Browsing by Author "Zhao, Yingnan"

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  • The Cu migration of Cu-SAPO-34 catalyst for ammonia selective catalytic reduction of NOx during high temperature hydrothermal aging treatment
    (2019-05-01) Li, Xianghui; Zhao, Yingnan; Zhao, Huawang; Liu, Mengke; Ma, Yuhan; Yong, Xin; Chen, Hong; Li, Yongdan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Two kinds of Cu-SAPO-34 catalysts, prepared with a one-pot technique using Cu- tetraethylenepentamine as co-template and an ion-exchange method, were hydrothermally treated at 750 °C for at least 16 h. The migration of Cu species during hydrothermal treatment and the corresponding effect on the selective catalytic reduction (SCR) of NOx were examined and characterized. A certain amount of CuO exists outside and inner the crystallites in the as prepared ion-exchanged sample, whereas copper is mainly atomically dispersed in the one-pot sample existing as isolated Cu2+. After hydrothermal treatment for 16 h, the amount of the inner nanosized CuO in the ion-exchanged sample reduced and the copper disperses to form more isolated Cu2+. However, surface CuO particles increase at the sacrifice of isolated Cu2+ with extending the hydrothermal treatment to 24 h. Aggregation of Cu2+ species also happens during the aging treatment over the one-pot prepared sample where the initial Cu is atomically dispersed as isolated Cu2+. The increase of the amount of the isolated Cu2+ enhances the low-temperature (<350 °C) performance. However, the increase of the amount of surface CuO particles in the aged samples promotes the nonselective NH3 oxidation reaction in the high temperature range and results in the lowering of the SCR activity by limiting NH3 supply.
  • Dependence of carbon dioxide hydrogenation on the structure of zirconia-based rhodium catalyst
    (2018-11-06) Dahal, Roshi
     Kemian tekniikan korkeakoulu | Master's thesis
    Catalytic CO2 conversion into value added products has been one of the major study due to high energy demand and increasing atmospheric CO2 concentration. A catalytic reaction itself fulfills the Principles of Green Chemistry, but finding a catalyst for CO2 conversion at optimal temperature and atmospheric has been a greatest challenge. Studies have shown the structure of the catalyst is vital in CO2 hydrogenation for the product selectivity and reaction conditions. Support plays an important role in a reaction; where ordered struc-ture, high surface area and active sites are of high concern for a promising catalyst. This thesis has been made to study the rely of CO2 hydrogenation on the structure of the cata-lyst. Support monoclinic zirconia nanorods (ZrO2 NRs) were prepared via hydrothermal synthe-sis and Rhodium (0.5 and 2 wt%) was loaded via wet impregnation. Activity tests were con-ducted for carbon dioxide hydrogenation under atmospheric pressure and at 200 °C. The performance of the catalyst was compared with Rh loaded catalyst on commercial mono-clinic zirconia support (com ZrO2). During the experiment, the effect of parameters such as the Rhodium content and WHSV on the performance of the catalysts were compared. 200 mg of catalyst was tested in CO2 hydrogenation, which was carried out for 4 h with WHSV 1500 h-1 to 6000 h-1. Catalyst was diluted with SiC for the higher loading of Rhodium. Catalyst prepared 0.5 wt% Rh in com ZrO2 support resulted higher conversion and CH4 se-lectivity (C = 5.23 %, SCH4=64.9 %) than with ZrO2 NRs (C = 4.7 %, SCH4=36.9 %) . With 2 wt% Rh, CH4 selectivity increased for com ZrO2 supported catalyst (SCH4=75.7 %). From the sorp-tion experiments, the Rhodium particles were bigger in size on ZrO2 NRs than on com ZrO2 which could have resulted less conversion and CH4 selectivity. An interesting result, with the formation of small amounts of higher alkanes (ethane, propane) during hydrogenation, was observed. The conversion and selectivity of ZrO2 NRs supported catalyst could not result better than com ZrO2 supported catalyst. The capping agent, NaOL, was found to be occupying the active sites on the ZrO2 NRs support and thorough removal of it could result better conversion. Nevertheless, the conversion and selectivity of zirconia-based Rhodium catalyst in CO2 hydrogenation at low temperature and atmospheric pressure could open up a promising objective for the future research.
  • Effect of chlorine on performance of Pd catalysts prepared via colloidal immobilization
    (2017) Zhao, Yingnan; Liang, Wanwei; Li, Yongdan; Lefferts, Leon
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This contribution shows the effect of residual chlorine on the catalytic performance of a Pd-based catalyst in the hydrogenation of nitrite for cleaning of drinking water. The catalyst was prepared via immobilization a colloidal Pd nanoparticles using activated carbon as support. Different amount of hydrochloric acid (HCl) was added to immobilize the Pd colloid on the carbon support, facilitating the removal of the residual stabilizer, polyvinyl alcohol (PVA), from the surface of the Pd nanoparticles (NPs). The catalysts were characterized by TEM, CO-chemisorption, XRF, N2 physisorption, UV-vis spectroscopy, and XPS. The activity and selectivity of the catalysts were measured for nitrite hydrogenation in semi-batch operation. The results show that PVA can be removed completely at pH below 2. The residual chlorine on the catalysts can be removed by reduction in H2/N2 at a mild temperature, i.e. 200°C, regardless the amount of HCl used. Nevertheless, high concentration of HCl during immobilization (pH 1) causes partial Pd re-dissolution according to UV-vis spectroscopy, resulting in formation of highly dispersed Pd clusters that could not be detected with TEM. Reduction of this catalyst with high chlorine content in H2 at 200°C is resulting in formation of relatively large Pd particles via sintering. Without pre-reduction at 200°C, residual chlorine can also be removed almost completely during the hydrogenation reaction at room temperature. The activity of the Pd catalyst is insensitive to the chlorine concentration below 30μmolL-1 in the aqueous reaction mixture. Interestingly, the selectivity to N2 is improved by adding chlorine to the reaction mixture, independent of the way chlorine is added, i.e. via the catalyst or added directly to the reaction solution.
  • Enhanced hydrothermal stability of a Cu-SSZ-13 catalyst for the selective reduction of NOx by NH3 synthesized with SAPO-34 micro-crystallite as seed
    (2019-09) Zhao, Huawang; Zhao, Yingnan; Ma, Yuhan; Yong, Xin; Wei, Miao; Chen, Hong; Zhang, Cuijuan; Li, Yongdan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The distribution of framework Si and Al in the Cu-SSZ-13 catalyst, for NH3 selective catalytic reduction of NOx, is manipulated via a new strategy, using SAPO-34 as a seed in hydrothermal synthesis instead of the conventional SSZ-13 micro-crystallite. The SAPO-34 seed has a strong impact on the hydrothermal stability of the catalyst, moderating the dealumination as well as the agglomeration of the active Cu2+ ions in the Cu-SSZ-13 with hydrothermal treatment at 800 °C.
  • Phosphorus modification to improve the hydrothermal stability of a Cu-SSZ-13 catalyst for selective reduction of NOx with NH 3
    (2019-09-05) Zhao, Huawang; Zhao, Yingnan; Liu, Mengke; Li, Xianghui; Ma, Yuhan; Yong, Xin; Chen, Hong; Li, Yongdan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Phosphorus is introduced to modify the Cu-SSZ-13 catalyst via incipient wetness impregnation, with P/Cu-SSZ-13 = 1 and 2 wt.%, and Si/Al = 4, for selective catalytic reduction of NOx with NH 3 . N 2 physisorption and XRD results show the incorporation of phosphorus as phosphate acid enhanced the hydrothermal stability of Cu-SSZ-13 significantly, during hydrothermal aging in 10 vol.% H 2 O/air at 750 °C for 16 h. NMR and Raman results suggest that phosphate ions migrate and coordinate with the framework-bonded Al species, forming a framework silicoaluminophosphate interface, thus impeding further dealumination and structure collapse. Before the hydrothermal aging, the isolated Cu 2+ ions partly interact with the phosphate ions, forming Cu-phosphate species and reducing the SCR performance. Nevertheless, the appropriate content of phosphate ions can prevent the structure collapse caused by the hydrothermal aging, remaining the isolated Cu 2+ ions as well as excellent SCR performance.
  • The promotion effect of nickel and lanthanum on Cu-ZSM-5 catalyst in NO direct decomposition
    (2019-05-01) Liu, Mengke; Zhao, Yingnan; Zhao, Huawang; Li, Xianghui; Ma, Yuhan; Yong, Xin; Chen, Hong; Li, Yongdan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A number of M-Cu-ZSM-5 (M = La, Ni, La-Ni) samples were prepared via an aqueous solution ion-exchange method. The co-doping with Ni and La into a Cu-ZSM-5 catalyst enhanced the NO decomposition activity in a temperature range 350–550 °C. The characterization results indicate that doping with La effectively improved the dispersion of the Cu species forming more Cu2+ ions in the sample, while the effect of Ni is likely to facilitate the implantation of Cu2+ to form (Cu2+-O2–-Cu2+)2+ dimers. The synergistic effect of La and Ni contributes to the increased (Cu2+-O2−-Cu2+)2+ content in the co-doped sample, thus enhancing the NO decomposition activity.