铈掺杂的介孔分子筛的水热合成与结构性能

以硅酸钠、硝酸铈铵为原料,十六烷基三甲基溴化铵为模板剂,通过水热法合成铈掺杂的介孔分子筛CeMCM-41.分别采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)、红外光谱(FT-IR)、紫外-可见分光光度计(UV-Vis)和N2吸附-脱附等技术对产物的晶相、结构、形貌、比表面积和孔径进行表征.同时研究硅铈物质的量比对合成材料结构性能的影响.实验结果表明:水热条件下成功合成出铈掺杂的MCM-41介孔分子筛,其比表面积为480.5～1 295.2m2/g,平均孔径在2.70～6.29 nm之间.随着稀土元素铈的掺杂量的增加,CeMCM-41介孔分子筛的比表面积和孔体积变小,介孔有序性变差.     

微孔-介孔复合分子筛HY-SBA-15的表征及应用

用后合成法制备了微孔-介孔复合分子筛HY-SBA-15(y) (y表示HY与SBA-15的质量比)。并用XRD、FT-IR、N₂吸脱附及NH₃-TPD等技术对HY-SBA-15进行表征。结果表明,HY-SBA-15既具有微孔结构又具有介孔结构,当y=0.10时,微孔与介孔混合晶相显著,且HY-SBA-15(0.10)复合分子筛具有B酸和L酸,酸性强于HY。用浸渍法将Ni-W活性组分担载在HY-SBA-15(0.10)载体上,制备加氢脱芳烃催化剂Ni-W/HY-SBA-15(0.10),选用茂名石化FCC柴油为原料,考察了催化剂的加氢脱芳烃性能。实验结果表明,Ni-W/HY-SBA-15(0.10)催化剂具有良好的芳烃加氢饱和性能和开环活性。     

Tuning of textural properties of germanosilicate zeolites ITH and IWW by acidic leaching

The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions(e.g.temperature, p H, duration) of acidic leaching was shown. While the growth of the temperature of acid treatment caused the increasing amount of leached Ge atoms and enhancing volumes of both micro and mesopores at 80 ℃, the mesopore volume in ITH(Si/Ge = 3.4 and 5.8) and IWW(Si/Ge = 3.3) zeolites changed with the duration of the treatment(p H = 2; T = 80 ℃) as follows: 96 h 1 h 24 h. Independently on the chemical composition and zeolite topology, the treatment of germanosilicate zeolites at p H = 2–7 resulted in development of both micro and mesoporosity accompanied by the extraction of substantial amount of Ge atoms, while the increasing acidity up to p H = 0 resulted in some reduction of Ge extraction and in the development of mesopores at maintained value of micropore volume when compared with initial germanosilicates. The higher activity(i.e. number of reactant molecules converted per active site) of germanosilicate with modified micro-mesoporous channel system in comparison with parent IWW zeolite in esterification of levulinic acid was attributed to enhanced accessibility of active sites.     

Characterization of iron-mesoporous molecular sieves obtained by a microwave-hydrothermal process

Fe-SBA-15 materials with different Si/Fe ratios (Si/Fe = 90, 50, 10) have been synthesized by a microwave-hydrothermal (M-H) process and characterized by several spectroscopic techniques. Electrons spin resonance and Mössbauer spectroscopies, along with electron microscopy and X-ray diffraction, allowed differentiation of several iron species. These species correspond to hematite particles, very small “isolated” or oligomeric Fe^III species possibly incorporated in the mesoporous silica wall, and Fe^III oxide clusters either isolated or agglomerated, forming “rafts” at the surface of the silica and exhibiting ferromagnetic ordering. Due to their agglomeration, these clusters appear with a two-peak size distribution, with one peak corresponding to the isolated clusters formed in the mesopores and still embedded in them (ca. 2 nm diameter) and the other corresponding to the agglomerates spread on the surface of the mesoporous silica particles (ca. 9 nm).     

Physicochemical and catalytic properties of CoAPO-5 and CoAPSO-5 molecular sieves

The physicochemical and catalytic properties of cobalt- and silicon-substituted AlPO-5 molecular sieves were studied by means of temperature-programmed reduction, temperature-programmed desorption of ammonia and the reaction of toluene disproportionation.     

Gemini quaternary ammonium salt cationic surfactant‐assisted hydrothermal synthesis: An effective way to tune the textural properties of zeolite and the acidity of Beta molecular sieves

Novel hierarchical Beta zeolites have been successfully synthesized via a one‐pot dual‐templates strategy utilizing gemini organic surfactant and tetraethylammonium hydroxide (TEAOH)through hydrothermal process. The influence of several parameters on the formation of hierarchical Beta zeolite, the change in acidity and a possible growth scheme were systematically investigated. The physicochemical properties of these catalysts were characterized by PXRD, BET, SEM, HRTEM SAED, TG and NH₃‐TPD techniques, and the performance as acid catalysts was verified using the transformation of EtOH as a model reaction. On one hand, WAXRD data indicated that decreasing the temperature of synthesis and increasing amounts of C_12‐6‐12 in the process of synthesis resulted in lower crystallinity of Beta zeolites due to the BEA nuclei formation and crystal growth constrained by C_12‐6‐12. On the other hand, SAXRD and HRTEM data evidenced that C_12‐6‐12 initially generated a pseudo‐ordered mesoporous phase which was then partially occupied by the zeolite. After a period of ~96 h for crystallization, the hierarchy zeolite possessing 765.7 m²·g^‐1 of Brunauer‐Emmett‐Tellerarea, and average mesopore size distribution of 3.51 nm can be synthesized, and its microporous structure has a good crystallinity and lower amounts of acid sites than that of the microporous Beta one. Furthermore, the as‐obtained hierarchical zeolite displayed lower deactivation rate mainly due to the less coke formation on the surface of catalyst. It is expected to develop more considerable potential application value for the hierarchical Beta zeolite structure in the near future.     

Transport properties of nanofiltration plasticized polyvinyl chloride membranes, molecular sieves

The modification of surfaces of solid-state potentiometric surfactant sensors with nanofiltration membranes (molecular sieves) with different diameters allows the detection of homologues of anionic, cationic, and nonionic surfactants. The quantitative characteristics of the membrane transport (permeability and ion flow) and the separating ability of plasticized polyvinyl chloride molecular sieves are evaluated. The permeabilities of nanofiltration membranes and ion flows through them depend on the nature of the blowing agent and the nature and concentration of the surfactants in the contacting solutions whose variation allows the separation of homologues of sodium alkyl sulfates, alkylpyridinium chlorides, and polyethoxylated nonylphenols in multicomponent mixtures.     

Textural and structural properties and surface acidity characterization of mesoporous silica-zirconia molecular sieves

Homogeneous mesoporous zirconium-containing MCM-41 type silica were prepared by supramolecular templating and their textural and structural properties were studied using powder X-ray diffraction, N₂ porosimetry, atomic force microscopy, EXAFS, XPS, and UV-VIS-NIR diffuse reflectance spectroscopy. Their acid properties were also studied by using IR spectroscopy and by the use of catalytic tests such as the decomposition of isopropanol and the isomerization of 1-butene. The materials prepared show a good degree of crystallinity with a regular ordering of the pores into a hexagonal arrangement and high thermal stability. The specific surface area of the prepared materials decreases as the zirconium content rises. Zirconium atoms are in coordination 7 to 8 and located at the surface of the pores such that a high proportion of the oxygen atoms bonded to zirconium corresponds to surface non-condensed oxygen atoms. Both facts are responsible for the acid properties of the solids that show weak Brønsted and medium strong Lewis acidity.     

Nanocomposites based on LaCoO3 and mesoporous molecular sieves: Preparation and physicochemical and catalytic properties

Individual perovskite-like LaCoO₃ obtained by the citrate method and LaCoO₃ supported onto the mesoporous molecular sieve MSM-41 have been characterized by X-ray powder diffraction, EPMA, low-temperature nitrogen adsorption, H₂ TPR, and EXAFS. The catalytic activity of the supported cobaltate in methanol oxidation is two orders of magnitude higher than the activity of the bulk cobaltate owing to nanosized LaCoO₃ particles in the pores of the molecular sieve.     

Ortho-selectivity in aluminophosphate molecular sieves: A molecular simulation study

Monte Carlo adsorption simulations of xylenes have been performed in aluminophosphate molecular sieve structures. A new force field fitted for o-xylene in AlPO₄-5 was used. It is shown that force fields have good transferability among the aluminophosphate sieves series and the new force field adequately describes the experimentally observed adsorption isotherms for xylene/AlPO₄-5. A previous investigation of adsorption isotherms and structural analysis has been extended to AlPO₄-8 and VPI-5 sieves. In AlPO₄-8, like in AlPO₄-5, the variations in the channels diameters and the corresponding interaction energy of the molecule-crystal lattice drive all molecular positioning. In VPI-5, the modulation between wide and narrow regions becomes negligible due to the larger pore diameter, so no ortho-selectivity was observed. The simulations confirm the ortho-selectivity mechanism proposed to aluminophosphates.     

Mesoporous molecular sieves and nanoperiodic materials

A review is given of literature data and some results of the authors on different approaches to the synthesis and the physicochemical properties of mesoporous molecular sieves and nanoperiodic structures made from inorganic oxides, phosphates, heteropolyacids, and surfactants. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 33, No. 5, pp. 322–337, September–October, 1997.     

Characterization of CoMCM-41 mesoporous molecular sieves obtained by the microwave irradiation method

CoMCM-41 mesoporous molecular sieves with different amounts of cobalt were synthesized via the microwave irradiation method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and N₂ adsorption-desorption technique, and thermal and hydrothermal stabilities of synthesized CoMCM-41 samples were also investigated. Results show that these synthesized materials have typical mesoporous structure of MCM-41. Also, specific surface area and pore volume of synthesized CoMCM-41 decrease with increasing amount of cobalt added, and mesoporous ordering also decreases. When the molar ratio of SiO₂:CoO in the starting material is 1.0:0.05, mesoporous ordering of synthesized CoMCM-41 is the best among the four doping contents. On the other hand, results of thermal and hydrothermal tests show that CoMCM-41 after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 5 days still retains mesostructure. However, mesoporous framework is entirely damaged after calcination at 850 °C for 3 h.     

Nature of acidic protons in metallosilicate molecular sieves as studied by variable temperature 1H MAS NMR

The dynamic properties of protons in H-[Ga]-ZSM-5, H-[B]-ZSM-5 and H-[Al-B]-ZSM-5 were compared with that of protons in H-[Al]-ZSM-5 by temperature dependence of ¹H MAS NMR in the range of 298 k and 473 K. The temperature dependence of the line width of ¹H MAS NMR reveals that protons in H-[Ga]-ZSM-5 were more mobile than those in H-[Al]-ZSM-5 at temperature as low as 373 K. The protons in H-[B]-ZSM-5 were not mobile at 473 K and fixed in the zeolite frame work as the bridging hydroxyl groups, ≡B-OH-Si≡. The thermal motion of protons in ≡Al-OH-Si≡ was suppressed by introducing B³⁺ cations into the framework of H-[Al]-ZSM-5.     

Synthesis and characterization of mesoporous molecular sieves

In the synthesis of mesoporous molecular sieves of the type MCM-41, different cationactive surfactants and sources of silicon were used. Moreover, Al-MCM-41 samples with different content of aluminium were synthesized. MCM-41 and Al-MCM-41 were synthesized at elevated temperature in stainless-steel autoclaves. Prepared mesoporous molecular sieves were characterized by powder X-ray diffraction (XRD), physical adsorption of nitrogen at the temperature of −197°C, sorption capacity of benzene, and by infrared spectroscopy (FTIR). Acidity was measured for Al-MCM-41 by temperature programmed desorption of ammonia (TPDA) and by FTIR of adsorbed pyridine. Acid catalytic activity of Al-MCM-41 was tested by isomerization of o-xylene. Influence of the synthesis reproducibility, surfactant used, source of silicon, synthesis time, source of aluminium, and Si to Al mole ratio on the properties of mesoporous molecular sieves were evaluated.     

Effect of titanium on the structure and properties of mesoporous MCM-41 molecular sieves

Mesoporous MSM-41 titanium silicate molecular sieves with high titanium content were synthesized. The hexagonal structure along with high specific surface and pore volume are retained up to Si/Ti≥5. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 177–182, May–June, 1999.     

Molecular sieves 5A as an acidic reagent: the discovery and applications

The first use of molecular sieves (MS) 5A as an acidic reagent is described. We observed the acidic property during a dehydration reaction of 2-methyl-4-phenyl-3-butyn-2-ol. The acidity was sufficient to introduce ethoxyethyl and methoxyisopropyl protecting groups into alcohols. Additionally, the employment of MS 5A improved the synthesis of 1,2,4-orthoacetyl-α-d-glucopyranose at the intramolecular transorthoesterification step. In the other step of the synthesis, MS 4A was also applied to demonstrate that the manipulation of MS simplified the total operations.     

介孔分子筛MCM-41的硅烷化改性及吸附性能研究

高硅分子筛MCM-41具有均匀的中孔孔径分布、较大的比表面积(>900m2/g)[1-2],应用前景广阔.已在硅基分子筛的基础上合成了各种含有杂原子分子筛、金属氧化物分子筛、有机官能团分子筛[3-8].改变介孔MCM-41分子筛的表面组成可以较好地调节其吸附性能[9].本文以直接反应的方法用三甲基氯硅烷来修饰MCM-41.通过XRD、红外吸收光谱和比表面和孔隙率测定对样品进行了表征,并分别对改性前后样品进行了水与苯的吸附性能研究.     

新型磷酸硅铝分子筛SAPO-56的合成与表征

以N,N,N',N'-四甲基-1,6-己二胺(TMHD)为模板剂,采用水热法在Al₂O₃-P₂O₅-SiO₂体系中合成了SAPO-56分子筛.固定模板剂和水,得到Al-Si-P三元体系相图.当原料物质的量比为0.52)/n(M)<0.7(M=SiO²⁺Al₂O³⁺P₂O₅),0.152O₃)/n(M)<0.4及0.12O₅)/n(M)<0.3时,出现SAPO-56合成的纯相区.固定合成凝胶中硅、铝、磷和水的量,模板剂的用量改变对合成影响较大.n(TMHD)/n(P₂O₅)≥2时,产物是纯SAPO-56.用XRD,SEM,IR,DTA-TG和吸附等方法研究了产物的物化性能.结果表明,SAPO-56分子筛具有较好的热稳定性(骨架坍塌温度为1150℃)和较大的水吸附量(41%).SAPO-56分子筛催化剂对甲醇转化制烯烃反应表现出了良好的催化活性和较高的C₂和C₃烯烃选择性.     

Thermogravimetry of molecular sieves note 1

Water-saturated molecular sieves were studied with a derivatograph. Apparent activation energies and orders of reaction were calculated and interpreted on the basis of the structures of the samples.