单层分散阈值和负载型催化剂的阈值效应

自发单层分散原理认为,许多负载型催化剂的活性组分可在载体表面自发分散。活性组分在载体表面的单层分散阈值可通过XRD相定量外推法等实验方法进行测定。通过单层分散阈值的测定可获取负载型催化剂表面结构、分散状态的有益信息,并为选择最佳的催化剂制备工艺条件提供依据。许多负载型催化剂活性组分的配比都可通过考察其单层分散阈值得以优化。负载型催化剂的许多物理化学性质突变值都与其单层分散阈值相联系,催化剂的阈值效应是明显的,阈值效应的提出为催化剂的研究提供了指导。     

Distribution threshold values of CaCl<Subscript>2</Subscript> onto the 10X-zeolite and macro-pore silica gel

The calcium chloride used for adsorption separation of ammonia is promising for its large adsorptive capacity and lower desorption temperature, but difficult to develop because of the liable expansion, lump and chip in the adsorption/desorption process. Composite adsorbents made by monolayer dispersion of calcium chloride onto carriers with high surface areas exhibit better adsorptive capacity and stability. Several models were developed to confirm the maximum monolayer dispersion capacity of calcium chloride onto the carriers (the distribution threshold value), and the closely packed monolayer dispersion model was considered the most suitable for this study. The distribution threshold values given by this model were 0.60 g CaCl₂/(g 10X-zeolite) and 0.38 g CaCl₂/(g SiO₂). When the divalent salt was dispersed onto the carriers, however, anions were separated into two types, causing that the entropy of the system tended to increase and the system was not stable. To minimize the entropy, a new model was put forward as the modified closely packed monolayer dispersion model. Based on this model, the distribution threshold values are 0.52 g CaCl₂/(g 10X-zeolite) and 0.33 g CaCl₂/(g SiO₂), respectively. The distribution threshold values were also gained experimentally by XRD quantitative phase analysis: 0.61 g CaCl₂/(g 10X-zeolite) and 0.31 g CaCl₂/(g SiO₂). Comparison between experimental values of distribution threshold with theoretical ones based on two different model showed that the closely packed monolayer dispersion model fits the monolayer dispersion of calcium chloride onto micro-pore carrier —10X-zeolite, and the modified closely packed monolayer dispersion model is more suitable for the bigger aperture carrier —macro-pore silica gel. Supported by the National Natural Science Foundation of China (Grant No. 20576080)     

纳米晶镍-钼合金电沉积层的结构与性能

研究了Ｃｒ２Ｏ３、ＭｏＯ３、ＳＯ２－４和ＣｕＳＯ４在ＳｎＯ２表面的单层分散及其对ＳｎＯ２超细粉热稳定性的影响．结果表明,几种化合物在ＳｎＯ２上均能单层分散且分散阈值都接近按密置单层模型估算的分散容量极限值;表面单层覆盖能十分有效地抑制ＳｎＯ２的高温烧结,单层覆盖率与经５００℃焙烧后样品中ＳｎＯ２的粒径和比表面有很好的对应关系,表现出很强的阈值效应;单层覆盖率达到一定程度,ＳｎＯ２高温烧结便可基本得到抑制．     

氯化亚铜在活性炭载体表面单层分散的密度泛函理论计算

 应用量子化学计算方法研究了活性炭载体表面CuCl活性组分的单层分散行为. 以C16H10,C13H9和C12H12原子簇模型模拟活性炭表面,用密度泛函理论中的B3LYP方法计算得到了CuCl在活性炭表面分散的活性位、稳定构型、相互作用能以及单层分散阈值. 结果表明,CuCl以铜端垂直附着在活性炭表面的顶位和桥位上,相互作用能为76.84～80.79 kJ/mol,单层分散阈值为0.471 g/g. 而XRD测得的单层分散阈值为0.467 g/g,与量子化学计算的结果一致; 按照密置单层模型计算得出的单层分散阈值为0.941 g/g,远大于实验测定结果. 因此,应用量子化学计算方法可以得到活性炭表面活性组分单层分散的丰富信息,并能确定活性组分的单层分散阈值.     

盐类和氧化物在载体上自发单层分散研究新进展

 盐类和氧化物在载体上自发单层分散的现象和原理自被发现以来在国内外得到了广泛认同，国内外这方面的工作越来越多．我们从国内外同行近年发表的上百篇有关论文中，选择一部分内容加上我们的部分工作做一个简单的综述，介绍有关自发单层分散原理在基础研究和应用两个方面的新进展．     

某些有机物在氧化物载体表面的自发单层分散

自发单层分散原理已在载负型催化剂制备、再生等方面得到越来越广泛的应用[1，2]．许多氧化物和盐类可以在载体表面形成单层分散或亚单层分散．有些分散物与载体混合后在低于其熔点的温度下处理，就可以自发分散到载体表面[1，3]．这一现象通过XRD、LRS、XPS、SIMS、ISS、EXAFS     

构建稳定的CuO/La2Sn2O7催化剂用于碳烟颗粒燃烧:CuO在La2Sn2O7烧绿石复合氧化物载体上的单层分散行为

柴油车尾气排放的碳烟颗粒造成了日益严重的环境污染.目前催化燃烧是消除碳烟颗粒污染的有效技术.针对金属氧化物负载体系,20世纪70年代末谢有畅教授等人提出了单层分散理论,是指导设计高效负载催化剂的一个重要思想,已被科研工作者们普遍接受.当负载催化剂体系用于某个特定反应时,通常会表现出单层分散阈值效应,即负载的活性组分含量为单层分散阈值时,催化剂往往具有最好的活性和选择性.为探究金属氧化物在复合氧化物载体上的分散行为,并期望研制出性能优良的碳烟颗粒消除催化剂,本文制备了系列不同负载量的CuO/La₂Sn₂O₇催化剂,并把实验表征技术和DFT计算方法相结合,对其构效关系进行了研究.结果表明,CuO可自发分散在La₂Sn₂O₇烧绿石载体,其单层分散容量为1.90 mmol CuO/100 m²La₂Sn₂O₇.CuO负载量不高于该容量时,以亚单层或单层分散状态存在.XPS、Raman、Bader电荷和DOS分析证明,亚单层/单层CuO中的Cu2+离子可把其电荷选择性地传递给La₂Sn₂O₇烧绿石载体结构中B位的Sn4+离子,因而与载体产生强相互作用.反之,Cu²⁺离子与载体结构中A位的La³⁺离子之间无电荷转移,不产生作用.这表明在含多种金属离子的复合氧化物载体上,被负载的金属氧化物可优先与载体中的一种金属离子产生相互作用.Raman、原位DRIFTS和XPS结果表明,在界面上形成的O2^?和O2^2?亲电氧离子是CuO/La₂Sn₂O₇催化剂表面的活性中心,其含量决定了催化剂碳烟颗粒燃烧的活性.在CuO负载量低于单层分散容量时,这些表面活性亲电氧离子含量随着CuO的负载量升高而增加,直至单层分散容量时达到最大.在CuO负载量高于单层分散容量时,CuO微晶开始形成,并对表面活性亲电氧离子的生成产生负面影响.上述结果表明,CuO/La₂Sn₂O₇催化剂用于碳烟颗粒燃烧具有明显的单层分散阈值效应;并可通过在La₂Sn₂O₇载体表面负载单层分散量的CuO获得活性最佳的催化剂.     

CuO/γ-Al2O3单分散催化剂的XAFS研究

采用XAFS方法研究浸渍法制备并于低温焙烧的CuO/γ-Al2O3催化剂的局域结构.对于CuO负载量小于单层分散阈值的CuO/γ-Al2O3(0.4 mmol/100 m2),结果表明,CuO物种是以层状分散的孤立原子簇存在于γ-Al2O3载体表面,其第一近邻Cu－O配位环境的结构与晶态CuO的相似,键长和配位数分别为0.195 nm和4.对于CuO负载量等于单层分散阈值的CuO/γ-Al2O3(0.8 mmol/100 m2),已有少量的CuO纳米颗粒生成.对于CuO负载量大于单层分散阈值的CuO/γ-Al2O3(1.2 mmol/100 m2),其结构与多晶CuO的相近.基于CuO在γ-Al2O3载体上的三种不同分散状态的结构特点,我们提出了CuO/γ-Al2O3催化剂的结构模型.     

有机酸在γ-Al~2O~3表面自发单层分散及苯甲 酸-γ-Al~2O~3表面结构的研究

有机酸如苯甲酸,水杨酸,邻-或对-苯二甲酸,酒石酸均可在γ-Al~2O~3表面自发单层分散,分散的临界温度取决于有机酸分子中极性基团的数目和极性的强弱。XRD,Raman,FT-IR,UV-vis和TG对苯甲酸-γ-Al~2O~3体系的表征结果表明,苯甲酸在室温下即可在γ-Al~2O~3表面自发单层分散;分散后,苯甲酸分子间的氢键缔合结构垮塌;苯甲酸的羧基与γ-Al~2O~3表面羟基发生相互作用并缩水形成类似羧酸盐的结构;分子中的苯环与载体表面没有直接的相互作用。XRD相定量测得的分散阈值为1.1mmol苯甲酸/100m^2γ-Al~2O~3,与按苯环垂直表面计算所得的最大分散容量1.2mmol/100m^2相近。     

负载型V2O5/TiO2催化剂表面分散状态和性质对氨选择性催化还原NO性能的影响（英文）

采用多种物理化学手段研究了不同负载量V2O5/TiO2催化剂的VOx物种分散状态、表面酸性、可还原性及其选择性催化还原(SCR)NO性能.结果表明,V2O5在锐钛矿TiO2表面的实测单层分散容量约为1.14mmol V/100m2TiO2,与"嵌入模型"的估算值相符,表明分散态的钒离子应键合在TiO2表面的八面体空位上.随着V2O5负载量的增加,V2O5/TiO2催化剂上NO转化频率(TOF)先急剧增加,至0.70mmol V/100m2TiO2(略超过分散容量的一半)时达到极大(约8.3×10-3s-1),然后又急剧下降;同时,孤立VOx物种可能倾向于分散在相邻的八面体空位上,且通过V-O-V化学键相连形成聚合的VOx物种,V-O-V键所占比例增加而V-O-Ti键所占比例减小,催化剂表面单位钒离子的Brnsted酸中心量增加,故催化剂的TOF急剧增加.随着负载量进一步增加,虽然催化剂表面单位钒离子的Brnsted酸中心量仍缓慢增加,但V-O-Ti键所占比例减少,导致钒离子的可还原性下降,另外,分散容量以上时晶相V2O5的形成也导致钒离子表面利用率下降,从而导致催化剂的TOF下降.桥式Brnsted酸位(V-O(H)-V)也是SCR反应活性中心之一,不同负载量V2O5/TiO2催化剂上SCR活性与表面VOx物种的分散状态、表面酸性和钒离子可还原性密切相关.     

制备高比表面负载型催化剂的一种新方法

In this paper, a new way to increase the specific surface areas of supported catalysts has been suggested. The results for MoO_3/ZrO_2, WO_3/ZrO_2, CuO/ZrO_2, SO_4~(2-)/ZrO_2, NiO/ZrO_2, Fe_2O_3/ZrO_2, Fe_2(SO_4)_3/ZrO_2, MoO_3/TiO_2, WO_3/TiO_2, SO_4~(2-)/TiO_2, NiSO_4/TiO_2, NiO/TiO_2, V_2O_5/TiO_2 etc. systems show that the specific surface areas of the samples, prepared by impregnating some hydroxides then calcinating at high temperature, are much larger than those of the samples prepared with a traditional method——impregnating their oxides calcinated at the same temperature. Using this way, the specific surface areas of some supported catalysts can increase by several times. The surface areas of some supports such as zirconia and titania are not large enough, and they are easy to sinter at high temperature. In these cases, the advantage of of this preparation method is fully displayed, and the specific surface areas of the resulting zirconia-or titania-supported catalysts can compare favourably with those of the catalysts prepared from some classical supports (such ar γ-Al_2O_3, SiO_2).In addition, it has been proved by means of XPS, XRD, LRS, and DTA that as an active component disperse on a support as a monolayer and its content comes up to its monolayer dispersion capacity, the specific surface area of the obtained catalyst would be the largest. We suggest a mechanism that an active component covered on a support can not only segregate its particles, but also hinder the surface diffusion of support, and as a result, its crystalline growth, an accompanying phase transformation and inter-crystalline sintering are all retarded.     

Distribution threshold values of CaCl_2 onto the 10X-zeolite and macro-pore silica gel

The calcium chloride used for adsorption separation of ammonia is promising for its large adsorptive capacity and lower desorption temperature,but difficult to develop because of the liable expansion,lump and chip in the adsorption/desorption process.Composite adsorbents made by monolayer dis-persion of calcium chloride onto carriers with high surface areas exhibit better adsorptive capacity and stability.Several models were developed to confirm the maximum monolayer dispersion capacity of calcium chloride ...     

TG Study of the Dispersion Threshold of Mn2O3 on γ-Al2O3

Mn₂O₃/-Al₂O₃ catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn₂O₃ on the surface of -Al₂O₃ was determined to be 13.08% from the decomposition mass loss of supported Mn(NO₃)₂ in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn₂O₃ on the surface of -Al₂O₃.This revised version was published online in November 2005 with corrections to the Cover Date.     

乙醇羰化反应负载型催化剂的研究

本文由七种负载型催化剂中选出两种比较好的乙醇羰化催化剂,研究了影响反应转化率和选择性的因素,考察了活性组份的价态和载体的酸性。此外,还对催化剂进行了能量色散X射线分析。从其结果看,谱图上只有活性中心铑的谱峰而没有氯的谱峰,说明铑是以离子形式进入载体,而不是以化合物形式被吸附于载体上。     

SSIMS表征催化剂的表面状态和结构层次

自Benninghoven。A 提出静态二次离子质谱(Static Secondary Ion Mass Spectrometry或SSIMS)方法以来,它就成为一种极灵敏的表面分析技术。近年来,SSIMS技术在多相催化研究中的应用日益广泛。我们曾成功地用SSIMS表征过MoO_3-NiO-P_2O_5/γ-Al_2O_3催化剂的表面结构层次.本工作中,我们应用SSIMS,并结合XPS对新型催化剂MoO_-CoO/TiO_2-Al_2O_3的表面结构层次和表面状态作了研究.实验结果和我们原先用PASCA(Positron     

Zeolites modified by CuCl for separating CO from gas mixtures containing CO2

Although zeolites such as NaY and 13X adsorb CO₂ much more than CO, the adsorption amount of CO₂ and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO₂. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO₂ adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO₂, N₂, H₂ and CH₄. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO₂. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.     

CuCl2/NaY体系表面分散态研究

铜负载分子筛作为催化剂或吸附剂，在石油化工、环境保护等方面有许多用途[1，2]．已有研究发现，铜交换的Y型分子筛对NO分解等反应具有较高活性及稳定性［3-5］．因此研究铜负载Y型分子筛对有关吸附剂和催化剂的制备有重要意义．我们实验室在研究活性组分在载体表面分散现象时     

负载型催化剂的表面相互作用及其在大气分子污染物NO和CO消除中的应用基础研究

负载型催化剂具有重要的应用背景,研究表面分散组分与载体之间的相互作用.对于了解催化过程的本质,进而设计开发高效实用的催化剂均有重要的指导意义.本课题组近年来在该领域中进行了一些探索研究,涉及的催化剂以负载型金属氧化物(如CuO/γ-Al_2O_3,CuO/Ce_xZr_(1-x)O_2和CuO/Ti_xSn_(1-x)O_2等)为主,涉及的反应包括CO完全氧化和NO+CO反应.通过改变活性组分的负载量、添加改性剂和改变样品制备条件等制得一系列样品,用多种固体催化剂表征手段考察各组分在催化剂中的作用以及在上述催化反应中的活性变化规律.研究表明:(1)金属氧化物和卤化物等离子化合物在氧化物载体表面的分散容量和分散后的一些性质均可从"嵌入模型"的考虑得到解释;(2)处于不同载体表面的活性物种或同一载体表面不同结构的活性物种,由于其存在状态的差异使得其氧化还原性质和催化性质不同;(3)在相关催化剂体系中进行的CO完全氧化和NO+CO反应的结果显示,通过探索催化剂的"组成-结构-性质"间的关系,有可能为实际催化剂的设计提供理论参考.     

MoO3负载在新型TiO2/γ-Al2O3载体上的表面状态与性质

MoO_3担载在TiO_2或γ-Al_2O_3载体上是一类重要的工业催比剂, 其表面状态和表面性质国内外已有过许多报导, 本文报导~[1-5], MoO_3负载在我们所研制的新型TiO_2/γ-Al_2O_3载体(指以γ-Al_2O_3为骨架, 表面上铺以TiO_2物种的载体)上的表面状态与性质。     

金属酞菁化合物在TiO2表面的分散研究

Dispersion of copper(Ⅱ) phthalocyanine (CuPc), copper(Ⅱ) phthalocyaninesulfonate (CuPcS) and cobalt(Ⅱ)phthalocyaninetetrasulfonate (CoPcTS) on the surface of titanium dioxide was investigated by XRD, XPS, FT-IR and UV-Vis techniques. Results show that interaction between CuPc and TiO2 was very weak and CuPc was difficult to disperse on the surface of the support. While partly sulfurized CuPcS could be dispersed on the surface of support through sulfo-groups and its dispersion capacity was determined to be 0.085 g CuPcS/g TiO2. Completely sulfurlzed CoPcTS could also be dispersed on the surface of TiO2 as a monolayer and its dispersion capacity was 0.12 g CoPcTS/g TiO2. Interactions of the sulfo-groups as well as the electrons of CoPcTS with the surface of TiO2 could be evidenced by FT-IR characterization. Therefore, it was suggested that CoPcTS molecules be adsorbed on the surface of TiO2 in a flat-lying mode while CuPcS in a slanting one. UV-Vis spectra show that the dispersed CuPcS and CoPcTS molecules exist in both forms of monomers and dimers.