Abstract
In many heterogeneous catalytic reactions, such as low-temperature CO oxidation, the preparation conditions, and the role of the CeO2 support (oxygen vacancies and redox properties) in the dispersion and the chemical state of Au, are considered critical factors for obtaining gold nanoparticle catalysts with high catalytic performance. In this work, the physical and chemical preparation methods were compared, aiming at understanding how the preparation method influences the catalytic activity. The Au/CeO2 nanoparticle catalysts with 5% Au loading were prepared via the Physical Laser Vaporization Controlled Condensation method (LVCC), and the chemical Deposition-Precipitation method (DP) was used to investigate the effect of synthesis methods on the structure and the catalytic activity toward the CO oxidation. In this manuscript, we compare the activity of nanostructured Au/CeO2 catalysts. The structure and the redox properties of the catalysts were investigated by the XRD, SEM, TEM, TPR, and XPS. The catalytic activity for low-temperature CO oxidation was studied using a custom-built quartz tube flow reactor coupled with an infrared detector system at atmospheric pressure. The study reveals that the prepared CeO2-supported Au nanoparticles’ catalytic activity was highly dependent on the preparation methods. It showed that the sample prepared by the DP method exhibits higher catalytic efficiency toward CO oxidation when compared with the sample prepared by the LVCC method. The high catalytic activity could be attributed to the small particle size and shape, slightly higher Au concentration at the surface, surface-active Au species such as Au1+, along with the large interface between Au and CeO2. This study suggests that the stability, dispersion of Au nanoparticles on CeO2, and strong interaction between Au and CeO2 lead to strong oxidation ability even below room temperature. Considering the universal character of different physical and chemical methods for Au/CeO2 preparation, this study may also provide a base for supported Au-based catalysts for many oxidation reactions in energy and environmental applications.
Highlights
Metal and metal oxide nanocatalysts, with controlled particle size and high surface area, can significantly improve catalytic performance over conventional catalysts
This study demonstrates that the synthesis method can affect the size, morphology, dispersion, reducibility, nature surface active site, and the Au/CeO2 nanoparticle catalyst’s catalytic properties
The characterization data and catalytic CO oxidation results reported in this paper reveal the successful synthesis of crystalline Au nanoparticles—with a size of 3–10 nm for the Laser Vaporization Controlled Condensation method (LVCC)
Summary
Metal and metal oxide nanocatalysts, with controlled particle size and high surface area, can significantly improve catalytic performance over conventional catalysts. This research aims at the possibility of designing nanostructured catalysts that possess unique catalytic properties such as low-temperature activity, selectivity, stability, and resistance to poisoning and degradation [1,2,3]. These catalysts find applications in many fields such as environmental protection, indoor air quality, Catalysts 2020, 10, 1351; doi:10.3390/catal10111351 www.mdpi.com/journal/catalysts. Supported precious metals such as platinum, rhodium, and palladium with high activity and stability, even in the presence of moisture and sulfur compounds, have been widely used in CO oxidation and gas exhaust emissions control [4]. CO oxidation over supported Au catalysts was found to be sensitive to the deposition method of Au, the Au-support interface, the structure/chemical composition of the support, as well as the pre-treatment condition of the catalyst, which is critical in determining the
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