazlett, University of Houston

Stricter fuel economy standards have led the automotive industry to develop higher efficiency lean combustion modes. These modes need to meet environmental policies placed on the vehicle emissions before they are able to be commercially implemented. With the lower exhaust temperatures and higher CO and hydrocarbon concentrations, current catalytic exhaust systems may not be able to provide adequate activity. One of the key components due to the higher CO and hydrocarbon levels is the diesel oxidation catalyst (DOC). For this reason, we studied CO and propylene oxidation kinetics over bimetallic Pt-Pd/γ-Al2O3 catalysts commonly used as oxidation catalysts in diesel exhaust systems.
Powder catalysts containing Pt and Pd and various ratios thereof supported on Al2O3 were tested under simulated exhaust conditions on a bench scale reactor as well as using an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) apparatus. From these experiments, surface intermediates observed in DRIFTS were related to observed light off behavior from bench scale reactor data for the different catalysts and some conclusions were drawn about the oxidation mechanisms of CO and propylene on the different Pt:Pd ratios. For instance, for CO oxidation, deactivation of Pd-rich catalysts by carbonates was observed, while CO poisoning by dicarbonyl species was observed on Pt-rich catalysts.

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