Effect of initial nickel particle size on stability of nickel catalysts for aqueous phase reforming

The deactivation behavior by crystallite growth of nickel nanoparticles on various supports（carbon nanofibers, zirconia, Si C, α-Al2O3 and γ-Al2O3） was investigated in the aqueous phase reforming of ethylene glycol. Supported Ni catalysts of ~10 wt% were prepared by impregnation of carbon nanofibers（CNF）,Zr O2, SiC, γ-Al2O3 and α-Al2O3. The extent of the Ni nanoparticle growth on various support materials follows the order CNF ~ ZrO2〉 SiC 〉 γ-Al2O3〉〉 α-Al2O3 which sequence, however, was determined by the initial Ni particle size. Based on the observed nickel leaching and the specific growth characteristics; the particle size distribution and the effect of loading on the growth rate, Ostwald ripening is suggested to be the main mechanism contributing to nickel particle growth. Remarkably, initially smaller Ni particles（~12 nm） supported on α-Al2O3 were found to outgrow Ni particles with initially larger size（~20 nm）. It is put forward that the higher susceptibility with respect to oxidation of the smaller Ni nanoparticles and differences in initial particle size distribution are responsible for this behavior.

Effect of nano-particle size on product distribution and kinetic parameters of Fe/Cu/La catalyst in Fischer-Tropsch synthesis

Effects of nano-particle size on hydrocarbon production rates and distributions for precipitated Fe/Cu/La catalysts in Fischer-Tropsch synthesis were investigated.Nano-structured iron catalyst was prepared by micro-emulsion method.The concept of two superimposed AndersonSchulz-Flory （ASF） distributions has been applied for the representation of the effects of reaction conditions and nano-particles size on kinetics parameters and product distributions.These results reveal that by reducing the particle size of catalyst,the break in ASF distributions was decreased.Also useful different kinetics equations for synthesis of C3 to C9 and C10 to C22 were determined by using α1 and α2 chain growth probabilities.

Effects of support pore size on new Cs_(2.5)H_(0.5)PW_(12)O_(40)/SiO_2 catalysts for the ring-opening polymerization of tetrahydrofuran

Mesoporous silica supported Cs2.5H0.5PW12O40 catalysts were prepared by impregnation method, and several silica supports with different pore size were utilized. N2 adsorption, XRD and ICP-AES techniques were utilized to characterize the silica supports and catalysts. XRD results showed that the dispersion of Cs2.5H0.5PW12 was better for the silica support with larger pore size. The catalytic activity results showed that the pore size played important role on the catalyst activity and the molecular weight of PTHF. When Cs2.5H0.5PW12O40 was dispersed on larger pore size silica support, the catalysts showed good performances for the synthesis of PTHE The molecular weight of PTHF product on the sample in which Cs2.5H0.5PW12O40 was dispersed on larger pore support was higher than that on the catalyst with smaller pore support. The leaching amounts of the active components for the supported Cs2.5H0.5PW12O40 catalysts were much lower. After five reaction cycles, there were still good activities and stabilities for the supported Cs2.5H0.5PW12O40 catalysts with larger pore silica supports. These results were much better than those of the supported heteropolyacid H3PW12O40 catalyst.

Influence of MgO contents on silica supported nano-size gold catalyst for carbon monoxide total oxidation

A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, O2 temperature-programmed desorption （O2-TPD）, and inductively coupled with plasma atomic emission spectroscopy （ICP-AES） techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO （Mg/SiO2 weight ratio） shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.

Effect of the Ni size on CH4/CO2 reforming over Ni/MgO catalyst：A DFT study

Carbon deposition is sensitive to the metal particle sizes of supported Ni catalysts in CH_4/CO_2 reforming.To explore the reason of this phenomenon,Ni4,Ni8,and Ni12 which re flect the different cluster thicknesses supported on the MgO(100) slabs,have been employed to simulate Ni/MgO catalysts,and the reaction pathways of CH_4/CO_2 reforming on Nix/MgO(100) models are investigated by density functional theory.The reforming mechanisms of CH_4/CO_2 on different Nix/MgO(100) indicate the energy barriers of CH_4 dissociated adsorption,CH dissociation,and C oxidation three factors are all declining with the decrease of the Ni cluster sizes.The Hirshfeld charges analyses of three steps as described above show only Ni atoms in bottom two layers can obtain electrons from the MgO supporters,and the main electron transfer occurs between adsorbed species and their directly contacted Ni atoms.Due to more electron-rich Ni atoms in contact with the MgO supporters,the Ni/MgO catalysts with small Ni particles have a strong metal particle size effect and lead to its better catalytic activity.

EFFECT OF Ni CRYSTAL SIZE DISTRIBUTION ON THE ANTICOKING BEHAVIOR OF La-MODIFIED Ni/α-Al_2O_3 CATALYSTS

The crystal size distribution（CSD）was determined with small angle X-ray scattering technique.Theanticoking property of Ni-catalysts was investigated with the steam reforming of n-heptane in a TG-monitoredflow reactor.The results of this study show that the rate of coking on the supported Ni-catalysts depends main-ly on the percentage content of the large size fraction（25-70nm）of Ni-crystallites,and that the dispersion ofNi-crystallites and the anticoking property of the Ni/α-Al2O3 catalysts were promoted obviously by theLa2O3-modification method.The variation of the Ni-CSD and the anticoking property of the catalysts were fur-ther tested through different periods of hydrothermal treatment.It is found that the content of the largeNi-crystal size fraction and the coking rate pass correspondingly through a maximum.

Mathematical Modeling for Optimizing the Structural Properties of Catalysts Used for Series Multiple Reactions

One of the main challenges in the design and operation of catalytic reactors for reactions with multiple paths/steps is the occurrence of undesirable reactions and products. In these cases, two main factors need to be considered in the reactor performance: the “conversion” of the feed and the “selectivity” of the process, which is the conversion split between the desired and the undesired products. In this work, a comprehensive model is developed and used to assess the impact of pore-size distribution (PSD) on both conversion and selectivity in series catalytic reactions. In particular, the evaluation considers the effects of various combinations of micro- and macro-porosity, the potential advantages of radial variation of the porosity in the catalyst pellets, and the effect of pellet size. Results show that, for series reactions, when the formation of the desired product is followed by an undesirable degradation reaction, higher porosity in pellets, particularly in the micro-range, gives higher overall conversion, but lowers selectivity towards the formation of the desired product. Selectivity in these pellets can be improved by using a non-uniform PSD that provides a radial gradient of effective diffusivity in pellets increasing from the center to the outer pellet surface. The pellet size also has a significant effect, and larger pellets show lower selectivity in most cases. In general, conversion and selectivity trends move in opposite directions with changes in PSD and the pore structural properties of pellets. Therefore, finding the optimum design of pellets is an optimization process that requires process modeling. Consequently, selecting the best catalyst properties involves optimization, and the needed tool is a comprehensive mathematical model that takes into account the details of mass transport and reaction kinetics in the catalyst pellets. Our primary objective has been the development of a flexible mathematical model that would be applicable to a wide range of conditions and can be used as a design tool and an optimization platform.

Recent advances in understanding the key catalyst factors for Fischer-Tropsch synthesis

Catalytic conversion of synthesis gas （CO＋H2） into hydrocarbons, also known as Fischer-Tropsch （FT） synthesis, is a crucial reaction for the translbrmation of non-petroleum carbon resources such as coal, natural gas, shale gas, coal-bed gas and biogas, as well as biomass into liquid fuels and chemicals. Many factors can influence the catalytic behavior of a FT catalyst. This review highlights recent advances in understanding some key catalyst factors, including the chemical state of active phases, the promoters, the size and the microenvironment of active phase, which determine the CO conversion activity and the product selectivity, particularly the selectivity to C5 ＋ hydrocarbons.

Preparation of Pt/C Catalyst with a New and Simple Organic Sol Method

It is reported for the first time that the Pt/C catalyst can be prepared with a new and simple organic sol method using SnCl2 as the reductant. It was found that the average size of the Pt particles in the Pt/C catalysts could be controlled with controlling the preparation conditions. The effect of the average sizes of the Pt particles in the Pt/C catalysts obtained with this method on the electrocatalytical activity of the oxidation of methanol was investigated.

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-H 2 ）,and XRD techniques.Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H 2 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.

Effects of Ru nanoparticle sizes confined in cavities of SBA-16 on the catalytic performance of Fischer-Tropsch synthesis reaction

Ru nanoparticles with different sizes confined in the cavities of mesoporous SBA-16 have been successfully synthesized by incipient wetness impregnation method with a Ru loading of 4 wt%. The catalysts were characterized by XRD, N2 adsorption-desorption, H2-TPR, H2-TPD, O2-titration and TEM. The catalytic performance of Fischer-Tropsch synthesis over the catalyst was tested in a fixed-bed reactor. The addition of citric acid in the impregnation procedure shows a significant influence on the size of Ru nanoparticles. The selectivity to C5＋ increases, while the selectivities to methane and C2-C4 light hydrocarbons decrease with Ru average particles size from 2.0 nm to 9.3 nm, . The Ru catalyst confined in the SBA-16 with average nanoparticle size of 5.3 nm gives the best activity.

Solvent-free synthesis of alumina supported cobalt catalysts for Fischer–Tropsch synthesis

A novel mechano-synthesis method has been elaborated in this work for the design of efficient cobalt-based Fischer–Tropsch catalysts. The process aims to reduce the total number of steps involved in the synthesis of solid catalysts and thus to avoid relevant toxic solutions generated during the catalyst preparation. The mechano-synthesis of the Co/Al2O3catalyst was processed in a low-energy vibratory micro mill and high energy planetary ball mill. Porous spherical γ-aluminas (1860 µm and 71 µm mean particle diameter) were used in this work as host compounds. Co3O4(3 µm mean particle diameter) has provided guest particles for mechano-synthesis. The catalysts were characterized by textural (surface area, porosity and particle size) and structural analyses (X-ray diffraction, TPR, SEM-EDX and microprobe). The microprobe images show deposition of Co3O4on the surface of the alumina and indicated no Co3O4diffusion inside the alumina pores. SEM-EDX mapping illustrated that cobalt coating tended to occur on surface of rounded shape of cracked alumina fragments. After milling, the crystallite size of Co3O4decreased to 15 nm from 30 to 50 nm. The TPR profiles indicated very low concentrations of inactive cobalt aluminate mixed compounds which are usually produced during the catalyst preparation by impregnation. In Fischer–Tropsch synthesis, the catalysts prepared using mechano-synthesis methods showed catalytic performance comparable to the catalysts prepared by impregnation. © 2016 Science Press

Fischer–Tropsch synthesis on impregnated cobalt-based catalysts:New insights into the effect of impregnation solutions and pH value

The Co-based catalysts were prepared with different cobalt acetate solutions. Effects of pH value were studied deeply on Fischer–Tropsch synthesis (FTS) through a semi-batch reactor. Among all impregnation solutions (water, butanol, amyl alcohol, acetic acid, nitric acid and ammonium nitrate), the catalyst prepared by NH4NO3solution showed the highest catalytic activity due to its small particle size and high reduction degree. However, the catalyst with the smallest particle size derived from water as impregnation solution exhibited low activity as well as high methane selectivity since it was difficult to be reduced and inactive in FTS. According to FT-IR spectra results, the low intensity of absorbed CO on the catalyst prepared from water solution resulted in low FTS activity. Whereas, the high activity of catalysts prepared from NH4NO3solution could be explained by the high intensity of absorbed CO on the catalysts. The cobalt species on the catalysts prepared under lower pH conditions exhibited smaller particle size distribution as well as lower CO conversion than those prepared at higher pH value. © 2016 Science Press

Interaction between the Components of FeCl_3-Al(i-Bu)_3-bipyridine Catalyst

The interactions between the components of FeCl3-Al (i-Bu)3-bipyridine -catalyst were studied by the electric conductivity of these components in a hydrogenated gasoline medium at 25℃. It was found that Al (i-Bu) existed in an 3 associated state and was then dissociated into ion pairs. The reaction between FeCl3 and Al (i-Bu)3 is the chief reaction in the formation of nano-sized particles. Simultaneously, Al (i-Bu)3 reduced Fe3+ into Fe2+. The reaction between Fe2+ and bipy generated a Fe (bipyridine)2+ complex compound, which prevented Al (i-Bu)3 from reducing Fe2+ to a lower valence (Fe+, Fe0). The excessive Al (i-Bu)3 was dissociated into ion pairs and formed a double layer, which stabilized the nano-sized particles.

微波诱导高分散Pd/FeP催化剂构筑及其电催化性能研究

微波技术作为一种新型过程强化手段,已被广泛应用于材料制备过程。利用微波对吸波型载体的选择性加热,使其产生局部高温诱导催化剂颗粒的沉积,有望构筑高分散钯(Pd)催化剂结构,而这一特殊结构对提高催化剂电催化氧化甲酸活性、提升甲酸燃料电池的性能至关重要。为探究微波诱导高分散钯催化剂便捷制备的可行性,本文首先通过水热法制备了强吸波的空心海胆状磷化铁(FeP)作为催化剂载体,而后分别在常规加热与微波加热条件下通过乙二醇还原法在FeP表面沉积Pd。使用XRD、TEM、SEM技术表征Pd/FeP产品的形貌和微观结构,探究微波加热对催化剂表面金属钯颗粒分散的影响作用。使用循环伏安法和线性伏安法评价所制备催化剂的催化活性,通过探讨催化剂结构与其电催化活性的构效关系,揭示微波合成对Pd/FeP催化剂性能的强化作用机制。研究结果表明,空心海胆状的FeP颗粒具有较强的微波吸收能力,因而在受到微波辐射时,其表面形成的局部过热诱导Pd的原位沉积,使得微波水热法制备的Pd催化剂具有良好的分散特性,然而溶剂主体温度的过高会增加Pd之间的团聚。相对于常规手段合成的催化剂,利用微波水热法在120°C下制备的催化剂电化学活性面积提升了约3.5倍,对甲酸电催化氧化活性提升了约54倍。

纳米丁腈橡胶胶乳的制备与催化加氢

采用常规乳液聚合法结合低温间歇聚合工艺制备了丁腈橡胶胶乳,使用自制钌系催化剂对该胶乳进行乳液加氢,系统研究了催化剂用量和氢气压力对丁腈橡胶胶乳加氢效果的影响规律。结果表明,所制备丁腈橡胶胶乳的平均粒径为69.13 nm,加氢前后胶乳的粒径基本保持不变且胶乳稳定性良好;氢气压力越大催化加氢效果越好;当催化剂质量分数为0.017 5%时,可制得氢化度为99%以上且不含凝胶的产品。

制备条件对Ziegler-Natta催化剂性能的影响

介绍了聚烯烃技术的核心关键是催化剂,其中催化剂的制备条件对催化剂的性能有较大的影响;主要考察了母液转移时间、TiCl4与MgCl2物质的量比、内给电子体(ID)与MgCl2物质的量比、陈化反应温度等对Ziegler-Natta(Z-N)聚烯烃催化剂性能的影响。结果表明,母液转移时间、载钛过程搅拌转速、TiCl4与MgCl2物质的量比对催化剂平均粒径影响较大;ID与MgCl2物质的量比对催化剂的颗粒形貌及催化活性影响较大;陈化反应温度对催化剂的钛含量及催化活性影响较大。

Ni/Al_(2)O_(3)催化十二氢-N-乙基咔唑分解的粒径效应及动力学分析

采用浸渍法制备了不同粒径的Ni/Al_(2)O_(3)催化剂,利用XRD、H2化学吸附、N2吸附-脱附等方法对催化剂进行了表征,考察了Ni粒径和反应条件对十二氢-N-乙基咔唑(12H-NEC)脱烷基及脱氢反应性能的影响。实验结果表明,随Ni负载量的增加,Ni平均粒径逐渐增大,Ni/Al_(2)O_(3)催化剂对12H-NEC的脱氢及脱烷基活性均呈先增大后下降趋势。Ni/Al_(2)O_(3)催化剂的Ni粒径在10~70 nm范围内,Ni粒径越小越有利于12H-NEC稳定性,适宜的脱氢温度为220℃。在10Ni/Al_(2)O_(3)催化剂作用下,12H-NEC脱烷基反应为一级动力学控制,指数前因子和表观活化能分别为1.27×10^(6) h^(-1)和79.30 kJ/mol。