Ruihuan Jiang,Shaomian Liu,Liang Li,Yongjun Ji,Huifang Li,Xiangfeng Guo,Lihua Jia,Ziyi Zhong,Fabing Su
Graphical Single Ir atoms : In the CO+NO reaction, the catalyst with single-sited Ir atoms (0.28 wt %) anchored on a mesoporous WO 3 (Ir 1 /mesoporous-WO 3 ) showed much higher NO conversion and N 2 selectivity under oxygen-rich conditions than the catalysts supported with Ir nanoparticles on the same catalyst support (Ir NPs/mesoporous-WO 3 ) and on a non-mesoporous WO 3 (Ir/non-mesoporous-WO 3 ). Under oxygen-rich conditions, achieving a selective and efficient reduction of NO by CO is always challenging. Here, we report the synthesis of the catalyst consisting of single Ir atoms anchored on mesoporous WO 3 (denoted as Ir 1 /m-WO 3 ) using a facile template method followed by wet impregnation. X-ray diffraction and transmission electron microscope studies indicated that the Ir atoms were distributed uniformly on the internal surface of m-WO 3 . When tested for the reduction of NO by CO, the Ir 1 /m-WO 3 catalyst with a low Ir loading of 0.28 wt % exhibited excellent catalytic performance in the presence of 2 vol % O 2 (volume ratio of CO to O 2 being 1 : 10), achieving a NO conversion of 73 % and N 2 selectivity of 100 % at 350 °C. In particular, its turnover frequency (TOF) value reached 0.30 s −1 at 200 °C, which is six times higher than that of the catalyst with Ir nanoparticles supported on mesoporous WO 3 (0.05 s −1 ). The superior catalytic performance of Ir 1 /m-WO 3 is attributed to the formation of the isolated Ir atoms and the more newly generated Ir-WO 3 interfaces that can promote the adsorption and activation of NO, and the presence of accessible mesopores in m-WO 3 that facilitates the mass transfer of NO and CO. This study brings a new fundamental understanding of active sites in Ir-based catalysts for the CO+NO reaction and provides a new way to the design and synthesis of single-atom catalysts, especially precious metal catalysts for emissions control.
Wei Chen,Huan Shen,Xiaoxiao Zhu,Guoli Liu,Chuanqi Pan,Fajun Huang,Yarong Fang,Yanbing Guo,Zhu Luo
In this study, CuO loaded on anatase TiO2catalysts (CuO/anatase) with oxygen vacancies was synthesized via reduction treatments by NaHB4and H2(CuO/anatase-B, CuO/anatase-H), respectively. The characterizations suggest that different reduction treatments bring different concentration of oxygen vacancies in the CuO/anatase catalysts, which finally affect the CO catalytic performance. The CuO/anatase-B and CuO/anatase-H exhibit CO conversion of 90% at 182 and 198 °C, respectively, which is lower than what occurred for CuO/anatase (300 °C). The XRD, Raman, and EPR results show that the amount of the oxygen vacancies of the CuO/anatase-H is the largest, indicating a stronger reduction effect of H2than NaHB4on the anatase surface. The in situ DRIFTS results exhibit that the Cu sites are the adsorption sites of CO, and the oxygen vacancies on the anatase can active the O2molecules into reactive oxygen species. According to the in situ DRIFTS results, it can be concluded that in the CO oxidation reaction, only the CuO/anatase-H catalyst can be carried out by the Mvk mechanism, which greatly improves its catalytic efficiency. This study explained the reaction mechanisms of CO oxidation on various anatase surfaces, which offers detailed insights into how to prepare suitable catalysts for low-temperature oxidation reactions.Keywords:CuO/anatase;H2reduction treatment;oxygen vacancies;CO catalytic oxidation;CO reaction mechanism
As an ideal substitute for the precious metals in the selective catalytic reduction of NO by CO, transition metal oxides perform very well. Thus, a series of CuO - Co 3 O 4 symbiotic oxide porous nanosheet catalysts are prepared with a CTAB-assisted hydrothermal method. Cu5 with the ratio of Cu and Co is 5 : 10, has the best activity on the premise of maintaining the nanosheet structure. Reduction pretreatment of Cu5 with H 2 is carried out, and the surface will be rapidly oxidized in air. In this period, Cu, CuO and Co 3 O 4 were produced and coexisted on surface. Cu5-re-163 exhibits greatly higher N 2 selectivity but a little inferior NO conversion. Further DFT calculation and characterizations proved that [N] free radicals exist during the reaction. The reaction on Cu5 and Cu-re-163 follow L-H and E-R mechanism respectively. [N] radicals on the latter are much easier to desorb, so that they are easy to combine with each other to form N 2 rather than with NO to generate N 2 O, as the reason why Cu5-re-163 has better selectivity.
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