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411.
Heterogeneous reactions of NO2 on different surfaces play an important role in atmospheric NOx removal and HONO formation, having profound impacts on photochemistry in polluted urban areas. Previous studies have suggested that the NO2 uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime. However, the uptake behavior of NO2 varies with different surfaces, and different uptake coefficients were used or derived in different studies. To obtain a more holistic picture of heterogeneous NO2 uptake on different surfaces, a series of laboratory experiments using different flow tube reactors was conducted, and the NO2 uptake coefficients (γ) were determined on inorganic particles, sea water and urban grime. The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions, with the measured γ varied from <10?8 to 3.2 × 10?7 under different humidity. A photo-enhanced uptake of NO2 on urban grime was observed, with the obvious formation of HONO and NO from the heterogeneous reaction. The photo-enhanced γ was measured to be 1.9 × 10?6 at 5% relative humidity (RH) and 5.8 × 10?6 at 70% RH on urban grime, showing a positive RH dependence for both NO2 uptake and HONO formation. The results demonstrate an important role of urban grime in the daytime NO2-to-HONO conversion, and could be helpful to explain the unknown daytime HONO source in the polluted urban area. 相似文献
412.
成功制备出羧基功能化的MnFe2O4磁性催化剂(MnFe2O4-COOH),采用X射线衍射(XRD)、N2吸附-脱附、振动样品磁强计(VSM)、红外光谱(FT-IR)、透射电子显微镜(TEM)、H2-程序升温还原(TPR)及X-射线光电子能谱(XPS)等技术对其理化性质进行了表征,并通过非均相Fenton氧化降解水中头孢噻肟钠抗生素对MnFe2O4和MnFe2O4-COOH的催化性能进行了考查.结果表明,经过表面修饰之后的MnFe2O4-COOH比MnFe2O4的催化活性高,头孢噻肟钠的去除率可以达到85.5%,TOC的去除率达到58.1%.同时,对溶液pH的影响、Fe的流失、主要的活性物种及羧基修饰基团的作用进行了研究.结果表明,羟基自由基(?OH)是非均相Fenton氧化过程中的主要活性物种,羧基修饰后催化活性的提高主要归因于团聚的抑制、活性组分Fe流失的降低及还原能力的提高.此外,稳定性和重复使用性的研究结果表明,MnFe2O4-COOH经过3次 循环使用后,仍能保持较高的催化活性. 相似文献
413.
Linke Wu Jiguang Deng Yuxi Liu Lin Jing Xiaohui Yu Xing Zhang Ruyi Gao Wenbo Pei Xiuqing Hao Ali Rastegarpanah 《环境科学学报(英文版)》2022,34(6):209-219
Catalytic combustion is thought as an efficient and economic pathway to remove volatile organic compounds, and its critical issue is the development of high-performance catalytic materials. In this work, we used the in situ synthesis method to prepare the silicalite-1 (S-1)-supported Pd nanoparticles (NPs). It is found that the as-prepared catalysts displayed a hexagonal prism morphology and a surface area of 390−440 m2/g. The sample (0.28Pd/S-1-H) derived after reduction at 500°C in 10 vol% H2 showed the best catalytic activity for toluene combustion (T50% = 180°C and T90% = 189°C at a space velocity of 40,000 mL/(g·hr), turnover frequency (TOFPd) at 160°C = 3.46 × 10−3 sec−1, and specific reaction rate at 160°C = 63.8 µmol/(gPd·sec)), with the apparent activation energy (41 kJ/mol) obtained over the best-performing 0.28Pd/S-1-H sample being much lower than those (51−70 kJ/mol) obtained over the other samples (0.28Pd/S-1-A derived from calcination at 500°C in air, 0.26Pd/S-1-im derived from the impregnation route, and 0.27Pd/ZSM-5-H prepared after reduction at 500°C in 10 vol% H2). Furthermore, the 0.28Pd/S-1-H sample possessed good thermal stability and its partial deactivation due to CO2 or H2O introduction was reversible, but SO2 addition resulted in an irreversible deactivation. The possible pathways of toluene oxidation over 0.28Pd/S-1-H was toluene → p-methylbenzoquinone → maleic anhydride, benzoic acid, benzaldehyde → carbon dioxide and water. We conclude that the good dispersion of Pd NPs, high adsorption oxygen species concentration, large toluene adsorption capacity, strong acidity, and more Pd0 species were responsible for the good catalytic performance of 0.28Pd/S-1-H. 相似文献
414.
利用ELPI(电子低压冲击器)对不同转速、不同负荷以及安装DOC(氧化催化转化器)前后颗粒物排放及粒径分布进行了研究. 结果表明:无论安装DOC与否,柴油机排放颗粒物数浓度均随发动机转速的增加而增加. 增大负荷,颗粒物数浓度峰值处的粒径也随之增大. 经过DOC催化转化后,柴油机排放颗粒物的大部分仍呈单峰正态分布,且DOC对核模态粒子的氧化转化效率较高. 经过DOC后,在低转速下,不同粒径的颗粒物数浓度均有所降低;中、高转速下,DOC对粒径大于120 nm的颗粒物数浓度无明显降低作用. 相似文献
415.
416.
考察了5%H2/Ar还原再生丙烷催化还原NOx中硫中毒Cu-Ir/H-ZSM-5催化剂的工艺参数影响,采用N2吸附、X射线衍射、X射线光电子能谱和氢气程序升温还原等手段研究了催化剂再生行为的构效关系.结果表明,硫中毒Cu-Ir/H-ZSM-5催化剂由于CuSO4的生成导致催化剂活性位损失,比表面积、微孔面积和孔体积的减小.H2还原再生的最佳工艺参数为再生温度500℃和再生气体用量42.8L/g催化剂,再生催化剂的活性可恢复到新鲜催化剂的95%.在最佳再生条件(500℃和42.857L/g催化剂)下,再生催化剂表面CuSO4含量最低(0.4%),且再生催化剂的比表面积、微孔面积和孔体积较失活催化剂有较大提高. 相似文献
417.
《Process Safety and Environmental Protection》2014,92(6):822-827
A series of Pd–Ce supported ZSM-5 zeolite catalysts for CO oxidation at low temperature were prepared by co-impregnation method. The effect of Pd–Ce synergistic function, Ce loadings, and properties of ZSM-5 zeolite on low temperature CO catalytic oxidation was investigated in detailed. The results showed that the Pd and Ce loading on ZSM-5 zeolite support at the same time enhanced catalytic activity compared with only Pd or Ce loading on ZSM-5 zeolite support. The properties of ZSM-5 zeolite had a strong influence for CO oxidation. Through the research, the ZSM-5 zeolite with high silicon aluminum ratio and small size also was helpful for CO oxidation. Among these catalysts, the catalyst with 19 wt% Ce loading displayed the highest catalytic activity. Chemical and physical properties of catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and TEM showed that Pd species were highly dispersed on the surface of ZSM-5 zeolite, which was strongly dependent on the amounts of Ce loading and the interaction among Pd species, Ce promoter and ZSM-5 support. The addition of CeO2 improved the dispersion of Pd species over ZSM-5, and synergistic function of Pd and CeO2 enhanced the catalytic activity. XPS characterization indicated that as the addition of Ce increased, Pd species was easy to enrich on the surface of the catalyst. 相似文献
418.
《Process Safety and Environmental Protection》2014,92(5):442-446
A hybrid catalyst (CZ50) of cuprous oxide and zeolite was prepared and used in a catalytic system in which gaseous 1,2-dichloroethane (1,2-DCE) was degraded. The effects of relative humidity (15 and 65%) and wavelength of irradiation (ultraviolet, blue, green and red light) on the degradation of 1,2-DCE were studied. The experimental results reveal that the hybrid catalyst degraded the hazardous material under visible light. A comparison of the results obtained under ultraviolet and red irradiation at a relative humidity of 15% revealed almost equal degradation efficiencies of 83.8 and 82.2%, respectively. In the system with hybrid catalysts, a lower relative humidity favored 1,2-DCE degradation, indicating that relative humidity critically affects the degradation of hazardous materials. The most important result was that the intermediates of the degradation of 1,2-DCE included ethane, carbon dioxide, and formic acid yielded, which are mostly harmless and non-toxic materials. The experimental results indicated that the method could effectively be used to degrade hazardous materials to provide a healthy and safe environment for workers. 相似文献
419.
Hongbo Na Tianle Zhu Zhiming Liu Yifei Sun 《Frontiers of Environmental Science & Engineering》2014,8(5):659-665
The effect of Zr on the catalytic performance of Pd/y-A1203 for the methane combustion was investigated. The results show that the addition of Zr can improve the activity and stability of Pd/γ-Al2O3 catalyst, which, based on the catalyst characterization (N2 adsorption, XRD, CO- Chemisorption, XPS, CHa-TPR and O2-TPO), is ascribed to the interaction between Pd and Zr. The active phase of methane combustion over supported palladium catalyst is the Pd^0/Pd^2+ mixture. Zr addition inhibits Pd aggregation and enhances the redox properties of active phase Pd^0/ Pd^2+. H2 reduction could effectively reduce the oxidation degree of Pd species and regenerate the active sites (Pd^0/ pd^2+). 相似文献
420.
以共浸渍法制得的氧化铝负载铈锆固溶体为载体,并浸渍贵金属Pd得到了Pd/CZ/Al2O3催化剂.实验结果表明,该催化剂在老化前后都表现出良好的三效催化活性,新鲜样品Pd/CZ/Al2O3活性与Pd/CZ相当,老化后样品前者优于后者.结合XRD,BET,TPR等表征手段,讨论了Pd/CZ/Al2O3的催化活性特别是高温老化后活性与其组成结构之间的内在关系,揭示了其老化后仍具有较高活性的主要原因在于保持了Pd与CZ/Al2O3复合载体之间的强相互作用(SMSI). 相似文献