(148h) Wash-Coat Development for Lean-Burn Engine-Exhaust Aftertreatment: A Novel Way of Incorporation of Binder to Pd Supported on Sulfated Zirconia

Sreshtha S. Majumdar, Gokhan Celik, Anne-Marie Alexander, Umit S. Ozkan^*The Ohio State University, Columbus, Ohio 43210, U.S.A.

*ozkan.1@osu.edu

As the environmental regulations are getting more stringent, it is of great importance to develop a catalytic aftertreatment system for natural gas-fired lean-burn engines to reduce the emissions of nitrogen oxides (NO_x), unburned hydrocarbons (CH_4, C₂H_6, and C₃H₈) and carbon monoxide efficiently. We have developed a dual-catalyst aftertreatment system which utilizes the hydrocarbons present in the exhaust streams of lean-burn engines for reducing NO_xemissions. The dual-catalyst aftertreatment system is a physical mixture composed of a reduction catalyst, palladium supported on sulfated zirconia (Pd/SZ), and an oxidation catalyst, cobalt supported on ceria. Such a catalytic system which utilizes methane in the exhaust stream offers several advantages considering that the emissions of air-pollutant greenhouse gases are controlled in a single unit without a need of injecting and handling an external reducing agent such as ammonia [1-3]. Development of a catalytically active washcoat for monolith cores is essential for the practical use of this dual-catalyst system. However, if the washcoat adheres poorly to the monolith core, the aftertreatment unit will suffer from the irreversible loss of the catalytically active phase. In order to improve the adhesive properties, conventionally, binders are used in a catalyst slurry.

In this study, we have aimed to improve the adhesive properties at the molecular level. For this purpose, alumina, as a binder, was incorporated in situ to the sol-gel medium of Pd/SZ prior to the gelation during synthesis. Samples prepared by this novel approach have shown superior differences in terms of catalytic performance than the samples prepared by the conventional method. Addition of binder before gelation to the sol-gel medium also resulted in changes of textural and structural properties of binder-free samples, and adhesive properties of the washcoat as shown by N₂ physisorption, in-situ X-ray diffraction (XRD) calcination, ²⁷Al-NMR, laser RAMAN and infrared spectroscopy, scanning electron microscopy (SEM) and ultrasonication, Water and sulfur tolerance as well as hydrothermal stability of the binder-incorporated catalyst will be presented as well.

[1] B. Mirkelamoglu, M. Liu, U.S. Ozkan, Catalysis Today, 151 (2010) 386-394.

[2] P. Gawade, A.-M.C. Alexander, R. Silver, U.S. Ozkan, Energy and Fuels, (2012).

[3] P. Gawade, B. Bayram, A.-M.C. Alexander, U.S. Ozkan, Applied Catalysis B: Enviromental (2012).