Affiliation:
1. Energy Research Institute, Nanjing Institute of Technology, Nanjing 211167, China
2. School of Environmental Engineering, Nanjing Institute of Technology, Nanjing 211167, China
3. Institute of Catalysis, Zhejiang University, Hangzhou 310028, China
4. Zhejiang NHU Co., Ltd., Shaoxing 312500, China
Abstract
5Cu-USY and Ce-doped 5Cu8Ce-USY zeolite catalysts were prepared by the conventional impregnation method. The obtained catalysts were subjected to the hydrothermal ageing process. The catalytic performance of the selective catalytic reduction of NOx with NH3 (NH3-SCR) was evaluated on both fresh and aged catalysts. Physical/chemical characterizations such as X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were performed, along with detailed in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) experiments including CO adsorption, NH3 adsorption, and NO + O2 reactions. Results showed that, for the 5Cu-USY catalyst, hydrothermal ageing treatment could somehow improve the low-temperature SCR activity, but it also led to significant formation of unfavorable byproducts NO2 and N2O. Such an activity change can be attributed to hydrothermal ageing inducing the migration of isolated Cu+ species in the sodalite cavities towards the super cages of the USY zeolites. The increased content of Cu+ species in the super cages was beneficial for the low-temperature activity improvement, but, at the same time, it also facilitated ammonia oxidation at high temperatures. Ce doping after hydrothermal ageing has a “double-edged sword” effect on the catalytic performance. First of all, Ce doping can inhibit Cu species migration by self-occupying the internal cage sites; thus, the catalytic performance of 5Cu8Ce-USY-700H remains stable after ageing. Secondly, Ce doping introduces a CuOx–CeO2 strong interaction, which facilitates lattice oxygen mobility by forming more oxygen vacancies so as to increase the concentration of surface active oxygen. These changes, on the one hand, could help to promote further oxidative decomposition of nitrate/nitrite intermediates and improve the catalytic performance. But, on the other hand, it also causes the byproduct generation to become more severe.
Funder
National Key Research and Development Program of China
Jiangsu Province Science and Technology Plan Special Fund
Key Research and Development Program of Anhui Province
Natural Science Foundation of Jiangsu Province
Scientific Research Fund of Nanjing Institute of Technology
Students’ Science and Technology Innovation Fund of Nanjing Institute of Technology
provincial key project of the Innovation and Entrepreneurship Training Program for College Students in Jiangsu Province
Subject
Physical and Theoretical Chemistry,Catalysis,General Environmental Science