Hydroxylation of phenol over MeAPO molecular sieves synthesized by vapor phase transport

In this study, MeAPO-25 (Me = Fe, Cu, Mn) molecular sieves were first synthesized by a vapor phase transport method using tetramethyl guanidine as the template and applied to hydroxylation of phenol. The zeolites were characterized by XRD, SEM, FT-IR, and DR UV–Vis. As a result, MeAPO-21 and MeAPO-15 were synthesized by changing the Me/Al ratio. UV–Visible diffuse reflectance study suggested incorporation of heteroatoms into the framework and FT-IR study also supported these data. Effects of heteroatoms, contents of Me in MeAPO-25, reaction temperature, phenol/H₂O₂ mole ratios, reaction time and concentration of catalyst on the conversion of phenol, as well as on the selectivity were studied. FeAPO-25 exhibited a high catalytic activity at the mole ratio of FeO and Al₂O₃ equal to 0.1 in the synthesis gel, giving the phenol conversion of 88.75% and diphenols selectivity of 66.23% at 60°C within 3 h [n(phenol)/n(H₂O₂) = 0.75, m(FeAPO-25)/m(phenol) = 7.5%]. Experimental results indicated that the FeAPO-25 molecular sieve was a fairly promising candidate for the application in hydroxylation of phenol.     

Anchored metal-to-metal charge-transfer chromophores in a mesoporous silicate sieve for visible-light activation of titanium centers

Binuclear metal-to-metal charge-transfer (MMCT) moieties consisting of a Ti and a Cu(I) or a Ti and a Sn(II) center were obtained in a MCM-41 silicate sieve along with isolated metal centers when exposing Ti-grafted MCM-41 to Cu(I) or Sn(II) precursors featuring highly labile CH3CN ligands. Fourier transform infrared (FT-IR) spectroscopy revealed complete removal of the labile CH3CN ligands of the metal precursor and the formation of Cu(I)-O-Ti, Cu(I)-O-Si, and corresponding Sn(II) linkages on the pore surface. Optical and FT-IR difference spectroscopy upon oxidation of Cu(I) (Sn(II)) allowed assignment of the Cu(I)-O (642 cm(-1)) and Sn(II)-O (610 cm(-1)) bond modes of the MMCT moiety. The visible-light-absorbing Ti(IV)-O-Cu(I) MMCT chromophore extends from the UV to 600 nm, the corresponding Ti(IV)-O-Sn(II) absorption to 470 nm. Electron paramagnetic resonance monitoring of the TiSn(II)-MCM-41 sieve following photoexcitation of the MMCT transitions at cryogenic temperature confirmed that Ti is reduced to Ti(III) under visible light. Assembly of inorganic MMCT sites inside high-surface-area mesoporous silicates with each metal in a preselected oxidation state opens up activation of catalytically important metal centers under visible light.     

Photocatalytic reduction of CO2 over Cu-TiO2 /molecular sieve 5A composite

TiO(2) and different Cu wt% loaded TiO(2) (TC(0.5-5.0)), 10 wt% TC(2.0) supported on molecular sieve 5A (10 wt% TC(2.0)/MS) were prepared by impregnation and solid-state dispersion methods. The photocatalysts prepared were characterized using XRD, SEM, and UV-Vis DRS, TEM, XPS spectroscopy techniques. Photocatalytic reduction of CO(2) in water and alkaline solution are investigated in a batch reactor. The yield of oxalic acid increased notably when TC was supported on molecular sieve. The Cu-TiO(2) supported on molecular sieve catalyst promotes the charge separation that leads to an increase in the selective formation of oxalic acid in addition to methanol, acetic acid and traces of methane. The product formation is due to the high adsorption of CO(2), water and product shape selectivity of the composite photocatalyst. The maximum yield of oxalic acid was found to be 65.6 μg h(-1) g(-1) per cat using 0.2 N NaOH containing solution over 10 wt% TC(2.0)/MS photocatalyst. The difference in the photocatalytic activity is related to its physicochemical properties.     

Structure of the first silicate molecular sieve with 18-ring pore openings, ECR-34

The three-dimensional microporosity of zeolite frameworks have allowed their widespread use in industry as heterogeneous catalysts, absorbents, and ion-exchangers. While the phosphate analogues of zeolites having up to 24 tetrahedral atoms in the pore openings are known, silicate-based zeolites have, until now, been limited to 14-membered ring pore openings. We now disclose the structure and characterization of the synthetic zeolite ECR-34, which can be prepared from a mixed alkali metal reaction gel containing tetraethylammonium (TEA) cations. Its structure has been determined from powder diffraction data and shows ECR-34 to be hexagonal with the dimensions a, b = 21.030(1) A, c = 8.530(1) A, containing one-dimensional, 18-ring pores with 10 A diameter free openings. ECR-34 is stable to 800 degrees C and is able to absorb and ion-exchange large organic molecules. The existence of ECR-34 suggests the potential of preparing other thermally stable silicate molecular sieves with extra-large pores.     

Ba2Ti2Si2O9F2, a new titanium silicate

Dibarium dititanium difluoride dioxide heptaoxidodisilicate, Ba₂Ti₂Si₂O₉F₂, is a new edge‐sharing titanate with a unique titanium silicate framework. All atoms in the structure are in general positions. Titanium oxyfluoride octahedra combine with silicon tetrahedra to form a double stacked chain, which is the base unit of the layered framework. The Ba atoms lie in channels that extend along the a axis.     

Photo-oxidation of phenol over titania pillared zirconium phosphate and titanium phosphate

The photodegradation of phenol was studied in the aqueous solutions over titania pillared zirconium phosphate and titanium phosphate under solar radiation and compared with that of the UV-radiation (6 W low pressure Hg vapor lamp). This reaction was studied by varying different parameters such as catalyst dose, initial phenol concentration, pH of solution and irradiation time. The degradation rate of phenol was favourable under neutral pH condition. The degradation process approximately obeyed first-order kinetics with apparent rate of degradation constant increasing with decreasing the initial phenol concentration.     

介孔分子筛P-SBA-1催化合成柠檬酸三丁酯

采用后合成法制备了介孔分子筛催化剂P-SBA-1,并用XRD和SEM对催化剂进行分析,表征结果表明催化剂P-SBA-1具有立方结构(空间点群Pm3n)。选用液体酸H2SO4和微孔分子筛HY、ZSM-5与SBA-1进行对比,结果表明催化剂的活性高低顺序为:H2SO4SBA-1HYZSM-5。将改性后的介孔分子筛P-SBA-1作为固体酸催化剂合成柠檬酸三丁酯。重点考察了催化剂用量、酸醇摩尔比、反应温度、反应时间等因素以及催化剂的重复使用性能。结果表明P-SBA-1催化合成柠檬酸三丁酯的最佳条件为:反应温度140℃,酸醇摩尔比1∶6,催化剂用量为反应物总质量的1.5%,反应时间5h。催化剂P-SBA-1重复使用性能良好。     

Effect of structure of the redox molecular sieve TS-1 on the oxidation of phenol, crotyl alcohol and norbornylene

A range of crystalline TS-1 samples with different morphologies as well as the corresponding TS-1 precursor structures have been synthesised using hydrothermal crystallisation. The materials have been characterised using powder X-ray diffraction, IR and Raman spectroscopy and electron microscopy. The materials were used as catalysts for the oxidation of crotyl alcohol, phenol and norbornylene and, in particular, the reactivity of the precursor structures was contrasted with crystalline TS-1. The oxidation of crotyl alcohol, selected as a relatively non-reactive substituted alkene, did not require the TS-1 structure for reactivity and TS-1 precursor structures are active, although crystalline TS-1 was found to be more reactive than the precursor structures. In contrast, phenol hydroxylation is only catalysed by crystalline TS-1. The reaction of phenol is observed to occur only on the exterior surface of large TS-1 crystallites. With smaller crystallites of TS-1, i.e. the size range of interest for catalysis, the rapid subsequent reaction of hydroquinone makes it difficult to determine whether reaction occurs solely on the exterior of the crystallites or at sites within the porous structure. Hence it is suggested that this reaction has limited scope as a probe reaction for the reactivity of sites within the crystallites. It is, however, feasible that phenol hydroxylation is a viable probe reaction for TS-1 type structural units. Norbornylene was studied as an example of a reactant too large to enter the internal pore structure of TS-1 and hence only reaction at pore mouths and external surface sites was possible. Larger TS-1 crystallites were more active for this substrate than suggested by surface area considerations. The results are discussed in terms of the selection of model reactions for the study of TS-1 catalysts.     

The transition state shape-selective aromatic alkylation over MnAPO-11 molecular sieve catalysts

MnAPO-11 molecular sieves with medium size elliptical pore are synthesized and characterized. Transition state shape-selective catalysis of these molecular sieves are studied. Methylation of alkylaromatic compounds were efficiently catalyzed by these molecular sieves while aromatic ethylation was almost negligible. The size of the alkylating agents was the key factor for the transition state dimension in the aromatic alkylation, not the size of aromatic compounds. The mole fraction of o-isomer for methylation of alkylaromatic compounds was dependent on the size of the alkyl groups.     

Time-dependent CO2 sorption hysteresis in a one-dimensional microporous octahedral molecular sieve

The development of sorbents for next-generation CO(2) mitigation technologies will require better understanding of CO(2)/sorbent interactions. Among the sorbents under consideration are shape-selective microporous molecular sieves with hierarchical pore morphologies of reduced dimensionality. We have characterized the non-equilibrium CO(2) sorption of OMS-2, a well-known one-dimensional microporous octahedral molecular sieve with manganese oxide framework. Remarkably, we find that the degree of CO(2) sorption hysteresis increases when the gas/sorbent system is allowed to equilibrate for longer times at each pressure step. Density functional theory calculations indicate a "gate-keeping" role of the cation in the tunnel, only allowing CO(2) molecules to enter fully into the tunnel via a highly unstable transient state when CO(2) loadings exceed 0.75 mmol/g. The energy barrier associated with the gate-keeping effect suggests an adsorption mechanism in which kinetic trapping of CO(2) is responsible for the observed hysteretic behavior.     

Iron(III) chloride supported on MCM-41 molecular sieve as a catalyst for the liquid-phase oxidation of phenol

FeCl₃ was supported on MCM-41 mesoporous molecular sieve via adsorption or coordination bonding and by embedding as an anionic constituent of covalently immobilized imidazolium ionic liquid (IL). The synthesized materials were characterized by N₂-BET, SEM, TEM, FT-IR, ¹H, ¹³C, and ²⁹Si NMR, and DSC-TG. All of the catalysts were shown to be active for the liquid-phase oxidation of phenol by hydrogen peroxide. Supported FeCl₃ species present as tetrachloroferrate counterions of immobilized IL are the most resistant to iron leaching.     

Protein adsorption on the mesoporous molecular sieve silicate SBA-15: effects of pH and pore size

A mesoporous molecular sieve silicate, SBA-15, with three pore sizes (38.1 A, 77.3 A, and 240 A) has been synthesized using a non-ionic, tri-block copolymer as a template in a sol-gel method. The effects of synthesis conditions on the pore size and pore-size distribution of this adsorbent have been described. The adsorption of proteins on these crystalline, ordered, materials has been studied. The kinetics of adsorption and equilibrium capacity have been probed with three proteins of different dimensions. The effects of electrostatic interactions and protein size are illustrated. It has been shown that SBA-15 materials can be tailored to show size selectivity for proteins, and very high capacities (450 mg/g) can be obtained. Furthermore, the rates of adsorption are shown to be dependent on the pore size, protein structure and solution pH.     

Effects of water vapor on the radiolysis of methane over molecular sieve 5A

Effects of the addition of H₂O on the radiation-induced chemical reaction of methane over molecular sieve 5A at 460°C have been studied by product analysis. Hydrogen, carbon monoxide, carbon dioxide and hydrocarbons consisting mainly of C₂ and C₃ alkanes and alkenes were produced from CH₄ + H₂O mixtures at high conversion levels. The yields of hydrocarbons from 3:1 and 3:2 CH₄ + H₂O mixtures decreased slightly with time but those from 3:4 mixture showed no decrease with time. When the molecular sieve 5A that had been irradiated in flowing methane was reirradiated in the presence of H₂O, carbonaceous solid produced from methane on molecular sieve 5A was readily decomposed to carbon dioxide, carbon monoxide, hydrogen and hydrocarbons, mainly alkanes. Therefore, it is concluded that the suppression of decrease of product yields with time by the addition of H₂O is mainly ascribed to decomposition of the carbonaceous solid by H₂O under electron beam irradiation. The role of added H₂O is also discussed in connection with the conventional methane-steam reforming reaction.     

Characterization of a molecular sieve coating using ellipsometric porosimetry

Ellipsometric porosimetry was used to determine the adsorption isotherms of toluene, methanol, and water on b-oriented Silicalite-1 coatings with a thickness of less than ca. 250 nm and to obtain adsorption kinetics. The adsorption isotherms are of sufficient quality to reveal several aspects of the pore structure such as the adsorbate capacity and the adsorbate/framework affinity. The use of a combination of different molecular probes in ellipsometric porosimetry to elucidate the molecular accessibility of Silicalite-1 pores is demonstrated. It is shown that ellipsometric porosimetry is an appropriate technique for probing the influence of aging of the Silicalite-1 coating and of planarization polishing on the porosity, pore accessibility, and adsorbate/framework affinity.     

铁改性的HMS分子筛催化苯酚羟基化反应合成二酚

邻苯二酚和对苯二酚是重要的精细化工中间体,在各个行业中具有广泛的应用。苯酚与过氧化氢反应合成苯二酚是一条反应条件温和、环境友好的合成路线,该合成路线的关键是催化剂的选择和反应条件的优化。本文以铁改性的HMS分子筛为催化剂,研究了金属负载量、催化剂使用量、反应温度、反应时间等因素对催化性能的影响,优化了反应条件。以水为溶剂,n(Fe)∶n(Si)=0.04,n(苯酚)∶n(H2O2)=2∶1,反应温度50℃,催化剂用量0.1g,反应4h,苯酚的转化率达45.5%,苯二酚选择性为94.9%。N2吸附-脱附结果表明,Fe/HMS具有良好的介孔结构,铁进入HMS材料的骨架中,并且催化剂具有良好的稳定性,循环使用后骨架保持完整。     

Synthesis, characterization and catalytic properties of a nanocrystalline Ti-containing mesoporous molecular sieve

Two templates namely an inorganic template, CaCO₃ and an organic template cetyltrimethylammonium bromide were used to synthesize a nanocrystalline Ti-containing mesoporous molecular sieve. The results show that the material is mesoporous and titanium is present in tetrahedral and octahedral environment. Compared to Ti-MCM-41, this catalyst shows higher conversion and selectivity.     

SAPO-34分子筛中多甲基苯分子与卤代甲烷偕甲基化反应的密度泛函理论研究

利用周期性密度泛函理论研究了SAPO-34分子筛催化转化卤代甲烷制取低碳烯烃反应的碳池主要成分多甲基苯分子的偕甲基化反应。氯甲烷和溴甲烷分子在SAPO-34分子筛内的吸附能分别是–18和–22 kJ/mol,由于氯和溴原子相似的电负性,氯甲烷和溴甲烷分子的吸附能并未被精确区分。以氯甲烷和溴甲烷为甲基化试剂,得到了几种多甲基苯分子的偕甲基化反应能及能垒,结果表明,六甲基苯分子(HMB)的偕甲基化反应为放热反应,而其余甲基苯分子的偕甲基化反应为吸热反应。对于上述两种甲基化试剂,体积最大的HMB均表现出最低的偕甲基化反应能垒,这可能是由于分子筛骨架与多甲基苯分子之间的静电相互作用增强了HMB的反应活性所致。     

MSU-x介孔分子筛的改性研究

以脂肪醇聚氧乙烯醚为模板剂,正硅酸乙酯为Si源,分别以偏钨酸铵,硫酸铝作为W源和Al源进行改性,合成出W-MSU-x以及Al-MSU-x介孔分子筛.并且通过X射线扫描、N_2吸附-脱附、原位红外表征考察W和Al的加入对介孔分子筛的影响.结果得到,W的加入提高了分子筛的有序度,Al的加入使介孔分子筛的孔径减小,比表面积增大.     

Experimental and theoretical study of D2/H2 quantum sieving in a carbon molecular sieve

The present work aims at providing additional insight into the crucial effect of pore size and pressure on the adsorption of H₂ and D₂ in porous carbons by means of Grand Canonical Monte Carlo simulations in model slit micropores at 77 K. In order to address the quantum behavior of the molecules the Feynman–Hibbs corrected LJ interaction potential is used for fluid–solid and fluid–fluid interactions. Based on the GCMC isotherms for the two isotopes, D₂ selectivity over H₂ is deduced for pores with different sizes as a function of pressure. Furthermore, GCMC results are coupled with experimental high pressure H₂ and D₂ adsorption data at 77 K for a commercial carbon molecular sieve (Takeda 3A).