水溶性介质中CO2电催化还原研究进展

介绍了在水溶性介质中利用电化学催化的方法还原CO2的研究现状:电催化还原机理、电极材料催化剂的分类和选择;综述了温度、电流密度以及压力等对还原选择性和法拉第效率的影响;展望了CO2电催化还原方法的研究方向和应用前景。     

A cooperative effect between support and the heterogenised metalloporphyrins on electrocatalytic oxygen reduction

A new general method to heterogenise porphyrins and different metalloporphyrins (Co, Fe) on silica, mesoporous MCM-41 and delaminated zeolites ITQ-2 and ITQ-6 yields stable materials, which act as active catalysts for the electrochemical oxygen reduction, without catalyst desorption from the electrode.     

电催化还原CO2生成多种产物催化剂研究进展

电催化还原CO₂生成含碳产物技术,能有效解决CO₂过量导致的温室效应及能源短缺问题。但是,电催化还原CO₂会生成多种产物,因此,研究制备催化活性较好的高选择性催化剂是研究重点。本文简述了电催化还原CO₂的基本原理、不同还原产物的形成途径、活性中间体、速控步及活性催化剂,分析了电催化还原CO₂生成不同产物存在的问题。并且针对催化剂催化活性及催化反应过程中的这些问题,提出了提高催化剂催化活性的方法,总结了催化剂发展趋势,一般策略包括制造纳米结构材料、催化剂负载在高比表面积的载体上、杂原子掺杂、合金化、引入缺陷等,分析了这些方法通过改变电子传输等因素对催化剂活性及选择性的影响。     

煤焦异相还原N2O的反应机理

采用两种不同的简化煤焦模型,利用量子化学密度泛函理论研究了煤焦异相还原N₂O的反应机理。通过计算反应物、中间体以及过渡态的结构和能量明确了反应的过程,并通过热力学分析和动力学分析深入分析煤焦异相还原N₂O的反应机理。研究结果表明：单个碳原子无法体现N₂O分子在煤焦表面的吸附和脱附过程,不适于作为煤焦模型研究煤焦异相还原N₂O的反应,六环苯环簇碳基模型可以成功地研究煤焦异相还原N₂O的反应。煤焦异相还原N₂O的反应共经历三个过渡态和两个中间体将N₂O还原成N₂,N₂O分子在煤焦表面的吸附反应的活化能为51.01 kJ·mol^-1,煤焦表面吸附N₂O的过程容易进行。煤焦异相还原N₂O的反应在所研究的温度范围（298.15~1500 K）内为放热反应,可以自发发生,反应平衡常数大于10⁵,可以完全进行,认为是单向反应。煤焦异相还原N₂O的反应在所研究的温度范围（298.15~1500 K）内反应速率较快,反应活化能为43.55 kJ·mol^-1,Arrhenius表达式为1.24×10¹⁰exp（-5238.15/T）。     

恒流充放电过程中双电层电容器温度特性

温度特性是双电层电容器的重要特性之一,在电容器充放电过程中伴随着可逆热和不可逆热的产生。利用有限元技术对双电层电容器在恒流充放电循环过程中的内部及外部传热进行数值模拟。同时,对一个双电层电容器样品在循环过程中的内部及外部温度变化进行了测量。对数值模拟结果和实验数据进行对比,分析了恒流充放电循环过程中双电层电容器内部和外部的传热特性、温度分布及其发展变化,讨论了循环过程中电容器可逆热的变化规律及其影响因素,以及由可逆热引起的温度波动的变化。另外,实验数据表明,超级电容器在大电流充放电过程中需要进行冷却。     

A2N2双污泥系统反硝化除磷工艺的启动与稳定

采用低C/N比实际生活污水,以A₂N₂-SBR（厌氧/硝化/缺氧/硝化）双污泥系统为研究对象,重点考察了A₂N₂系统启动过程中的脱氮除磷特性。试验结果表明：采用在A²/O-SBR和N-SBR单元分别接种种泥,分开培养驯化聚磷菌污泥和硝化菌生物膜,并利用A²/O-SBR单元的出水作为N-SBR单元的进水,25 d好氧硝化菌生物膜挂膜成功,氨氮去除率稳定在93%以上;A²/O-SBR单元采用先厌氧/好氧（A/O）后厌氧/缺氧（A/A）的运行方式,43 d成功培养富集了反硝化聚磷菌（DPAOs）,DPAOs占PAOs的67.81%,反硝化除磷率在77.9%以上;启动成功后原水中约73%和13%的COD分别在A²/O-SBR单元的厌氧段和N-SBR单元曝气过程中被去除,系统出水COD、NH⁺₄-N、PO₄^3--P、TN浓度分别为40.6、0、0.4、13.5 mg·L^-1,达到国家《城镇污水处理厂污染物排放标准》（GB 18918-2002）一级A排放标准。     

NiCo2O4@quinone-rich N–C core–shell nanowires as composite electrode for electric double layer capacitor

The bind-free carbon cloth-supported electrodes hold the promises for high-performance electrochemical capacitors with high specific capacitance and good cyclic stability. Considering the close connection between their performance and the amount of carbon material loaded on the electrodes, in this work, NiCo₂O₄ nanowires were firstly grown on the substrate of active carbon cloth to provide the necessary surface area in the longitudinal direction. Then, the quinone-rich nitrogen-doped carbon shell structure was formed around NiCo₂O₄ nanowires, and the obtained composite was used as electrode for electric double layer capacitor. The results showed that the composite electrode displayed an area-specific capacitance of 1794 mF∙cm^–2 at the current density of 1 mA∙cm^–2. The assembled symmetric electric double layer capacitor achieved a high energy density of 6.55 mW∙h∙cm^–3 at a power density of 180 mW∙cm^–3. The assembled symmetric capacitor exhibited a capacitance retention of 88.96% after 10000 charge/discharge cycles at the current density of 20 mA∙cm^–2. These results indicated the potentials in the preparation of the carbon electrode materials with high energy density and good cycling stability.     

Carbon dioxide reduction mechanism via single-atom nickel supported on graphitic carbon nitride

In many photocatalytic reaction paths, the breaking of the first C O bond in a CO₂ molecule is often the key step that becomes the rate-controlled reaction step. In this paper, a graphitic carbon nitride (g-C₃N₄) supported nickel single-atom catalyst (Ni@g-C₃N₄) was successfully constructed, and the mechanism of CO₂ catalytic reduction was systematically studied based on density functional theory (DFT). The introduction of nickel promotes the adsorption of small molecules, especially for the CO₂ activation. According to density of states (DOS) and frontier orbital analysis, the photogenerated carriers tend to jump from nitrogen atoms to carbon atoms, forming an electron transfer in real space, after g-C₃N₄ is excited by light. With the appearance of nickel-doped levels, the DOS of Ni@g-C₃N₄ is no longer symmetric with respect to the spin up and down, especially around the original band gap of g-C₃N₄. Single-atom nickel has abundant frontier orbitals and high activity and is a favourable place for chemical reactions. The presence of surface hydrogen can promote the recovery of CO₂, and the energy barrier of Ni@g-C₃N₄ with hydrogen is only 15% of the clean g-C₃N₄ surface. This paper provides a new idea for the development of efficient single-atom catalysts for CO₂ reduction.     

Catalytic reduction of N2O with CH4 and C3H6 over Ag–Rh/Al2O3 bimetallic catalyst in the presence of oxygen

A study of nitrous oxide (N₂O) reduction with methane (CH₄) and propene (C₃H₆) in the presence of oxygen (5%) over Ag/Al₂O₃, Rh/Al₂O₃ and Ag–Rh/Al₂O₃ catalysts, with Ag and Rh loadings of 5 wt% and 0.05 wt% respectively, has been performed. From the results, it was observed that the Ag–Rh bimetallic catalyst was the most active for both nitrous oxide removal (more than 95%) and hydrocarbon oxidation. This high activity seems to be connected with a synergistic effect between Ag and Rh. The findings from X‐ray diffraction and X‐ray photoelectron spectroscopy studies showed also, that there were no strong interactions (eg alloying) between Ag and Rh. Copyright © 2005 Society of Chemical Industry     

The capacitance of the diffuse layer of electric double layer of electrodes in molten salts

Similarly to aqueous electrolytes, the electric double layer of electrodes in molten salts is assumed to be composed of compact and diffuse layers. The charge density of the compact layer, formed as a monolayer of specifically adsorbed anions (primary ionic shell), is calculated as the difference between the charge of the primary ionic shell and the charge removed by the exchange current density. The centre of the specifically adsorbed anions create the inner Helmholtz plane (iHp). The counterions to the specifically adsorbed anions in the primary ionic shell, take place in the numerous neighbouring holes, introduced into the molten salt structure by the melting process, and being subjected to thermal motion, create the diffuse layer. The electrostatically adsorbed metal cations form the outer Helmholtz plane (oHp) with the value of the inner potential equal φ₂. Using the Boltzman and Poissone equations, the equation for the capacitance of the diffuse layer of the metallic electrode in molten salt is derived and tested on some literature experimental results.     

Numerical simulation of probing the electric double layer by scanning electrochemical potential microscopy

Computational modeling of probing the electric double layer (EDL) by scanning electrochemical potential microscopy (SECPM) was carried out in order to evaluate the applicability of this method. The modeling is based on a continuum approach for the electric double layer in dilute solution using the modified Poisson-Boltzmann equation. This model takes into account the finite ion size and prevents steric effects near the charged surface. The approach of the SECPM probe towards a charged electrode, immersed in electrolyte solution, is simulated obtaining the potential profile in the direction normal to the electrode. The effects of the shape and the size of the metallic protrusion at the apex of the probe were studied. A clear dependence of the probe potential on the apex geometry was observed, and correlated to the apex surface charge density distribution. The overlap of the EDLs located at the probe and the electrode is studied by setting different initial open circuit potentials, i.e., different charging, to the probe. We have found that the obtained potential profiles are consequences of the EDL overlap, characterized by an ionic distribution in the gap separating the probe and electrode. Depending on the strength of both EDLs and their polarity, the Debye screening effect severely influences the probe potential.     

A_2N工艺的固有弊端分析及其对策研究

基于反硝化除磷理论开发的A2N双污泥工艺已经成为国内外污水生物处理领域的研究重点,介绍了A2N双污泥反硝化除磷工艺的原理及其发展,深入分析了该工艺的固有弊端,综述了国内外学者针对A2N工艺的弊端所提出的对策和改进工艺,并对其进行评价,指出了当前研究中存在的主要问题,提出了今后的研究方向。     

A study on the characteristics of the SO2 reduction using coal gas over SnO2-ZrO2 catalysts

SO₂, which is an air pollutant causing acid rain and smog, can be converted into elemental sulfur in direct sulfur recovery process (DSRP). SO₂ reduction was performed over catalyst in DSRP. In this study, SnO₂-ZrO₂ catalysts were prepared by a co-precipitation method, and CO and coal gas, which contains H₂, CO, CO₂ and H₂O, were used as reductants. The reactivity profile of the SO₂ reduction over the catalysts was investigated at the various reaction conditions as follows: reaction temperature of 300–550 °C, space velocity of 5000–30,000 cm³/g_-cat. h, [reductant]/[SO₂] molar ratio of 1.0–4.0 and Sn/Zr molar ratio of SnO₂-ZrO₂ catalysts 0/1, 2/8, 3/5, 5/5, 2/1, 3/1, 4/1 and 1/0. SnO₂-ZrO₂ (Sn/Zr = 2/1) catalyst showed the best performance for the SO₂ reduction in DSRP on the basis of our experimental results. The optimized reaction temperature and space velocity were 325 °C and 10,000 cm³/g_-cat. h, respectively. The optimal molar ratio of [reductant]/[SO₂] varied with the reductants, that is, 2.0 for CO and 2.5 for coal gas. SO₂ conversion of 98% and sulfur yield of 78% were achieved with the coal gas.     

Optimization of the N2 generation selectivity in aqueous nitrate reduction using internal circulation micro-electrolysis

The reduction of nitrate using internal circulation micro-electrolysis technology (ICE) was investigated. The effect of the reaction time, initial pH, Fe/C ratio, and aeration rate on the nitrate reduction was investigated using a single factor experiment. Based on the results of the single factor experiment, a response surface methodology (RSM) was applied to optimize the N₂ generation selectivity. The effects and interactions of three independent variables were estimated using a Box-Behnken design. Using the RSM analysis, a quadratic polynomial model with optimal conditions at pH=8.8, Fe/C=1:1, and an aeration rate of 30 L·min^-1 was developed by means of the regression analysis of the experimental data. Using the RSM optimization, the optimal conditions yielded a N₂ generation selectivity of 72.0%, which is in good agreement with experimental result (73.2%±0.5%) and falls within the 95% confidence interval (IC:66.8%-77.3%) of the model results. This indicates that the model obtained in this study effectively predicts the N₂ generation selectivity for nitrate reduction by the ICE process, thus providing a theoretical basis for process design.     

Cobalt(II) porphyrin complex immobilized on the binary oxide SiO2/Sb2O3: electrochemical properties and dissolved oxygen reduction study

In this work, SiO₂/Sb₂O₃ prepared by the sol-gel processing method, having a specific surface area, S_BET, of 790 m² g⁻¹, an average pore diameter of 1.9 nm and 4.7 wt.% of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μ mol g⁻¹. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid-solution interface, occurred at −0.25 V versus SCE in 1.0 mol l⁻¹ KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation-reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O₂ concentrations, between 1.0 and 12.8 mg l⁻¹, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples.     

粒子电极制备条件对三维电催化处理嘧啶醇的影响

以陶土为基体、金属氧化物为活性组分,采用固相焙烧制备了一系列的粒子电极,并以三维电催化氧化降解2-二乙胺基-6-甲基-4-羟基嘧啶模拟废水实验考察了各粒子电极的催化活性及稳定性。结果表明：氧化铜与氧化锌的配比分别为0.25 mol和0.1 mol每千克陶土,1000 ℃下焙烧2 h制备的粒子电极催化活性最高,在槽电压15 V,初始pH值为3、极板间距6 cm、支持电解质30 g/L,曝气40 L/h,处理150 min后,2-二乙胺基-6-甲基-4-羟基嘧啶和COD的去除率可分别达到83.45%和35.17%,且催化性能稳定。对降解机理的研究表明,2-二乙胺基-6-甲基-4-羟基嘧啶的主要降解反应为嘧啶环开环转化成小分子含氮化合物,而嘧啶开环后产物的矿化速度相对较慢。     

NH4Cl辅助热解制备镍-氮-碳纳米管催化剂及其电还原CO2性能

二氧化碳（CO₂）的资源化利用是实现“碳达峰,碳中和”的重要手段。在众多CO₂转化技术当中,电催化CO₂还原反应因反应条件温和、工艺过程简单等优点,被认为是极具应用前景的减碳技术之一,其关键在于高效、高稳定性电催化剂的开发。过渡金属-氮-碳（M-N-C）材料是电还原CO₂生成CO的有效催化剂,针对其高温热解制备过程中活性金属原子容易聚集且氮原子流失严重,进而使得活性位密度降低,催化性能下降等问题,本文提出以双氰胺（DCDA）为碳源和氮源,以乙酰丙酮镍（Ni（acac）₂）为金属源,以氯化铵（NH₄Cl）为第二氮源和造孔剂,采用简单的NH₄Cl辅助热解-酸刻蚀的方法制备得到镍-氮-碳纳米管（Ni-N-CNTs）电还原CO₂催化剂,并详细考察NH₄Cl添加量对催化剂结构和催化性能的影响。表征结果表明：NH₄Cl的加入有利于催化剂纳米管状形貌和多级孔结构的生成,同时有利于催化剂中Ni-Nx （1.6%,摩尔分数）和pyridinic-N （1.75%,摩尔分数）物种含量的增加。一系列性能测试结果表明：催化剂的活性中心为Ni-Nx,同时pyridinic-N的存在也有利于催化性能的提高,当前体中NH₄Cl加入量与氮源和金属源总质量比为1∶1时,所得Ni-N-CNTs-1催化剂催化性能最好,在电压为-0.65 V （vs RHE）时,CO法拉第效率最高达92%,此时CO部分电流密度为8 mA·cm^-2。此外,该催化剂还表现出良好的催化稳定性,连续恒电位电解12 h,催化性能基本不变。该催化剂制备工艺简单,制备条件可控,研究结果可为高效M-N-C电还原CO₂催化剂的设计和制备提供一种切实有效的研究思路和方法。     

Shell气化炉以CO_2代替N_2作为粉煤输送气的研究

介绍了Shell粉煤加压气化工艺中CO_2替代N_2作为煤粉输送气的工艺流程及项目实施情况,并对掺入CO_2后的合成气组成及尾气排放量,粗甲醇产量等指标进行了对比。掺入CO_2后,减少了甲醇生产装置中N_2含量,提高了甲醇产量,开辟了副产CO_2应用的新途径。     

TiO2基催化剂还原CO2研究进展

能源危机和环境污染是当今世界发展面临的两大挑战,如何有效缓解煤、石油等不可再生化石资源过度消耗所引发的能源危机,以及由此造成CO₂过量排放引起的温室效应问题,是当前人类发展亟待解决的重大科学问题之一。基于此,本文综述了近年来以TiO₂为光催化剂,以绿色、清洁的太阳光能催化还原CO₂成低价态含碳燃料(如CH₄、CH₃OH、HCHO、HCOOH、C₂H₅OH等)研究进展。在TiO₂光还原CO₂机理基础上,对元素掺杂、半导体复合与染料敏化、高活性晶面调控、低维纳米结构设计、助催化剂、Z型结构设计和单原子催化等方法来提高光还原CO₂反应效率和选择性进行分析,并指出目前研究存在的关键问题和未来CO₂光还原的发展方向。     

CO2和N2吸附的研究札记

Experiments were made for the adsorption of CO2 and N2 on typical adsorbents to investigate the effects of porous structure and surface affinity of adsorbents as well as those of adsorption temperature and pressure that might cause the variation of adsorption mechanism. It is shown that polar surface tends to enlarge the adsorption difference between CO2 and N2, and the difference is more sensitive to temperature than the adsorbents with non-polar surface. The adsorbents with non-polar surface are not much sensitive to the effect of water vapor, though the water vapor interferes the separation remarkably. The separation coefficient linearly increases with the micropore volume per unit surface area of activated carbons, but no rule is shown on mesoporous silicon materials. The function of adsorption mechanism on the separation is not as much as expected.