New Nb-containing SBA-3 mesoporous materials—Synthesis, characteristics, and catalytic activity in gas and liquid phase oxidation

The synthesis and characterization of NbSBA-3 mesostructured materials – the first hexagonally ordered mesoporous molecular sieves without extra framework Nb-oxide phase – are described in this paper. The effect of the synthesis medium (basic or acidic) and Nb source in the efficiency of niobium incorporation is discussed. A higher Nb content in the final material is reached when Nb(V) chloride is used instead of Nb(V) ammonium trisoxalate complex in the synthesis. All NbSBA-3 materials prepared in this work are very attractive catalysts in ODH of propane and epoxidation of cyclohexene and more effective than the corresponding NbMCM-41 and NbSBA-15 catalysts.     

Synthesis, Characterization and Catalytic Activities of Mesoporous AlMSU-X with Wormhole-Like Framework Structure

Mesoporous AlMSU-X molecular sieves with high acidity have been prepared from preformed beta nanoclusters under strong acidic conditions in the presence of nonionic TX-100 as structure directors. These materials were characterized by XRD, HRTEM, N₂-adsorption, ²⁷Al MAS NMR, NH₃-TPD, IR-pyridine adsorption and catalytic cracking of cumene and 1,3,5-triisopropylbenzene. The experimental results showed that Al heteroatoms had been successfully incorporated into the framework structure of mesoporous MSU-X, and so-produced catalysts exhibited superior catalytic properties.     

Characterization and catalytic evaluation of mesoporous and microporous molecular sieves containing niobium

The synthesis and characterization of the novel microporous aluminophosphate NbAPO-5 is described. The novel material has been studied by X-ray powder diffraction, SEM, TG/DTA-MS, electron spin resonance, and ultraviolet-visible (UV-Vis) spectroscopy The catalytic properties have been tested in the epoxidation of 1-hexene and cyclohexene, respectively, in comparison with niobium-containing silicalite-1 and NbMCM-41. The results of the physical characterization indicate that it is possible to prepare niobium-containing aluminophosphates, where isolated Nb(V) species are connected to framework defect sites via formation of Nb–O–P or Nb–O–Al bonds. The results of this study allow the preparation of microporous and mesoporous niobium-containing molecular sieves which are active catalysts in oxidation reactions.     

Niobium rich SBA-15 materials – preparation, characterisation and catalytic activity

Hexagonally ordered mesoporous niobiosilicates of SBA-15 type were synthesised by a new synthesis route in which the use of hydrochloric acid was avoided. This route allowed the incorporation of much higher amounts of niobium into the mesoporous network (Si/Nb between 15 and 5) as compared to the conventional method of preparation. The location of niobium was determined by UV–Vis and XRD techniques. The latter combined with N₂ adsorption measurements allowed the estimation of texture/structure parameters. The high niobium content in the NbSBA-15 had a significant impact on the sulphurisation of methanol leading to the formation of organic sulphur compounds. It is well correlated with the acidity of the materials measured by pyridine adsorption followed by FTIR studies. Such a relationship was not observed for oxidation of methanol and epoxidation of cyclohexene showing that the redox properties are not linear related to the amount of niobium if Si/Nb is equal or below 15 (as applied in this work).     

含钛中孔分子筛Ti-MSU的合成、表征与催化氧化性能

分别以两种非离子表面活性剂C₁₈(EO)₁₀、C₁₂Ph(EO)₁₀为模板剂,硅酸四乙酯（TEOS）为硅源,钛酸四丁酯（TBOT）为钛源,乙醇、异丙醇为溶剂分别合成了两种含钛中孔分子筛Ti-MSU-1和Ti-MSU-2.采用XRD、FT-IR、UV-Vis、元素分析（ICP）法、N₂吸附-脱附等方法对合成的分子筛进行了结构测试和表征.将得到的Ti-MSU-1分子筛前体在高压釜中进行水热处理后,其孔道对称性或有序性显著增强,焙烧过程中热诱导的晶层收缩不再明显,而同样条件的热处理对Ti-MSU-2分子筛孔道结构改性不大.两种Ti-MSU分子筛均对苯乙烯具有催化氧化性能.苯乙烯转化率随中孔分子筛中含钛量的增大而增大.Ti-MSU-1分子筛与Ti-MSU-2分子筛在催化性能上没有太大差别,这与其结构的相似性是一致的.     

The role of niobium in MCM-41 supported with Pt and Au—A comparative study of physicochemical and catalytic properties

This paper reviews a series of results, partly published recently, on niobosilicate mesoporous molecular sieves of MCM-41 type modified with noble metals (Pt, Au). Platinum is introduced to MCM-41 by impregnation technique, whereas gold is incorporated by two methods: during the synthesis by co-precipitation (COP) and by impregnation (IMP). Three fundamental features of the prepared materials have been considered: (i) texture/structure, (ii) noble metal state and dispersion, and (iii) catalytic activity. The latter has been tested in selective reduction of NO by propene, methanol oxidation and WGS process. The role of niobium, as well as the effect of the nature of noble metals and the preparation method on the physicochemical and catalytic properties of the final materials based on NbMCM-41 (in comparison with siliceous MCM-41) is demonstrated.     

MCM-41介孔分子筛研究进展

介绍了介孔材料的定义,总结了MCM-41介孔分子筛的合成方法,针对其目前存在的孔径较小及酸性较小的缺点,综述了国内外对MCM-41介孔分子筛的孔径扩大分的最新研究进展。     

Synthesis of highly stabilized mesoporous molecular sieves using natural clay as raw material

Mesoporous molecular sieves were hydrothermally synthesized from natural clay and sodium silicate by using cetyl trimethyl ammonium bromide (CTAB) as a template. The samples were characterized by means of XRD, TEM, TPR, FT-IR and N₂ physical adsorption. The results show that well-ordered and highly stabilized mesoporous molecular sieves were obtained by adjusting the proportion of raw materials. The pore structure of the as prepared mesoporous molecular sieves was not damaged after calcination at 850 °C for 3 h or hydrothermal treatment at 100 °C for 10 days. The mesoporous ordering became better after hydrothermal treatment, but the pore shrank and the surface area decreased after thermal treatment. The stability of the as prepared mesoporous molecular sieves depends on the stability of the clay present in mesoporous pore walls. The presence of clay in the walls can be certified by the regular pore channel images as determined by TEM and XRD analyses.     

用富含介孔的硅基材料合成微孔-介孔复合分子筛

以富含介孔的硅基材料为硅源,四乙基氢氧化铵为模板剂,NaAlO2为铝源,调节投料硅铝的摩尔比(n(SiO2)/n(Al2O3)),通过半固相原位合成法,制备了具有不同晶型的微孔-介孔复合分子筛。采用X射线衍射仪分析样品组成,扫描电镜观测样品晶体形态,使用容量吸附分析仪测量样品孔结构。结果表明,所得样品具有微孔-介孔复合结构,在较低硅铝摩尔比条件下(n(SiO2)/n(Al2O3)=20~50),产物主要为β微孔-介孔复合分子筛;硅铝摩尔比较高时(n(SiO2)/n(Al2O3)200),合成产物为ZSM-5微孔-介孔复合分子筛。     

SELECTIVE OXIDATION OF ALCOHOLS BY REDOX MOLECULAR SIEVES

High-throughput synthesis and screening of libraries consisting of redox zeolites and molecular sieves have been developed for the selective oxidation of 2-butyl-5-hydroxymethyl-imidazole to the corresponding aldehyde in the liquid phase. Libraries consisting of 96 catalysts were prepared and screened for catalytic activity using high-throughput software, robotics, reactor, and screening technologies. The integrated synthesis and screening workflow allowed ∼5000 samples to be screened in less than one month. Promising hits identified in the high-throughput primary screens were successfully scaled up and optimized in conventional laboratory test units. Best results have been obtained with doubly or triply doped mesoporous sieves containing both an impregnated and framework-substituted metal. PtBi-doped framework-substituted V-MCM-41 redox mesoporous sieves were found to be efficient catalysts for aerobic oxidation under relatively mild reaction conditions (100-150°C, 15-400 psi air, 4-10 h reaction time). MIBK/H₂O/t-BuOH mixtures were identified as efficient solvent systems for this reaction. Isolated yields confirm high selectivities of more than 90% with quantitative conversions. Spent catalysts were shown to be fully regenerable by high temperature calcination in air.     

SELECTIVE OXIDATION OF ALCOHOLS BY REDOX MOLECULAR SIEVES

High-throughput synthesis and screening of libraries consisting of redox zeolites and molecular sieves have been developed for the selective oxidation of 2-butyl-5-hydroxymethyl-imidazole to the corresponding aldehyde in the liquid phase. Libraries consisting of 96 catalysts were prepared and screened for catalytic activity using high-throughput software, robotics, reactor, and screening technologies. The integrated synthesis and screening workflow allowed ～5000 samples to be screened in less than one month. Promising hits identified in the high-throughput primary screens were successfully scaled up and optimized in conventional laboratory test units. Best results have been obtained with doubly or triply doped mesoporous sieves containing both an impregnated and framework-substituted metal. PtBi-doped framework-substituted V-MCM-41 redox mesoporous sieves were found to be efficient catalysts for aerobic oxidation under relatively mild reaction conditions (100–150°C, 15–400 psi air, 4–10 h reaction time). MIBK/H₂O/t-BuOH mixtures were identified as efficient solvent systems for this reaction. Isolated yields confirm high selectivities of more than 90% with quantitative conversions. Spent catalysts were shown to be fully regenerable by high temperature calcination in air.     

Water adsorption and desorption isotherms of silica and alumina mesoporous molecular sieves

Mesoporous molecular sieves of silica, and alumina, and porous materials of titania, zirconia, and niobia were synthesized by cationic and/or neutral templating methods. These porous materials were characterized by powder X-ray diffraction, transmission electron microscopy, N₂ adsorption-desorption isotherms and water adsorption-desorption isotherms. Mesoporous molecular sieves of silica with surface areas of 956 and 1072 m²/g and of alumina with surface area of 407 m²/g were synthesized. The Ti₁ Zr and Nb oxide porous materials, however, showed smaller surface areas of 258, 178, and 77 m²/g, respectively, after calcination at 300°C and exhibited only small peaks for mesopores as determined by the pore-size. distributions.Water adsorption-desorption isotherms of silica and alumina mesoporous molecular sieves showed Type V (weak interaction) and Type IV isotherms, respectively. The property of sudden filling of mesopores in theP/P ₀ range of 0.45 to 0.55 in silica mesoporous molecular sieves with well-defined hysteresis during desorption, can be used in the design of humidity sensors. The titania, zirconia and niobia porous materials showed Type I water adsorption-desorption isotherms which suggests that these are mainly microporous. These results suggest that water adsorption-desorption isotherms provide valuable information about mesoporous molecular sieves for their potential use as humidity sensors.     

组合处理工艺下硅藻土微观组织演变及孔隙结构变化

将硅藻土制成硅藻土/分子筛复合材料,其比表面积和吸附能力将显著提高。本文利用水洗-烧结-酸性水热系列组合处理工艺制备硅藻土/磷酸铝分子筛复合材料,同时验证外加铝源形成磷酸铝分子筛的可行性,探讨高品质硅藻土形成时的微观组织演变行为及孔隙结构变化规律。结果表明:硅藻土的孔隙结构包括大孔、介孔和少量的微孔结构,水洗处理仅有物理提纯作用;500 ℃烧结可以疏通硅藻土壳体的孔洞,但烧结温度过高会导致管状结构的坍塌;酸性水热处理能够合成具有介孔结构的磷酸铝分子筛,而且随着外加铝源的加入,硅藻土/分子筛复合材料中磷酸铝分子筛含量增加,当外加铝源为硅藻土中铝含量的1.5倍时,其比表面积和吸附性能达到最大。     

Preparation of mesoporous In–Nb mixed oxides and its application in photocatalytic water splitting for hydrogen production

A series of mesoporous In–Nb mixed oxides was synthesized using NbCl₅ and In₂O₃ as the starting material and triblock copolymer P123 as template. We investigated the influence of indium content on the synthesis and characteristics of the mesoporous In–Nb mixed oxides, and their photocatalytic activities for water splitting. The materials were characterized by small angle X-ray scattering, powder X-ray diffraction, extended X-ray absorption fine structure, transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometer, N₂ sorption and UV–vis spectroscopy. The surface area of mesoporous In–Nb mixed oxides was greater than 90 m²/g with a wormhole framework. The optimization of synthesis condition of the mesoporus In–Nb oxides catalyst contained a small fraction of highly dispersed indium (In/Nb = 0.13) species intercalated into the framework of mesoporous niobium oxides and exhibited a high photocatalytic activity for water splitting reaction which was about 2.7 times as compared to mesoporous Nb₂O₅ and was about 19 times higher than commercial bulk Nb₂O₅.     

Effects of tunable acidity and basicity of Nb‐KIT‐6 catalysts on ethanol conversion: Experiments and kinetic modeling

The relative amounts of acidic and basic sites in niobium‐containing ordered mesoporous silicates (Nb‐KIT‐6) are tunable with metal loading. The acidity and basicity change from 0.11 to 0.34 mmol NH₃‐equiv./g cat. and 0.17 to 0.31 mmol CO₂‐equiv./g cat., respectively, as the Nb loading is increased from 1.5 to 10.9%. This work harnesses this unique feature to better understand acidity and basicity effects on ethanol conversion activity and product selectivity. It is shown that the yields of ethylene and acetaldehyde, the dominant products, are tuned with Nb loading. Catalyst characterization results and designed kinetic experiments provide evidence of acid‐base pairs involved in the formation of various products. A macrosite kinetic model based on these observations and published mechanistic pathways fits the data for formation of the major products (ethylene, acetaldehyde, diethyl ether, and ethane) remarkably well. These results provide guidance for the rational design of bifunctional mesoporous materials exhibiting tunable acidity and basicity. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2888–2899, 2017     

铌掺杂介孔氧化锆复合催化材料的合成与表征

以氧氯化锆（ZrOCl2·8H2O）为锆前驱体,乙酰丙酮（ACAC）作为水解抑制剂,十六烷基三甲基溴化铵（CTAB）为模板剂,用无水乙醇稀释的氨水调节溶液的pH,采用溶胶-凝胶法于溶剂无水乙醇中合成介孔氧化锆。在此基础上以草酸铌为铌前驱体,将铌元素掺杂到介孔氧化锆体系,制备介孔Nb2O5-ZrO2复合氧化物催化剂。采用低温氮气吸附-脱附、X射线粉末衍射（XRD）、Hammett指示剂法对样品进行表征。结果显示,将铌掺入介孔氧化锆后,可制备出介孔 Nb2O5-ZrO2复合氧化物,当n（Nb）∶n（Zr）＝0.05时,其产品BET表面积为122.42 m2/g,孔径为3.68 nm,与未掺杂介孔氧化锆的样品相比,虽然并没有产生新的酸位,但总酸量有所增加。     

中孔分子筛材料的研究进展

介绍了中孔分子筛MCM系列、HMS系列、MSU系列、SBA系列等在合成方法和改性方法上的研究进展;评述了掺入杂原子、引入有机基团、硅源前处理、混合模板剂等赋予中孔分子筛新的催化性能和选择性氧化性能及其应用前景。     

介孔磷酸铝分子筛的研究进展

从合成方法、特性和应用三个方面综述了介孔磷酸铝分子筛(AlPO4)的国内外研究进展,分析了水热或溶剂热在合成介孔AlPO4分子筛工艺上的特点,介绍了介孔AlPO4分子筛的结构组成和在化工领域中的一些应用。     

超微粒介孔分子筛Ti-MC M-41的制备及催化氧化乙苯合成苯乙酮和α-苯乙醇

在强酸性及常温常压下 ,以无水乙醇和异丙醇为混合溶剂 ,合成了n(Si)∶n(Ti)分别为 30∶1、5 0∶1和 70∶1的超微粒介孔分子筛Ti MCM 41。经X衍射光谱、Fourier红外光谱 (FTIR)和扫描电镜表征 ,该分子筛具有规则的晶体结构 ,颗粒直径为 0 0 5～ 0 1μm ,在FTIR的 96 0cm-1处表现出Si—O—Ti的特征吸收峰。同时研究了该分子筛在乙苯液相氧化中的催化行为 ,讨论了催化剂及反应条件的影响。结果表明 ,在Ti MCM 41催化下 ,双氧水可以将乙苯氧化为苯乙酮和α 苯乙醇。当催化剂n(Si)∶n(Ti)由 70∶1降至 30∶1,催化剂加入量由 10 0mg增加到 30 0mg ,n(H2 O2 )∶n(乙苯 )由 1 0∶1 0增至 3 0∶1 0 ,反应时间由 1h延长至 10h ,反应温度由 15℃升高到6 0℃时 ,乙苯的转化率分别提高到 3 3倍、1 4倍、2 6倍、1 7倍和 2 2倍。以氯仿、丙酮和甲醇为溶剂时 ,乙苯的转化率分别为 0 6 4%、1 2 7%和 3 5 5 %。     

n-heptane hydroconversion over aluminosilicate mesoporous molecular sieves

Aluminosilicate mesoporous molecular sieves (designated Al-MMS) have been prepared at room temperature using the primary amine hexadecylamine as organic templating surfactant. The materials have textural properties typical of mesoporous materials with short-range hexagonal order but exhibit higher Brønsted acidity compared to aluminium-containing MCM-41. The Pt-impregnated materials are efficient catalysts for the hydroconversion of n-heptane. At low Si/Al ratio (≤ 10) the materials have total conversions and selectivity comparable to that of USY zeolite (Si/Al = 21) and in addition exhibit considerable cyclisation at temperatures above 350°C. Our catalytic results show that the Pt-impregnated Al-MMS samples attain a good balance between the metal and acidic functions and that activity and selectivity are dependent on the Brønsted acid content and consequently on the amount of tetrahedral aluminium in the catalysts. The amount of Pt (in the range 0.25-1 wt%) mainly affects the selectivity to cyclised products which increases with Pt content at the expense of cracking; total conversion and selectivity to isomers remain largely unaffected.