(560fr) One-Pot Synthesis of Gold Embedded Ceria Nanoshapes for Catalytic NO Reduction By CO

Li, M., Oak Ridge National Laboratory
Zhang, X., ORNL
Dai, S., Oak Ridge National Laboratory
Wu, Z., Oak Ridge National Laboratory
Growing environmental concern in recent years has resulted in the introduction of more rigorous and stringent environmental laws and regulations. NOx is considered as one of the primary pollutants of the atmosphere because it is responsible for the formation of photochemical smog, acid rain, and the greenhouse effect. The catalytic reduction of NOx by a series of reducing agent (ammonia, H2, CO and hydrocarbons) is one of the most widespread method and effective technology to decrease the impact of NOx on the environment. The Au-based materials possess high activity at low temperatures, which makes it suitable for catalytic application during the cold start of the vehicles. Oxides like ceria are commonly used as supports due to its outstanding redox ability and high oxygen storage capacity (OSC) associated with the formation of oxygen vacancies. Particularly, the introduction of metal cations into the ceria system will promote its redox behavior and catalytic activity significantly due to the formation of more oxygen vacancies. In this work, differently shaped ceria with embedded gold (Au-CeO2-rod and Au-CeO2-cube) were synthesized by one-pot hydrothermal method. XRD measurements show the distinct fluorite CeO2 patterns with no detected Au related peaks, suggesting that Au atoms are well dispersed into CeO2 matrix. Their catalytic property was probed by the model reaction: reduction of nitric oxide (NO) with carbon monoxide (CO) under both oxidizing and reducing pre-treatment conditions. Preliminary results present that Au embedded into rod-shaped CeO2 exhibits higher NO conversion and N2 selectivity than Au-CeO2-cube at all reaction temperatures. The catalysts have been further characterized by multiple techniques (TPR, TEM, Raman, etc.) to investigate the support morphology, noble metal dispersion, oxygen defects effect on their catalytic behaviors in NO-CO reaction. In-situ FT-IR combined with mass spectrometer is also employed to study the surface chemistry and reaction mechanism of NO reduction by CO over the different Au-CeO2 catalysts.

ACKNOWLEDGEMENTS: This work is supported by the Center for Understanding and Control of Acid Gas-Induced Evolution of Materials for Energy (UNCAGE-ME), an Energy Frontier Research Center funded by U.S. Department of Energy, Office of Science, Basic Energy Sciences. Part of the work including the IR and Raman was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.