Synthesis of Ni／Mg／Al Layered Double Hydroxides and Their Use as Catalyst Precursors in the Preparation of Carbon Nanotubes

Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni) : n(Mg) : n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [ n( Ni)/n( Mg)/n(Al) = 1/1/1 ] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.     

Activation of Carbon Dioxide and Synthesis of Propylene Carbonate

Cycloaddition of carbon dioxdie and propylene oxide to propylene carbonate catalyzed by tetra-tert-butyl metal phthalocyanine in the presence of tributylamine(TBA) shows higher yield than catalyzed by unsubstituted metal phthalocyanine.Comparing different catalysts of diverse metals,(t-Bu)4PcMg is more active than (t-Bu)PcFe ,But(t-Bu)4PcCo and (t-Bu)4PcNi only have low catalytic activities towards the reaction.Moreover,the yield will increase as the temperature increases.     

Study on the Reaction Mechanism for Carbon Dioxide Reforming of Methane over supported Nickel Catalyst

The adsorption and dissociation of methane and carbon dioxide for reforming on nickel catalyst were extensively investigated by TPSR and TPD experiments. It showed that the decomposition of methane results in the formation of at least three kinds of surface carbon species on supported nickel catalyst, while CO2 adsorbed on the catalyst weakly and only existed in one kind of adsorption state. Then the mechanism of interaction between the species dissociated from CH4 and CO2 during reforming was proposed.     

The Influence of Temperature on the Heat Effects of Acid—Base Interaction in Aqueous Solutions of Citric Acid

The heat effects of interaction of a solution of citric acid with solutions of HNO₃ and KOH at 288.15, 298.15, and 308.15 K and ionic strength values 0.5, 1.0, and 1.5 (KNO₃) were measured calorimetrically. The heat effects of acid dissociation were calculated using the HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined.     

Effect of Citric Acid Solution Treatment on Textural Properties and Alkylation Activity of Zeolite Beta Catalyst

Zeolitebetaisalarge porecrystallinealuminosil icate,whichwasfirstsynthesizedbyWadlingeretal[1] in 196 7.Duetoitspeculiarframeworktopologyandsuitableacidity ,zeolitebetahasreceivedincreas ingindustrialinterestforsomeimportantreactionssuchasalkylationofbenzenewithlightolefins[2 ] andalkylationofisobutanewithbutene[3] .Manylitera turepapershavereportedmethodstomodifytheacid ityofzeolitebeta ,whichincludeion exchange ,hy drothermaltreatment ,andacidtreatment .Forexam ple ,Xieetal[4 ] investigated…     

Studies on the Synthesis and the Structure of Ferric Aluminum Magnesium Hydrotalcite—like Compounds

Hydrotalcite-like compounds (HTlc) are composed of trivalent and divalent metal ions, the general formula 1 is: [M2+1-xM3+x(OH)2]x+An-x/n·mH2O M3+ is trivalent metal ions, M2+is divalent metal ions, A is negative ions whose valence is n, and m is the amount of water in the crystal, and x is the molar ratio of trivalent metal ions to all metal ions. A lot of studies have been done on the synthesis and property of HTlc, which is made up of two kinds of the metal ions. It has been found …     

Effect of CeO2 and CaO Promoters on Ignition Performance for Partial Oxidation of Methane over Ni/MgO-Al2O3 Catalyst

The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane （POM） to synthesis gas was investigated. It was found that the POM reaction could not be ignited over lwt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of lwt%Ni/MgO-Al2O3 catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reactiorrconditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.     

Synthesis and Properties of Melt Processed Poly（thiourea-azo- sulfone）/Carbon Nanotubes Nanocomposites

An aromatic azo-polymer, poly(thiourea-azo-sulfone)(PTAS), has been prepared using 4-(4-aminophenylsulfonyl)benzenamine and diazonium salt solution of 2,6-diaminopyridine. PTAS was easily processable using polar solvents and had high molar mass 63 × 103g mol 1according to GPC. Mechanically and thermally stable and electrically conducting polymer/CNTs nano-composites were obtained via melt processing technique. Fine distribution of CNTs in a polymer matrix performed an essential role in the preparation of polymer/CNTs nano-composites based on interfacial interaction between CNTs and polymer matrix. Scanning electron micrographs showed good dispersion of filler and adhesion of matrix on the surface of nanotubes. Accordingly, increasing the amount of CNTs from 0.1 wt% to 5 wt% increased the electrical conductivity from 2.99 S cm 1to 3.56 S cm 1. Mechanical strength of functional nanotubes-based hybrids was enhanced from 43.22 MPa to 65.02 MPa compared with that of hybrids with non-functional filler in matrix 37.21 MPa. A rapport between nanotube loading and thermal stability of the materials was also observed. 10% gravimetric loss temperature was increased from 528 °C to 578 °C, while glass transition was improved from 241 °C to 271 °C. Adding up of small quantity of functional CNTs strongly affected the tensile, electrical and thermal properties of materials. Improvement of the physical properties of CNT-reinforced polymer nano-composites was ascribed to the melt processing technique.     

Synthesis of a Novel Carbon Based Acid Catalyst and Its Catalytic Activity for the Acetalization and Ketalization

A novel carbon based strong solid acid catalyst has been synthesized successfully. The catalytic activity for acetalization and ketalization was investigated. The results showed that the novel catalyst was very efficient with the average yield over 92%. The novel heterogeneous catalyst also has the advantages of high activity, wide applicability even to the preparation of 7 membered ring acetals and ketals, strikingly simple workup procedure, non-pollution and reusability, which will contribute to the green process greatly.     

Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane

The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature (excluding 800 ℃). The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature.The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking.     

柠檬酸用量对碳纳米管制备的影响

Carbon nanotubes (CNTs) were prepared by chemical vapor catalytic deposition using the catalyst prepared by citric acid complexometry. The effect of the dosage of citric acid on the CNTs yield and morphologywas studied. The transmission electron microscopy and X-ray diffraction were used to characterize CNTs morphology and crystal structures of the catalysts, respectively. The results show that the dosage of citric acid can greatly affect the CNTs yield and morphology: the CNTs have a high yield about 1 345.8% (1 h) at a 2∶1 molar ratio of citric acid and metal ion, and the obtained CNTs diameter is relatively narrow distributed (25～30 nm); when themolar ratio of citric acidto metal ion is 3∶1, the CNTs yield is about 407.2% (1 h), and the obtained CNTs diameter is relatively wide distributed (25～50 nm), moreover, the CNTs is more rough than that obtained with 2∶1 molar ratio of citric acid to metal ion.     

碳纳米管的活化处理及对其电化学容量影响的研究

采用KOH为活性剂,对碳纳米管进行活化处理,经透射电子显微镜和高分辨透射电子显微镜从不同角度观察,发现得到了两端开口,管长较短,管壁粗糙的活性碳纳米管．用氮气自动吸附仪测试了活化前后两种碳纳米管的比表面积,发现活性碳纳米管具有比活化前碳纳米管更高的有效比表面积,将这两种碳纳米管分别作为电极材料应用于电化学超级电容器,经测试,发现活化后的碳纳米管的电化学容量大大提高,在有机电解液中达到了50F／g．     

镍基板上低温合成定向纳米碳管

纳米碳管具有非常优异的场发射效应 ,亮度高、均匀且稳定的纳米碳管场效应发射器 ,例如平板显示器、阴极射线管以及信号灯等有着非常广阔的应用前景 [1] .由于纳米碳管的场发射效应与纳米碳管的方向性有关[2 ] ,因此定向纳米碳管的制备及其场发射性能研究是当前的一个研究热点     

MWPCVD低温合成纳米碳管的生长机理

The synthesis of carbon nanotubes (CNTs) at low temperature has received a great deal of attention and be-comes a challenging issue. But few model which accounts for the growth of CNTs is suited for the synthesis of CNTs by microwave plasma chemical vapor deposition (MWPCVD) at low temperature because most researchers conclude that the growth mechanism is determined by the catalyst-supporter interaction while ignored the diffusion of carbon in the catalyst. In this paper, under the catalytic effect of cobalt supported by SiO₂ and Al₂O₃, CNTs are synthe-sized by MWPCVD at about 500℃, and tip-growth, the model which accounts for the catalytic growth of CNTs is outlined. It is the temperature difference between the upper and bottom of the catalytic particle that results in the diffusion of carbon atoms from upper to the bottom, and precipitation of saturated carbon on the bottom surface to form CNTs.     

2-十一烷基-N-羧甲基-N-羟乙基咪唑啉在柠檬酸溶液中对碳钢的缓蚀作用

采用失重实验、极化曲线和交流阻抗等方法研究了缓蚀剂2-十一烷基-N-羧甲基-N-羟乙基咪唑啉在质量分数为2%柠檬酸溶液中对碳钢的缓蚀性能。 失重实验表明,该缓蚀剂在柠檬酸溶液中能够有效地抑制碳钢的腐蚀,当其质量分数为0.4%时,缓蚀效率达到86.4%。 极化曲线表明,该缓蚀剂为混合型缓蚀剂,Nyquist图中单一的容抗弧变化表明碳钢电极表面的腐蚀过程主要由电荷转移步骤控制。 该缓蚀剂的吸附行为符合Langmuir吸附等温式,吸附机理是介于物理吸附和化学吸附之间的一种吸附。     

苹果渣酶制备柠檬酸

苹果渣是苹果汁生产的废料 ,约占鲜苹果质量的 2 5 %左右 .苹果渣中含有一定量的还原糖和水分 ,还有约 2 4.8%左右的粗纤维和 6 .41 %的粗蛋白 ,容易腐烂 ,造成环境污染 .目前将其当作垃圾掩埋 ,造成了资源浪费 .对纤维素进行化学预处理是提高酶解效率的有效措施 ,但以苹果渣为底物的酶解却未见报道[1 ,2 ] .本文报道对苹果渣中的粗纤维用纤维素酶酶解成葡萄糖 ,并进而制备柠檬酸的尝试 .苹果渣由陕西泾阳果品加工厂提供 ,烘干后粉碎 ,过筛 .A6号粗纤维素酶粗酶液 ,由陕西省酶科学研究所提供 .黑曲霉麦芽汁 (9Bx)琼脂培养基由陕西合阳柠檬…     

活化条件对活性碳纳米管比表面积的影响

以KOH为活化剂, 研究了多壁碳纳米管在制备活性碳纳米管过程中四个重要影响因素: 活化剂用量、活化温度、活化时间和活化过程中保护气体的流速对所得活性碳纳米管BET比表面积的影响并解释了原因. 研究表明上述四个因素都会对活性碳纳米管的比表面积产生较大的影响, 其中活化剂用量的影响最大, 在研究范围内可引起比表面积增大约241 m²•g^-1. 在这四个影响因素中除活性碳纳米管的比表面积随活化温度的增加而不断增加外, 其他三个影响因素的变化都会使活性碳纳米管的比表面积出现最大值, 而且四个影响因素的改变, 都不改变活性碳纳米管的孔洞主要是中孔和大孔的特点.     

竹节状碳纳米管有序阵列的合成和表征

用1,4-偶氮二异丁基腈作碳源,以载有催化剂Co的多孔Al₂O₃膜作模板,用化学气相沉积法在较低温度(600℃)下方便地制得了单分散碳纳米管有序阵列。透射电子显微分析表明,所得碳纳米管的形态为竹节形状,端口是闭合的,这和同样用Al₂O₃膜作模板但以乙烯或乙炔作碳源热分解制得的中空碳纳米管的情形明显不同。对该纳米管的生成机理进行了初步探讨。     

柠檬酸改性对掺Ba纳米MgO及其担载的Ru氨合成催化剂性能的影响

采用超声-静电吸附法制备了-系列经柠檬酸改件的掺Ba纳米MgO及其负载的氨合成Ru催化剂.并采用场发射手扫描电镜、X射线粉末衍射、N2物理吸附-脱附、电感耦合等离子体发射光谱及红外光谱等手段对样品进行了表征.结果表明,适量添加柠檬酸町有效调控Ba的掺杂量,从而使Ba-MgO结构与化学性质发生变化,其表面性能得到极大改善...     

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

Thermal decomposition of citric acid is one of the most common synthesis methods for fluorescent carbon dots; the reaction pathway is, however, quite complex and the details are still far from being understood. For instance, several intermediates form during the process and they also give rise to fluorescent species. In the present work, the formation of fluorescent C-dots from citric acid has been studied as a function of reaction time by coupling infrared analysis, X-ray photoelectron spectroscopy, liquid chromatography/mass spectroscopy (LC/MS) with the change of the optical properties, absorption and emission. The reaction intermediates, which have been identified at different stages, produce two main emissive species, in the green and blue, as also indicated by the decay time analysis. C-dots formed from the intermediates have also been synthesised by thermal decomposition, which gave an emission maximum around 450 nm. The citric acid C-dots in water show short temporal stability, but their functionalisation with 3-aminopropyltriethoxysilane reduces the quenching. The understanding of the citric acid thermal decomposition reaction is expected to improve the control and reproducibility of C-dots synthesis.