Fe/Dy非晶多层膜的晶化反应及相演化研究

由 Miedema半经验公式计算的 Fe/Dy二元系自由能图 ,及退火时 Fe/Dy非晶多层膜晶化过程的 XRD结果得出 :多层膜晶化受热力学和动力学两种因素控制 ,Fe,Dy晶态自由能低于初始非晶态提供了晶化的驱动力 。

TS-1分子筛研究进程及催化应用

TS-1是一类独特的用于液相选择性氧化反应的分子筛催化剂,在高结晶沸石框架中具有四面体配位Ti^(4+)离子。TS-1/H_(2)O_(2)绿色反应体系已经取得了相当大的突破。TS-1分子筛的催化性能与其拓扑结构、晶体形态、四面体Ti的含量和反应微环境有关。当前石油化工和精细化工等行业对大分子氧化催化剂的需求日益增长,开发催化性能显著提高的新型TS-1的研究成为热点。综述TS-1分子筛近年的研究进展及催化应用。

利用钾长石粉体水热合成13X沸石分子筛的晶化过程

实验研究了以钾长石粉体为原料水热合成13X沸石分子筛的晶化过程,确定了晶化过程的诱导期、晶化期和沸石晶体的平均生长速率。以钾长石焙烧熟料为前驱物合成13X沸石,反应混合物首先转变为铝硅酸钠(钾)凝胶,再逐步水热晶化为13X沸石;在反应物未完全转变为铝硅酸钠(钾)凝胶之前,13X沸石已开始结晶。13X沸石晶体的生成主要发生在凝胶相内部,是凝胶结构逐步趋于有序化的过程。13X沸石晶体生成是由凝胶相内的[TO4]四面体相互连接,互套构成笼状结构。推测13X沸石形成机理为:硅酸根离子和铝酸根(+铁酸根)离子发生聚合反应,生成次级结构单元双六元环;双六元环进一步缩合,生成方钠石型笼;最后,方钠石型笼进一步相互联结,生成13X型沸石分子筛的硅铝骨架结构。

氧对Zr_(50)Cu_(40)Al_(10)块体金属玻璃晶化动力学的影响

利用不同锆原材料、采用电弧炉坩埚倾斜铸造法制备了具有不同氧含量的Zr50Cu40Al10三元锆基块体金属玻璃,研究了氧对合金热稳定性及晶化动力学的影响.研究结果表明:合金的热稳定性随其氧含量的增加而降低,但晶化表观激活能却随氧含量的增加而增加;氧是通过提高晶化反应速率常数而降低合金热稳定性的,热稳定性与反应速率常数之间存在良好的对应关系,反应速率常数可以较好地表征具有强烈动力学效应的块体金属玻璃晶化过程;氧提高合金晶化反应速率常数的原因是由于它增大了反应的频率因子.

高岭土微球原位合成NaY沸石体系中的非原位结晶反应

以XRD、SEM等方法表征了高岭土微球原位合成NaY过程中产生的非原位结晶,研究了非原位结晶的形成与晶化体系化学组成、晶种、搅拌速度等对非原位结晶的影响,提出了控制非原位晶化反应的可能方法.

离子交换法改性NaY分子筛微球催化剂制备研究

Y型分子筛是裂化催化剂的优良前驱体,其经改性后制备的催化剂广泛应用于催化裂化领域。因此,其改性技术一直是此领域的研究重点之一。笔者利用原位晶化法制备了NaY分子筛微球;采用离子交换等方法对所制备微球进行改性,得到了改性Y型分子筛,分析了其化学组成及离子交换度,并考察了其使用性能。利用原位晶化法制备了NaY分子筛微球,并通过分析其晶化反应硅钠比,得到了其结晶度为34.3%。利用氢离子、铵根离子、稀土离子、磷离子等对上述微球进行离子改性,得到了改性Y型分子筛(HD-C催化剂)。利用常规化学分析方法,对其离子交换后母液中硅、铝、稀土等离子含量进行了分析,得到了催化剂组成及离子交换度,催化剂钠、稀土、铝、铁含量分别为0.28%、4.11%、36.24%、0.23%;总Na_2O交换度达到96.0%。利用程序升温脱附法(TPD)考察HD-C及对比剂的酸特性,并对其选择性、活性、抗金属污染等使用性能进行了评价,HD-C总酸度达到3.16;老化4 h时HD-C活性为69.6,QD为79.1,74.2;800℃,100%水蒸汽老化4 h,镍∶钒(4∶1) 4 000 ppm污染量时,HD-C活性为55.7,QD活性为40.8;800℃,100%水蒸汽老化4 h时,HD-C选择性为88.72,QD选择性为85.97。结果表明,所制备的改性Y型分子筛能完全满足商用要求。

Regulating crystal phase of TiO_(2) to enhance catalytic activity of Ni/TiO_(2) for solar-driven dry reforming of methane

Ni/TiO_(2) catalyst is widely employed for photo-driven DRM reaction while the influence of crystal structure of TiO_(2) remains unclear.In this work,the rutile/anatase ratio in supports was successfully controlled by varying the calcination temperature of anatase-TiO_(2).Structural characterizations revealed that a distinct TiO_(x) coating on the Ni nanoparticles(NPs)was evident for Ni/TiO_(2)-700 catalyst due to strong metal-support interaction.It is observed that the TiOx overlayer gradually disappeared as the ratio of rutile/anatase increased,thereby enhancing the exposure of Ni active sites.The exposed Ni sites enhanced visible light absorption and boosted the dissociation capability of CH4,which led to the much elevated catalytic activity for Ni/TiO_(2)-950 in which rutile dominated.Therefore,the catalytic activity of solar-driven DRM reaction was significantly influenced by the rutile/anatase ratio.Ni/TiO_(2)-950,characterized by a predominant rutile phase,exhibited the highest DRM reactivity,with remarkable H_(2) and CO production rates reaching as high as 87.4 and 220.2 mmol/(g·h),respectively.These rates were approximately 257 and 130 times higher,respectively,compared to those obtained on Ni/TiO_(2)-700 with anatase.This study suggests that the optimization of crystal structure of TiO_(2) support can effectively enhance the performance of photothermal DRM reaction.

Fe_2O_3对13X沸石分子筛合成条件及性能的影响研究

对江苏丰县的富钾页岩进行预处理,得到不同Fe2O3 质量分数的钾长石粉体原料FXY1、FXY2,经中温焙烧得到偏铝硅酸盐前体化合物,水热晶化合成了13X沸石分子筛。采用正交实验法,确定了水热晶化反应的优化工艺条件,原料中Fe2O3 质量分数的不同导致水热晶化反应的工艺参数有所不同。合成的两种沸石的性能与13X沸石分子筛的工业产品相似,吸附量均达到国家化学工业产品标准HG/T 2690 95的要求。对比实验表明,原料中Fe2O3 质量分数的降低可使其在更宽的碱度范围内合成性能更优的13X沸石产品。由低Fe2O3 质量分数的FXY2为原料合成的沸石,其物相纯度、热稳定性、白度、比表面积、吸附性等性质更优。合成沸石均可用于对含重金属离子废水的深度净化处理,由FXY2为原料合成的13X沸石还可用作洗涤助剂。

Preparation of Zn-modified nano-ZSM-5 zeolite and its catalytic performance in aromatization of 1-hexene

The promoting effect of introducing Zn into nano-ZSM-5 zeolites by conventional impregnation method and isomorphous substitution on the performance of 1-hexene aromatization was investigated. The nano-ZSM-5 zeolite was synthesized by a seed-induced method without organic templates. The Zn-modified nano-ZSM-5 zeolite catalysts, xZ n/HNZ5 and y Zn/Al-HNZ5, were prepared by the conventional impregnation method and isomorphous substitution, respectively. The structure, chemical composition and acidity of the catalysts were characterized by XRD, XRF, N2 adsorption, SEM, NH3-TPD and Py-IR, while the catalytic properties were evaluated at 480 °C and a weight hourly space velocity（WHSV） of 2.0 h-1 in the aromatization procedure of 1-hexene. Compared with xZ n/HNZ5, y Zn/Al-HNZ5 exhibited smaller particles and higher dispersion of Zn species, which led to greater intergranular mesopore and homogeneous acidity distribution. Experimental results indicated that the synergy effect between the Brnsted and Lewis acid sites of the isomorphously substituted nano-ZSM-5 zeolites could significantly increase aromatics yield and improve catalytic stability in the 1-hexene aromatization.

Abnormality of Magnetic Behavior and Resistivity of La_(0.7-x)Dy_x Sr_(0.3)MnO_3 (0.00≤x≤0.30)System at Low Temperature

By measuring M-T curves, ρ-T curves and MR-T curves of the samples under different temperatures, the influence of Dy doping （0.00 ≤ x ≤0.30） on the magnetic and electric properties of La0.7-xDyxSr0.3MnO3 has been studied. The experimental results show that, with the increase of the Dy content, the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order. For the samples with x=0.20 and 0.30, their magnetic behaviors are abnormal at low temperature, and their resistivities at low temperature have a minimum value. These peculiar phenomena not only come from the lattice effect induced by doping, but also from extra magnetic coupling induced by doping.

Carbon supported IrM(M= Fe,Ni,Co) alloy nanoparticles for the catalysis of hydrogen oxidation in acidic and alkaline medium

We studied the alloying effect in lr-based alloys on the catalysis of the hydrogen oxidation reaction （HOP,） in both acidic and alkaline medium. IrFe, lrNi and IrCo alloy catalysts with nanoparticle size of 〈S nm were obtained by our solvent-vaporization plus hydrogen reduction method. The second metal played an important role in tuning the crystal structure and surface electronic structure of the Ir-based alloy catalyst. Among the lrFe, IrCo and lrNi alloy catalysts, Ni induced a mid-sized contrac- tion of the lr lattice, and gave the best HOR activity in both acidic and alkaline medium. In acidic medium, the weakening of the Ir-Had interaction caused by the electronic effect of M （M = Fe, Ni, Co） alloying is responsible for the enhancement of HOR activity. The oxophilic effect of the catalytic metal surface, which affects OHad adsorption and desorption and surface Had coverage, has a large impact on the HOR activity in the case of alkaline medium,

Hydrotalcite-wrapped Co–B alloy with enhanced oxygen evolution activity

Water oxidation is one of the most attractive techniques for intermittent renewable energy conversion and storage.The oxygen evolution electrocatalytic performance of an amorphous Co-B alloy and its derivatives were studied.These materials were chemically synthesized by reducing a Co salt with NaBH4.The amorphous Co-B alloy showed good electrocatalytic activity in oxygen evolution but its stability was poor.A hydrotalcite‐wrapped Co-B alloy was synthesized by mild oxidation.The electrocatalytic activity of this material in the oxygen evolution reaction was better than that of a commercially available Ir/C catalyst.

Secondary Crystallization of Na_2CO_3-Modified HZSM-5 Zeolites with Tetrapropylammonium Hydroxide and Their Catalytic Performance in Thiophene Alkylation Reaction

The Na2CO3-modified HZSM-5 zeolites were further treated by tetrapropylammonium hydroxide(TPAOH) solution. The effect of TPAOH concentration on the secondary crystallization process was investigated. The resulting samples were characterized by a complementary combination of X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy, X-ray fluorescence spectroscopy, XPS, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, BET and temperature-programmed desorption techniques. The results showed that the secondary crystallization of the HZSM-5 zeolite could result in migration of non-framework species from the internal channels to the zeolite surface and their transformation into framework species. The catalytic activity of these modified samples for thiophene alkylation was evaluated. Both the activity and stability of the catalysts were improved after secondary crystallization.

Efficient spinel iron‐cobalt oxide/nitrogen‐doped ordered mesoporous carbon catalyst for rechargeable zinc‐air batteries

A robust oxygen‐related electrocatalyst,composed of spinel iron‐cobalt oxide and nitrogen‐dopedordered mesoporous carbon(NOMC),was developed for rechargeable metal‐air batteries.Electrochemicaltests revealed that the optimal catalyst Fe_(0.5)Co/NOMC exhibits superior activity with ahalf‐wave potential of 0.89 V(vs.reversible hydrogen electrode)for the oxygen reduction reactionand an overpotential of 0.31 V at 10 mA cm^(−2)for the oxygen evolution reaction.For demonstration,the catalyst was used in the assembly of a rechargeable zinc‐air battery,which exhibited an exceptionallyhigh energy density of 820 Wh kg−1 at 100 mA cm^(−2),a high power density of 153 mW cm^(−2)at1.0 V,and superior cycling stability up to 432 cycles(144 h)under ambient air.

Comparative experimental study on reactive crystallization of Ni(OH)2 in an airlift-loop reactor and a stirred reactor

The objective of this work is to study the reactive crystallization in an airlift-loop reactor （ALR） using the precipitation of Ni（OH）2 as a model reaction. The growth of Ni（OH）2 particles in an ALR and a stirred tank was quantified by scanning electronic microscope （SEM）, X-ray diffraction （XRD）, laser particle analyzer, tap densitometer and optical microscope, and the growth process of Ni（OH）2 particles is analyzed. It is found that the Ni（OH）2 particles prepared in an ALR have a better sphericity than those in a stirred tank and the growth of Ni（OH）2 particle tap density mainly depends on the size of crystallites： the bigger the size of crystallites, the bigger the tap density is. Based on these, the growth process of Ni（OH）2 particles in ALR is elaborated. Crystallites precipitated from solution aggregate to form large particles with much void. These constituting crystallites continue to grow up, that takes up the void inside particles and makes the tap densitv increase.

Numerical simulation of chemical vapor deposition reaction in polysilicon reduction furnace

Three-dimensional model of chemical vapor deposition reaction in polysilicon reduction furnace was established by considering mass, momentum and energy transfer simultaneously. Then, CFD software was used to simulate the flow, heat transfer and chemical reaction process in reduction furnace and to analyze the change law of deposition characteristic along with the H_2 mole fraction, silicon rod height and silicon rod diameter. The results show that with the increase of H_2 mole fraction, silicon growth rate increases firstly and then decreases. On the contrary, SiHCl_3 conversion rate and unit energy consumption decrease firstly and then increase. Silicon production rate increases constantly. The optimal H_2 mole fraction is 0.8-0.85. With the growth of silicon rod height, Si HCl3 conversion rate, silicon production rate and silicon growth rate increase, while unit energy consumption decreases. In terms of chemical reaction, the higher the silicon rod is, the better the performance is. In the view of the top-heavy situation, the actual silicon rod height is limited to be below 3 m. With the increase of silicon rod diameter, silicon growth rate decreases firstly and then increases. Besides, SiHCl_3 conversion rate and silicon production rate increase, while unit energy consumption first decreases sharply, then becomes steady. In practice, the bigger silicon rod diameter is more suitable. The optimal silicon rod diameter must be over 120 mm.

UV Laser Regulation of Surface Oxygen Vacancy of CoFe2O4 for Enhanced Oxygen Evolution Reaction

Oxygen evolution reaction is one of the key processes in the promising renewable energy technique of electrocatalytic water splitting.Developing high ecient oxygen evolution reaction(OER)catalysts requires determination of the optimal values of the descriptor parameters.Using spinel CoFe2O4 as the model catalyst,this work demonstrates that irradiation with pulsed UV laser can control the quantity of surface oxygen vacancy and thus modify the OER activity,in a volcano-shape evolution trend.This strategy sheds light on quantita-tively investigation of the relationship between surface cation valence,anion vacancy,and physicochemical properties of transition-metal-based compounds.

Earth-abundant amorphous catalysts for electrolysis of water

The generation of hydrogen through the electrolysis of water has attracted attention as a promising way to produce and store energy using renewable energy sources.In this process,a catalyst is very important to achieve a high‐energy conversion efficiency for the electrolysis of water.A good catalyst for water electrolysis should exhibit high catalytic activity,good stability,low cost and good scalability.Much research has been devoted to developing efficient catalysts for both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).Traditionally,it has been accepted that a material with high crystallinity is important to serve as a good catalyst for HER and/or OER.Recently,catalysts for HER and/or OER in the electrolysis of water splitting based on amorphous materials have received much interest in the scientific community owing to the abundant unsaturated active sites on the amorphous surface,which form catalytic centers for the reaction of the electrolysis of water.We summarize the recent advances of amorphous catalysts for HER,OER and overall water splitting by electrolysis and the related fundamental chemical reactions involved in the electrolysis of water.The current challenges confronting the electrolysis of water and the development of more efficient amorphous catalysts are also discussed.

Thermodynamic analysis of manufacturing polysilicon from Si HCl_3,Si Cl_4 and H_2

Production of polysilicon by chemical vapor deposition of SiHCI3 with a fluidized bed reactor is a competitive technology. As equilibrium conversion can be approached in a fluidized bed reactor, a reliable thermodynamic analysis is very important. However, inconsistent thermodynamic analysis results have been reported in the lit- erature. The present work studied the effects of thermodynamic data and species selection, and recommended that JANAF was the best Cp data source and the minimum set of species included the following eight species： H2, HCI, SiC[4, SiCl2, SiHCI3, SiH2CI2, SiH3C] and Si. Then, the influence of operating conditions on the equilibrium was studied. For the SiHC｜3-H2 system, both the yield of silicon and selectivity to silicon reached their maximum at （up to 1100 ℃）, and low pressure and high H2 feed ratio were of benefit for silicon production. For the SiHCI3- SiCI4-H2 system, silicon could be produced only at 900-1400 ℃, and reducing pressure and increasing H2 feed ratio enhanced the yield of silicon. Meanwhile, the operation map for zero net by-production of SiCI4 by directly recycling the produced SiCl4 was determined.

Monte Carlo Simulation of Propylene Selective Oxidation and Ammoxidation overβ-Bi2Mo2O9 Catalyst under Anaerobic Condition

A random walk Monte Carlo （RWMC） simulation model of catalytic particle was established on the basis of the structures of bismuth molybdate catalysts and mechanisms of catalytic reactions with propylene selective oxidation and ammoxidation. The simulation results show that rationality of the RWMC model is proved on the basis of pulse experimental data. One of the most remarkable factors affecting catalytic behavior is the transfer of bulk lattice oxygen, which decides the rate of ammonia-consuming and propylene-consuming. The selectivity of main products reaches the maximum after the reduction of catalysts to a certain degree. It is inferred that catalytic performance improves greatly if the ratio of capacity for dehydrogenation from adsorbed propylene molecule on catalytically active site of molybdenum metal-imido group （Mo=NH） to that on catalytically active site of molybdenum metal-oxo group （Mo=O） becomes much higher.