超声作用下MCM-36分子筛的快速合成

以四甲基铵硅酸盐为柱化剂,考察了超声作用对MCM-36分子筛合成的影响.结果表明,超声处理显著缩短了柱化剂进入已撑开的MCM-22(P)层间的插层过程的时间.通过控制插层过程的超声时间可以合成出具有不同层间距的MCM-36分子筛,而且合成的MCM-36分子筛内各层的层间距较均一.     

层剥离MWW结构分子筛的直接可控合成

分子筛是一类重要的催化材料,在石油和煤制化学品工业中应用广泛.目前,国际分子筛协会结构委员会确认的248种分子筛骨架结构中的19种已经商业化应用,如FAU,MFI,*BEA,MOR和MWW.具有多层结构的MCM-22是MWW结构分子筛的典型代表,已应用于苯与乙烯液相烷基化制乙苯.然而,烷基化反应主要发生在位于MCM-22分子筛晶体外表面的半超笼内,位于10元环孔道和12元环超笼内的酸性位对乙烯转化率几乎没有贡献.因此,有必要制备能够容纳更多半超笼的具有超大外比表面积的新型MWW结构分子筛.厚度仅2.5 nm的单层MWW结构分子筛ITQ-2具备以上特征,但是其较弱的酸性质及复杂的制备过程使其无法工业应用.受到采用具有长碳链的双子季铵阳离子两亲性有机结构导向剂直接合成层状MFI分子筛的启发,其有机结构导向剂同时起到导向MFI结构和抑制晶体沿b轴方向生长的作用.类似地,层剥离MWW结构分子筛也被直接合成出来,但所得材料的催化性能不理想,且有机结构导向剂不易得.通过对MCM-22分子筛的结构分析发现,其合成态是由多个MWW结构层有序组装而成,可以通过溶胀处理增大层间距,削弱层间相互作用,经超声处理即可实现层剥离.鉴于此,本文采用向合成MCM-22分子筛的常规体系中加入二环己基胺充当有机添加剂构筑'双功能'合成体系的策略,开展层剥离MWW结构分子筛新材料的直接合成.X射线衍射(XRD)结果表明,与MCM-22分子筛相比,在二环己基胺参与下合成的分子筛SCM-1(DCHA/SiO2=0.4)和SCM-6(DCHA/SiO2=0.6)的XRD谱中与MWW结构c轴方向有关的(101)和(102)晶面的衍射峰出现偏移和重叠的现象,表明其沿c轴方向有序性降低.扫描电子显微镜显示,所有样品均为片状形貌,其中SCM-6含有少量无定形物种.氩气及氮气物理吸附结果表明,SCM-1和SCM-6具有超大外比表面积,而微孔体积小于MCM-22分子筛.透射电子显微镜表征结果表明,MCM-22为多层结构,厚度约为20 nm,而SCM-1和SCM-6的厚度分别约为5.0和2.5 nm,对应双层和单层结构,表明在有机添加剂参与下直接合成了层剥离的新型MWW结构分子筛.值得注意的是,通过调节添加剂用量,可以调节剥离程度,即实现可控层剥离,得到完全(单层)或部分(双层)剥离的MWW结构分子筛.该方法所采用的添加剂的尺寸是关键因素,选用尺寸大于有机结构导向剂的添加剂才能有效抑制晶体沿c轴方向的有序生长,实现层剥离MWW结构分子筛的直接合成.采用该方法合成的新型MWW结构分子筛具有超大外比表面积和更多的表面半超笼,在苯与乙烯液相烷基化反应中,SCM-1催化的乙烯转化率明显高于MCM-22分子筛.SCM-6因结晶度低而未能表现出优势.进一步比较SCM-1和MCM-22的催化稳定性发现,SCM-1的稳定性更好,经过64 h连续反应,其吸附的有机物及积碳更少.在1,3,5-三异丙苯裂解反应中,SCM-1的催化性能也明显优于MCM-22.     

超声老化对MCM-49分子筛合成的影响

 以六亚甲基亚胺为模板剂,在静态水热合成条件下,考察了超声老化对MCM-49分子筛合成的影响. 结果表明,凝胶经超声老化处理后,即使使用比表面积小的硅源(硅胶或白碳黑)也能合成出不含杂晶且结晶良好的MCM-49分子筛. 超声老化处理缩短了MCM-49分子筛的晶化时间,扩大了分子筛的晶化范围,同时降低了模板剂的用量. 合成的MCM-49分子筛结晶度高,颗粒度小.     

MCM-22分子筛的合成及其性质研究

以己内酰胺催化加氢得到的有机混合物水溶液(OMS)为模板剂合成了纯MCM-22分子筛，考察了晶化条件对合成产物的影响。采用XRD、SEM和NH3-TPD对所合成MCM-22分子筛的性质进行了研究。结果表明，原料碱度是影响合成产物的重要因素，合成纯MCM-22的硅铝比范围不大，同时原料中水含量对合成产物的影响也不容忽视；改变硅铝比及水蒸气处理可以调节MCM-22分子筛的酸性。     

硅源对MCM-22分子筛合成及物化性质的影响

在动态水热条件下,研究了硅溶胶、白炭黑、硅酸及硅胶为硅源时对MCM-22分子筛合成及物化性质的影响。以硅溶胶、白炭黑、硅酸三种硅源均可合成出高结晶度且无杂晶的片状MCM-22分子筛,其平均粒径分别为190、220和750 nm。硅源影响分子筛的聚集形态,三种硅源分别形成晶粒分散、晶粒半分散及晶粒聚集形态。三组样品的酸强度分布基本一致,都具有较多的中强酸分布,由硅溶胶和硅酸所得MCM-22分子筛在中强酸范围具有更高的B/L酸比值,以白炭黑合成的分子筛总酸量最高。NMR结果表明,样品中的铝以骨架铝为主,不存在明显的非骨架铝。由于硅胶对合成体系中游离水的吸附作用,水热反应难以发生,不能得到MCM-22分子筛,硅胶作为分子筛合成硅源时需要选择合适的反应条件。     

ITQ-2分子筛的静态法制备及性能

以硅溶胶为原料, 在静态法合成MCM-22(p)的基础上, 以十六烷基三甲基溴化胺(CTAB)和四丙基氢氧化铵(TPAOH)为扩孔剂, 通过对MCM-22(p)进行扩孔合成了ITQ-2分子筛, 并通过XRD, SEM, BET, NH3-TPD方法对制备的ITQ-2分子筛进行表征. 结果表明, 当各组分比例为MCM-22(p):CTAB:TPAOH=1:4:1时, 扩孔效果最好; 时间和温度对扩孔效果的影响不是很大; 除了CTAB与TPAOH组合的扩孔剂以外, CTAB与四丁基氢氧化铵(TBAOH)的组合也可以作为ITQ-2分子筛的扩孔剂; ITQ-2分子筛存在一定量的介孔比表面积和孔容, ITQ-2分子筛的酸强度比MCM-22分子筛弱, 但以ITQ-2分子筛为载体, 以NiW为活性组分的催化剂上减压瓦斯油(VGO)加氢裂化活性和中间馏分油的选择性均高于以MCM-22为载体的催化剂, 表明催化剂载体中由于存在介孔, 提高了重油大分子在催化剂中的扩散性能, 因而以ITQ-2分子筛为载体的催化剂具有较高的活性及中油选择性.     

氧化锌对MCM-22分子筛晶化的影响

 采用静态水热合成法,以六亚甲基亚胺为模板剂,在氧化锌存在下合成了MCM-22分子筛,考察了氧化锌对MCM-22晶化的影响. 结果表明,少量氧化锌的添加抑制了杂晶的生成,缩短了晶化诱导期,提高了晶化速度,扩大了硅铝比的范围,降低了模板剂的用量.     

层剥离MWW结构分子筛的直接可控合成（英文）

分子筛是一类重要的催化材料,在石油和煤制化学品工业中应用广泛.目前,国际分子筛协会结构委员会确认的248种分子筛骨架结构中的19种已经商业化应用,如FAU, MFI,*BEA, MOR和MWW.具有多层结构的MCM-22是MWW结构分子筛的典型代表,已应用于苯与乙烯液相烷基化制乙苯.然而,烷基化反应主要发生在位于MCM-22分子筛晶体外表面的半超笼内,位于10元环孔道和12元环超笼内的酸性位对乙烯转化率几乎没有贡献.因此,有必要制备能够容纳更多半超笼的具有超大外比表面积的新型MWW结构分子筛.厚度仅2.5 nm的单层MWW结构分子筛ITQ-2具备以上特征,但是其较弱的酸性质及复杂的制备过程使其无法工业应用.受到采用具有长碳链的双子季铵阳离子两亲性有机结构导向剂直接合成层状MFI分子筛的启发,其有机结构导向剂同时起到导向MFI结构和抑制晶体沿b轴方向生长的作用.类似地,层剥离MWW结构分子筛也被直接合成出来,但所得材料的催化性能不理想,且有机结构导向剂不易得.通过对MCM-22分子筛的结构分析发现,其合成态是由多个MWW结构层有序组装而成,可以通过溶胀处理增大层间距,削弱层间相互作用,经超声处理即可实现层剥离.鉴于此,本文采用向合成MCM-22分子筛的常规体系中加入二环己基胺充当有机添加剂构筑"双功能"合成体系的策略,开展层剥离MWW结构分子筛新材料的直接合成.X射线衍射(XRD)结果表明,与MCM-22分子筛相比,在二环己基胺参与下合成的分子筛SCM-1 (DCHA/SiO2=0.4)和SCM-6 (DCHA/SiO2=0.6)的XRD谱中与MWW结构c轴方向有关的(101)和(102)晶面的衍射峰出现偏移和重叠的现象,表明其沿c轴方向有序性降低.扫描电子显微镜显示,所有样品均为片状形貌,其中SCM-6含有少量无定形物种.氩气及氮气物理吸附结果表明, SCM-1和SCM-6具有超大外比表面积,而微孔体积小于MCM-22分子筛.透射电子显微镜表征结果表明, MCM-22为多层结构,厚度约为20 nm,而SCM-1和SCM-6的厚度分别约为5.0和2.5 nm,对应双层和单层结构,表明在有机添加剂参与下直接合成了层剥离的新型MWW结构分子筛.值得注意的是,通过调节添加剂用量,可以调节剥离程度,即实现可控层剥离,得到完全(单层)或部分(双层)剥离的MWW结构分子筛.该方法所采用的添加剂的尺寸是关键因素,选用尺寸大于有机结构导向剂的添加剂才能有效抑制晶体沿c轴方向的有序生长,实现层剥离MWW结构分子筛的直接合成.采用该方法合成的新型MWW结构分子筛具有超大外比表面积和更多的表面半超笼,在苯与乙烯液相烷基化反应中,SCM-1催化的乙烯转化率明显高于MCM-22分子筛.SCM-6因结晶度低而未能表现出优势.进一步比较SCM-1和MCM-22的催化稳定性发现, SCM-1的稳定性更好,经过64 h连续反应,其吸附的有机物及积碳更少.在1,3,5-三异丙苯裂解反应中,SCM-1的催化性能也明显优于MCM-22.     

以四甲基铵硅酸盐为柱化剂合成层柱状MCM-36分子筛

以层状MCM-22P为前驱体,四甲基铵硅酸盐为柱化剂,采用动态水热法考察了MCM-36分子筛的合成条件,并通过XRD、N2物理吸附、TEM、27Al-MAS NMR以及NH3-TPD等手段对合成分子筛进行了表征。结果表明,与传统的采用正硅酸乙酯为柱化剂的柱化过程相比,以四甲基铵硅酸盐为柱化剂时,已溶胀的前驱体不经干燥处理即可直接在含水体系进行柱化插层合成得到层间距均一的层柱状MCM-36分子筛,适宜的合成条件为:先在80℃的高pH值(约13.5)环境下对前驱体溶胀24 h,然后在100℃下柱化插层24 h。表征结果表明,MCM-36分子筛具有层内微孔和层间介孔的复合孔道结构以及较大的比表面积(特别是外比表面积);与HMCM-22相比,HMCM-36的表面酸性虽明显降低,但其层间介孔结构的形成使大量B酸中心暴露于大分子易于接近的层间介孔孔壁,可为涉及较大分子的催化反应提供更多可接近的活性位中心。     

不同硅铝比的MCM-22分子筛的气相硅烷化处理

对不同硅铝比的MCM-22分子筛进行气相硅烷化处理,并采用X射线衍射、固体核磁、N₂吸附-脱附和甲苯吸附等技术对样品进行了表征. 结果显示,原料硅铝比为50~100的MCM-22分子筛均可以利用气相硅烷化,在不脱除骨架铝的基础上,将Si(OH)₂柱撑结构引入其层间超笼系统,从而使层间距增大,孔体积增加; 将密度泛函理论用于计算硅烷化前后的MCM-22分子筛的N₂吸附等温线,成功得到十元环孔道和超笼体系的比表面积和孔体积,发现气相硅烷化使MCM-22分子筛超笼体系的比表面积和孔体积增大,而十元环孔道减小.另外,气相硅烷化可有效提高不同硅铝比MCM-22分子筛的甲苯平衡吸附量.     

Quadrupole moments of the alkali dimers,Li2, Na2, and K2

The quadrupole moments (Θ) of Li₂, Na₂, and K₂ have been determined using SCF, B3LYP, and CCSD(T). Included in this study is the effect of valence and core–valence correlation. The variation of Θ as a function of bond length has also been evaluated from which vibrational contributions have been determined. Additionally, the shape and relative magnitude of Θ vs. bond length are attributed to the s–s nature of the bonding. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Temperature dependence of the rate constants of the reactions of oxygen atoms with trans-2-butene,cis-2-butene, 2-methylpropene, 2-methyl-2-butene,and 2,3-dimethyl-2-butene

The kinetics of the reactions of ground state oxygen atoms with trans-2-butene, cis-2-butene, 2-methylpropene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene was investigated in the temperature range 200 to 370K. In this range, the rate constants are (in units 10^?11 cm³ s^?1): (1.1 ± 0.1) exp[+(180 ± 24)K/T]; (0.98 ± 0.09) exp[+(149 ± 23)K/T]; (1.14 ± 0.13) exp[+(128 ± 33)K/T]; (2.34 ± 0.16) exp[+(250 ± 16)K/T]; and (3.31 ± 0.50) exp[+(257 ± 36)K/T], respectively. The atoms were generated by the H₂ laser photolysis of NO and detected by the time resolved chemiluminescence in the presence of NO. The concentrations of the O(³P) atoms were kept so low that secondary reactions with products are unimportant. © 1995 John Wiley & Sons, Inc.     

Exploring the actinide-actinide bond: theoretical studies of the chemical bond in Ac2, Th2, Pa2, and U2

Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemical bond in the actinide diatoms Ac2, Th2, Pa2, and U2. Scalar relativistic effects and spin-orbit coupling have been included in the calculations. In the Ac2 and Th2 diatoms the atomic 6d, 7s, and 7p orbitals are the significant contributors to the bond, while for the two heavier diatoms, the 5f orbitals become increasingly important. Ac2 is characterized by a double bond with a 3Sigmag-(0g+) ground state, a bond distance of 3.64. A, and a bond energy of 1.19 eV. Th2 has quadruple bond character with a 3Dg(1g) ground state. The bond distance is 2.76 A and the bond energy (D0) 3.28 eV. Pa2 is characterized by a quintuple bond with a 3Sigmag-(0g+) ground state. The bond distance is 2.37 A and the bond energy 4.00 eV. The uranium diatom has also a quintuple bond with a 7Og (8g) ground state, a bond distance of 2.43 A, and a bond energy of 1.15 eV. It is concluded that the strongest bound actinide diatom is Pa2, characterized by a well-developed quintuple bond.     

Comparative theoretical study of the dissociation process of the isoelectronic molecules BH3CO,CH2CO,HNCO, CO2 and BH3N2, CH2N2, HN3, N2O

Anab initio study of the electronic structure of several 22-electrons molecules is presented. The equilibrium geometries of their ground state are calculated at the SCF level using the 6–31G basis set and are found to be in good agreement with the experimental geometries. The dissociation process of these molecules leading to the isoelectronic products CO or N₂ on the one hand and BH₃, CH₂, NH and O on the other hand is studied. The least-energy dissociation paths of the ground states determined at the SCF level are compared on the basis of electron density interactions. The dissociation energies corresponding to the two lowest dissociation channels are calculated. In these calculations, the correlation energy is taken into account using a non-variational method developed previously. The calculated values of dissociation energies are in good agreement with the existing experimental values. The results permit to predict values for HNCO, BH₃CO and CH₂N₂ and to confirm the instability of BH₃N₂.Aspirant du Fonds National Belge de la Recherche Scientifique.     

哌啶酮催化氢化制备哌啶醇催化剂的研究

研究了2,2,6,6-四甲基-哌啶酮-4-催化氢化合成2,2,6,6-四甲基-哌啶醇-4。重点研究催化剂种类对催化反应的影响。确定RaneyNi(4)为最适宜催化剂,并对其最佳用量进行了研究。对哌啶酮催化氢化的反应历程进行了探讨。选用常压塔式反应器进行氢化。对其它有关工艺参数进行研究,确定最佳条件:哌啶酮浓度为30%,20%异丙醇水溶液为溶剂、催化剂用量为20%、温度为80℃、时间为2h,哌啶醇产率97.3%,m.p.130.0-131.0℃。     

Atomic Layer Deposition of the Metal Pyrites FeS2, CoS2, and NiS2

Atomic layer deposition (ALD) of the pyrite‐type metal disulfides FeS₂, CoS₂, and NiS₂ is reported for the first time. The deposition processes use iron, cobalt, and nickel amidinate compounds as the corresponding metal precursors and the H₂S plasma as the sulfur source. All the processes are demonstrated to follow ideal self‐limiting ALD growth behavior to produce fairly pure, smooth, well‐crystallized, stoichiometric pyrite FeS₂, CoS₂, and NiS₂ films. By these processes, the FeS₂, CoS₂, and NiS₂ films can also be uniformly and conformally deposited into deep narrow trenches with aspect ratios as high as 10:1, which thereby highlights the broad and promising applicability of these ALD processes for conformal film coatings on complex high‐aspect‐ratio 3D architectures in general.     

Theoretical study of isomerism in the molecules N2O,PNO, P2O,N2S,PNS, and P2S

We have carried out nonempirical calculations of the potential surface for isomeric rearrangements of the molecules N₂O, N₂S, PNO, PNS, P₂O, and P₂S. It was found that for the molecules N₂O and N₂S a linear structure is considerably more favorable than a cyclic one, which lies 60 kcal·mole^–1 higher and has low stability. For P₂O and P₂S the linear and cyclic isomers have similar energies. For PNO and PNS there are two linear isomers and one cyclic isomer. The isomers are separated by appreciable barriers and can exist independently. It is predicted for the ABC molecules with 16 valence electrons that if two or all three of the atoms belong to the third or a later period, then the cyclic isomers should be favored to at least the same extent as the linear isomers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 794–802, April, 1990.