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。     

Al2O3-SiO2-CaO-FeO四元体系煤灰结构及流动性关系的实验和理论研究

将分子动力学、热力学计算与实验结合研究了Al₂O₃-SiO₂-CaO-FeO四元体系灰渣黏度变化机理。在Al₂O₃-SiO₂-CaO-FeO四元体系中,钙铁质量比（简称钙铁比,下同）增加,黏度下降,黏温曲线类型由结晶渣转变为玻璃渣,钙铁比为2时为黏温特性转变的拐点。钙铁比小于2时,体系中的矿物质主要是结晶矿物质,体系中降温过程中生成晶体矿物较多,当钙铁比大于2时,体系以无定形矿物质为主;从微观角度分析,钙铁比增加导致体系中Al由六配位（[AlO₆]^9-）转变为四配位（[AlO₄]^5-）,钙铁两种原子对体系中六配位铝的影响存在竞争作用。体系中的桥氧含量降低,体系的聚合程度降低,稳定性降低。通过四元体系的氧键为桥梁,建立了碱性组分含量与黏度的函数关系。     

Methane dehydrogenation and aromatization in the absence of oxygen on Mo/HZSM-5: A study on the interaction between Mo species and HZSM-5 by using Al and Si MAS NMR

By using a high-resolution solid state nuclear magnetic resonance spectrometer with ²⁷Al and ²⁹Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al₂(MoO₄)₃. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by ²⁷Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The Si/Al ratio measured from ²⁹Si MAS NMR further confirms the dealumination process observed by ²⁷Al MAS NMR. The MAS NMR results give us an evidence that Al₂(MoO₄)₃ crystallites are much less active for the reaction.     

金属负载型分子筛催化剂在NH3-SCR反应中水热稳定性的研究进展

NO_x控制是目前大气污染控制领域的重要研究内容，NH₃选择性催化还原技术（NH₃-SCR）是消除NO_x最有效的技术之一，其核心是高性能催化剂的开发。本研究综述了金属负载型分子筛催化剂（Cu基和Fe基分子筛催化剂）的NH₃-SCR活性、水热稳定性以及水热老化失活机制，并对影响催化剂水热稳定性的因素（包括Si/Al比、分子筛拓扑结构、活性金属负载量、粒径和合成方法等）进行了系统阐述，总结了一些有效提高催化剂水热稳定性的改性方法，比如磷改性、第二活性金属改性、碱金属改性和外表面改性等。最后，对进一步提高金属负载型分子筛催化剂在NH₃-SCR反应中的水热稳定性进行了展望。     

酸处理对斜发沸石结构影响的研究

采用不同浓度硝酸对斜发沸石（HEU）进行改性处理,结合元素分析（ICP-AES）、N₂物理吸附、X射线粉末衍射（XRD）、魔角旋转固体核磁（MAS NMR）等测试手段及DFT理论计算,研究了酸处理对斜发沸石结构的影响。结果表明,硝酸处理对不同平衡阳离子的HEU（Na-K-HEU、NH₄-HEU、H-HEU）具有不同的脱铝效果。酸处理后Na-K-HEU和NH₄-HEU的硅铝比、比表面积均显著升高。随硝酸浓度增大两个沸石样品的脱铝程度逐渐增加,同时骨架结构也逐渐破坏,硝酸浓度达到4 mol/L时其相对结晶度已低于50%。而H-HEU样品的骨架结构稳定,随硝酸浓度的增大铝含量轻微降低,硝酸浓度达到6 mol/L时相对结晶度仍高达94.8%。阳离子反交换实验结果证明,平衡阳离子的类型不是影响HEU骨架稳定性的主要因素。Na-K-HEU和经硝酸铵交换后的NH₄-HEU中铝都以骨架铝的形式存在,而在后者焙烧成为H-HEU时出现部分非骨架铝,伴随了骨架的稳定化过程。     

甘油脱水合成丙烯醛ZSM-5催化剂的孔结构和酸性调控

研究了ZSM-5 孔结构和表面酸性对甘油脱水合成丙烯醛反应性能的影响. 在碱浓度为0.2 mol·L^-1的NaOH溶液中, 分别在65和85 ℃条件下对ZSM-5进行化学刻蚀, 成功地制备了含微介孔的ZSM-5催化剂, 提高了催化剂的表面强酸密度. 碱处理后的ZSM-5催化剂在甘油脱水反应中的稳定性得到显著提高, 在ZSM-5-at85 (经85 ℃碱处理的ZSM-5)催化剂上甘油转化率在反应10 h 后仍可保持95%以上, 丙烯醛选择性达到78%. 采用N₂吸附-脱附等温线、X射线粉末衍射(XRD)、²⁷Al 固体核磁共振(²⁷Al MAS-NMR)和透射电子显微镜(TEM)等手段对ZSM-5 结构和表面性质进行了表征, 实验结果表明在碱处理过程中骨架中的硅发生了溶脱现象, 在分子筛表面上形成了大量介孔, 但是ZSM-5 的MFI 拓扑结构没有发生变化, 骨架中的大部分铝得到保持. X射线光电子能谱(XPS)、X射线荧光光谱(XRF)和氨气程序升温脱附(NH₃-TPD)证实了在碱处理后ZSM-5分子筛外表面的Si/Al 摩尔比低于其骨架中的比例, 由此表明脱硅现象主要发生在ZSM-5 的外表面, 在新产生的介孔区域由于Si/Al 摩尔比的降低使得强酸密度得到提高. 具有微介孔结构和较高酸密度的ZSM-5催化剂增强了反应物扩散性能和容碳能力, 这对于提高甘油脱水合成丙烯醛催化剂的活性和稳定性起到了关键作用.     

Synthesis and derivative chemistry of [Ru2(μ-PPh2) (μ-OH) 2(μ-p-cymene) 2]

The cationic diphenylphosphido-bridged compound [Ru₂(μ-PPh₂)(μ-OH)₂(η⁶-p-cymene)₂][PF₆) (2) has been prepared by reaction of the tri-μ-hydroxo complex [Ru₂(μ-OH)₃(η-p-cymene)₂][PF₆] (1) with diphenylphosphine. Complex 2 eliminates water on reaction with protic acids, incorporating the conjugate base of the added acid as a bridging ligand. Formic acid, acetic acid, phenol, and aniline react with 2 to give the monosubstituted compounds [Ru₂(μ-PPh₂)(μ-OH)(μ-L)(η⁶-p-cymene)₂]PF₆] (L = HCO₂, MeCO₂, OPh, or NHPH), whereas methanol, thiophenol, 1,2-benzenedithiol, hydrochloric acid and isopropanol afford the disubstituted derivatives [Ru₂(μ-PPh₂)(μ-L)₂(η⁶-p-cymene)₂]PF₆] (L = OMe, SPh, S₂C₆H₄, Cl, or H).     

Stability of the silicon-ruthenium bond in the presence of a strong nucleophile. Phase sensitive H NMR COSY and crystal structure of Ru(CO)2(NH2CH2C6H5)2(Si(C6H5)(CH3)2)I

The ruthenium(II) complex Ru(CO)₂(NH₂(NH₂CH₂C₆H₅)₂(Si(C₆H₅)(CH₃)₂)I has been prepared by the reaction of Ru(CO)₄(Si(C₆H₅)(CH₃)₂)I with benzylamine. Two-dimensional homonuclear ¹H NMR experiments examine the scalar coupling of the enantiotopic amino and methylene protons of the benzylamine ligand. X-ray analysis of Ru(CO)₂(NH₂CH₂C₆H₅)₂(Si(C₆H₅)(CH₃)₂)I·1/3C₅H₁₂ (triclinic; P ; a = 14.266(4), b = 15.748(5), c = 20.082(6) Å; = 94.38(3), β = 96.30(2), γ = 101.52(2)°) indicates three crystallographically unique complexes form a clathrate with a pentane guest.     

硼改性HZSM-5对催化MTP反应活性影响

水热晶化一步合成了BHZSM-5分子筛，投料SiO₂/Al₂O₃=100、200，其中，B₂O₃/Al₂O₃=1，研究了其甲醇制丙烯（MTP）催化活性。硼改性提高了丙烯选择性，并有利于稳定活性。硼修饰引起合成样品的强B酸量减少；水热（480℃）环境条件下，BHZSM-5的强B酸量保留量约50%，相比HZSM-5，酸性位点保留较多，显示增强的水热稳定性；同时骨架Al分布发生了变化：位于晶体直孔道和正弦孔道的Al稳定，孔道交叉口的Al易于脱除，有利于基于烯烃循环机理的MTP活性。水热处理空速由1 h^-1增加到9 h^-1，B酸量进一步下降，晶体孔道交叉口的Al脱除更多。     

CVD法制备Sn掺杂MFI分子筛膜及其对乙醇/水体系的分离性能

采用化学气相沉积(CVD)法对MFI分子筛膜进行Sn掺杂, 制备了一种Sn-MFI分子筛膜, 并研究了其渗透汽化分离乙醇/水体系的性能. XRD, ²⁹Si NMR, UV-Vis及分离实验结果表明, 采用CVD法在将Sn引入MFI膜时, 膜层结构基本得到保持, Sn可以进入分子筛骨架, 有效地减少了膜表面的硅羟基缺陷, 提高了膜分离乙醇/水体系时的稳定性. 在SnCl₄用量为3 mL、 修饰时间为1 h时, 所得到的Sn-MFI分子筛膜的渗透汽化分离性能最佳, 并可在60 ℃下分离5%(质量分数)乙醇/水混合物时保持良好的稳定性. 在经过连续50 h渗透气化分离后, 其渗透通量仅从1.52 kg·m^-2·h^-1下降至1.38 kg·m^-2·h^-1, 分离因子从18下降至16.     

ZnCrO_x/HZSM-5催化合成气直接转化制异构烷烃

分别采用共沉淀法和水热法制备了ZnCrO_x复合金属氧化物和HZSM-5沸石,通过物理混合得到双功能催化剂,实现了合成气一步高选择性制备异构烷烃。采用XRD、TEM、氮吸附和NH3-TPD等技术对催化剂进行了表征,考察了双功能催化剂中HZSM-5沸石组分硅铝比以及ZnCrO_x/HZSM-5质量比(OX/ZEO mass ratio)对合成气催化转化反应性能的影响。结果表明,随着HZSM-5硅铝比的增加,催化剂酸密度下降,CO转化率略有下降,产物中C5+选择性显著提高,异构烷烃比例不断增加。此外,在保证CO转化率的前提下提高双功能催化剂中ZnCrO_x组分的比例,产物中C5+的选择性也显著上升。在400℃、2.0 M Pa、进料空速(GHSV)为3600 mL/(h·gcat)的条件下,合成气(H2/CO(volume ratio)=2)转化率达到35%,C5+选择性超过44%,且C5+中异戊烷比例高达65%。     

晶种法合成UZM-9分子筛及其CO2/CH4/N2吸附分离性能

以TEAOH和TMAOH为有机模板剂,酸处理的UZM-9分子筛为晶种,采用水热法在48 h内合成出分子筛UZM-9,并对其CO₂/CH₄/N₂的吸附分离性能进行了研究。采用XRD、ICP、TG、SEM与气体吸附等手段对晶种法合成的UZM-9分子筛结构、耐水稳定性与吸附性能进行了研究。结果表明,晶种法可以在2 d内合成出硅铝原子比在3以上、收率达到65%的UZM-9分子筛;所得分子筛的CO₂吸附容量可以达到5 mmol/g以上,吸附热为34 kJ/mol,CO₂/CH₄、CO₂/N₂与CH₄/N₂的平均分离因子分别为100、240与2.4,CO₂分离性能优良且具有一定耐水性能。     

Synthesis of chemically stable PGI2 analogs II - synthesis of halogen substituted PGI2 analogs

Syntheses of several stable PGI₂ analogs substituted by halogen atoms(s) at C-5 or(and) C-7 are described. Reaction of protected PGI₂ methyl ester ( ) with -chlorosuccinimide gave 5-chloro-Δ⁶-PGI₁ derivative ( ), which was transformed into 5-chloro- and 5,7-dichloro-PGI₂ [( ) and ( )] by subsequent isomerization or chlorination. Similarly, reaction of with -bromosuccinimide gave 5-bromo-Δ⁶-PGI₁ derivative ( ), which was further transformed into 7-fluoro-PGI₂ ( ) by silver fluoride treatment. These halogenated PGI₂ analogs were found to be much more stable than PGI₂.     

A non-empirical molecular orbital study on loewenstein''s rule and zeolite composition

The role of the “aluminum avoidance rule” in zeolite frameworks and its relation to the electronic structure and stability of various structural units of alumosilicates were studied by non-empirical SCF—MO techniques. Al—O—Al-type linkages are unstable according to the calculations. The presence of cations in the neighbourhood of T₁—O—T₂ bridges (T₁, T₂ = Si or Al) is the least stabilizing when T₁ = T₂ = Al.     

Ab initio studies on photochemical reactions of Al atoms with H2 molecules

Potential energy surfaces are computed for the five lowest electronic states of the Al + H₂ system in its symmetric nuclear arrangement. Mechanisms of photochemical reactions of Al atoms with H₂ molecules are proposed, based on the calculated potential energy surfaces. The insertion reaction of the ground-state Al atom into the H₂ molecule is difficult under normal conditions. However, photoexcited Al atoms are capable of reacting with H₂ molecules along different pathways. The results obtained are consistent with experimental findings. The potential energy profiles of the dissociation reaction, AlH₂ → AlH + H, are traced by employing the UMP2 energy gradient method. Photocexcited Al atoms react with H₂ molecules along the 2 ²A₁ state pathway, and the AlH₂(²Σ_g⁺) formed dissociates easily into AlH(¹Σ) and H(²S). The dissociation reaction of ground-state AlH₂ is difficult.     

Group 4 metallacarboranes of constrained geometries derived from B(cage)- and C(cage)-silylamido-substituted carborane ligands: a synthetic and structural investigation

The reactions of RNHSi(Me)₂Cl (1, R=t-Bu; 2, R=2,6-(Me₂CH)₂C₆H₃) with the carborane ligands, nido-1-Na(C₄H₈O)-2,3-(SiMe₃)₂-2,3-C₂B₄H₅ (3) and Li[closo-1-R′-1,2-C₂B₁₀H₁₀] (4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me)₂N(H)R]-2,3-(SiMe₃)₂-2,3-C₂B₄H₅, (5, R=t-Bu) and closo-1-R′-2-[Si(Me)₂N(H)R]-1,2-C₂B₁₀H₁₀ (6, R=t-Bu, R′=Ph; 7, R=2,6-(Me₂CH)₂C₆H₃, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)₂NH(2,6-(Me₂CH)₂C₆H₃)]-1,2-C₂B₁₀H₁₁ (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the “carbons apart” carborane trianion, [nido-3-{Si(Me)₂N(2,6-(Me₂CH)₂C₆H₃)}-1,3-C₂B₁₀H₁₁]³⁻ (8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl₄ (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at −78 °C, resulted in the formation of the corresponding half-sandwich neutral d⁰-metallacarborane, closo-1-M[(Cl)(THF)_n]-2-[1′-η¹σ-N(2,6-(Me₂CH)₂C₆H₃)(Me)₂Si]-2,4-η⁶-C₂B₁₀H₁₁ (M=Ti (9), n=0; M=Zr (10), n=1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, ¹H-, ¹¹B-, and ¹³C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P2₁/c with a=8.2357(19) Å, b=28.686(7) Å, c=9.921(2) Å; β=93.482(4)°; V=2339.5(9) ų, and Z=4. The final refinements of 7 converged at R=0.0736; wR=0.1494; GOF=1.372 for observed reflections.     

Co-Mo/SiO2-Al2O3润滑油加氢处理催化剂的制备

以Pluronic P₁₂₃作结构导向剂,采用Al （NO₃）₃-NaAlO₂双水解法合成氧化铝,在成胶过程中加入正硅酸乙酯,制备硅质量分数分别为5%、10%、15%的SiO₂-Al₂O₃载体,并通过共浸渍法制备出Co-Mo/SiO₂-Al₂O₃润滑油加氢处理催化剂。通过XRD、N₂吸附-脱附、Py-FTIR、NH₃-TPD、H₂-TPR、TEM和XRF等手段对载体及催化剂的性质进行表征。结果表明,硅质量分数为10%的SiO₂-Al₂O₃具有优良的孔结构、较多的中强酸以及部分有序的介孔结构。以此为载体制备的Co-Mo/10% SiO₂-Al₂O₃催化剂中,MoS₂颗粒均匀地分散在载体上,具有更多的B酸性位和Ⅱ型CoMoS活性相。以减二线蜡油为原料油的固定床活性评价结果表明,生成油中主要组分为链烷烃与环烷烃;尤其Co-Mo/10% SiO₂-Al₂O₃催化剂具有优良的加氢性能,在15 MPa、380℃、氢油比为1000、空速为0.6 h^-1的反应条件下,其HDS和HDN数值均超过99%,产品中S含量小于10 μg/g,N含量小于2 μg/g,可以满足后续异构脱蜡等对原料的要求。     

A型沸石/活性炭复合材料的制备及甲烷/氮气吸附分离性能

以沥青和煤矸石为原料,经炭化、活化后获得型体活性炭材料(AC),并在此基础上进行水热晶化,研究晶化时间对复合材料中4A沸石的形成、孔结构和甲烷、氮气吸附性能的影响。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、77 K下的氮气吸附-脱附以及273 K下的CO_2吸附等温线对样品进行表征,结果表明水热晶化后,复合材料中的硅铝形成立方结构的4A沸石,出现了0.45~0.6 nm的微孔,微孔孔容增加,并伴有少量的中孔和大孔。复合材料在298 K下的甲烷(CH_4)和氮气(N_2)吸附等温线的结果表明,晶化时间6 h的复合材料AC-2的甲烷吸附量被提高至10.8 m L/g,并保持较高的CH4/N2平衡分离比(3.7)。     

CVD modified KL zeolite supported Pt for n-hexane aromatization

Modification of non-acidic KL zeolite by chemical vapor deposition (CVD) of Si(OEt)₄ and (CH₃)₃Si–O–Si(CH₃)₃ followed by Pt loading was used to study the influence of zeolite support on the aromatization of n-hexane. Deposited on the framework oxygen ions of the non-acidic zeolite, the silica layer effectively narrowed the pores of KL zeolite. But owing to the appearance of new basic sites, such as potassium oxide (K₂O), the interaction between Pt metal and zeolite support was strengthened, causing Pt particles to be more electron-excess. n-Hexane pulse-flow microreactions were carried out to study the effects on the aromatization reactivity and sulfur poisoning properties.     

超微NaY分子筛的合成(Ⅰ)──添加轻稀土离子的影响

导向剂的陈化时间和反应胶的晶化温度可以影响NaY分子筛的晶化行为.随导向剂陈化时间的增加,NaY分子筛的晶化速度加快,晶粒尺寸减小;随晶化温度的升高,NaY分子筛的晶化速度加快,但晶粒尺寸增加.而向合成体系中添加轻稀土离子(Ln³⁺)对NaY分子筛的晶化行为影响更为明显.与未添加稀土离子时相比较,在一定的稀土离子添加量范围内[n(Ln³⁺)/n(Al³⁺)<0.2],NaY分子筛的晶化速度明显加快而晶粒尺寸显著减小,同时所合成出的NaY分子筛的n(SiO₂)/n(Al₂O₃)比也有较大的提高.添加稀土离子使合成体系中形成异晶晶种的Ln(OH)₃微晶,从而进一步引发NaY分子筛的成核.