Lin Zhang,Yang Zheng,Guoliang Li,Jiajia Gao,Yali Tong,Tao Yue
With the rapid development of adsorbents for removal of elemental mercury (Hg 0 ) from coal combustion flue gas, the preparation of adsorbents with superior performance, lower cost and environmental friendliness remains an important challenge. An incipient wetness impregnation method followed by in-situ selenization was used to load copper selenide (CuSe) onto the surface of optimal magnetic biochar (OMBC). The results showed that CuSe significantly enhanced the Hg 0 removal performance of the OMBC, and CuSe loading ratio of 10 % (10CuSe/OMBC) had the best Hg 0 removal performance. 10CuSe/OMBC maintained its Hg 0 removal efficiency above 95 % for 150 min at 30∼150 °C, and it had a good resistance to SO 2 . The equilibrium adsorption capacity of 10CuSe/OMBC could reach up to 8.73 mg/g, which was close to the theoretical value 12.99 mg/g, and the adsorption rate was up to 20.33 µg/(g·min) Meanwhile, 10CuSe/OMBC had strong magnetism that is not permanently magnetized, which could be separated from desulfurization gypsum and recycled many times. Characterization results demonstrated that Se 2 2- , Cu 2+ and O β played essential roles in the oxidation of Hg 0 , and Se 2 2- and Se 2- can immobilize Hg 2+ to HgSe. 10CuSe/OMBC has important guiding significance for practical application because of its low cost, high performance and low mercury leaching characteristic to form HgSe.
Developing efficient sorbents with rapid kinetics is the main challenge encountered for Hg0 capture from coal combustion flue gas in a sorbent injection scenario. Binary mineral sulfide-based materials combining copper sulfide (CuS) and zinc sulfide (ZnS) to exert their capabilities for Hg0 capture at the low- and high-temperature was for the first time reported for Hg0 removal to realize a wide temperature range sorbents. When the molar ratio between CuS and ZnS was 10%, the as-synthesized 10Cu-Zn nanocomposite exhibited excellent Hg0 uptake rate at 150°C that could degrade 40 μg/m3 of Hg0 to undetectable level at the end of a 60-s experiment with the dosage of only 1 mg. This Hg0 uptake rate is folds higher compared to that when bare CuS or ZnS was adopted alone at this specific temperature. The typical flue gas atmospheres had negligible effect on Hg0 removal over 10Cu-Zn in a short contact time, which further suggests that the binary sorbents were proper to be injected before the electrostatic precipitator system. Moreover, it is found that, by adjusting the ratio between CuS and ZnS, it is potential to develop binary sorbent suiting any temperature conditions that may achieve an exceedingly high Hg0 capture performance. Thus, this work not only justified the candidature of 10Cu-Zn as a promising alternative to traditional activated carbon for Hg0 capture from coal combustion flue gas but also guided the future development of multi-component mineral sulfide-based sorbents for Hg0 pollution remediation from various industrial flue gases.
Mercury has a significant impact on environment and is mainly derived from coal-fired power plant. Herein, we report a potential route for efficient removal of Hg 0 via oxidation reactions using Ce-doped LaCoO 3 supported on CeO 2 catalyst. Catalyst characterization results proved that Ce can successfully substitute a desired part of Co into the LaCoO 3 crystal lattice via a sol–gel method. The Hg 0 removal experiments suggest that Hg 0 removal efficiency decreased in the order of La 0.875 Ce 0.125 CoO 3 /CeO 2 > La 0.875 Ce 0.125 CoO 3 > LaCoO 3 . The presence of O 2 provided more active oxygen and resulted in approaching 100% Hg 0 removal efficiency. Introducing H 2 O and sole SO 2 would significantly reduce the Hg 0 removal efficiency as a result of competitive adsorption on the actives sites of the catalyst. On the other hand, SO 2 could reacted with Hg 0 in the presence of O 2 and thereby recover the high Hg 0 removal efficiency and the La 0.875 Ce 0.125 CoO 3 /CeO 2 catalyst presented a good performance towards sulfur resistance. Furthermore, the catalyst still exhibited a high Hg 0 removal efficiency performance after five times consecutive recycles.
Water poisoning remains a significant challenge for Mn-based catalysts in the purification of low-temperature industrial flue gas. In this study, a water-resistant catalyst, Cu-doped MnO x dispersed on a flower-like hollow sphere carrier (Cu 0.1 Mn 1 -Al 2 O 3 (NF)), was developed. The introduction of 5 % water vapor into simulated flue gas reduced the o-xylene oxidation efficiency of the unmodified MnO x /γ-Al 2 O 3 catalyst by 20 %, whereas Cu 0.1 Mn 1 -Al 2 O 3 (NF) exhibited only a 5 % reduction, and it shows a water resistance surpasses those of most of the reported MnO x catalysts. Upon water vapor withdrawal, Cu 0.1 Mn 1 -Al 2 O 3 (NF) showed a 2 % irreversible efficiency loss, compared to 9 % for MnO x /γ-Al 2 O 3 . Mechanistic studies highlight the role of the flower-like morphology in reducing hydrogen-bonded H 2 O and the primary contribution of Cu + doping in suppressing –OH generation on metal sites, likely due to weakened H 2 O dissociation at Mn-Ov-Cu oxygen vacancies. Additionally, Cu 0.1 Mn 1 -Al 2 O 3 (NF) has improved water desorption capability evidenced by 8 °C lower endothermic temperature for H 2 O volatilization than that of MnO x /γ-Al 2 O 3 . Furthermore, a H 2 O-involved Mars-van Krevelen (MvK) mechanism was proposed to explain the ∼ 2 % irreversible efficiency reduction for Cu 0.1 Mn 1 -Al 2 O 3 (NF) in wet gas − attributed to H 2 O dissociation at oxygen vacancies hindered lattice oxygen replenishment. Based on this mechanism, an air-purging regeneration protocol was developed to enhance the catalyst’s operational stability under wet flue gas conditions.
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