Au／ZnO，Pd／ZnO和Au-Pd／ZnO催化剂甲醇部分氧化制氢性能的研究

采用PVP保护乙醇还原法制备Au/ZnO,Pd/ZnO和Au-Pd/ZnO催化剂,研究了Au,Pd和Au-Pd负载ZnO催化荆对甲醇部分氧化制氢性能的影响,并运用XRD,TPR和TPD等手段对催化剂进行了表征.结果表明,与Au/ZnO和Pd/ZnO催化剂相比,Au-Pd/ZnO双金属催化剂显示出较高的催化活性和氢气选择性、较低的CO选择性以及较好的稳定性.表征结果表明,Pd的加入抑制了Au粒子的烧结,使Au粒子变小,生成了富Au型Aux,Pdy合金,且Au-Pd与载体之间发生了一定的协同作用,从而提高了催化刺的活性和稳定性.     

Mn/W催化剂上甲烷氧化偶联反应机理的Monte Carlo模拟

通过对Mn-Na2WO4/SiO2催化剂的甲烷氧化偶联反应机理进行初步研究,以Mn/W双金属活性中心为基础,分析了CH4和O2共进料氧化偶联制C2烃的反应模型,并采用Monte Carlo方法对该反应的微观过程进行模拟,在与实验相近的条件下,得到了较准确的模拟结果.在模拟实验中,考察了活性位规模和原料气组成对反应结果的影响以及反应过程中表面吸附物种的变化规律.结果表明:活性位规模增大将减缓表面反应的速度,而不同进料烷氧比将对甲烷转化率以及C2烃收率产生影响;同时在对表面吸附物种的考察中发现,反应末期催化剂催化活性不高与晶格氧的补充不足有关,而C2H6和C2H4的反应更多地发生在气相主体.     

Ni/M_xO_y/CeO_2-ZrO_2(M=Cu,Ba,Al)复合催化剂的制备及其甲烷部分氧化性能

首先采用柠檬酸络法制备了系列Mx Oy/CeO2-ZrO2(M=Cu,Ba和Al)固溶体载体,然后浸渍活性组分Ni,制得系列Ni/Mx Oy/CeO2-ZrO2复合催化剂。考察了掺杂助剂元素(Cu,Ba和Al)对CeO2-ZrO2固溶体结构和负载Ni催化剂的甲烷部分氧化生成合成气催化性能的影响。采用氮气物理吸附,X射线粉末衍射(XRD),氢-程序升温还原(H2-TPR),扫描电子显微镜(SEM),氨-程序升温脱附(NH3-TPD)和热重(TG)等技术对反应前后催化剂的理化性质进行表征。甲烷部分催化氧化表明,催化剂的活性顺序为Ni/Al2O3/CeO2-ZrO2Ni/BaO/CeO2-ZrO2Ni/CeO2-ZrO2Ni/CuO/CeO2-ZrO2。催化剂表征结果表明,掺杂助剂元素后复合载体的主要结构仍然为CeO2-ZrO2固溶体;掺杂的助剂Ba和Al能和CeO2-ZrO2固溶体产生较强的相互作用,生成Mx Oy/CeO2-ZrO2三元复合固溶体载体,并使复合载体的比表面积增大,其中掺杂Al的效果最为明显,能使CeO2-ZrO2固溶体载体颗粒细化,表面结构更丰富,从而有利于活性组分Ni的分散;虽然掺杂Al使载体的表面酸性略有增强,但是Ni/Al2O3/CeO2-ZrO2复合催化剂仍表现了最高的活性和良好的稳定性。掺杂助剂Cu后,Cu与活性组分Ni之间的氢溢流效应增强了催化剂中Ni的还原性,生成的Cu0与Ni0之间产生的相互作用导致CuNi合金的生成,减少了Ni0活性中心的数目,导致该催化剂对甲烷部分氧化的活性下降。     

Facile synthesis and characterization of acetate intercalated Co-La layered double hydroxide

Layered double hydroxide(LDH) comprising of Co~(2+) and La~(3+)-ions with acetate counter anion was successfully synthesized by hydrogen peroxide catalyzed hydrolysis reaction and characterized extensively. The observed reflections in the powder X-ray diffraction pattern could be indexed in P3 space group with a=0.316 nm and c=2.97 nm. Lattice fringes of distances corresponding to the peaks observed in X-ray diffraction pattern were observed in high resolution transmission electron microscopic images. UV-visible diffuse reflectance spectroscopy results confirmed the presence of Co(OH)_6 along with the presence of charge-transfer band due to the interlayer carboxylate anion. Magnetization measurements at room temperature indicated high spin configuration of Co~(2+)-ion in the sample exhibiting paramagnetic behavior. The mixed metal oxide from calcination was used to reconstruct the parent layered structure. Intercalation experiments with other organic anions in Co-La LDH proved be successful.     

Enhanced photocatalytic degradation of organic dyes from aqueous environment using neodymium-doped mesoporous layered double hydroxide

Neodymium-doped Zn–Al layered double hydroxide (Nd/Zn-Al LDH) with excellent photocatalytic activity was prepared by a one-step hydrothermal method. The morphology and physicochemical properties of as-synthesized photocatalysts were well analyzed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL), UV-diffuse reflectance spectroscopy (UV-DRS), and Brunauer-Emmett-Teller (BET) surface analysis. Doping Nd³⁺ into Zn–Al LDH enhances the overall catalytic activity of the nanocomposite, like better electron–hole pair separation, increase in interplanar distance, fast electron transfer, and large surface area. The as-prepared nanocomposite shows excellent degradation of three different dyes under visible light irradiation. The degradation efficiency of these dyes follows the order of Congo red > rose Bengal > fast green. Furthermore, liquid chromatography-mass spectrometry (LC-MS) was employed to propose a possible photocatalytic degradation pathway for Congo Red and Rose Bengal dyes by Nd/Zn–Al LDH. With the help of radical trapping experiments, it is revealed that during the photoexcitation process, the primary reactive intermediates are hydroxyl radicals.     

NOx-assisted soot oxidation over K/CuCe catalyst

CeO2 and CuOx-CeO2 supported potassium catalysts were synthesized by wetness impregnation method. The catalysts were characterized by BET, NO-TPO, NOx-TPD and soot-TPO measurements. By the decoration of potassium and copper, the maximum soot combustion temperature of the ceria-based catalyst decreased to 338 and 379 °C in the presence and absence of NO under a loose contact mode, re- spectively. The pronouncedly enhanced NO oxidation ability by copper introduction and NOx storage capacity by potassium modif...     

Kinetics of pyrite oxidation in sodium hydroxide solutions

The kinetics of pyrite oxidation in sodium hydroxide solution were investigated in a stirred reactor, under temperatures ranging from 50 °C to 85 °C, oxygen partial pressures of up to 1 atm, particle size fractions from -150 + 106 to -38 + 10μm (-100 + 150 mesh to -400 mesh + 10 μ), and pH values of up to 12.5. The surface reaction is represented by the rate equation:-dN/dt = Sbk″pO^0.5 ₂[oH^{- 0.25}/(1 +k‴ pO₂ ^0.5) where N represents moles of pyrite, S is the surface area of the solid particles,k″ andk″ are constants,b is a stoichiometric factor, pO₂ is the oxygen partial pressure, and [OH^-] is the hydroxyl ion concentration. The corresponding fractional conversion (X) vs time behavior follows the shrinking particle model for chemical reaction control: 1 - (1 -X)^1/3 =k _ct The rate increases with the reciprocal of particle size and has an activation energy of 55.6 kJ/mol (13.6 kcal/mol). The relationship between reaction rate and oxygen partial pressure resembles a Langmuir-type equation and thus suggests that the reaction involves adsorption or desorption of oxygen at the interface. The square-root rate law may be due to the adsorption of a dissociated oxygen molecule. The observed apparent reaction order with respect to the hydroxyl ion concentration is a result of a complex combination of processes involving the oxidation and nydrolysis of iron, oxidation and hydrolysis of sulfur, and the oxygen reduction. Formerly Graduate Student, Department of Mineral Engineering, Pennsylvania State University     

Preparation,luminescence and photofunctional performances of a hybrid layered gadolinium-europium hydroxide

The design and fabrication of rare earth ions incorporated into the inorganic/organic hybrid materials have attracted growing attention for seeking improved optical properties and photofunctional performances.In this paper,a novel hybrid composite based on the layered rare earth hydroxides was successfully prepared by the ion-exchange and intercalation chemical process.The rare earth elements in the composite contain gadolinium(Gd) and europium(Eu) and the molar ratio of Gd to Eu is kept constan...     

Effect of different mixing ways in palladium/ceria-zirconia/alumina preparation on partial oxidation of methane

The effect of the mixing ways of Ce0.7Zr0.3O2-Al2O3 mixed oxides on the partial oxidations of methane （POM） was investigated over Pd/Ce0.7Zr0.3O2-Al2O3 catalysts, the mixing ways including salt precursor mixing （ATOM）, precipitator mixing （MOL）, and powder mechanically mixing （MECH）, respectively. The test results indicated that among the three samples, Pd/ATOM had the best catalytic activity while Pd/MOL had the best stability in the stability test. Both the activity sequences of the fresh and used samples were consistent with the order of Pd dispersion. According to the X-ray diffraction （XRD） and BET characterization, the interaction of Ce^4＋, Zr^4＋, and Al^3＋ in the ATOM mixed oxide was in favor of performing higher catalytic activity and thermal stability. The stability test indicated that Pd/MOL had the highest Pd dispersion and least coke formation on the active sites calculated by the Hz-chemisorption and TG results, which was considered to relate to its superior activity of POM to other catalysts.     

低功耗微热板ZnO甲烷传感器仿真及性能研究

随着微机电系统(MEMS)的发展,运用该技术的半导体传感器也跟着迅速发展,逐渐走向微型化、集成化和智能化。基于MEMS的微加热板(MHP)的金属氧化物甲烷传感器具有功耗小、响应快等优点,广泛应用于甲烷检测。其中,氧化锌(ZnO)甲烷敏感材料因其灵敏度高、中毒效应小、工作温度低等优点,广受关注。但是,该敏感材料制备的传感器响应性能依然受加热温度及热量分布的强烈影响。使用有限元分析(FEA)软件COMSOL中的Multiphysics模块对物理场中的温度进行仿真分析与比较,揭示了在相同工作条件下加热电极结构对温度分布的影响,优选的微加热板达到300 ℃时需要75 mW左右的功率。在商用微加热板的叉指电极上采用无遮挡全表面溅射氧化锌敏感材料构建ZnO薄膜甲烷传感器,并使用合肥微纳公司HIS9010测试了气体传感器的响应。采用静态测量的方法向1 L的气体腔内注射甲烷气体,经过测试,与现在不同形貌的ZnO相比,本课题组使用的磁控溅射制备的氧化锌薄膜气体传感器,在(1000～10000)×10?6甲烷浓度区间内响应线性度比较好,对浓度为10000×10?6的甲烷响应值达到了30。与国内外商用甲烷传感器的甲烷响应性能进行了对比,结果表明本课题组制作传感器响应更高,更具有应用优势。      

Effects of water on CO catalytic oxidation over Pd/CeO_2

The role of water in CO oxidation was investigated on Pd/CeO_2 with different morphologies(rods(R),cubes(C) and octahedrons(O)).Compared with the absence of water,CO oxidation activity increases 2 times in the presence of water on Pd/CeO_2-C;but a decrease is found on Pd/CeO_2-R.Catalyst characterization reveals that Pd is mainly in the form of solid solution(Pd_xCe_(1-x)O_(2-σ)) on Pd/CeO_2-R and a mixture of metal and Pd_xCe_(1-x)O_(2-σ) solid solution on Pd/CeO_2-C.The strong interaction between Pd and CeO_2-R results in the form of stable bidentate carbonates species;while the relatively weak interaction between Pd and CeO_2-C leads to the produce of unstable monodentate carbonates species.The effects of water on CO oxidation activity closely relate with the Pd chemical state and the types of carbonates species.Water restrains CO adsorption on Pd_xCe_(1-x)O_(2-σ) solid solution,but it has negligent effects on metallic Pd species.In the presence of water,bidentate carbonates species remains stable but the decrease in the amount of monodentate carbonates species is observed.