Robust and Efficient Low Temperature Diesel Oxidation over Noble Metal Supported TiO2 Nano-array Integrated Catalytic Converters

Pu-Xian  Gao, University of Connecticut

More stringent emission regulation standards are expected in the near term, particularly aiming to reduce greenhouse gases and improve fuel economy for light duty vehicles.(1) Current advances in engines and powertrain technologies can increase fuel efficiency significantly, but at the same time reduces exhaust temperature enough to compromise the functionality of current diesel oxidation catalysts (DOC). Therefore, it is critical to develop advanced DOCs that function at low temperatures to ensure advanced combustion technologies can be implemented while still meeting the stringent emissions regulations. Conventionally, DOC catalysts rely on Platinum group metal (PGM) supported metal oxide nanoparticle powders, which are wash-coated on cordierite monoliths. However, the current wash-coat technology lacks the control over the catalyst’s physical and chemical structures, uniformity of the coating layer, and adhesion to the substrate, thus compromising material utilization efficiency and catalytic performance. Recently, we have invented a generic approach for the hydrothermal integration of nanostructure arrays (nano-arrays) of brookite TiO2 and some other metal oxides (ZnO, Co3O4, and CeO2) onto monolithic honeycomb substrates with well-defined size, shape, orientation, thickness, and chemical compositions.(2-7) These nano-array-based catalysts have displayed exceptional robustness and catalytic performance comparable to the industrial wash-coated catalysts while reducing the material (noble metal and metal oxides). Here we report scalable approaches for the preparation of Pt and/or Pd supported rutile and anatase TiO2 nano-array integrated DOC monolithic catalysts. (8-10) With significantly reduced PGM usage with respect to the commercial DOC references, these TiO2 nano-array integrated catalytic converters showed robust and efficient activities for both CO and HCs oxidation at temperatures as low as 150 oC under simulated exhaust conditions protocoled by US DRIVE, thanks to the selective and enhanced Pt/Pd species’ dispersion and unique mesoporous nano-array support structures. These nano-array integrated catalytic converters feature various outstanding merits including enhanced gas-solid interaction, metal-support interaction, S-poisoning resistance, as well as hydrothermal stability.

References
1. Register, F., Federal Register. 2012; Vol. 77, pp 62623-63200.
2. Guo, Y.; Ren, Z.; Xiao, W.; Liu, C.; Sharma, H.; Gao, H.; Mhadeshwar, A.; Gao, P.-X., Nano Energy 2013, 2 (5), 873-881.
3. Ren, Z.; Botu, V.; Wang, S.; Meng, Y.; Song, W.; Guo, Y.; Ramprasad, R.; Suib, S.L.; Gao, P.-X., Angew. Chem. Int. Ed., 2014, 53(28), 7223–7227.
4. Ren, Z.; Guo, Y.; Gao, P.-X.; Cat. Today 2015, 441-453.
5. Wang, S.; Ren, Z.; Guo, Y.; Gao, P.-X., CrystEngComm 2016, 18, 2980 – 2993.
6. Du, S.; Tang, W.; Guo, Y.; Binder, A.; Kyriakidou, E.; Toops, T.; Wang, S.; Ren, Z.; Hoang, S.; Gao, P.-X., Emission Control Sci. Tech. 2016, 3(1), 18-36.
7. Tang, W.; Ren, Z.; Lu, X.; Wang, S.; Guo, Y.; Hoang, S.; Du, S; Gao, P.-X., ChemCatChem, 2017, in revision.
8. Gao, P.-X. US Department of Energy Annual Merit Review Meeting, June 8, 2017.
9. Hoang, S.; Gao, P.-X.; et al., to be submitted, 2017.
10. Lu, X.; Gao, P.-X.; et al., to be submitted, 2017.