超细NaY分子筛的深度脱铝

通过优化和组合不同脱铝补硅方法,依次经氟硅酸铵处理、600oC水热处理、硅溶胶+草酸处理和800oC水热处理过程,成功实现了200nm超细NaY分子筛的深度脱铝,最终产品骨架硅铝比高达27.3,比表面积为581.9m2/g,分子筛结晶度保持在65%以上.结果表明,对于超细NaY分子筛脱铝,第一步采用氟硅酸铵进行部分缺陷修补尤为重要.根据分子筛晶粒尺寸不同,需严格控制氟硅酸铵用量和处理次数.当晶粒为200nm时,氟硅酸铵与分子筛骨架铝的摩尔比为0.16,处理一次较为适宜.在连续脱铝过程中及时补修脱铝产生的缺陷是保障超细NaY分子筛成功脱铝的关键,而采用氟硅酸铵、硅溶胶、800oC高温水热处理,可有效实施这种骨架修正作用.     

La交换NaY分子筛中的离子定位和迁移规律

以NaY分子筛为原料,采用二次交换二次焙烧工艺,制得了LaNH₄Y-1,LaY-1,LaNH₄Y-2和LaY-2四种分子筛样品.采用粉末X射线衍射结合Rietveld结构精修确定了La离子在分子筛中的分布.结果表明,在离子交换过程中,La离子首先定位于分子筛超笼里;经焙烧脱水后,La离子迁移到分子筛方钠石笼并定位在SI′位置.T-O-T键角的变化表明,LaNH₄Y-1表现出最大的骨架扭曲性和结构不稳定性.La离子定位在SI′位置与O3配位,增加了T-O3的键长,表明稀土离子不仅通过控制骨架脱铝抑制晶胞收缩,还可能通过影响T-O3键长使晶胞增大.在REY分子筛中,稀土的主要作用是稳定分子筛结构,从而调节其酸性和催化活性.采用红外光谱和NH₃程序升温脱附考察了La离子和NH₄⁺对分子筛酸性的影响,并总结了稀土离子稳定Y型分子筛的机理.     

柠檬酸溶液中NaY分子筛的脱铝行为

硅铝分子筛有机酸配合脱铝是提高其稳定性、引入介孔的一种重要方法.采用X射线衍射、N₂物理吸附、高分辨透射电镜、傅里叶变换红外光谱、²⁷Al和²⁹Si固体魔角自旋核磁共振光谱等方法研究了NaY分子筛柠檬酸脱铝行为.结果表明，柠檬酸浓度对NaY分子筛骨架Al原子的脱出影响尤为显著.反应起始阶段，分子筛骨架铝原子快速脱出，其晶体结构遭到严重破坏.随着反应的进行，分子筛硅铝比和结晶度皆有所增加，表明其骨架结构可能进行了重新排列.75℃下，0.10 mol/L柠檬酸处理2 h的脱铝分子筛样品，与NaY分子筛样品相比，其骨架硅铝比增加了0.6、外表面增加了17 m²·g^-1，脱铝同时产生了大量无定形硅.     

碱处理脱硅与提高Y型分子筛硅铝比——矛盾的对立与统一

考察了 "水热处理"以及"碱处理+水热处理"两种方法所制得的超稳 Y 分子筛的骨架硅铝比、孔结构特征以及酸量, 并探讨了"碱处理+水热处理"方法对起始 NaY 分子筛的适应性. 结果表明, 在水热处理前, 对 NaY 分子筛进行碱处理脱硅可在不改变最终样品的骨架超稳化水平和酸量的同时, 样品的介孔体积显著增加. 直接水热处理 NaY 分子筛所得样品介孔体积不超过 0.14 cm3/g, 而先碱处理后水热处理, 所得样品介孔体积可达 0.22 cm3/g. 该法适用于制备骨架硅铝比高的 NaY 分子筛. 起始原料的骨架硅铝比较低时, 所得样品的介孔体积增幅小, 而且微孔受损严重.     

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.     

介孔调变对CuY催化剂甲醇氧化羰基化反应活性的影响

碱溶液处理NaY分子筛形成的介孔有利于反应物及产物分子的扩散,调节碱溶液浓度可控制Y分子筛中的介孔结构,通过溶液离子交换法制备CuY催化剂,研究了NaY分子筛介孔结构调变对CuY催化剂催化甲醇氧化羰基化反应活性的影响。通过BET、~(29)Si-NMR、XRD、NH_3/CO-TPD、H_2-TPR和TEM等表征及催化活性分析表明,在碱溶液处理过程中,NaY分子筛骨架中的Si(0Al)和Si(1Al)原子被优先脱除,且笼结构坍塌使得临近超笼连接,逐步形成直径为3.47~3.66 nm,孔容介于0.142~0.226cm~3·g~(-1)的介孔,在提高反应物分子和产物分子扩散性能的同时,提高了活性物种的可接近性。随着碱液浓度的增加,CuY催化剂的催化活性先升高后降低。当碱液浓度为0.2 mol·L~(-1)时,NaY分子筛介孔直径为3.47 nm,孔容达到最大(0.226 cm~3·g~(-1)),相应CuY催化剂DMC的时空收率、选择性和甲醇转化率分别达到204.0 mg·g~(-1)·h~(-1)、67.8%和14.0%,活性最佳。     

草酸脱铝改性USY的表征及加氢裂化性能

采用草酸脱铝对USY分子筛进行了改性,考察了草酸加入量对USY相对结晶度(CRX)、硅铝比(nS iO2/nA l2O3)、比表面积、孔结构及加氢裂化性能的影响,并采用程序升温脱附和原位红外光谱技术对改性USY型分子筛的酸性进行了表征。结果表明,随草酸加入量的增加,在脱除USY中非骨架铝的同时,骨架铝被脱除的量也逐渐增多,致使USY的相对结晶度先提高而后降低、硅铝比提高、酸强度和酸量降低。正癸烷的加氢裂化结果表明,当草酸的加入质量比为0.2时,正癸烷的转化率和一次裂化产物的选择性分别为68.5%和80.1%。草酸改性USY具有高催化活性是因为该分子筛具有空旷的介孔结构和较多的可接近的酸性位;一次裂化产物选择性高是因为空旷的介孔结构使裂化产物快速离开酸性位而避免了二次裂化。     

AlMCM-41介孔分子筛的合成及表征

以拟薄水铝石为铝源、水玻璃为硅源、十六烷基三甲基溴化铵为模板剂,在110℃时水热晶化合成了含Al的MCM-41介孔分子筛.采用X射线衍射(XRD)、N2吸附-脱附、固体29Si、27Al魔角旋转核磁共振技术(MASNMR)、扫描电镜(SEM)及吡啶吸附傅里叶变换红外(FTIR)光谱技术对AlMCM-41分子筛进行了表征.结果表明:AlMCM-41分子筛具有六方排列的孔道结构,同时具有很高的相对结晶度、比表面积和孔容,且孔分布单一;AlMCM-41分子筛中Si原子在骨架内键合的程度更高,使AlMCM-41分子筛具有更好的骨架晶化程度;同时具有四配位骨架铝,使AlMCM-41介孔分子筛具有适当的酸性.     

CuO/SBA-15催化剂上巴豆醛选择性加氢

通过γ-氨丙基三甲氧基硅烷(APTS)偶联与Cu2 离子络合两步法将CuO负载到介孔分子筛SBA-15上,制得CuO/SBA-15催化剂,考察了催化剂的巴豆醛选择性加氢反应性能.通过X射线粉末衍射、氮气吸脱附和程序升温还原(TPR)技术对催化剂进行了表征.结果表明,SBA-15分子筛负载CuO后保持原有的介孔结构,但是孔容和比面表积随着CuO负载量的增大而下降.TPR结果表明CuO/SBA-15系列催化剂有三种CuO物种:高分散CuO、晶相CuO和进入SBA-15分子筛骨架的Cu2 .高分散CuO物种对巴豆醛加氢反应的催化活性最高,晶相CuO物种次之,而进入SBA-15分子筛骨架的Cu2 物种几乎没有活性.     

高硅Y沸石“二次孔”结构的物理吸附法研究

用低温氮物理吸附法研究了化学法和水热法相结合制备的两个系列Y沸石的孔结构性质。研究结果表明, 用不同化学试剂处理Y沸石形成的孔结构有明显差别。但是, 当把由此得到的Y沸石在相同条件下交替进行水热处理和化学处理时, 孔结构却呈现类似的变化趋势, 即总比表面积、微孔比表面积和微孔体积是先下降后上升, 经第二次水热和化学处理是再次下降再次回升。而过程中产生的“二次孔”比表面积却呈现先上升后下降, 又回升又下降的相反的变化趋势。这种变化趋势, 可能与水热处理和化学处理过程中非骨架铝物种的形成与消失有关。     

Y型分子筛结构破坏的动力学分析(英文)

Y型分子筛是催化裂化(FCC)的速率控制组分.FCC过程中,催化剂在反应器和再生器中往往面临高温水蒸气存在的苛刻环境.因此,分子筛的热稳定性和水热稳定性是催化剂最为关注的性能之一.由于FCC原料中通常含有V、Ni、Na、Fe等不同数量的金属污染物,会对催化剂造成污染及钝化.进料中存在的卟啉类有机复合物持续不断的沉积在催化剂表面,由于含钒的有机金属卟啉化合物在反应中转化形成V_2O_5,V_2O_5在水热条件下形成H_3VO_4组分,在高温水热气氛下加速分子筛骨架结构水解,破坏了Y型分子筛的晶体结构,从而降低了催化剂活性,影响产品选择性.稀土Y型分子筛在FCC中扮演重要的角色,稀土交换分子筛可以提高催化酸性、裂化活性和热与水热稳定性.此外,Na在高温水蒸气条件下也会对分子筛结构造成破坏.一方面,钠能够中和Y型分子筛B酸中心,降低催化裂化活性;另一方面,水热条件下钠的存在会加速破坏Y型分子筛的结构.有关Y型分子筛结构破坏的机理解释较多,然而该过程的动力学研究鲜有报道.反应动力学不能提供一个直接的反应机理,但是任何反应机理的提出必须符合反应动力学的数据.本文采用离子交换法分别制备了一系列不同Na含量USY,不同稀土含量USY,以及含钠和稀土的USY分子筛,通过固相动力学模型考察了上述Y型分子筛水热结构破坏活化能的变化及钒对其活化能的影响.结果表明,Y型分子筛的结构破坏存在三种路径,分别是脱铝、脱硅和La-O键的断裂.钒加速了分子筛骨架水解速率;钒钠具有协同作用,同时存在时对分子筛破坏作用更加显著;NaOH的形成是速率控制步骤;稀土稳定了分子筛的结构,降低了分子筛的水热脱铝速率;钒与定位于分子筛小笼里稀土作用,破坏分子筛的[RE-OH-RE]~(5+)的RE-O键夺取分子筛的骨架氧,导致骨架结构崩塌.由于稀土本身稳定了分子筛的结构,同时钒稀土作用时形成稳定的REVO_4固定了钒的流动性,因此钒对REY结构的影响是几种因素相互叠加和抵消的结果.     

P-RE-USY沸石的稳定性、酸性和裂化反应特性

采用NH3-TPD、FT-IR、XRD和元素分析方法研究了稀土和磷改性沸石P-RE-USY的酸性、水热稳定性,并在小型固定流化床反应装置中评价了含有这种改性沸石催化剂的反应性能。结果表明,由于磷促进了稀土离子由超笼向方钠石笼中的迁移,阻止了沸石在水热条件下的脱铝作用,从而改善了P-RE-USY沸石的水热稳定性；P-RE-USY沸石酸性分布更集中在中强酸范围,有利于发生氢转移反应,而强酸数量的降低有利于减少焦炭形成,改善了焦炭选择性。评价表明含有这种改性沸石的催化剂显示了优越的降低汽油烯烃的效果,柴油产率可增加2.31%。     

新型高硅Y(NHSY)沸石的研究:Ⅰ.NHSY沸石的制备

新型高硅Ｙ（ＮＨＳＹ）沸石的研究　Ⅰ．ＮＨＳＹ沸石的制备刘兴云，裴站芬，佘励勤，李宣文（北京大学化学系，北京１００８７１）关键词ＮａＹ沸石，骨架改性，化学脱铝，ＮＨＳＹ沸石，草酸为了提高用于制备裂化催化剂的Ｙ沸石的稳定性，必须对其骨架进行改性．实用的...     

In Situ Synthesis of NaY Zeolite with Coal—Based Kaolin

NaY zeolites were in-situ synthesized form coal-based kaolin via the hydrothermal method. The effects of various factors on the structure of the samples were extensively investigated.The samples were characterized by N2 adsorption,XRD,IR and DTG-DTA methods,and the results show that the crystallization temperature and amount of added water play an important role in the formation of the zeolite structure.The 4A and P zeolites are the competitive Phaes present in the resulting product.However,NaY zeolites wiht a higher relative crystallinity,excluding impure crystals and the well hydrothermal stapore size distribution,and this means that optimization of this process might result in a commercial route to synthesize NaY zeolites form coal-based kaolin.     

Gadolinium(III)-loaded nanoparticulate zeolites as potential high-field MRI contrast agents: relationship between structure and relaxivity

The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+-loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non-dealuminated materials. Analysis of the 1H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd3+-loaded cavities did not change significantly, which suggests that the windows of the Gd3+-loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd3+-loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+-doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T1 MRI contrast agents at low field, and as T2 agents at higher fields.     

Electron trapping in polar-solvated zeolites

Of current interest in our laboratory is the nature of photoinduced processes in the cavities of zeolites completely submerged in polar solvents, or polar-solvated zeolites (PSZ). The present study addresses the nature of electron trapping in PSZ with emphasis on the zeolites NaX and NaY. Free electrons were generated by two-photon, pulsed-laser excitation of either pyrene or naphthalene included in zeolite cavities. Trapped electrons were monitored by diffuse transmittance, transient absorption spectroscopy at visible wavelengths. In anhydrous alcohols, electron trapping by Na(4)(4+) ion clusters was observed in both NaX and NaY. The resulting trapped electrons decayed over the course of tens of milliseconds. No evidence for alcohol-solvated electrons was found. More varied results were observed in solvents containing water. In NaX submerged in CH(3)OH containing 5% or higher water, species having microsecond lifetimes characteristic of solvated electrons were observed. By contrast, a 2 h exposure of NaY to 95/5 CH(3)OH/H(2)O had no effect on electron trapping relative to anhydrous CH(3)OH. The difference between NaX and NaY was explained by how fast water migrates into the sodalite cage. Prolonged exposure to water at room temperature or exposure to water at elevated temperatures was necessary to place water in the sodalite cages of NaY and deactivate Na(4)(4+) as an electron trap. Additional studies in NaY revealed that solvent clusters eventually become lower energy traps than Na(4)(4+) as the water content in methanol increases. In acetonitrile-water mixtures, electron trapping by Na(4)(4+) was eliminated and no equivalent species characteristic of solvated electrons in methanol-water mixtures was observed. This result was explained by the formation of low energy solvated electrons which cannot be observed in the visible region of the spectrum. Measurements of the rate of O(2) quenching in anhydrous solvents revealed rate constants for the quenching of ion cluster trapped electrons that were 2-4 times higher than that for pyrene triplets. In NaX, the rate constant in methanol was 10(4) times smaller than that in cyclohexane, showing greater inhibition of O(2) reactivity in the medium of PSZ. The results of this study point out the conditions under which Na(4)(4+) is active as an electron trap in PSZ and that water must be present in the sodalite cage to produce solvated electrons in the supercage.     

Molecular dynamics study of hydrated faujasite-type zeolites

Molecular dynamics (MD) simulations of hydrated zeolite NaX (Si/Al = 1.0) and NaY (Si/Al = 2.0) were done at a temperature of 300 K. The calculation results show that the adsorption of water occurs via a three-step mechanism in zeolite NaX: (1) adsorption around Na, (2) formation of a monolayer on the walls, and (3) pore filling in the supercage during which adsorbed water molecules are localized around the 12-membered rings. Zeolite NaY adsorbs in a similar manner. However, at intermediate hydration states, cluster formation occurs around Na instead of monolayer formation. The calculated energy distribution functions suggest that in zeolite NaX, the water vapor adsorption can be expressed by using the Langmuir model with two adsorption sites, but in zeolite NaY, it is not Langmuir-type adsorption.     

超声陈化法制备纳米NaY分子筛及形成机理研究

Nano-sized NaY zeolite was synthesized from metakaolin in the hydrothermal synthesis system by using ultrasonic during aging time.The process of crystallizing NaY zeolite was studied by XRD、SEM、ICP OES ,and the formation mechanism of nano-sized NaY zeolite was researched,finally the conditions of synthesizing nano-sized zeolite NaY had been brought forward.