多维NaY分子筛的水热稳定性研究

引入功能梯度化设计概念,合成了表面多维化的NaY分子筛,采用X射线衍射仪、X射线荧光光谱仪、比表面积、微反活性和小型流化床催化剂评价装置(ACE)等表征分子筛及其催化剂老化前后的性能。结果表明,由多维NaY分子筛制备的稀土Y型分子筛REY-D, 其水热稳定性低于常规NaY分子筛所制得的REY-C分子筛。当分子筛与基质结合后,结果相反,多维NaY分子筛催化剂的老化活性高于常规NaY分子筛所制得的催化剂,且随着老化时间的延长,效果更明显。ACE选择性测试结果表明,采用多维NaY分子筛所制得的催化剂汽油收率高,而重油和柴油收率低,且汽油产品中烯烃含量低,液化气中的低碳烯烃含量高。     

稀土元素(Y、Nd、Ce、La)改性NaY分子筛催化乳酸脱水制丙烯酸

采用浸渍法以稀土元素(Y、Nd、Ce、La)对NaY分子筛进行改性,并以改性后的分子筛为催化剂,考察催化乳酸脱水制丙烯酸反应活性。通过NH₃-TPD、CO₂-TPD和XRD等对催化剂进行表征,结果表明,稀土元素进入NaY分子筛骨架,其中,La对分子筛晶体结构影响最小;随着负载稀土元素离子半径的增大(Y³⁺＜Nd³⁺＜Ce³⁺＜La³⁺） ,总酸性位数量减少,除了重稀土元素Y,弱酸性位比例和中等强度碱性位数量增多,La改性最有利于丙烯酸的生成。稀土元素改性的NaY分子筛在一定程度上提高丙烯酸收率,抑制乙醛生成。以质量分数38%的乳酸为原料,在空速3 h^-1、反应温度325 ℃和2%La/NaY分子筛为催化剂时,丙烯酸收率为54.2%,而未改性NaY分子筛上丙烯酸收率仅为34.7%。     

薄片状Y型分子筛的合成及其裂化性能

采用导向剂法,以聚乙二醇-600（PEG-600）为形貌控制剂和分散剂,制备了具有薄片状形貌的小晶粒Y型分子筛。通过X射线衍射（XRD）、扫描电镜（SEM）、N₂吸附-脱附、吸附吡啶的原位红外和NH₃程序升温脱附（NH₃-TPD）技术对合成的Y型分子筛及制备的催化剂进行了表征。结果表明,所合成的Y型分子筛大部分呈薄片状形貌,相对于传统八面体形貌Y型分子筛来说,具有较高的外比表面积。1,3,5-三异丙基苯的催化裂化反应结果表明,与传统八面体形貌的Y型分子筛制备的催化剂相比,薄片状Y型分子筛具有较高的1,3,5-三异丙基苯裂化活性和裂化产物选择性。     

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。     

胶束化行为对Cu-HMS介孔分子筛结构及催化性能的影响

通过改变EtOH/H2O比,制备了一系列不同粒径和比表面积的Cu-HMS分子筛,使用红外,XRD,SEM和BET对其进行表征,研究不同乙醇/水的用量下,胶束化行为对Cu-HMS结构和表面形貌的影响。不同粒径的Cu-HMS与活性组分PdCl2结合制成氧化羰基合成碳酸二乙酯的催化剂,均表现出较好的选择性。其中EtOH/H2O比为1.0的Cu-HMS分子筛,由于较大的比表面积在相同钯含量下表现出较高的催化活性。     

稀土-Cu-K/Y分子筛催化剂的制备与性能研究

采用浸渍法制备了分别以Y型分子筛和γ-Al2O3为载体的几种含铈、镨、钕的氯化氢氧化催化剂.运用XRD、ESEM、BET等不同测试手段对两种催化剂进行了表征,测试了这两种催化剂对于氯化氢氧化反应的活性.XRD检测结果表明:以γ-Al2O3为载体的催化剂表面形成了明显的稀土氧化物及氯化钾晶相的特征衍射峰,且主要以CeO2相存在,而以Y型分子筛为载体的催化剂表面并没有检测到相关的物相;ESEM检测表明在Y型分子筛中引入铜、钾及稀土元素后并没有破坏Y型分子筛的结构.在氯化氢氧化反应中,稀土-Cu-K/Y显示了良好的催化活性,在648 K,V(HCl)/V(O2)＝1.5的条件下,氯化氢的转化率达到了85%.     

用分形方法研究负载型聚烯烃催化剂的表面形貌及其对聚合活性的影响

以Ｍｇ（ＯＥｔ）２和ＴｉＣｌ４作为钛镁体系聚乙烯催化剂的代表,在不同反应上制备了Ｔｉ－Ｍｇ体系负载型聚乙烯催化剂,并用扫描电镜（ＳＥＭ）技术对其亚微观结构进行研究,证实其具有分形特征。应用分形理论及其改进的盒子维法对催化剂的亚微观结构进行了详细的分析计算,给出了催化剂表面结构的分维数,结果发现,催化剂分维值Ｄｔ随着催化剂表面的不规则度及催化剂内部孔隙的增多而增大,而其聚合活性与催化剂表面分维值的关系较为复杂,只在适宜的催化剂分维值范围内,才可获得较高的聚合活性,研究证明了分维值可作为比较两个分形无规则度对象的表征参量。     

Zr改性Y分子筛中油型加氢裂化催化剂设计制备

采用等体积浸渍法对Y分子筛进行了Zr修饰改性,系统考察了不同用量Zr对改性Y分子筛的结构、催化剂的理化性质和加氢裂化反应性能的影响规律。通过XRD、NH₃-TPD、H₂-TPR和TEM等方法对改性分子筛和催化剂进行表征分析。结果表明：Zr改性降低了Y分子筛的酸量,随着改性Zr用量的增加,这种变化趋势不断增大。同时,Zr改性有效地削弱了分子筛催化剂中金属活性组分与载体间的作用,提高了W物种在催化剂表面的分散程度。加氢裂化反应结果表明：与Y分子筛催化剂相比,Zr改性Y分子筛催化剂的减压馏分油(VGO)转化率降低,中间馏分油选择性提高约20%,随着改性Zr用量的增加,VGO的转化率不断降低,中间馏分油选择性略有增加。     

磷渣粉体颗粒表面粗糙度的定量表征

采用盒维数估计其表面粗糙程度,并研究盒维数与需水量比和泌水率的关系。结果表明：分维值的大小定量表征了磷渣粉体颗粒表面的粗糙程度,分维值愈大,其表面愈粗糙,需水量比亦愈大,而泌水率愈小。     

Zr改性Y分子筛中油型加氢裂化催化剂设计制备

采用等体积浸渍法对Y分子筛进行了Zr修饰改性,系统考察了不同用量Zr对改性Y分子筛的结构、催化剂的理化性质和加氢裂化反应性能的影响规律。通过XRD、NH_3-TPD、H_2-TPR和TEM等方法对改性分子筛和催化剂进行表征分析。结果表明:Zr改性降低了Y分子筛的酸量,随着改性Zr用量的增加,这种变化趋势不断增大。同时,Zr改性有效地削弱了分子筛催化剂中金属活性组分与载体间的作用,提高了W物种在催化剂表面的分散程度。加氢裂化反应结果表明:与Y分子筛催化剂相比,Zr改性Y分子筛催化剂的减压馏分油(VGO)转化率降低,中间馏分油选择性提高约20%,随着改性Zr用量的增加,VGO的转化率不断降低,中间馏分油选择性略有增加。     

Catalytic activity of FeZSM-5 zeolites in benzene hydroxylation by N2O: The role of geometry characterized by fractal dimensions

The fractal dimensions of FeZSM-5 zeolites were used to characterize the change in their geometry depending on different post-synthesis treatments. The fractal dimension values were estimated from the Dubinin–Astakhov isotherms of nitrogen adsorption and related to the activity of these zeolites in the benzene hydroxylation to phenol by nitrous oxide. The zeolites had two different iron contents (350 and 5800 ppm) and a Si/Al ratio of 42. The catalysts were activated by steaming (823 K) and/or calcinations in He (1323 K). The FeZSM-5 activated by steaming exhibited fractal dimensions lower than the samples activated by calcinations. The steamed samples also had activities in the benzene hydroxylation per Fe(II) site (TOF values) somewhat higher as compared to the zeolites activated by calcinations. This indicates the importance of the zeolite geometry for the reaction of bulky benzene molecule within a confined space.     

片状粉末表面特性的分形分析

根据片状粉末表面几何特征,提出了用分形方法对其进行描述. 将数码相机拍摄的不同片状粉末的显微照片输入计算机,采用计算分形盒子维的DBC算法对其灰度值进行编程计算,可获得颗粒表面的分形维数. 计算得到的分维数的数值在2~3之间,且粉体表面越不光滑,表现在灰度值的起伏越大,则分维数的数值也越大,与人们视觉上对粗糙表面的观察相吻合. 在一定程度上可有效地反映粉体表面的光滑性,从而为片状粉体表面特性的分析和研究提供了一个新思路.     

化工设备材料表面及其对界面黏附强度的影响

设备材料的表面粗糙程度对污垢颗粒界面黏附力的影响较大。本文以设备材料粗糙表面为研究对象,考察了传统指标和分形指标的尺度独立性,发现分形指标随尺度的变化分为不稳定分形区和稳定分形区。通过对二维表面轮廓线的分析,将区域分隔临界点的求取转化为取样长度和夹角α值的定量关系求解,通过实验得出其定量关系,找出稳定分形区。采用原子力显微镜测颗粒在不同粗糙表面的黏附力,结合固体污垢清除机理分析,发现表面的粗糙程度对界面黏附力的影响较大。研究表明Ra<0.4627μm时,随着表面粗糙度增加,黏附力减小;1.3461μm< Ra <2.9755μm时,黏附力逐渐增大;Ra>3μm时,黏附力保持稳定。黏附力随着分形指标的变化而变化,其变化趋势与传统指标正好相反。随着分形维数的增大,黏附力先是保持稳定,后逐渐增大,随着加工工艺的改变,表面粗糙程度有个剧烈的变化,分维值锐减,后逐渐增大。     

Fractal approach for modeling the morphology evolution of olefin polymerization with heterogeneous catalysts

Fractal theory and methodology were used to investigate the morphology of titanium–magnesium‐supported polyethylene catalysts and their relevant polymer particles. Through an analysis of the submicrostructures using scanning electron microscopy images, the surface fractal dimensions of the related particles were estimated with the box‐counting method. With consideration given to the fact that the growth process of a polymer is an evolving fractal process, which is controlled on the one hand by the initial conditions, including the initial fractal dimensions of the catalysts and the initial reaction conditions, and on the other hand by the previous morphology characteristics of the system, a novel polymerization fractal growth model was constructed. The simulation results showed good agreement with the experiment data. Moreover, the morphology evolution with the prepolymerization technique was predicted, and it was suggested that the duration of polymerization was 10–30 min. It was proven that the use of the surface fractal dimension as an important parameter describing the surface morphologies of the particles, either of catalysts or polymers, was real and effective. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1463–1470, 2003     

Fractal analysis of surfaces roughened by grit blasting

Surfaces roughened by grit blasting influence the adhesion strength of plasma-sprayed ceramic coatings. The average surface roughness has been used to evaluate the surface topography of such surfaces. It is well known that the adhesion strength of ceramic coatings reaches a maximum value at a certain substrate surface roughness. However, this result cannot be understood based on only surface roughness. The blasted surface has fractal characteristics. There are two types of fractal surfaces, which are characterized by self-similarity and self-affinity. Using fractal analysis to evaluate the surface topography of substrates, the fractal dimension was measured for the roughened surfaces. The maximum fractal dimension was attained at a blasting angle of 75°, where the adhesion strength also reached approximately its maximum value. It is concluded that the fractal dimension is a more appropriate measure than the average surface roughness for evaluation of the adhesion strength of ceramic coatings.     

沸石分子筛表面分形维数与孔性质的关联分析

为了研究模板材料对沸石分子筛表面形貌和孔结构性质的影响以及在焙烧除模板材料过程中分子筛表面复杂程度和孔道分布的变化,分别采用X射线衍射和氮气物理吸附-脱附对沸石分子筛进行表征,基于分形学理论引入分形维数及其计算,并将计算结果与分析结果进行对比讨论。结果表明,分形维数与分子筛表面的复杂程度密切相关,分子筛表面越复杂、沟壑越多,分形维数越大,反之则越小;模板材料影响分子筛不同指数晶面的生长速率和生长取向,进而影响分子筛的外观形貌和孔道结构性质,在焙烧除模板材料后,分子筛表面部分较大孔道发生塌陷,致使整体结构趋于平整化,分形维数减小。     

Fractal characterization of ceramic crack patterns after thermal shocks

This work utilized a combination of experimental evidence and fractal geometric method to assess the effect of crack extension concerning the thermal shock on residual strength of ceramics. Sintered alumina (Al₂O₃) ceramic slabs were bundled and quenched in water under different thermal shock temperatures. The fractal dimension of thermal shock crack patterns on the interior surface and the cooled surface was calculated by the Box-counting method. Fracture energy of a fractal pattern of microcracks in quasi-brittle solids was employed to explain the relationship between crack length and fractal dimensions. The results show that if the crack propagation has the same crack length but a larger fractal dimension, it will absorb more fracture energy. The thermal shock crack patterns of Al₂O₃ ceramics with different grain sizes were analyzed, and the smaller grain size ceramic had a higher fractal dimension of crack patterns than the larger one.     

Electrocatalytic activity of nitrogen doped carbon nanotubes with different morphologies for oxygen reduction reaction

Nitrogen doped carbon nanotubes (NCNTs) were synthesized by a single step chemical vapor deposition technique using either ferrocene or iron(II) phthalocyanine as catalyst and pyridine as the carbon and nitrogen precursor. Variations in surface morphology and electrocatalytic activity for oxygen reduction reaction (ORR) were observed between the NCNTs synthesized using different catalysts. The structural and chemical characterizations were carried out using transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical activity of NCNTs was evaluated with rotating ring disc electrode (RRDE) voltammetry. Structural characterization suggested more defects formed on the NCNTs synthesized from ferrocene (Fc-NCNTs) which led to a rugged surface morphology compared to the NCNTs synthesized from iron(II) phthalocyanine (FePc-NCNTs). Based on the RRDE voltammetry study, Fc-NCNTs demonstrated much higher activity for ORR than FePc-NCNT. Evidences from the structural and chemical characterizations illustrate the potential impact of catalyst structure in shaping the surface structure of NCNTs and the positive effect of surface defects on ORR activity. These results showed that potential improvements on ORR activity of NCNTs could be achieved by tailoring the surface structure of NCNTs by using catalysts with different structures.