酸性金属氧化物对锰铈氧化物催化剂脱硝温度窗口的调控作用

利用溶胶-凝胶法,采用三种酸性金属氧化物（氧化铌、氧化钨和氧化钼）对锰铈复合氧化物催化剂进行了改性. 测试了催化剂的氮氧化物选择性催化还原（SCR）活性,以筛选对应不同温度窗口的合适酸性氧化物改性剂. 同时评价了催化剂的NO氧化和NH₃氧化活性. 利用X射线衍射、BET比表面积测试、H₂程序升温还原、NH₃/NO_x程序升温脱附和NH₃/NO_x吸附红外光谱等手段对催化剂进行了表征. MnO_x-CeO₂催化剂表现出良好的低温（100-150 ℃）活性. 酸性金属氧化物的添加削弱了催化剂的氧化还原特性,从而抑制了NH₃的活化和NO₂辅助的快速SCR反应. 与此同时,相对高温（250-350 ℃）区NH₃的氧化也受到了抑制,B酸和L酸上的NH₃吸附得以增强. 因此,催化剂的SCR脱硝温度窗口向高温移动,改性效果Nb₂O₅ < WO₃ < MoO₃.     

Ultra-Broadband Infrared Metamaterial Absorber for Passive Radiative Cooling

Infrared metamaterial absorber(MMA) based on metal-insulator-metal(MIM) configuration with flexible design,perfect and selective absorption,has attracted much attention recently for passive radiative cooling applications.To cool objects passively,broadband infrared absorption(i.e.8-14 μm) is desirable to emit thermal energy through atmosphere window.We present a novel MMA composed of multilayer MIM resonators periodically arranged on a PbTe/MgF_2 bilayer substrate.Verified by the rigorous coup led-wave analysis method,the proposed MMA shows a relative bandwidth of about 45%(from 8.3 to 13.1 μm with the absorption intensity over 0.8).The broadband absorption performs stably over a wide incident angle range(below 50°) and predicts 12 K cooling below ambient temperature at nighttime.Compared with the previous passive radiative coolers,our design gets rid of the continuous metal substrate and provides an almost ideal transparency window(close to 100%)for millimeter waves over 1 mm.The structure is expected to have potential applications in thermal control of integrated devices,where millimeter wave signal compatibility is also required.     

介质材料二次电子发射特性对微波击穿的影响

以介质填充的平行板放电结构为例,本文主要研究了介质填充后微波低气压放电和微放电的物理过程.为了探究介质材料特性对微波低气压放电和微放电阈值的影响,本文采用自主研发的二次电子发射特性测量装置,测量了7种常见介质材料的二次电子发射系数和二次电子能谱.依据二次电子发射过程中介质表面正带电的稳定条件,计算了介质材料稳态表面电位与二次电子发射系数以及能谱参数的关系.在放电结构中引入与表面电位相应的等效直流电场后,依据电子扩散模型和微放电中电子谐振条件,分别探讨了介质表面稳态表面电位的大小对微波低气压放电和微放电阈值的影响.结果表明,介质材料的二次电子发射系数以及能谱参数越大,介质材料的稳态表面电位也越大,对应的微波低气压放电和微放电阈值也越大.所得结论对于填充介质的选择有一定的理论指导价值.     

Efficient Removal of Metolachlor and Bacterial Community of Biofilm in Bioelectrochemical Reactors

Applied Biochemistry and Biotechnology - The microbial fuel cell (MFC) provides an inexhaustible electron acceptor to generate current and enhance the degradation of organic compounds. In MFCs with...     

加强实验教学环境内涵建设 提高环境育人质量

在实验室里的实验教学过程涉及到教书育人、管理育人、服务育人和环境育人。一个良好的实验环境不仅能够对学生起到潜移默化的教育作用,而且对教书育人、管理育人和服务育人工作的开展和实施也能起到推动和促进作用。本文主要介绍厦门大学化学国家级实验教学示范中心"以学生为中心",在强化实验教学环境内涵建设、提高实验环境育人质量方面的一些做法和体会,以期更好地为实验教学"思政"提供可复制、可推广的建设方案。     

富缺陷BN负载的高分散Cu催化乙醇脱氢制乙醛

生物乙醇作为平台分子通过催化转化的方法可以制备烯烃、乙醛、丁醇和芳香化学品等,其中乙醛是生产乙酸、季戊四醇、三氯乙醛、山梨酸等重要化学品的原料.随着乙醛的需求量逐年增加,发展以乙醇直接脱氢生成乙醛的工艺,具有联产氢气、原子经济性高、产物易分离的优点,符合国际绿色低碳发展战略要求,有望替代当前乙烯氧化法生产工艺.乙醇分子...     

“元素化学实验”中的“异常”现象(一)--Mn元素化学实验中的“异常”现象及其探析

大一学生在“元素化学实验”教学过程中,对反应条件如温度、催化剂、酸度、浓度或试剂用量等因素的影响考虑不周,可能出现某些实验现象和预想的或理论分析的结果不一致的“异常”现象。本文就学生在Mn元素化学实验过程中遇到的一些“异常”现象进行分析和总结,借助生动直观的演示实验,引导学生探究“异常”现象产生的可能原因和直观认识反应条件对反应结果的影响,培养学生的观察、分析、判断、归纳、推理和解决实际问题的能力。     

Highly oxidized graphene with enhanced fluorescence and its direct fluorescence visualization

We prepared hyper-oxidized graphene (HOG) as a form of graphene derivative by additional oxidation of graphene oxide (GO) sheets. HOG, which formed more functional groups and isolated conjugated clusters on the sheets, accordingly showed high solubility in water and alcohols, high transmittance and film transparence, longer fluorescence decay constant time, and enhanced fluorescence in states of solution and solid. By contrast, GO has much weaker fluorescence in solution and its fluorescence is totally quenched in solid. The influences of concentration, metallic ions, and pH on HOG fluorescence in aqueous solution were also investigated in detail. Due to HOG’s strong fluorescence, direct visualization was realized on substrates and in solution. In addition, direct 3D fluorescence visualizations of HOG phase in polymer composites were achieved. These results show the great potential of HOG in a broad range of applications, from biological labeling, probes, and drug carriers to high-performance composites and nanomanipulation.     

Effect of Calcination Temperature and Pretreatment with Reaction Gas on Properties of Co/γ‐Al2O3 Catalysts for Partial Oxidation of Methane

The effects of calcination temperature and feedstock pretreatment on the catalytic performance of Co/γ‐Al₂O₃ catalysts were studied for partial oxidation of methane (POM) to synthesis gas, with emphasis on the role of feedstock pretreatment. The physicochemical properties of the catalysts were characterized by N₂ adsorption, X‐ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature‐programmed reduction (H₂‐TPR), and Raman spectroscopy. The results showed that the pretreatment of the catalyst by reaction gas significantly improved the catalytic activity and stability for the POM reaction. On the other hand, the effect of calcination temperature was less significant. Although the initial activity was increased by an increased calcination temperature, the catalyst without the feedstock pretreatment suffered a rapid deactivation. The reaction‐atmosphere pretreatment was revealed as a process that mainly modified the surface structure of the catalyst. In that process, the formation of a CoAl₂O₄‐like compound led to high Co metal dispersion after reduction, and the transformation of the carrier into α‐Al₂O₃ occurred over the catalyst surface. Both the high dispersion of cobalt and the presence of α‐Al₂O₃ surface phase were assumed as the important factors resulting in an excellent catalytic performance in terms of high activity and high stability.