吸附量热技术和多相催化微观动力学

本文介绍了多相催化研究中的吸附量热技术、多相催化微观动力学及其计算机模拟, 以及吸附量热技术在定量表征固体催化剂表面中心和在多相催化微观动力学分析中的重要作用。     

微量热法研究燃料电池PtRu/C催化剂的CO微分吸附热

用微量热法技术测量CO的微分吸附热以探测碳负载的单金属Pt,Ru及双金属Pt-Ru催化剂的CO表面吸附位.结果表明,单金属Pt催化剂显示出最高的初始微分吸附热(q_initial=125 kJ·mol^-1);单金属Ru催化剂具有最低的初始微分吸附热(q_initial=109 kJ·mol^-1);三种双金属PtRu催化剂的初始微分吸附热(q_initial=124～112 kJ·mol^-1)界于两种单金属之间.当双金属PtRu催化剂Pt:Ru原子比为1:2时,催化剂Pt原子表面上的强CO吸附位(> 112 kJ·mol^-1)被Ru原子所覆盖而完全消失.     

BaX分子筛的阳离子分布及其吸附分离对二甲苯的机理

 BaX分子筛是用于从C8芳烃中分离高纯度对二甲苯的吸附剂. 应用多晶XRD技术,通过电子密度函数法和Rietveld法,对吸附速率和分离度不同的两个BaX分子筛样品进行了结构的测定,并通过结构分析探讨了BaX分子筛的吸附机理. 结果表明,不同工艺制备的BaX分子筛中Ba2+离子的定位略有不同. BaX分子筛中Ba2+离子主要分布在SⅠ′ 和SⅡ位置上,定位于SⅠ′ 位的Ba2+离子稳定了分子筛的骨架; 而定位于超笼的SⅡ位置的Ba2+离子,当其接近占满并且每个Ba2+极化两个配位水时,可在超笼中产生一个对称性为D2群的吸附力场,这是BaX分子筛吸附分离对二甲苯的必要条件. 若Ba2+离子在SⅡ位置的占有率下降或在超笼中存在着SⅡ位置以外的低占有率的阳离子,则破坏了上述吸附力场的对称性,削弱了分子筛的选择吸附能力.     

HZSM-5分子筛中邻近酸中心上的协同催化作用

总结了HZSM-5分子筛中邻近的酸中心协同催化作用的研究进展, 包括布朗斯特酸(B酸)和路易斯酸 (L酸)的协同催化、 B酸和B酸的协同催化作用. 综述了通过多种表征手段下协同催化作用机理的研究进展, 以及实验与理论计算相结合并相互验证的研究结果, 对邻近酸中心协同作用下反应分子的共同吸附、 活化与转化路径的特点进行了分析与总结, 提出了对邻近酸中心协同催化作用进行深入研究的关键科学问题和可能的解决方案.     

Correlation and Calculation of Multicomponent Adsorption Equilibria Data Using a Generalized Adsorption Isotherm

Enhanced by the need for reliable and accurate data of multicomponent gas adsorption equilibria on porous solids like activated carbons or zeolites, a new method to measure and correlate coadsorption equilibria has been developed. This method is a combination of gravimetric or volumetric measurements of the total load of pure or multicomponent adsorbates (Staudt, 1994; Gregg and Sing, 1982) and a correlation and calculation procedure using a new adsorption isotherm (AI) (Keller, 1990). This AI is thermodynamically consistent and describes adsorbates with fractal dimension for single- or multicomponent systems and load dependent adsorption energies. This method allows calculation of partial loads of multicomponent coadsorption equilibria from pure component data and the total loads of the mixture adsorption equilibria. This will be demonstrated for binary and ternary adsorption equilibria of CH₄, C₂H₄ and C₂H₆ on activated carbon (Reich et al., 1980).     

Analysis of Adsorbate–Adsorbate and Adsorbate–Adsorbent Interactions to Decode Isosteric Heats of Gas Adsorption

A qualitative interpretation is proposed to interpret isosteric heats of adsorption by considering contributions from three general classes of interaction energy: fluid–fluid heat, fluid–solid heat, and fluid—high‐energy site (HES) heat. Multiple temperature adsorption isotherms are defined for nitrogen, T=(75, 77, 79) K, argon at T=(85, 87, 89) K, and for water and methanol at T=(278, 288, 298) K on a well‐characterized polymer‐based, activated carbon. Nitrogen and argon are subjected to isosteric heat analyses; their zero filling isosteric heats of adsorption are consistent with slit‐pore, adsorption energy enhancement modelling. Water adsorbs entirely via specific interactions, offering decreasing isosteric heat at low pore filling followed by a constant heat slightly in excess of water condensation enthalpy, demonstrating the effects of micropores. Methanol offers both specific adsorption via the alcohol group and non‐specific interactions via its methyl group; the isosteric heat increases at low pore filling, indicating the predominance of non‐specific interactions.     

金属-有机骨架对苯二甲酸酯-铝吸附水中酚类化合物动力学和热力学

以吸附等温线、动力学和热力学等方法研究了金属-有机骨架对苯二甲酸酯-铝[MIL-53(Al),MIL:Materials of Institut Lavoisier]对水中邻硝基苯酚、苯酚和邻苯二酚的吸附行为。 MIL-53(Al)对上述酚类化合物的吸附符合准二级吸附动力学模型,且包含表面吸附和孔内扩散两个过程。 吸附热力学结果表明,MIL-53(Al)对酚类化合物的吸附是自发的,且为吸热和熵增加过程。 在40 ℃条件下,MIL-53(Al)对邻硝基苯酚、苯酚和邻苯二酚的吸附量分别为78.6、30.5和16.5 mg/g。     

Acidity and Catalytic Activity of Sulfate Modified Mixed Oxides of Tin and Praseodymium

A comparitive study of the acid-base properties and physico-chemical characteristics of pure SnO₂, sulfated SnO₂ and sulfated binary oxides of Sn and Pr was done. The data were correlated with the catalytic activity of the oxides towards benzoylation of toluene.     

Adsorption of normal and branched paraffins in faujasite zeolites NaY, HY, Pt/NaY and USY

The effect of chain length and branching of paraffins (from C6 to C12) on adsorption and diffusion in zeolites NaY, Pt/NaY, HY and USY has been investigated using the chromatographic method at 275–400°C. The Henry constants of the paraffins increase exponentially with the chain length (with a factor two per extra carbon group), the heats of adsorption increase with circa 7 kJ/mol per extra carbon group. Multicomponent sorption experiments reveal that longer chains are adsorbed preferentially over shorter chains, even at higher loadings. The multicomponent adsorption can be reasonably well described by an extended Langmuir adsorption isotherm, in which the stronger adsorption of the longer chains is reflected by their higher Henry constants. The molecular shape and zeolite type within this FAU group has only a small influence on the adsorption properties. Mass transfer in the pellets as used in catalytic conditions seems to be limited by macropore diffusion, rather than by micropore diffusion, which cannot be measured with the chromatographic method. Increasing the Si/Al-ratio of the zeolite reduces the adsorption capacity, but does not influence the relative adsorption properties.     

Evaluation of energy distribution on a heterogeneous surface from heat of adsorption and its application to the ammonia/Na-Y zeolite system

The— function (energy level function) which represents surface heterogeneity was derived from theq— function (experimental heat function) in the case of reversible adsorption. The Langmuir equation was extended and applied to the procedure of calculations. An iterative calculation led to the most probable— function by setting theq— function and adsorption temperature. As an example for actual cases, the— function of Na-Y zeolite was calculated from theq— function obtained by the measurement of heats of adsorption of ammonia at 373 K. The— function thus derived seemed to be consistent with the positional distribution of sodium ions.     

SAPO-34上甲醇及二甲醚吸附等温线及吸附热测量与分析(英文)

在25,60和100°C下分别测定了甲醇及二甲醚在SAPO-34分子筛上的吸附等温线,同时用微量热法测定了微分吸附热与覆盖率的关系曲线(量热线),提出了吸附数据需要利用双吸附位Langmuir方程拟合,并获取了相应的吸附参数.对比测得的吸附等温线与量热线发现,在一定压力下,当甲醇及二甲醚在SAPO-34上达到一定吸附量后,随着吸附质分压增加,量热线快速下降,而吸附等温线显示出吸附量仍然继续增加.由此推断,在SAPO-34分子筛上存在两种吸附位——常规吸附位及弱吸附位,其中弱吸附位在高分压下继续吸附.如缺乏量热数据提供的常规吸附位饱和吸附量数据,对吸附等温线进行单吸附位拟合获取吸附参数极易导致错误结果,尤其是当吸附质分压较高时.建议采用双吸附位Langmuir方程,参照量热线提供的常规吸附位的饱和吸附量,通过拟合可以获得两种吸附位的吸附参数.     

Pervaporation Separation and Catalysis Activity of Novel Zirconium Silicalite-1 Zeolite Membrane

Novel zirconium silicalite‐1 zeolite membrane was hydrothermally prepared on the mullite porous support at 150–185°C for 40–72 h by an "in situ" method using tetraethyl orthosilicate (TEOS), zirconium butoxide (ZBOT) and tetrapropylammonium hydroxide (TPAOH) as silica source, zirconium source and organic structure directing agent, respectively. X‐ray diffraction (XRD) patterns, fourier transformed infrared (FT‐IR) spectra, and inductively coupled plasma‐atomic emission spectrometry (ICP) of the accompanying zeolite powder confirmed that the zirconium was isomorphously incorporated into the zeolite framework. The surface chemical compositions of the obtained membrane were measured with an energy‐dispersive X‐ray spectral analyzer (EDS), and the membrane morphologies were observed by a scanning electron microscope (SEM). The results showed that the zeolite crystals growing on the support were zirconium silicalite‐1 zeolites, and the dense membrane layer was composed of the well inter‐growing zeolite crystals. The zirconium silicalite‐1 zeolite membrane, which was derived from the synthesis solution having a molar ratio of 1.00SiO₂:0.01ZrO₂:0.17TPAOH:120H₂O, showed high ethanol permselectivity with a flux of 1.01 kg/(m²·h) accompanied with a separation factor of 73 for ethanol/water (5/95, w/w) system under a pervaporation condition at 60°C. Moreover, this membrane displayed pervaporation‐aided catalysis activity for iso‐propanol oxidation with hydrogen peroxide as oxidant, and the corresponding iso‐propanol conversion was 35%.     

Adsorption and desorption of small molecules for the characterization of solid acids

The relative acid strength and acid amount of solid acids has been determined from the adsorption and desorption of small molecules, such as argon. The order of activation energy for desorption of Ar from a solid acid, determined using temperature-programmed desorption (TPD), is sulfated zirconia > Cs_2.5H_0.5PW₁₂O₄₀ > proton-type zeolites > silica–alumina. The adsorption isotherms were analyzed using Langmuir and Henry equations. The Henry-type adsorption isotherms were also analyzed using the theory of Cremer and Flügge. The heat of Ar adsorption was 22 kJ mol⁻¹ for sulfated zirconia and ca. 17 kJ mol⁻¹ for mordenite, ZSM-5, and beta-zeolite. Molybdenum oxides reduced at 623 and 773 K exhibited a large heat of adsorption (19.3 and 19.7 kJ mol⁻¹, respectively), and these materials are classified as superacids. W-Nb mixed-oxides and tungstated tin oxide (calcined at 1373 K), which are newly developed solid acids, had a heat of adsorption of 18.1 and 16.9 kJ mol⁻¹, respectively. The type of acid site could be distinguished by comparing the heat of adsorption of Ar and N₂. Our data indicate that Ar is useful for the characterization of solid acids.     

金属胶束催化体系中经Turing分支形成的空间有序结构与催化活性

摘要基于金属胶束催化反应的三元复合物动力学模型, 分析了金属胶束作为一类特殊的超分子体系, 其参与催化反应的特殊动力学行为与体系中可能出现的自组织结构的关系. 研究结果表明, 在一定的边界条件下, 即使基元反应是线性化学反应步骤, 由于扩散步骤与化学反应的耦合, 以及非理想性的组分热力学行为, 也将不可避免地出现经Turing分支形成的浓度场空间自组织. 计算结果表明, 这种宏观有序结构的形成将使金属胶束催化体系中呈现出以存在反应活性极高的位点为特征的反应活性的空间有序分布; 从自组织理论的角度对这类胶束体系催化活性的时空有序特征给予一定程度的阐释.     

Adsorption of Gases, Vapors and Liquids by Microporous Adsorbents

Adsorption of Xe, Kr, Ar, N₂, O₂, H₂ CH₄, CO₂, He, and freons by PAU-10 and ACC microporous carbon adsorbents as well as by A and X zeolites was investigated over a wide range of pressures (0.1 Pa – 20 MPa) and temperatures (77, 120–600 K). The amount of gases, vapors and liquids adsorbed by microporous adsorbents increases steadily with increasing pressure and does not change dramatically if phase transitions occur in the adsorptive. Isosteres of adsorption constructed as a curve of ln P against f(1/T)_a retain a linear form over a wide range of pressures and temperatures. The slope of isosteres does not vary on going through the critical temperature of the gaseous phase. At high pressures, due to non-ideality of the gaseous phase and non-inert behavior of the adsorbent the differential molar heat of adsorption is dependent on temperature. At high fillings of micropores the differential molar isosteric heat capacities of adsorption systems show maxima that indicate the occurrence of structural rearrangements in the adsorbate.     

EU-1分子筛相邻酸性位的DFT计算和酸性表征

利用量子力学中的密度泛函理论(DFT),对EU-1分子筛中与T1、T2、T3、T6、T7、T8位相邻的骨架铝原子的落位稳定性及酸强度进行理论计算.通过计算得知,双Al原子在EU-1分子筛骨架中优先落位于Al7(Si6-Si7)Al8、Al1(Si2-Si2)Al1、Al2(Si1-Si2)Al2、Al1(Si2-Si2)Al3、Al1(Si2)Al3;根据(Al/Si,H)取代能确定了质子的落位,质子氢较易落位于(O12-H)Al1-(O12-H)Al1、(O12-H)Al1-Al1(O13-H)、(O12-H)Al1-Al1(O12-H)、(O14-H)Al2-(O14-H)Al2、Al2(O12-H)-(O14-H)Al2、Al1(O12-H)-(O15-H)Al3、(O26-H)Al7-Al8(O28-H);且根据质子亲和势分析知,EU-1分子筛骨架中质子氢落位于NNN位的Brnsted酸强度小于NNNN位.借助1H MAS NMR分析合成的不同硅铝比的样品,可知硅铝比低的EU-1分子筛Brnsted酸吸收峰的面积增加;由NH3-TPD可知硅铝比低的EU-1分子筛的强酸脱附峰温度降低,酸强度减小.硅铝比低的EU-1分子筛的强酸表现出酸量高、酸强度低的性质.     

碳纳米管负载的铂催化剂对柠檬醛选择加氢及CO微分吸附热研究

碳纳米管(CNTs)是近年来发现的一种新型催化剂载体材料,将其作为α,β-不饱和醛的选择加氢的研究则报道较少．本文对柠檬醛[Citral,3,7-二甲基-2,6-辛二烯醛(3,7-Dimethyl-2,6-octadienal)]在Pt／CNTs和Pt／XC-72催化剂作用下的液相选择加氢进行了探索性研究．结果发现,碳纳米管(CNTs)负载的Pt催化剂具有生成不饱和醇的高选择性．     

丙烯水合反应中改性β沸石催化剂的酸性与催化活性

经酸交换，水蒸气处理及加入粘合剂后的催化剂表面酸性均比Ｈβ原粉要低，主要是Ｂ酸变化较为明显。β沸石在酸洗过程中，酸量降低较大，Ｂ酸下降幅度较大，这可能是与其脱铝程度明显有关。经水蒸汽处理后，除在４００℃水蒸汽处理下酸量变化不大外，其余均有所下降。     

Surface Energies and Heats of Oxygen Adsorption in Ceria/Ceria-Zirconia Solid Solutions: Analysis by Semiempirical Interacting Bonds Method

Semiempirical Interacting Bonds Method (IBM) in the slab approximation with due regard to relaxation after the free surface formation was used to calculate the surface energies and enthalpies of oxygen adsorption on the surface of ceria-based solid solutions. The IBM-estimated surface energies agree well with the published values obtained using electrostatic models or the periodic ab initio Hartree-Fock code CRYSTAL. The most weakly bound forms of the surface oxygen appear to be located at the (111) face on the cerium cations which have complex defects of non-stoichiometry in the subsurface layer.