[(C2H5)3NH]Cl/ZnCl2离子液体催化合成维生素E

维生素E合成过程中催化剂用量大、损失严重且不能循环使用, 后处理过程产生大量废液导致严重的环境问题。实验合成了几种Lewis酸性离子液体, 并应用于维生素E合成。研究发现, [(C₂H₅)₃NH]Cl/ZnCl₂离子液体催化合成维生素E效果最好, 该离子液体中无机阴离子起主要催化作用, 季铵阳离子易与异植物醇的羟基形成氢键, 能使异植物醇与主环发生定向缩合反应。采用FT-IR研究了[(C₂H₅)₃NH]Cl/ZnCl₂离子液体结构和酸性, 并系统考察了其对维生素E合成的影响。随着ZnCl₂摩尔分数增加, 离子液体的Lewis酸性增强。在ZnCl₂摩尔分数为0.66的[(C₂H₅)₃NH]Cl/ZnCl₂离子液体催化作用下, 维生素E的产率可达到87.4%, 该离子液体重复使用5次, 催化性能没有明显下降。     

ANALYSIS OF TEMPERATURE-PROGRAMMED DESORPTION FROM POROUS CATALYSTS IN A FLOW SYSTEM

A comparison is reported between experimental and simulation results obtained from temperature-programmed desorption (TPD) spectra for H₂ and CO from Ni/SiO₂ catalysts. The gas/solid system is selected as representative of these adsorbates interacting with a Group-VIII metal. Intraparticle concentration gadients can be minimized by using a bed of small porous catalyst particles perfused by a flow of carrier gas while under these conditions axial concentration gradients in the bed cannot be avoided.

Previous models providing design criteria for analysis of TPD curves predict these conclusions, yet are overly restrictive. When allowance is made for repulsive interactions between adsorbates, it is found that significant redistribution of the adsorbate within the bed occurs. This results in nearly uniform adsorbed concentration profiles which are obtained when experimental conditions are selected properly. Consequently, specific guidelines can be offered to guide the experimentalist and methods are thus proposed to obtain TPD curves which are indicative of the desorption kinetics of the adsorbate.     

Ce的掺杂对负载型催化剂LaMnO3/赤铁矿脱硝性能的影响

采用柠檬酸络合浸渍法,通过对A位离子进行掺杂或取代和调节Ce的掺杂量,制备了一系列的负载型催化剂La_1-xA_xMnO₃/赤铁矿（A=Ce、Co,x=0/0.1/0.2/0.3）,并将催化剂应用于固定床NH₃-SCR脱硝。采用XRD、BET、XRF、H₂-TPR、NH₃-TPD等表征手段对催化剂进行分析和表征。结果表明,Ce的掺杂提高了催化剂LaMnO₃/赤铁矿的低温脱硝效率和拓宽了催化剂的活性温度窗口,如La_0.8Ce_0.2MnO₃/赤铁矿催化剂,在180℃时,脱硝效率就高达98%,且在150～250℃温度区间的脱硝效率均在90%以上。结合表征分析证明,稀土元素Ce的适量掺杂,明显提高了LaMnO₃/赤铁矿催化剂的氧化还原能力和催化剂表面NH₃分子的吸附能力;稀土元素Ce的适量掺杂也改善了催化剂比表面积,也使活性物质高度分散在载体表面上。     

The importance of Fe loading on the N2O reduction with NH3 over Fe-MFI: Effect of acid site formation on Fe species

Effect of the loading amount of Fe over ion-exchanged Fe-MFI catalysts on the catalytic performance of N₂O reduction with NH₃ was investigated, and the results indicated that the turnover frequency (TOF) was almost constant in the Fe/Al range between 0.05 and 0.40. The activity of N₂O + NH₃ reaction was much lower than that of N₂O + CH₄ reaction over Fe-MFI (Fe/Al = 0.40), and the preadsorption of NH₃ decreased drastically the activity of N₂O + CH₄ reaction. The temperature-programmed desorption (TPD) of NH₃ showed the formation of stronger acid sites on Fe-MFI (Fe/Al = 0.24 and 0.40), and the amount of the acid sites agrees well with the desorption amount O₂ in O₂-TPD in the low temperature range. The acid sites gave a 3610 cm⁻¹ peak (Brønsted acid) in FTIR observation. These results suggest that the acid sites were formed on the bridge oxide ions in binuclear Fe species. Adsorbed NH₃ on the strong acid sites inhibited N₂O dissociation, which can be related to the low activity of N₂O + NH₃ reaction over Fe-MFI with high Fe loading.     

Simultaneous characterization of acidic and basic properties of solid catalysts by a new TPD method and their correlation to reaction rates

We propose a new TPD method for simultaneously characterizing the acidic and basic properties of solid catalysts by utilizing the co-adsorption of NH₃ and CO₂ on catalysts. First CO₂ was adsorbed on the catalyst sample; then NH₃ was adsorbed on it. Another adsorption sequence of NH₃ and CO₂, and CO₂ and NH₃ single adsorptions were also conducted. The TPD measurements were carried out by heating the catalyst sample from 373 to 773 K at a heating rate of 2.5 K min⁻¹ in a helium stream under a total pressure of 1.3 kPa. In solid acid catalysts, there is little difference in the NH₃-TPD spectra between single and co-adsorption systems. This results from the absence of any induction effect between the acid and base sites, because the number of base sites in the solid acid catalyst is very small. In contrast, in a solid acid–base catalyst of alumina, a remarkable difference in the NH₃-TPD spectra was observed between single adsorption and co-adsorption systems. The difference in the TPD spectra between single and co-adsorption systems was ascribed to a strong induction effect appearing on the acid and base sites, which was proved by an in situ IR measurement. The validity of the TPD method was examined by correlating the number of the strong acid sites to catalytic activities of dehydrolysis of ethanol over solid acid and solid acid–base catalysts. In solid acid–base catalysts, the number of strong acid sites was calculated from the activation energy distribution for the desorption of NH₃ in a co-adsorption system because of the strong induction effect. A proportional relationship between the intrinsic reaction rate constant, which is based on the concentration of ethanol within the catalyst, and the number of strong acid sites could be obtained, regardless of the catalysts or their types or pore structure.     

SELECTIVE CATALYTIC REDUCTION OF NITRIC OXIDE BY AMMONIA ON PILLARED CLAY CATALYSTS: POSSIBLE MECHANISM AND PROMOTERS

The delaminated Fe₂0₃-pillared clay shows high activities for selective catalytic reduction (SCR) of NO by NH₂. Temperature program desorption (TPD) studies show that large amounts of NO., are adsorbed on the pillared clay catalyst at the SCR reaction temperatures (i.e. near 400°C). This result indicates that a Langmuir-Hinshelwood type mechanism (for reaction between chemisorbed NO, and NH, on the surface to form N₂) is operative for the pillared clay catalyst, which is in contrast to the SCR reaction on the commercial vanadia-based catalysts. The SCR activities for the delaminated Fe₂0₃-pillared clay catalyst are higher than that of a commercial-type V₂O₅ + WO₃/TiO₂ catalyst under SO₂ + H₂0 free conditions, but became lower in the presence of SO₂ +l H₂0. However, when promoted by doping 1-3% Cr₂0₃, the pillared clay catalyst exhibits higher SCR activities than the commercial-type catalyst in the presence of S0₂ + H₂O at all practical SCR reaction temperatures     

超声浸渍无机盐改性Hβ分子筛催化合成乙基蒽醌

采用超声浸渍法将无机盐Al₂(SO₄)₃、(NH₄)₂SO₄、Ce(NH₄)₂(NO₃)₆和Fe(NO₃)₃负载于Hβ分子筛上,通过NH₃-TPD、XRD和吡啶-IR对分子筛进行表征,考察改性前后分子筛酸性能和晶相的变化。将改性的Hβ分子筛用于催化乙苯和苯酐合成乙基蒽醌。结果表明,不同无机盐超声浸渍改性分子筛的催化效果差别较大,其中,每克分子筛负载0.2 g的Al₂(SO₄)₃的Alβ分子筛催化效果最好,苯酐转化率为45.67%,乙基蒽醌选择性为50.12%。分子筛的酸性能（包括酸量、酸种类和酸强度）对催化性能影响较大。     

溶胶-凝胶原位合成宽活性温度V2O5/TiO2脱硝催化剂

利用溶胶-凝胶技术原位合成一系列不同V₂O₅担载量的V₂O₅/TiO₂催化剂,通过BET、XRD、NH₃-TPD及紫外-可见光等手段对催化剂进行表征。结果表明：制备的催化剂均具有介孔结构,V₂O₅在TiO₂表面高度分散,且存在3种典型的酸性位。通过选择性催化还原反应对V₂O₅/TiO₂催化剂进行活性评价,结果显示随着V₂O₅含量的增加,NO转化率大于75%的温度窗口向低温方向偏移,含10% （质量分数）V₂O₅的催化剂的NO转化率为80%的温度窗口最宽为200～450℃,240℃时20 h连续实验表现出稳定的抗硫抗水性能。结合紫外-可见光谱分析,揭示了钒掺杂所形成的单聚和低聚钒酸盐为催化剂的活性组分。     

碱性添加剂在钛硅分子筛/H2O2催化丙烯环氧化反应中的作用

考察了反应溶液中碱性添加剂{氨水（NH₄OH）、氢氧化钠（NaOH）、碳酸钠（Na₂CO₃）、碳酸铵[(NH₄)₂CO₃]和四甲基氢氧化铵（TMAOH）}及其浓度对钛硅分子筛（TS-1）催化丙烯环氧化反应性能的影响,并采用紫外拉曼光谱（UV-Raman）与气相色谱（GC）联用原位分析（Raman-GC）碱性添加剂的作用机理。结果表明：反应体系中添加碱性添加剂可有效改善TS-1催化丙烯环氧化反应的选择性。不同碱性添加剂对TS-1催化丙烯环氧化活性和稳定性影响不同,NaOH、Na₂CO₃和TMAOH的添加造成催化活性和稳定性降低。NH₄OH或(NH₄)₂CO₃作为添加剂改善环氧化反应选择性的同时提高了反应稳定性,其中以(NH₄)₂CO₃效果最佳。添加(NH₄)₂CO₃浓度为8.0×10^-4mol/L时,TS-1催化丙烯环氧化在固定床反应器上连续运行336h时,X(H₂O₂)仍保持在90%以上。原位Raman-GC分析发现,反应体系中NH₄OH和(NH₄)₂CO₃添加可加快反应活性中间体Ti-OOH(η²)基团的生成,促进反应产物从活性中心快速扩散,从而提高丙烯环氧化反应选择性和稳定性。     

Phase transitions in R2 SnCl6-type crystals (R = NH3 C2H3, NH3C2H5 and N(CH3)4)

The thermal dilatation in (NH₃ ·CH₃) SnCl₆, (NH₃ · C₂H₅) SnCl₆ and [N(CH₃)] SnCl₆ was measured, and as the results it has turned out that (NH₃ ⁶·C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnCl₆ undergo the first order transitions at 128 K and 158 K, respectively. The low temperature phases of (NH · C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnC1₆ are found to be monoclinic and tetragonal, respectively, No phase transition was observed in (NH₃ ·CH₃)₂ SnCl₆ down to 77 K.     

前驱体结构对多环芳烃选择性开环Pt/Beta催化剂的影响

以海绵铂为原料合成出［Pt（NH₃）₆］Cl₄络合物,采用热重分析（TG）、扫描电镜-能谱（SEM-EDS）、紫外-可见分光光度计（UV-Vis）、质谱（MS）、X射线光电子能谱（XPS）等手段确定了［Pt（NH₃）₆］Cl₄的结构组成;以H₂PtCl₆、Pt（NH₃）₄Cl₂和［Pt（NH₃）₆］Cl₄为前驱体,采用等体积浸渍法制得Pt/Beta催化剂,采用X射线衍射（XRD）、X射线荧光光谱（XRF）、氨程序升温脱附（NH₃-TPD）、氢氧滴定（H₂-O₂）、透射电镜（TEM）、氢气程序升温脱附（H₂-TPD）等表征了Pt/Beta催化剂的物化性质,并考察了Pt/Beta催化剂的多环芳烃选择性开环性能。结果表明,［Pt（NH₃）₆］Cl₄络合物具有更高的“抗自还原”能力,可从前驱体结构上降低铂氨前驱体受热分解时的自还原现象。前驱体结构对铂纳米颗粒的几何尺寸及分布有较大影响,一方面络合物的价态显著影响前驱体与分子筛间的静电作用,进而影响铂纳米颗粒的落位与尺寸;另一方面络合物的空间结构影响前驱体在分子筛微孔中的分布,影响铂纳米颗粒的Ostwald熟化速率。前驱体结构可调变Pt/Beta催化剂的双功能匹配关系,显著影响Pt/Beta催化剂转化甲基萘的活性、稳定性,采用［Pt（NH₃）₆］Cl₄前驱体制备的Pt/Beta催化剂具有更优的活性及长周期稳定性。     

Hydrodechlorination of CCl4 over Pt/Al2O3: effects of platinum particle size on product distribution

The impregnated platinum catalysts showed various platinum particle sizes depending on the nature of the platinum precursors (Pt(NH₃)₂(NO₂)₂ versus H₂PtCl₆) and on the pH of the Al₂O₃ suspension. The average platinum particle size increased with decrease in pH of the suspension in case of Pt(NH₃)₂(NO₂)₂, but this trend was vice versa for H₂PtCl₆. The product distribution in hydrodechlorination (HDC) of CCl₄ varied greatly with the platinum particle size; the larger the platinum particle size was, the higher was the selectivity to CHCl₃. To elucidate the origin of this platinum particle size effect on product distribution, CO chemisorption, NH₃ and CO₂ temperature-programmed desorption (TPD), high resolution transmission electron microscopy (HRTEM), temperature-programmed surface reaction (TPSR), Fourier-transformed-infrared spectra (FT-IR) and X-ray absorption fine structure (XAFS) experiments were carried out. The formation of completely dechlorinated CH₄ was favorable owing to the strong chemisorption of CCl₄ on the small platinum particles characterized by low surface coordination numbers and by an electron-deficient property. The nature of carbonaceous species formed on platinum surface at the beginning of reaction also varied greatly with platinum particle sizes and changes of electronic state of platinum particles affected catalytic activity and products’ distribution.     

Water vapor sensitivity of nanosized La(Co, Mn, Fe)1−x(Cu, Pd)xO3 perovskites during NO reduction by C3H6 in the presence of oxygen

A series of La(Co, Mn, Fe)_1−x(Cu, Pd)_xO₃ perovskites having high specific surface areas and nanosized crystal domains was prepared by reactive grinding. The solids were characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) of O₂, NO + O₂, C₃H₆, in the absence or presence of 5% H₂O, Fourier transform infrared (FTIR) spectroscopy, as well as activity tests towards NO reduction by propene under the conditions of 3000 ppm NO, 3000 ppm C₃H₆, 1% O₂, 0 or 10% H₂O, and 50,000 h⁻¹ space velocity. The objective was to investigate the influence of H₂O addition on catalytic behavior. A good performance (100% NO conversion, 77% N₂ yield, and 90% C₃H₆ conversion) was achieved at 600 °C over LaFe_0.8Cu_0.2O₃ under a dry feed stream. With the exposure of LaFe_0.8Cu_0.2O₃ to a humid atmosphere containing 10% water vapor, the catalytic activity was slightly decreased yielding 91% NO conversion, 51% N₂ yield, and 86% C₃H₆ conversion. A competitive adsorption between H₂O vapor with O₂ and NO molecules at anion vacancies over LaFe_0.8Cu_0.2O₃ was found by means of TPD studies here. A deactivation mechanism was therefore proposed involving the occupation of available active sites by water vapor, resulting in an inhibition of catalytic activity in C₃H₆ + NO + O₂ reaction. This H₂O deactivation was also verified to be strictly reversible by removing steam from the feed.     

Polymerization characteristics of in situ supported pentamethylene bridged dinuclear zirconocene

An in situ supporting method was applied to newly synthesized [(CH₂)₅(C₅H₄)₂][(C₉H₇)ZrCl₂]₂ catalyst and other commercial catalysts, and its effects on the polymerization characteristics of these catalysts were examined through reaction experiments. The changes in the molecular weight distribution varied depending on the metallocene catalyst while the changes in the catalytic activity, average molecular weight and the melting point showed the same trend. The reason for the decrease in the molecular weight with in situ supporting was discussed in relation to the co-catalysts. The polymerization characteristics of each catalyst also varied according to the alkyl aluminum, and so it is important to select a proper co-catalyst or a combination of co-catalysts to obtain a desired polymer product from each metallocene catalyst supported by in situ method.     

Gold catalysts supported on mesoporous zirconia for low-temperature water–gas shift reaction

Mesoporous ZrO₂ with high surface area and uniform pore size distribution, synthesized by surfactant templating through a neutral [C₁₃(EO)₆–Zr(OC₃H₇)₄] assembly pathway, was used as a support of gold catalysts prepared by deposition–precipitation method. The supports and the catalysts were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, N₂ adsorption analysis, temperature programmed reduction and desorption. The catalytic activity of gold supported on mesoporous zirconia was evaluated in water–gas shift (WGS) reaction at wide temperature range (140–300 °C) and at different space velocities and H₂O/CO ratios. The catalytic behaviour and the reasons for а reversible deactivation of Au/mesoporous zirconia catalysts were studied. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new Au/mesoporous zirconia catalyst was compared to the reference Au/TiO₂ type A (World Gold Council), revealing significantly higher catalytic activity of Au/mesoporous zirconia catalyst. It is found that the mesoporous zirconia is a very efficient support of gold-based catalyst for the WGS reaction.     

Low temperature SCR of NO with NH3 over carbon nanotubes supported vanadium oxides

A novel multiwalled carbon nanotube (CNTs) supported vanadium catalyst was prepared. The structure of catalyst prepared was characterized by TEM, BET, FTIR, XRD and temperature-programmed desorption (TPD) methods. The results indicated that vanadium particles were highly dispersed on the wall of carbon nanotubes. The V₂O₅/CNT catalysts showed good activities in the SCR of NO with a temperature range of 373–523 K. The Lewis acid sites on the surface of V₂O₅/CNT are the active sites for the selective catalytic reduction (SCR) of NO with NH₃ at low temperatures. It was suggested that the reaction path might involve the adsorbed NH₃ species reacted with NO from gaseous phase and as well as the adsorbed NO₂ species. The diameter of CNTs showed positive effect on the activities of the catalysts. Under the reaction conditions of 463 K, 0.1 Mpa, NH₃/NO = 1, GHSV = 35,000 h⁻¹, and V₂O₅ loading of 2.35 wt%, the outer diameter of CNTs of 60–100 nm, the NO conversion was 92%.     

Oxygen and nitrogen-doped metal-free carbon catalysts for hydrochlorination of acetylene

Activated carbon was tested as metal-free catalyst for hydrochlorination of acetylene in order to circumvent the problem of environment pollution caused by mercury and high cost by noble metals. Oxygen-doped and nitrogen-doped activated carbons were prepared and characterized by XPS, TPD and N2 physisorption methods.The influences of the surface functional groups on the catalytic performance were discussed base on these results.Among all the samples tested, a nitrogen-doped sample, AC-n-U500, exhibited the best performance, the acetylene conversion being 92% and vinyl chloride selectivity above 99% at 240 °C and C2H2 hourly space velocity30 h-1. Moreover, the AC-n-U500 catalyst exhibited a stable performance during a 200 h test with a conversion of acetylene higher than 76% at 210 °C at a C2H2 hourly space velocity 50 h-1. In contrary, oxygen-doped catalyst had lower catalytic activities. A linear relationship between the amount of pyrrolic-N and quaternary-N species and the catalytic activity was observed, indicating that these nitrogen-doped species might be the active sites and the key in tuning the catalytic performance. It is also found that the introduction of nitrogen species into the sample could significantly increase the adsorption amount of acetylene. The deactivation of nitrogendoped activated carbon might be caused by the decrease of the accessibility to or the total amount of active sites.     

钇掺杂三氧化二铁催化剂的脱硝性能研究

为提升三氧化二铁(Fe₂O₃)催化剂的脱硝性能,扩展催化剂的活性温度窗口,采用共沉淀法引入助剂钇(Y)元素对Fe₂O₃催化剂进行改性。通过X射线衍射(XRD)、氮气等温吸-脱附(N₂-BET)、X射线光电子能谱(XPS)、氨气程序升温脱附(NH₃-TPD)、氢气程序升温还原(H₂-TPR)等表征方法对样品进行了表征分析。XRD和N₂-BET结果表明,Y的掺杂使催化剂结构发生变化,比表面积增加、孔径减小。XPS和NH₃-TPD结果证明,Y掺杂Fe₂O₃具有更多的表面吸附氧(O_Ⅰ)、Fe²⁺以及更多的酸量。H₂-TPR结果表明,Y的掺杂使催化剂的氧化还原能力略有下降。测试了不同含量Y掺杂的Fe₂O₃催化剂在150～400℃的脱硝性能,其中Fe<...     

Transient kinetic study of the SCR-DeNOx reaction

The unsteady-state kinetics of the selective catalytic reduction (SCR) of NO with NH₃ is studied over V₂O₅–WO₃/TiO₂ model catalysts by means of the transient response method. NH₃ strongly adsorbs onto the catalyst surface whereas NO does not adsorb appreciably. A dynamic mathematical model based on a Temkin-type desorption process for NH₃ and a SCR reaction rate with a complex dependence on the ammonia surface coverage is well suited to represent the data.     

CuO含量对Pd/Al2O3催化剂乙醇氧化性能的影响

采用浸渍法制备了一系列具有不同CuO含量的Pd-CuO/Al₂O₃催化剂，并将其用于乙醇氧化反应，其结构与性质通过XRD、H₂-TPR和NH₃-TPD等手段进行分析。结果发现，催化剂的活性并不是随着CuO含量的增加而增强，Pd-1.0%CuO/Al₂O₃催化剂表现出最佳的活性，其点火温度和完全转化温度比Pd/Al₂O₃催化剂至少降低了50℃。与Pd/Al₂O₃催化剂相比，含CuO催化剂增强的衍射峰强度以及氢化钯分解峰的消失，说明Pd-Cu合金结构的形成有利于Pd、Cu物种之间的协同作用。对于Pd-1.0%CuO/Al₂O₃催化剂来说，还原峰向低温的移动以及还原峰面积的增大说明该催化剂上氧化性物质更易被还原且数量在增加，这对于氧化反应是十分有利的，新出现的还原峰表示Pd、Cu的相互作用生成了新物种。NH₃-TPD结果中更高含量的低温酸有利于高活性，而且新出现的脱附峰说明形成了新的酸性位点。