具有不同活性中心的固体催化剂的失活模式

 An approach is suggested to distinguish different types of active sites responsible for different reactions on bifunctional catalysts. The model assumes a non-uniform vulnerability of active sites that depends on their location. Problems on the relationship between the dispersion of the active phase and selectivity are discussed. The effect of coke formation on the activity change of different sites is analyzed.     

用于甲烷水蒸气重整的镍基催化剂的失活和再生

The deactivation of nickel catalysts used in Arak and Razi petrochemical complexes followed by catalyst regeneration was evalu-ated. The characterization of the different structures was made by powder X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),transmission electron microscopy(TEM),and carbon & sulfur analyzer. The Ni particle size was estimated from XRD patterns and TEM graphs. The agglomeration of nickel particle and the poison by sulfur components were recognized as the main reasons in deactivation of Arak and Razi catalysts,respectively. The activity of the used catalysts before and after regeneration was measured on methane steam reforming at a CH4:H2O ratio of 1:3 at 850 oC. The regeneration processes for Arak and Razi samples were performed with CO2 as an oxidative atmosphere and steam as a regenerating agent,respectively. The results show that,(1) no residual sulfur components were on the regenerated Razi catalyst surface without changing the structure of the catalyst and the regenerated catalyst has gained 80% of its catalytic activity,and that(2) the nickel particle size of regenerated Arak specimen decreased remarkably as measured by Debye-Scherrer equation from XRD patterns. TEM images were in agreement with the XRD results and indicated a decrease in nickel particle size of regenerated catalyst. Additionally,in both regenerated catalysts all the coke on the surface of the support was eliminated after regeneration.     

颗粒内传质参数作为工具用于催化剂颗粒的设计(英文)

A chromatographic method and a dynamic Wicke-Kallenbach method (DMWK) were used to determine the diffusion characteristics of two industrial copper containing catalysts. The first catalyst was used in nitrobenzene hydrogenation to aniline and the second was used in a low temperature water-gas shift reaction. Experimental results show that application of these two methods leads to similar results. Experimental data obtained allow for monitoring changes in the texture of the catalyst grains and intraparticle diffusivity of gaseous reagents at different states of the catalyst activity and use, which can be used as criteria for designing optimal industrial catalyst pellets.     

镍铁氰化物纳米粒子的合成及其多相催化无溶剂条件下苯甲醇氧化的潜能(英文)

Nickel hexacyanoferrate nanoparticles were synthesized and characterized using elemental analysis, thermal analysis, infrared spectroscopy, and X-ray diffraction. A FE-SEM image of the nickel hexacyanoferrate showed that it consists of nearly spherical particles with sizes ranging from 30 to 70 nm. The synthesized material was found to be a heterogeneous catalyst useful for the solvent-free oxidation of benzyl alcohol with H2O2 as an oxidant. A 36% conversion of benzyl alcohol to benzaldehyde was achieved under optimized reaction conditions using specific parameters such as the amount of catalyst, the temperature, the benzyl alcohol to H2O2 molar ratio, and the reaction time.     

多相催化研究中化学动力学的作用(英文)

The paper presents shortly some of the important elements of the theory and of the practical applications of the kinetics of heterogeneous catalytic reactions. Discussed are some of the most important concepts of the kinetics of complex heterogeneous catalytic reactions,methodology of building kinetic models and mathematical treatment of experimental data,influence of heat and mass transfer,types of laboratory reactors,kinetics and nanosized catalysts and others. Examples for use of the kinetic studies for the development and application of industrial catalysts and modeling of industrial reactors are presented.     

炼钢渣和炭的混合物用于微波辅助甲烷干气重整反应(英文)

The use of steel-making slag as catalysts for microwave-assisted dry reforming of CH4 was studied. Two carbon materials (an activated carbon and a metallurgical coke), mixtures of the carbon materials and Fe-rich slag, and mixtures of the carbon materials and Ni/Al2O3 were tested as catalysts. The mixtures of slag with carbons gave rise to higher and steadier conversions than those achieved over the carbon materials alone. In addition, the use of the metallurgical coke mixed with metal-rich catalysts gave rise to remarkable results. Thus, no CH4 and CO2 conversions were achieved when coke was used alone, whereas high conversions were obtained when it was mixed with the metal-rich catalysts.     

壳核结构纳米催化剂的研究进展(英文)

<正>1.Introduction During the past few decades,there have been comprehensive studies on nanocatalysts with many innovative advances in the precise manipulation of their structure and morphology on a nanometer scale by both chemists and material scientists[1].In comparison to bulk catalysts,nanocatalysts have a high surface-to-volume ratio due to the small     

电场或电磁场和光动力的协同效应对癌细胞失活和坏死的作用(英文)

应用弱正弦波电磁场改变细胞膜的穿透性并引起其失活和坏死.研究中,将人类癌细胞U 937和K 562放置于强度为10mT和39mT(50Hz)的正弦波电磁场内,并依次结合细胞毒素放线菌素 C以及其独特的光动力活性分别进行试验.     

费托合成反应中纳米铁催化剂上La和Ba助剂的协同效应(英文)

Effect of promoters such as Barium and Lanthanum has been investigated on the conventional nanostructured iron catalyst in Fischer-Tropsch synthesis (FTS). The nanosized iron-based catalysts were prepared by a microemulsion method with the general formulation of 100Fe/4Cu, 100Fe/4Cu/2La, 100Fe/4Cu/ 1La/1Ba, and 100Fe/4Cu/2Ba. The phase, structure, and morphology of the catalysts were characterized by X-ray diffraction, N2 adsorption, transmission electron microscopy, temperature-programmed desorption of CO2, and temperature- programmed reduction. The results indicated that the addition of promoters could improve the activity of Fe catalysts for FTS and WGS (water-gas shift reaction) and lower the gas fraction at the outlet. In addition, both Ba- and La-promoted Fe catalysts exhibit the highest activity due to the synergetic effect.     

非晶态金属-磷酸铝催化正庚醛和苯甲醛羟醛缩合制茉莉醛(英文)

Amorphous aluminophosphate (AlP) and metal‐aluminophosphates (MAlPs, where M=2.5 mol%Cu, Zn, Cr, Fe, Ce, or Zr) were prepared by coprecipitation method. Their surface properties and catalytic activity for the synthesis of jasminaldehyde through the aldol condensation of n‐heptanal and benzaldehyde were investigated. The nitrogen adsorption‐desorption isotherms showed that the microporosity exhibited by the aluminophosphate was changed to a mesoporous and macroporous structure which depended on the metal incorporated, with a concomitant change in the surface area. Temperature‐programmed desorption of NH3 and CO2 revealed that the materials possessed both acidic and basic sites. The acidic strength of the material was either increased or decreased depending on the nature of the metal. The basicity was increased compared to AlP. All the materials were X‐ray amorphous and powder X‐ray diffraction studies indicated the absence of metal oxide phases. The Fourier transform infrared analysis confirmed the presence of phosphate groups and also the absence of any M‐O moieties in the materials. The selected organic reaction occurred only in the presence of the AlP and MAlPs. The selectivity for the jasminaldehyde product was up to 75%with a yield of 65%. The best conversion of n‐heptanal with a high selectivity to jasminaldehyde was obtained with FeAlP as the catalyst, and this material was characterized to have less weak acid sites and more basic sites.     

非均相催化臭氧氧化反应机制

臭氧催化氧化作为高级氧化技术是目前水处理领域研究的热点,其中非均相臭氧催化氧化技术因其氧化能力强、降低臭氧投加量特别是能显著提高有机物矿化率等优点而备受关注。非均相催化臭氧氧化领域不断研究新的催化剂,但是其反应过程及机制更加复杂。催化臭氧氧化的性能很大程度上取决于催化剂及其表面性质。污染物在催化剂表面形成络合物,或者臭氧在催化剂表面分解产生不同的含氧物种如表面氧原子、过氧化物和羟基自由基等。本文评述了非均相臭氧催化氧化反应中存在的多种机理,主要是自由基理论、氧空位理论、表面原子氧理论、表面络合物理论和臭氧直接氧化理论。催化剂表面的羟基基团是主要的催化活性中心,本文探讨了表面羟基基团催化反应机制,得出催化剂表面性质决定其表面活性位点的特性及含量,对诱导臭氧分解产生含氧活性物种起了关键作用;概述了催化剂改性后的结构形态、比表面积及其性能和作用机制;并讨论了非均相臭氧催化氧化反应催化剂未来的发展趋势,为催化臭氧氧化污水处理技术提供了理论参考。     

Cooperative Effect of Platinum and Alumina on Catalyst Deactivation for Dehydrogenation Reaction

The cooperative effect on catalyst deactivation of Pt-based catalysts for dehydrogenation reaction was investigated using the combination of Pt-based/SiO₂ and Al₂O₃. The presence of the effect was confirmed by reaction test, CO adsorption, H₂-TPD and TPO. Considering conversion, active site, H₂ uptake and the nature and amount of coke, interestingly, the physical mixture of Pt-based catalyst supported on SiO₂ with 100-120 mesh and Al₂O₃ 60-80 mesh was similar to Pt-based Al₂O₃. The concept of combination of two catalytic functions, acidity and metallic species, will certainly provide the possibility of better catalyst design.     

浆态相甲醇合成催化剂的失活机理

 浆态床甲醇合成过程具有重要的工业应用价值,影响该过程工业化的根本原因是催化剂易失活. 以合成气为原料,医用液体石蜡为溶剂,在5 MPa, 260 ℃和 1100 ml/(g·h)的反应条件下于浆态床反应器中考察了铜基甲醇合成工业催化剂C301的稳定性,并采用程序升温还原、 X射线衍射、透射电镜、扫描电镜、 扫描电镜能谱、元素分析和N2物理吸附等表征方法对不同失活程度的催化剂的物相组成和形貌进行了表征. 结果表明,在本实验条件下,失活催化剂无中毒现象,但随着反应时间的延长,催化剂晶粒长大,比表面积减小,积炭和热烧结现象较明显,但不伴随活性组分铜的流失.     

复相催化反应实验中活性催化剂的探索

为了改善流动法测定催化剂活性的实验,通过原位还原置换法将Ag负载于Raney-Cu表面,制备Ag/Raney-Cu催化剂,并比较了Ag/Raney-Cu与Raney-Cu及传统ZnO/Al_2O_3催化剂对甲醇分解反应的催化性能。研究发现所制备的Ag/Raney-Cu及Raney-Cu均显示了高于ZnO/Al_2O_3催化剂的低温催化活性。在250℃时,Raney-Cu的活性高于Ag/Raney-Cu;随着温度升高,Ag/Raney-Cu的活性显著增强,当温度升高至350℃,其活性高于Raney-Cu的活性。     

肼分解催化剂表征及失活机理研究

Ir/ γ Al 2O 3 catalyst for hydrazine decomposition has been investigated by using XPS, SEM, H 2 TPD and H 2 isothermal adsorption. The results show that the iridium species enrich on the surface of the catalyst in more than one state, and that the metallic iridium is the active sites for the reaction. The iridium species were sintered seriously during the reaction, and the amount of H 2 adsorption on used sample was only a quarter of that on fresh sample. The concentration of Cl - species on the surface decreased quickly at the initial period of the reaction process and stayed at a certain low value. Obvious breakup of the surface structure of the used sample was found. In all, the sintering of metallic iridium and the damage of alumina surface structure are the reasons for deactivation of the catalyst, while the Cl - concentration has little effect on the reaction performance.     

甲醛氧化催化剂及反应机理

甲醛具有致畸和致癌性,是主要的室内污染物。催化氧化法甲醛转化效率高,没有二次污染,相关研究日益受到关注。本文详细介绍了贵金属和非贵金属两类主要的甲醛氧化催化剂,探讨了活性组分、载体、催化剂助剂等催化剂组成对于其理化性质和反应性能的影响规律,讨论了制备方法、反应物中的水含量等因素对于催化反应的影响,分析了催化剂失活的主要因素。研究表明,催化剂表面活性氧、表面羟基、氧空位数量以及对反应物的吸脱附和存储能力是影响催化活性的关键因素。贵金属催化剂,特别是Pt催化剂具有较好的催化性能,可在较低温度实现甲醛充分转化;非贵金属催化剂具有可变价态,通过催化剂的合理设计可以具有足够的催化活性,其原料资源丰富,价廉易得,应用前景广阔。     

非均相催化一步合成碳酸二苯酯的研究 Ⅶ．Pd－Sn催化剂的失活与再生

 用MS－GC对Pd－Sn催化剂再生洗涤液进行了分析，用XPS和等离子光谱对催化剂活性组分Pd含量进行了检测，以了解催化剂在使用过程中表面的积碳、表面活性元素价态的变化及活性组分流失的情况．结果表明，原料苯酚过多的吸附及Sn在催化剂表面上的富集而引起活性组分Pd浓度的相对下降，是造成催化剂失活的主要原因．再生实验结果表明，用浓度为23％的丙酮洗涤液在60℃下进行洗涤，在300℃进行干燥，所得再生催化剂的活性较高．此外，Ce的添加有利于延长催化剂的使用寿命．     

纳米金催化剂的存放失活

 采用共沉淀法制备了2.5%Au/ZnO催化剂,并用扫描隧道显微镜、 X射线衍射、 X射线光电子能谱和热重研究了纳米金催化剂在空气中存放失活的机理. 结果表明,纳米金催化剂在空气中存放失活是部分可逆的. 纳米金催化剂的存放失活有两方面原因: 一是纳米金粒子的长大,导致不可逆失活; 二是碳酸盐在催化剂表面的累积,这种失活可以通过高温焙烧来恢复,是可逆的.     

Deactivation studies of nano-structured iron catalyst in Fischer-Tropsch synthesis

A nano-structured iron catalyst for syngas conversion to hydrocarbons in Fischer-Tropsch synthesis (FTS) was prepared by micro-emulsion method. Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H2), and XRD techniques. Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H2 and XRD spectra and which were compared with those recorded on conventional co-precipitated iron catalyst. The results reveal that the catalyst deactivation results from the formation of inactive carbide phases and surface carbonaceous species like graphite, and it will be increased when the particle size of iron oxides was reduced in FTS iron catalyst.