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Highly Efficient and Stable Au/CeO2–TiO2 Photocatalyst for Nitric Oxide Abatement: Potential Application in Flue Gas Treatment

Zhu, Wei, Xiao, Shuning, Zhang, Dieqing, Liu, Peijue, Zhou, Hongjun, Dai, Wenrui, Liu, Fanfan, Li, Hexing
Langmuir 2015 v.31 no.39 pp. 10822-10830
active sites, ceric oxide, chemical bonding, dissociation, electrons, flue gas, gold, irradiation, lighting, microwave treatment, nanocrystals, nitric oxide, oxidation, oxygen, photocatalysis, photocatalysts, pollutants, power plants, superoxide anion, synergism, titanium dioxide
In the present work, highly efficient and stable Au/CeO₂–TiO₂ photocatalysts were prepared by a microwave-assisted solution approach. The Au/CeO₂–TiO₂ composites with optimal molar ratio of Au/Ce/Ti of 0.004:0.1:1 delivered a remarkably high and stable NO conversion rate of 85% in a continuous flow reactor system under simulated solar light irradiation, which far exceeded the rate of 48% over pure TiO₂. The tiny Au nanocrystals (∼1.1 nm) were well stabilized by CeO₂ via strong metal–support bonding even it was subjected to calcinations at 550 °C for 6 h. These Au nanocrystals served as the very active sites for activating the molecule of nitric oxide and reducing the transmission time of the photogenerated electrons to accelerate O₂ transforming to reactive oxygen species. Moreover, the Au–Ce³⁺ interface formed and served as an anchoring site of O₂ molecule. Then more adsorbed oxygen could react with photogenerated electrons on TiO₂ surfaces to produce more superoxide radicals for NO oxidation, resulting in the improved efficiency. Meanwhile, O₂ was also captured at the Au/TiO₂ perimeter site and the NO molecules on TiO₂ sites were initially delivered to the active perimeter site via diffusion on the TiO₂ surface, where they assisted O–O bond dissociation and reacted with oxygen at these perimeter sites. Therefore, these finite Au nanocrystals can consecutively expose active sites for oxidizing NO. These synergistic effects created an efficient and stable system for breaking down NO pollutants. Furthermore, the excellent antisintering property of the catalyst will allow them for the potential application in photocatalytic treatment of high-temperature flue gas from power plant.