H-MCM-22沸石分子筛中Brnsted/Lewis酸协同效应的~1H 和~(27)Al双量子魔角旋转固体核磁共振研究

采用各种固体核磁共振 (NMR) 技术详细研究了 H-MCM-22 分子筛中 Brnsted/Lewis 酸的协同效应. 二维 1H 双量子魔角旋转 (DQ-MAS) NMR 结果表明, 在脱铝 H-MCM-22 分子筛中 Brnsted 酸位 (骨架桥式羟基) 和 Lewis 酸位 (非骨架铝羟基) 之间是空间邻近的, 暗示着可能存在 B/L 酸协同效应. 二维 27Al DQ-MAS NMR 结果揭示了各种铝物种之间的空间邻近性, 表明 B/L 酸协同效应优先发生在 H-MCM-22 分子筛超笼中的骨架 T6 位铝和非骨架铝物种之间. 2-13C-丙酮探针分子实验发现, 因 B/L 酸协同效应而导致脱铝 H-MCM-22 分子筛酸性明显增强, 氘代吡啶探针分子实验也证实在 H-MCM-22 分子筛的超笼中发生了 B/L 酸协同效应. 上述结果将有助于我们理解在脱铝 H-MCM-22 分子筛上发生的多相催化机理.     

Measuring Brønsted acid densites in zeolite HY with diphosphine molecules and solid state NMR spectroscopy

The use of 31P MAS NMR spectroscopy, combined with diphenyldiphosphine Ph2P(CH2)nPPh2 probe molecules with two basic groups (n = 1, 3, and 6, corresponding to maximum P-P separations of approximately 3.0, 5.6, and 9.4 A, respectively), to investigate both acidities and distances between Br?nsted acid sites in zeolite HY (Si/Al = 2.6) is demonstrated in this communication. More than 90% of the Ph2P(CH2)6PPh2 molecules are doubly protonated on zeolite HY at a loading level of 12 molecules per unit cell, indicating that there are at least 12 pairs of Br?nsted acid sites about 9 A apart. Similarly, experiments involving Ph2P(CH2)3PPh2 show that there are only six pairs of Br?nsted acid sites separated by a distance of 6 A. Only approximately 60% of the Ph2PCH2PPh2 molecules were doubly protonated for a loading level of 4 molecules/unit cell, as not all of the Br?nsted acid sites were sufficiently acidic to protonate both ends of this molecule. 31P 2D double quantum NMR spectroscopy was used to confirm the spectral assignments.     

Local structure of the zeolitic catalytically active site during reaction

The structural changes of the catalytic active site that occur during catalytic reaction in an acidic zeolite are detected. The local structure of the zeolitic Br?nsted active site is a distorted tetrahedrally coordinated aluminum that has three short and one long aluminum-oxygen bond. Using in situ Al K edge X-ray absorption spectroscopy, the adsorption of a reactive intermediate in the oligomerization of ethene changed the local structure of the catalytic active site; the long aluminum oxygen bond is partially relaxed. At increasingly higher temperature, extensive coking of the catalyst frees the Br?nsted acid site from the reactive intermediate, restoring the asymmetric coordination. These measurements show that application of in situ Al K edge spectroscopy provides fundamental insight into the structure of zeolitic catalytically active sites during catalytic action.     

多级孔NiMo负载TS-1分子筛催化剂的制备及其加氢脱硫性能

钛硅(TS-1)分子筛的微孔孔道严重限制了其在复杂分子催化转化中的应用,为了克服这一问题,通过酸洗脱、碱刻蚀及二者相结合的方法制备了多级孔 TS-1 分子筛,并采用等体积共浸渍法制备了相应的 NiMo 负载型催化剂;使用 X 射线衍射(XRD)、N₂吸附-脱附、吡啶吸附红外光谱(Py-FTIR)、氢气程序升温还原(H₂-TPR)、X射线光电子能谱(XPS)和高分辨透射电子显微镜(HR-TEM)等方法对多级孔TS-1分子筛的理化性质进行了表征;以二苯并噻吩(DBT)为探针对催化剂的加氢脱硫(HDS)性能进行了评价。结果表明,和常规TS-1分子筛相比,多级孔TS-1分子筛保持了MFI拓扑结构,比表面积增大且具有介孔结构,分子筛表面形成了适量的Brønsted酸中心;相应催化剂上活性金属与载体间相互作用得以改善,MoS₂片晶长度和堆垛层数适宜,形成了更多的 NiMoS活性相;催化剂活性和选择性均有所提升,尤其是酸洗脱获得的 NiMo/AT-TS-1催化剂的活性相较未经处理的NiMo/TS-1催化剂提升了1.2倍,直接脱硫(DDS)路径选择性提升了22%。     

An investigation of the roles of surface aluminum and acid sites in the zeolite MCM-22

Ammonia adsorption studies reveal that the observed Lewis acidity in the zeolite MCM-22 is derived from at least two types of framework aluminum sites (AlF), that is, octahedral AlF and three-coordinate AlF. Comparative ammonia or trimethylphosphine (TMP) adsorption experiments with MCM-22 confirm that octahedral Al species gives rise to the signal at delta(iso) approximately 0 in the 27Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water-reconstructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to delta(iso)27Al approximately 55 from tetrahedral AlF, while the broad peak is assigned to nonframework aluminum which results from hydrothermal treatment. This study also demonstrates the effectiveness of 27Al magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectroscopy as a technique for the study of zeolite reactions.     

铝改性介孔二氧化硅泡沫载体材料合成及其DBT加氢脱硫性能

介孔二氧化硅泡沫(MCFs)材料具有超大的三维球形孔结构、超大孔容(1.0–2.4 cm3/g)、高比表面(1000 m2/g)、孔径可调范围较广(24–50 nm)且球形孔道之间通过窗口(9–22 nm)联结,因此具有优良的传质性能,能够促进加氢脱硫反应.但是,与传统的微孔分子筛相比,该纯硅类介孔材料酸性较弱,不利于一些酸催化反应;因此,对纯硅材料进行金属改性以增加其酸性,从而促进催化剂的催化活性.而一般对纯硅类介孔材料采用Al,Ti,Zr等金属,铝改性主要是为纯硅载体提供酸性,而钛锆改性则是为了调变活性金属以及促进金属的分散,从而提高催化剂的加氢脱硫活性.因此,我们主要采用后改性方法,以P123为微乳液体系中的表面活性剂,TEOS为硅源,TMB为扩孔剂,异丙醇铝为铝源,成功合成了一系列Si/Al比不同的介孔二氧化硅泡沫材料.通过改变异丙醇铝的加入量,成功合成了系列Si/Al比(x)的NiMo/Al-MCFs(x)(x=10,20,30,40和50)催化剂.对所合成的载体及相应的催化剂通过SAXS,N2吸附脱附,SEM,Py-FTIR,UV-Vis,H2-TPR,NH3-TPD,HRTEM,Raman及27Al MAS NMR等表征手段进行分析,并在高压加氢微反装置上对相应的NiMo负载型催化剂进行DBT HDS活性评价,系统分析了不同硅铝比对催化剂DBT HDS反应活性的影响.SAXS和SEM表征结果表明,Al后改性并没有破坏载体材料的结构;27Al MAS NMR表征结果表明,后改性法能成功把Al掺杂进纯硅材料的骨架中.催化剂UV-Vis和Raman表征结果表明,当Si/Al比为20时,NiMo/Al-MCFs(20)催化剂Mo物种的带隙能量最大,且氧化钼的平均粒径较小,Mo物种在该催化剂中的分散度较好;H2-TPR分析结果表明,NiMo/Al-MCFs(20)催化剂还原温度较低,最易还原.Py-FTIR结果表明,随着Al加入量的增大,其酸性逐渐增大,当Si/Al比为20时酸性达到最大,继续增加Al的加入量,其酸性不再增加;此外,NiMo/Al-MCFs(20)的硫化度最高,且其MoS2的堆垛层数较低.负载活性金属后制备了NiMo/Al-MCFs(x)催化剂,将其应用于DBT加氢脱硫反应,并与传统NiMo/γ-Al2O3催化剂加氢脱硫反应活性作对比.研究发现,所制备的NiMo/Al-MCFs(x)系列催化剂由于具有较大孔径、比表面积及孔容和较强的酸性,因而其DBT HDS活性明显高于传统的工业NiMo/γ-Al2O3催化剂,且催化剂活性在硅铝比达到20时最大,最高可达96%,因此它作为加氢脱硫催化剂载体具有很大的应用前景.     

31P MAS NMR固体核磁共振研究稀土改性Y分子筛的酸性

以三甲基磷氧（TMPO）和三丁基磷氧（TBPO）为探针分子,用³¹P魔角旋转核磁共振（³¹P MAS NMR）法对稀土改性Y型分子筛的酸性进行了定性和定量分析. 结果表明,以TMPO为探针分子的³¹P MAS NMR谱分别在δ = 78,70,65,62,58,55和53处存在与酸中心相关的吸收峰,其中δ = 78和70处吸收峰与分子筛内部和外部酸性有关,δ = 65,62,58和53处吸收峰归属于TMPO在分子筛内部Brönsted酸中心上的贡献,δ = 55处吸收峰归属于TMPO在分子筛内部Lewis酸中心上的贡献. 随着稀土含量的增加,中等强度Brönsted酸中心（δ = 62和58）数量显著增加,而强Brönsted酸中心（δ = 65）和较弱Lewis酸中心（δ = 55）数量显著降低. 结合分子筛骨架铝和非骨架铝对分子筛酸性的影响进一步探讨了稀土改型Y分子筛的酸性.     

Hydrodemethoxylation/Dealkylation on Bifunctional Nanosized Zeolite Beta

Mono-, and bimetallic Ni-, Ru-, and Pt-modified nanosized Beta zeolite catalysts were prepared by the post synthesis method and characterized by powder X-ray diffraction (XRD), nitrogen physisorption, HRTEM microscopy, temperature-programmed reduction (TPR-TGA), ATR FT-IR spectroscopy, and by solid-state MAS-NMR spectroscopy. The presence of nanosized nickel-oxide, ruthenium-oxide, and platinum species was detected on the catalysts. The presence of Brønsted and Lewis acid sites, and incorporation of nickel ions into zeolite lattice was proven by FT-IR of adsorbed pyridine. The structural changes in the catalyst matrix were investigated by solid state NMR spectroscopy. The catalysts were used in a gas-phase hydrodemethoxylation and dealkylation of 2-methoxy-4-propylphenol as a lignin derivative molecule for phenol synthesis.     

无粘结剂ZSM-5沸石催化剂骨架脱铝改性的研究

对比了无粘结剂和有粘结剂ZSM-5沸石催化剂的吸附性质, 证实前者的优良品质. 以27Al固体核磁共振(MAS NMR)考察了盐酸处理、水蒸气处理及水蒸气-盐酸相结合处理后无粘结剂ZSM-5沸石催化剂的骨架脱铝行为以及非骨架铝的状态. 以X射线粉末衍射(XRD), X射线荧光光谱(XRF), 低温氮吸附, NH3-TPD和吡啶吸附原位红外光谱(in situ IR)等详细表征了骨架脱铝对其晶体、元素组成及孔结构、表面强(S)酸与弱(L)酸、Brönsted(B)酸与Lewis(L)酸酸量分布等影响. 揭示了水蒸气处理的深度骨架脱铝强烈地调变沸石的结构和表面酸性的本质, 证明了该处理方式对调变S酸和B酸起主导作用.     

Isomorphous Substitution of Iron and Nickel into Analcime Zeolite

Studies on the effects of iron and nickel incorporation into the hydrothermal synthesis of ANA zeolite were carried out. The presented work reveals that pure Fe‐Al analcime is synthesized by using starting composition with a higher iron(III) content than reported in previous publications. Furthermore, the iron(III) and nickel(II) contents play important roles in the framework of the synthesized zeolite. XRD, FT‐IR spectroscopy, diffuse reflectance UV/Vis spectroscopy, nitrogen adsorption and SEM were used to characterize the synthesized zeolites. These investigations showed that loading of iron and nickel ions in ANA zeolite changes the pore size and morphology of analcime zeolite.     

Staining of fluid-catalytic-cracking catalysts: localising Brønsted acidity within a single catalyst particle

A time‐resolved in situ micro‐spectroscopic approach has been used to investigate the Brønsted acidic properties of fluid‐catalytic‐cracking (FCC) catalysts at the single particle level by applying the acid‐catalysed styrene oligomerisation probe reaction. The reactivity of individual FCC components (zeolite, clay, alumina and silica) was monitored by UV/Vis micro‐spectroscopy and showed that only clay and zeolites (Y and ZSM‐5) contain Brønsted acid sites that are strong enough to catalyse the conversion of 4‐fluorostyrene into carbocationic species. By applying the same approach to complete FCC catalyst particles, it has been found that the fingerprint of the zeolitic UV/Vis spectra is clearly recognisable. This almost exclusive zeolitic activity is confirmed by the fact that hardly any reactivity is observed for FCC particles that contain no zeolite. Confocal fluorescence microscopy images of FCC catalyst particles reveal inhomogeneously distributed micron‐sized zeolite domains with a highly fluorescent signal upon reaction. By examining laboratory deactivated FCC catalyst particles in a statistical approach, a clear trend of decreasing fluorescence intensity, and thus Brønsted acidity, of the zeolite domains is observed with increasing severity of the deactivation method. By comparing the average fluorescence intensities obtained with two styrenes that differ in reactivity, it has been found that the Brønsted acid site strength within FCC catalyst particles containing ZSM‐5 is more uniform than within those containing zeolite Y, as confirmed with temperature‐programmed desorption of ammonia.     

建筑形象那些事

含铜的SSZ-39分子筛（AEI拓扑结构）在机动车尾气氨气选择性催化还原(NH3-SCR)反应中性能优异,其中SSZ-39分子筛的骨架铝分布与对应的Br?nsted酸性质对反应性能影响至关重要。本文通过密度泛函理论计算同时结合固体核磁共振谱学实验探究了高硅和富铝SSZ-39分子筛骨架Al位置以及与相应Br?nsted酸强度之间的关系。通过比较骨架Al在不同位置的替代能发现,高硅H-SSZ-39分子筛的骨架铝主要以孤立Al形式存在,同晶取代后落位在T3位上,其相应的Br?nsted酸质子与O7结合时最稳定。而富铝SSZ-39分子筛的骨架铝主要以NNNN与NNN序列的2Al形式存在,当两个骨架铝原子分别位于六元环和四元环对位的T3位上时体系能量最低,此时两个Br?nsted酸质子指向分子筛的超笼和八元环孔道。在最优构型下计算质子亲核势、NH3吸附态微观结构与脱附能以及吸附氘代乙腈后1H NMR化学位移来表征Br?nsted酸性,发现随着SSZ-39分子筛铝含量增加相应的Br?nsted酸含量增加,而Br?nsted酸强度趋于减弱。这些理论计算结果与NH3-TPD及吸附氘代乙腈的1H MAS NMR实验结果一致。本文为调控SSZ-39分子筛酸性以及合理设计高效催化剂提供了依据。     

DFT计算结合固体NMR研究富铝SSZ-13的铝分布和Br?nsted酸性

具有菱沸石(CHA)结构的SSZ-13分子筛在甲醇制烯烃(MTO)及柴油机车尾气氨选择性催化还原(NH_3-SCR)反应中具有重要的应用,采用富铝SSZ-13可以调节MTO反应的烯烃选择性和提升NH_3-SCR的低温脱硝活性,因此SSZ-13中的铝含量和分布与对应的酸性决定了其催化性能。本文采用密度泛函理论结合固体核磁共振实验研究了富铝和富硅HSSZ-13的Al位置与Br?nsted酸强度的内在关系。通过计算取代能发现,对于孤立Al位,质子位于Al周围4个不同O位时能量差异较小,最稳定的B酸位点是O(1)―H。对于富铝SSZ-13,两个Al原子位于同一六元环的对位是Al-Si-Si-Al (NNNN)序列中最稳定的结构,而Al-Si-Al (NNN)序列中能量最优的Al分布是两个铝原子排布于六棱柱上下不同的六元环上。通过计算最稳定构型下的质子亲和势、NH3脱附能和吸附氘代乙腈后的1H NMR化学位移,发现富铝SSZ-13中含有Si(2Al)分布的NNN序列导致了其Br?nsted酸强度弱于高硅的分子筛。分峰拟合29Si魔角旋转核磁共振(MASNMR)谱图表明富铝SSZ-13中Si(2Al)的含量在43%以上,而吸附氘代乙腈后的1H MAS NMR实验显示富铝SSZ-13的桥羟基化学位移向低场移动,进一步证明富铝SSZ-13具有较弱的Br?nsted酸强度。     

FER分子筛中铝原子的受限落位

分子筛是一类具有规则孔道或笼状结构的多孔材料,因其独特的结构和可调的酸性而广泛用于石油化工、精细化学品合成、现代煤化工等诸多行业.2006年Iglesia等在具有8元环孔道结构/侧口袋的FER和MOR分子筛上实现了无卤素添加、无贵金属存在条件下,由二甲醚羰基化合成乙酸甲酯的反应.乙酸甲酯通过进一步加氢可实现煤基乙醇的绿色生产.MOR分子筛通常具有较高的催化活性,但失活迅速;FER分子筛表现出良好的催化稳定性,但活性较低.如何在保证FER分子筛稳定性的前提下,进一步提升其羰基化活性是目前研究的热点.前期理论和实验研究发现,二甲醚羰基化反应活性与分子筛8元环孔道中的Br?nsted酸位密度存在正相关.因此,通过优化合成条件,选择性调控铝原子分布在"ferrierite"笼中,可以提高FER分子筛的羰基化反应活性.尽管研究者已在调节FER分子筛铝分布方面进行了大量研究,但对于不同T位上Al原子的精准识别以及对应Br?nsted酸位的可接触性还缺少系统和深入的认识.本文选取了几种代表性模板剂,分别在碱性和含氟体系下制备了系列FER分子筛样品,利用Rietveld精修和模拟退火算法,在原子水平揭示了模板剂种类以及合成介质变化对Al原子在不同T位分布的影响,并结合二甲醚羰基化反应进行了结构和性能的关联.首先选取不同尺寸大小的环状胺(环己胺、哌啶、吡啶、吡咯烷)和链状胺(乙二胺)合成了具有相似形貌、孔结构、酸密度的系列FER分子筛样品.以CHA-Na-FER为例,PXRD精修结果显示,Na+(平衡35％的骨架负电荷)分布在10元环孔道中与O1形成氢键,质子化的环己胺分布在"ferrierite"笼中,并且环己胺上的N与O3形成氢键.这说明与O1相连的T3位以及与O3相连的T1位都有可能是Al富集的位置.为了进一步验证该结论,本文还精修了吸附探针分子吡啶的样品CHA-Na-FER-Py-60h.原粉以及吸附吡啶样品的精修结果表明,T1位和T3位是样品中铝富集的位置.随后,运用相同方法研究了Py-Na-FER,PI-Na-FER,En-Na-FER和Pyrr-HF-FER样品中的Al落位,发现T1/T3位均是样品中Al富集的位置.此外,理论计算结果表明T1/T3位上Al原子的取代能较低,说明Al优先取代T1/T3位上的Si,这与精修结果相一致.前期理论模拟结果表明,FER分子筛中T2-O5和T4-O7位点的CO插入反应能垒较低,是二甲醚羰基化反应的活性位.本文吡啶吸附实验、热重分析以及PXRD精修结果表明,FER分子筛中大部分Al富集在T1/T3位,与T2/T4位相关的Br?nsted酸约占18％～30％.最后,对各样品进行了二甲醚羰基化反应评价,结果显示PI-Na-FER,Py-Na-FER,En-Na-FER和CHA-Na-FER催化剂的乙酸甲酯生成速率相近,约为0.10 mol/(mol H+?h).Pyrr-HF-FER催化剂的乙酸甲酯生成速率最高,可达到0.16 mol/(mol H+?h),这可能是由于Pyrr-HF-FER催化剂具有更多T2/T4位相关的Br?nsted酸.虽然Pyrr-HF-FER催化剂的乙酸甲酯生成速率较其他四个催化剂有一定提升,但其仍远低于MOR分子筛上乙酸甲酯生成速率(0.40 mol/(mol H+·h)).综上,有机模板剂的选择与合成介质的改变对FER分子筛中Al分布的调控作用是有限的,即Al原子总是优先分布于T1/T3位.而与T1和T3位相关的Br?nsted酸位不是二甲醚羰基化反应的活性位点.因此与MOR相比,FER分子筛在二甲醚羰基化反应中表现出较低的催化活性.     

金属有机骨架材料负载镍纳米颗粒催化硝基苯加氢

以MIL-53(Al)、MIL-96(Al)和MIL-120(Al) (MIL: Material Institute of Lavorisier)三种金属有机骨架材料为载体, 采用浸渍法制备了负载廉价金属镍纳米颗粒的催化剂. 将其用于催化硝基苯加氢合成苯胺反应, 发现以MIL-53(Al)为载体制得的催化剂表现出优异的催化性能. 采用不同的镍前驱体, 如硝酸镍、醋酸镍、乙二胺合镍, 制备了一系列Ni/MIL-53(Al)催化剂. 通过X射线衍射、傅里叶变换红外光谱、电感耦合等离子体、N₂物理吸附、H₂程序升温还原、透射电镜等技术对其进行了表征, 研究了镍前驱体对金属-载体相互作用、镍颗粒尺寸以及分散程度的影响.结果表明:以乙二胺合镍为镍前驱体制得的催化剂具有金属-载体相互作用适中、镍纳米颗粒更小(4-5 nm)和分布更均匀的特点, 在硝基苯加氢反应中表现出优异的催化性能, 硝基苯转化率达到100%.回收重复使用5次后, 此催化剂仍保持催化活性,硝基苯转化率达92%.     

Identification and measurements of strong Brønsted acid site in ultrastable Y (USY) zeolite

By using the IRMS-TPD method in which IR (infrared) and MS (mass spectroscopy) worked together, acid sites of USY (ultrastable Y) zeolite were studied. A new band of OH playing a role of Br?nsted acid was clearly detected on Na2H2-ethylenediaminetetraacetic acid (EDTA)-treated USY at 3595 cm(-1) during an elevation in temperature after the adsorption of ammonia. MS-measured TPD (temperature-programmed desorption) of NH3 and IR-measured TPD of the NH4+ cation coincided well to show that this zeolite consisted of the Br?nsted acid sites. The MS-TPD profile at higher temperatures corresponded to the IR-TPD of the 3595-cm(-1) band, and therefore, this OH was identified as a strong acid site. From comparison between IR-TPD of OH and MS-TPD, numbers of three kinds of Br?nsted OH (i.e., those in super and sodalite cages of a Y zeolite structure) and created strong Br?nsted acid site were quantified. On the other hand, strength of the Br?nsted acid site DeltaH was determined individually by a simulation method, where the corrected IR-TPD of OH was simulated based on the proposed equation. Thus, a new strong Br?nsted acid site was identified in the EDTA-treated USY, and the amount and strength was measured quantitatively.     

Effect of surface structure on the catalytic behavior of Ni：Cu/Al and Ni：Cu：K/Al catalysts for methane decomposition

Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.     

铈含量对CeUSY分子筛抗镍性能的影响及机理研究

采用液相离子交换法制备了不同Ce含量的CeUSY分子筛,并通过Mitchell等体积浸渍法对其进行Ni污染,运用ICP-AES、XRD和N₂吸附等温线等方法对其织构性质进行表征,并利用微反应活性评价装置考察了其抗镍性能。结果表明,不同Ce含量改性的USY样品其抗镍效果存在差异,CeUSY分子筛的抗镍效果与Ce含量的关系呈现火山型变化。结合Ni污染前后CeUSY分子筛的H₂-TPR和Py-FTIR表征结果探讨了Ce物种的抗镍机制,证实了Ce物种形态的变化是不同Ce含量的CeUSY分子筛具有不同抗镍效果的重要成因,其中,SOD笼中的Ce（OH）²⁺在高温条件下可与Ni（OH）⁺相互作用,脱去一分子H₂O形成Ce³⁺-O-Ni²⁺的稳定结构,阻碍了Ni物种与骨架铝的结合导致CeUSY分子筛中B酸中心的破坏,同时有效抑制了易还原NiO物种的生成。而Ce含量过高使得SOD笼内的Ce物种变成二聚以及三聚物,与Ni（OH）⁺作用减弱,使其抗镍性能减弱。     

Direct Detection of Supramolecular Reaction Centers in the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 by 13C–27Al Solid‐State NMR Spectroscopy

Hydrocarbon‐pool chemistry is important in methanol to olefins (MTO) conversion on acidic zeolite catalysts. The hydrocarbon‐pool (HP) species, such as methylbenzenes and cyclic carbocations, confined in zeolite channels during the reaction are essential in determining the reaction pathway. Herein, we experimentally demonstrate the formation of supramolecular reaction centers composed of organic hydrocarbon species and the inorganic zeolite framework in H‐ZSM‐5 zeolite by advanced ¹³C–²⁷Al double‐resonance solid‐state NMR spectroscopy. Methylbenzenes and cyclic carbocations located near Brønsted acid/base sites form the supramolecular reaction centers in the zeolite channel. The internuclear spatial interaction/proximity between the ¹³C nuclei (associated with HP species) and the ²⁷Al nuclei (associated with Brønsted acid/base sites) determines the reactivity of the HP species. The closer the HP species are to the zeolite framework Al, the higher their reactivity in the MTO reaction.