甲烷在氧化铁表面还原NO的特性与反应机理研究

在程序控温电加热水平陶瓷管反应器中,在300~1 050 ℃,对N₂气氛中甲烷在氧化铁(充分氧化后的铁丝网卷)表面还原NO的特性进行了实验研究,测试了NO脱除效率、CO生成量以及反应后铁样品表面组分和微观状态的变化特点,分析了甲烷在氧化铁表面还原NO的反应机理。在此基础上,在1 000 ℃时,对模拟烟气条件下甲烷在氧化铁表面还原NO的持久性进行了实验研究。结果表明,甲烷在氧化铁表面能够高效地还原NO。在N₂气氛下,在850 ℃以上达到100%的NO脱除效率。在模拟烟气中,甲烷在氧化铁表面脱除NO的能力具有很好的持久性。实验结果表明,在1 000 ℃时,采用由体积分数为2.0%的O₂、16.8%的 CO₂和524×10^-6的 NO,N₂配平的模拟烟气,1.17% CH₄能够在连续100 h内保持100%的NO脱除效率,而未出现下降的趋势。对反应机理的研究结果表明,甲烷在氧化铁表面还原NO的机理包括甲烷通过再燃机理还原NO以及甲烷通过在氧化铁表面还原氧化铁为金属铁、金属铁进而直接还原NO两种主要反应机理。其中,后者为主要反应机理。     

Thermokinetic studies for reactions of lanthanum(III) and nickel(III) oxides with barium perchlorate trihydrate

TG, DTG and DTA have been used in non-isothermal investigations of binary systems of Ni₂O₃ and La₂O₃ with barium perchlorate trihydrate, BP·3 H₂O, in various molar ratios, carried out under an air (static) atmosphere from ambient to 1000°C. Ni₂O₃ catalysed the dehydration process of BP·3 H₂O and lowered its T_f by 20°C. The discontinuity on the TG curve due to an incomplete perchlorate—chlorate reaction vanished in the presence of either of the oxides: a mechanism is proposed. La₂O₃ lowered T_f by 50°C; T_i for the decomposition of BP was lowered by 150 and 100°C in the presence of La₂O₃ and Ni₂O₃, respectively. X-Ray diffractometry did not reveal any reaction between BP and the two oxides. Kinetic parameters for the decomposition steps in the presence of either of the oxides have been determined.     

SO_2对甲烷在金属铁表面还原NO的反应影响

采用卧式程序控温电加热陶瓷管反应器,在N2和模拟烟气气氛中、300~1 100℃下,研究了SO2对甲烷在金属铁及其氧化物表面还原NO反应的影响。采用XRD等手段对反应前后铁催化剂样品的组成变化进行了表征,分析了SO2在甲烷-铁脱硝反应中的作用机理。结果表明,甲烷在金属铁及氧化铁表面能够高效率地还原NO,NO还原效率不受烟气中SO2的影响。在SO2体积分数为0.01%~0.04%的N2气氛中,温度高于700℃时,金属铁上NO还原率和SO2脱除率可同时达到100%。在SO2体积分数为0.01%~0.04%的模拟烟气中,当温度高于850℃时,NO还原效率达到90%以上;温度为950℃时,NO还原效率达到98%,SO2对NO还原效率的影响可忽略。当反应温度为1 000℃时,在含0.02%SO2的模拟烟气中,甲烷的体积分数为1.13%时,持续100 h金属铁表面上的NO还原效率都能保持95%以上。     

CO2气氛对胜利褐煤热解过程的影响

以5-8 mm胜利褐煤为研究对象,利用固定床反应器,在400-700℃、CO₂气氛下进行热解实验,研究了CO₂气氛对煤热解气、液、固三相产物分布的影响,探讨了CO₂对煤焦结构作用的机理。研究表明,与N₂气氛相比,CO₂气氛热解提高焦油和热解水产率,降低热解气和半焦产率;400和500℃时,CO₂气氛下形成的半焦孔隙结构和总孔体积没有明显的变化,600和700℃时,CO₂气氛下所得半焦的比表面积及孔容较N₂气氛下的大,是与煤焦内部挥发分大量释放以及CO₂进入孔道与活性位反应有关;煤热解过程中CO₂的引入能促进煤焦中3-5环芳香结构的消耗,导致煤焦结构芳香度的提高;600和700℃时,CO₂气氛下热解气中H₂和CH₄产率低,同时CO₂能与煤焦发生气化反应显著提高CO含量。     

Reversible photobluing of CdSe/ZnS/TOPO nanocrystals

Photobrightening and photobluing effects of photoluminescence (PL) from CdSe/ZnS/TOPO nanocrystal ensembles, i.e. ca. 1000 nanocrystals, have been investigated in several environments. The PL intensity increases more than twice with blue shift under continuous light irradiation in a wet nitrogen (H₂O/N₂) atmosphere, while in a pure nitrogen atmosphere and vacuum their behaviors are nothing particular. In addition, increasing rates of both the brightening and bluing effects in the H₂O/N₂ atmosphere depend on irradiation intensities. These results suggest that both effects should be associated with photo-adsorption of water molecules onto nanocrystal surfaces. As for the brightening effect, we propose that the photo-adsorption of water molecules provides some restoring functions to PL-quenching defects or trap-sites on or near nanocrystal surfaces. On the other hand, the origin of the bluing effect is not clear from the results of the ensemble measurements. To get further insight into the bluing effect, PL spectra from single nanocrystals are measured under continuous light irradiation in cyclic environments in which the H₂O/N₂ atmosphere and vacuum are alternating. As a result, blue-shifted PL induced by the light irradiation in the H₂O/N₂ atmosphere recovers almost to its initial one reversibly under evacuation. The mechanism of the photobluing effect will be discussed also on the bases of the photobrightening model introduced above.     

MnO_X-C@SiO_2核壳微球的制备及催化性能

为了制备高性能的Fenton反应催化剂以降解水中污染物,采用SiO_2包覆聚丙烯酸-二氧化锰复合胶团(PAA-Mn@SiO_2)然后碳化的方法,制备了以氧化锰-碳复合物为核,SiO_2为壳的核壳型纳米催化剂(MnO_X-C@SiO_2),该方法简单易行。通过X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、比表面积等测试手段对产物进行了分析。结果表明,MnO_X-C@SiO_2中形成了对Fenton反应具有高催化活性的低价氧化锰(Mn_3O_4和MnO)。此外,SiO_2壳层能有效防止氧化锰在碳化过程中长大并阻止产物聚集,其内部的碳组分还能进一步稳定氧化锰纳米粒子并促进有机污染物的富集。MnO_X-C@SiO_2的比表面积为317.3 m~2/g,在水中具有良好的分散性,在Fenton反应催化降解亚甲基蓝(MB)溶液的过程中,仅经过40 min,降解率就可达到96.8%。     

Oxidative decarboxylation of levulinic acid by cupric oxides

In this paper, cupric oxides was found to effectively oxidize levulinic acid (LA) and lead to the decarboxylation of levulinic acid to 2-butanone. The effects of cupric oxide dosage, reaction time and initial pH value were investigated in batch experiments and a plausible mechanism was proposed. The results showed that LA decarboxylation over cupric oxides at around 300 °C under acidic conditions produced the highest yield of butanone (67.5%). In order to elucidate the catalytic activity of cupric oxides, XRD, AFM, XPS and H(2)-TPR techniques was applied to examine their molecular surfaces and their effects on the reaction process.     

甲烷在金属铁及氧化铁表面还原NO的研究

在程序控温电加热水平陶瓷管反应器、N₂气氛和模拟烟气气氛及300~1 100℃时,对甲烷在金属铁及其氧化铁表面还原NO的特性进行了实验研究。为使甲烷在脱硝反应后完全燃尽以及脱硝反应过程生成的CO等中间产物完全燃尽,在第一段加热炉后串联了第二段加热炉,补充氧气,实现燃尽。结果表明,甲烷在金属铁及氧化铁表面能够高效地还原NO。在N₂气氛中,在900℃以上温度范围内甲烷在金属铁表面的脱硝效率超过95%,与甲烷在氧化铁表面的脱硝效率差别很小。在模拟烟气条件下,当过量空气系数小于1.0时,在900℃以上时,甲烷在金属铁和氧化铁表面的脱硝效率都能超过90%,且未燃尽和燃尽两种条件下NO的还原率相差不大。NO同时通过金属铁的直接还原和甲烷的再燃还原两种反应机理脱除。而甲烷则通过还原氧化铁为金属铁,从而使金属铁直接还原NO可持续进行。同时,甲烷再燃反应的中间产物HCN/NH₃等被氧化铁还原,从而使燃尽后的脱硝效率不下降。研究结果表明,甲烷和金属铁或氧化铁在富燃料条件下可有效地还原NO。     

Thermal oxidation of oxynitride perovskites in different atmospheres

Oxynitride perovskites with bright and variable colour have the potential to be employed as non-toxic pigments, and to substitute colourants that contain harmful heavy metals. For this application it is extremely important to have a precise knowledge about the materials stability. The thermal stability of oxynitride perovskites in different atmospheres was measured by thermogravimetry in combination with mass spectroscopy (MS). The studied compounds, namely LaTiO₂N, SrNbO₂N and SrTaO₂N, were heated up to 1200 °C in argon–oxygen mixtures with varying oxygen contents. It was found that the thermal behaviour of the studied oxynitrides changes drastically with the oxygen concentration. When heated up in pure argon the oxynitrides transform to oxides containing transition metals of lower oxidation state and/or binary nitrides. For oxygen contents between 0.5% and 20% the samples were completely oxidised. The oxidation rate increases with oxygen content. MS analysis of the gaseous products (including N₂, NO and NO₂) reveals a complex reaction mechanism, which is strongly modified by the composition of the atmosphere.     

CO气氛下褐煤加压快速热解过程中CH_4的逸出规律

在管式反应器上进行了霍林河褐煤加压快速热解实验,研究了CO气氛下CH4逸出规律。在加压快速热解条件下,由于CO解离态吸附的O(a)吸附在煤上,提供了活性中心,电负性强的O(a)诱发其周围其他原子的电子云向O(a)偏移,减弱了原来化学键的强度,导致芳香环的开裂,侧链、醚键和脂肪链的断裂提供更多的自由基,稳定煤热解生成的碎片,促进了CH4的生成和逸出。因此,CO气氛下CH4产率较N2气氛下的高,在900℃、1.0 MPa时,50%CO气氛下的CH4产率较N2气氛下的提高了12.5%,并且CH4产率随着温度升高、压力的增大而增大。     

基于金属氧化物材料的二氧化碳电催化还原

The CO₂ level in the atmosphere has been increasing since the industrial revolution owing to anthropogenic activities. The increased CO₂ level has led to global warming and also has detrimental effects on human beings. Reducing the CO₂ level in the atmosphere is urgent for balancing the carbon cycle. In this regard, reduction in CO₂ emission and CO₂ storage and usage are the main strategies. Among these, CO₂ usage has been extensively explored, because it can reduce the CO₂ level and simultaneously provide opportunities for the development in catalysts and industries to convert CO₂ as a carbon source for preparing valuable products. However, transformation of CO₂ to other chemicals is challenging owing to its thermodynamic and kinetic stabilities. Among the CO₂ utilization techniques, electrochemical CO₂ reduction (ECR) is a promising alternative because it is generally conducted under ambient conditions, and water is used as the economical hydrogen source. Moreover, ECR offers a potential route to store electrical energy from renewable sources in the form of chemical energy, through generation of CO₂ reduction products. To improve the energy efficiency and viability of ECR, it is important to decrease the operational overpotential and maintain large current densities and high product selectivities; the development of efficient electrocatalysts is a critical aspect in this regard. To date, many kinds of materials have been designed and studied for application in ECR. Among these materials, metal oxide-based materials exhibit excellent performance as electrocatalysts for ECR and are attracting increasing attention in recent years. Investigation of the mechanism of reactions that involve metallic electrocatalysts has revealed the function of trace amount of oxidized metal species—it has been suggested that the presence of metal oxides and metal-oxygen bonds facilitates the activation of CO₂ and the subsequent formation and stabilization of the reaction intermediates, thereby resulting in high efficiency and selectivity of the ECR. Although the stability of metal oxides is a concern as they are prone to reduction under a cathodic potential, the catalytic performance of metal oxide-based catalysts can be maintained through careful designing of the morphology and structure of the materials. In addition, introducing other metal species to metal oxides and fabricating composites of metal oxides and other materials are effective strategies to achieve enhanced performance in ECR. In this review, we summarize the recent progress in the use of metal oxide-based materials as electrocatalysts and their application in ECR. The critical role, stability, and structure-performance relationship of the metal oxide-based materials for ECR are highlighted in the discussion. In the final part, we propose the future prospects for the development of metal oxide-based electrocatalysts for ECR.     

Thermal decomposition of ammonium vanadyl oxalate supported on various oxides

The thermal decomposition of ammonium vanadyl oxalate supported on La₂O₃, MgO, SiO₂, Al₂O₃, ZrO₂, TiO₂, SAPO-5, and ZSM-5 oxides in a dynamic atmosphere of dry air was compared by thermal gravimetric analysis (TG) and differential thermal analysis (DTA). The calcined catalysts were characterized by X-ray diffractometry (XRD). The TG and DTA results demonstrate that the surface acid-base properties of the oxides play a significant role in the decomposition behaviour of the supported ammonium vanadyl oxalate, i.e. the basic oxides exhibit an endothermic effect and the acidic oxides show an exothermic effect. Two mechanisms are suggested for thermal decomposition of ammonium vanadyl oxalate on basic and acidic oxides, respectively. After transformation of the ammonium vanadyl oxalate to vanadia, subsequent rearrangement of the vanadia on the surface of the supports was also observed. During the thermal treatment or calcination in air, solid state reactions of vanadia with the surface of oxides such as La₂O₃, ZrO₂ and TiO₂ took place to form new phases.     

薄膜CdSe及CdSexTe1-x电极的光电子能谱研究

用X射线光电子能谱(XPS)研究了不同含氧气氛中烧结的薄膜CdSe及Cdse_xTe_1-x电极表面,以及薄膜与Ti底基之间的界面。研究中发现,二种薄膜电极的表面形成了CdO,SeO₂及TeO₂氧化物,与薄膜接触的Ti底基表面上形成了TiO₂。用俄歇电子能谱(AES)对在电极表面及Ti表面所生成的氧化层分别进行了深度分析。结果表明,各种氧化物形成的程度有很大的不同,氧化层厚度也存在差异。对影响薄膜电极的光电性能的因素进行了讨论。     

矿物质氧化物对燃煤烟气中砷/铅的吸附特性研究

选取典型的矿物质氧化物为吸附剂，在两段式固定床反应器中研究了模拟烟气气氛下吸附剂吸附As₂O₃、PbO的特性，吸附反应的原子态密度、吸附位、吸附能等通过密度泛函理论（DFT）计算获得。结果表明，CaO的砷吸附容量最大，900 ℃吸附砷容量为5.25 mg/g；其次是Fe₂O₃、MgO、Al₂O₃，吸附的砷以As³⁺和As⁵⁺的砷酸盐形式存在，高岭土和飞灰具有较大的PbO吸附容量，最大吸附容量分别为6.69和2.75 mg/g；其次是SiO₂和Al₂O₃，并且50%SiO₂/50%Al₂O₃ 混合吸附剂的铅吸附容量高于单一氧化物，吸附剂表面O原子是As₂O₃的吸附活性位点，吸附剂暴露的不饱和Si和Al原子是PbO的吸附活性位点，此外温度、烟气气氛对吸附容量和吸附产物有显著影响。     

Facile-fabricated iron oxide nanorods as a catalyst for hydrogenation of nitrobenzene

Iron oxide nanorod catalysts were fabricated by wet chemistry method followed annealing. The facilefabricated FeOOH nanorods with an efficient catalytic performance for transfer hydrogenation of nitrobenzene with hydrazine hydrate are presented.     

TiO2/clay as a heterogeneous catalyst in photocatalytic/photochemical oxidation of anionic reactive blue 19

A TiO₂-coated Tunisian clay (TiO₂–clay) was synthesized by a typical impregnation method. The physicochemical characterization points to a successful impregnation of titania on the clay surface. The activity of this structured catalyst was studied in the photocatalytic/photochemical oxidation of anionic reactive blue 19 (RB 19). The effect of UVA and solar irradiation (UV-solar) was studied at room temperature. TiO₂–clay demonstrated an effective degradation of RB 19 under both types of irradiation. Moreover, in this study, the effects of various oxidants such as hydrogen peroxide (H₂O₂), potassium peroxodisulfate (K₂S₂O₈) and sodium carbonate (Na₂CO₃) were thoroughly investigated. H₂O₂ was a promising oxidant for promoting RB 19 degradation under UV_A. The kinetics of discoloration of RB 19 followed a pseudo-first-order rate law. We can remark that 20 min of UV irradiation was enough to achieve 100% discoloration of the aqueous solution. However, under UV–Vis, HPLC and chemical oxygen demand measurements indicated, that a longer reaction time (of around 45 min) was required for achieving the complete dye mineralization. The findings clearly demonstrated the applicability of this TiO₂/clay catalyst for the photocatalytic oxidation of RB 19.     

Unusual photoreactivity of zinc oxide irradiated by concentrated sunlight

The decrease of fluorescence emission of phenol was studied in the presence of photoactive oxides (TiO₂, ZnO and Fe₂O₃) irradiated with a sodium lamp, direct sunlight (1 sun) and concentrated sunlight (40–50 suns) in aqueous solutions. As expected photodegradation of phenol was seen to be faster for all of the oxides irradiated by concentrated sunlight. The photodegradation capacity of titanium dioxide (TiO₂) is superior to that of zinc oxide (ZnO) and ferric oxide (Fe₂O₃) under a sodium lamp and direct sunlight, but ZnO is found to be as reactive as TiO₂ under concentrated sunlight. It has been shown that ZnO is a low cost alternative solar photocatalyst to TiO₂ for degradation of organics in aqueous solutions.     

A new experimental technique for validating exchange models of carbon dioxide between the atmosphere and sea-water

The mechanism of CO₂-exchange between the atmosphere and sea-water was re-examined by simultaneously measuring pH and pO₂ in artificial sea-water exposed to CO₂ and air atmospheres. The data were fitted to an exchange model by using both the differential and integral forms of the diffusion equation. It was found that the pH and pO₂ data support the assumption that the exchange for these gases is driven by the gradient of the partial pressure of the gas across the imaginary solution-gas boundary layer (the z layer) and is not affected by chemical reaction or hydration rate under the experimental conditions used, viz. 1–100 meq/l., alkalinity, pH 4.5–8.3 and z-layer thickness 2–500 μm. It is concluded that the rate of hydration of CO₂ plays an insignificant role in the exchange mechanisms between the atmosphere and the oceans.     

流化床O2/CO2气氛下添加石灰石对燃煤PM2.5的控制

采用小型流化床研究了在O₂/CO₂气氛下添加石灰石对PM_2.5(空气动力学直径小于2.5 μm的颗粒物)的控制.实验采用荷电低压撞击器(ELPI)采集和分析燃烧后的PM_2.5.结果表明,添加石灰石是燃烧过程中影响PM_2.5生成的重要因素.添加石灰石后,生成PM_1.0的数量浓度均降低,而PM_1.0~2.5的数量浓度均略有增加;PM_2.5质量粒径分布均呈双峰分布,峰值分别出现在0.2和2.0 μm左右.随着Ca/S物质的量比的增加,PM_2.5中Si、Na、K、S和Cu的含量呈减少的趋势;随着颗粒粒径的减小,S、Cu、K和Na的含量有增大的趋势,而Si的含量有减少的趋势.     

First detection of the Cs symmetric isomer of carbon hexaoxide (CO6) at 10 K

Carbon oxides of the form CO_n (n = 2–8) have long been known as important molecules in atmospheric and solid state chemical reactions. Here, we report on the first infrared spectroscopic detection of the cyclic (C_s) isomer of carbon hexaoxide (¹²C¹⁶O₆) via its ν₁ vibrational mode centered around 1876 cm⁻¹ under matrix isolation conditions; the identification of the ¹²C¹⁸O₆, ¹³C¹⁶O₆, and ¹³C¹⁸O₆, isotopologues supported by ab initio calculations confirm the assignments. We also discuss possible formation routes of this molecule.