Enantioselective Hydrolytic Kinetic Resolution of Epoxides Catalyzed by Chiral Co(III) Salen Complexes Immobilized in the Membrane Reactor

The supported ZSM-5 film was synthesized hydrothermally on the porous supports such as Anodisc and alumina tube. The enantioselective hydrolytic resolution of racemic epoxides was performed in the ZSM-5/Anodisc membrane reactor containing chiral salen complexes. The chiral (Co-salen)⁺PF₆ ^- and (Co-salen)⁺BF₄ ^- complexes immobilized on the membrane showed a very high enantioselectivity and recyclability in the hydrolysis of epichlorohydrine, 1,2-epoxybutane, 1,2-epoxyhexane and styrene oxide. It was easy to separate the products, and the catalysts could be recycled without observable loss in activity and enantioselectivity using the batch-type and continuous-type membrane reactor. The obtained epoxide product remained in the organic phase and the hydrophilic water-soluble diols diffused into the aqueous phase through the ZSM-5 film layer.     

Chiral (Salen) Cobalt Complexes Encapsulated in Mesoporous MFI as an Enantioselective Catalyst for Asymmetric Ring Opening of Terminal Epoxides

MFI structural zeolite (ZSM-5 and Sililcalite) was treated with hot NaOH solution to make mesoporous channels in the microporous crystals. Inner mesopore size could be controlled by changing the concentration of NaOH solution. The pore structure of alkaline-treated MFI zeolite was studied by instrumental analysis. To obtain the cage type mesopores, Ti-coating on the outside MFI crystals before alkaline treatment was investigated to be the most effective. Co(III) salen complexes monomers were successfully encapsulated in mesoporous MFI-type zeolite by “ship-in-a-bottle” method. The heterogeneous catalyst could be applied in asymmetric ring opening of terminal epoxides by phenol derivatives. It showed very high enantioselectivity with yield in the catalysis.     

Silica Gel Anchored Chiral Mn(III)Salen Complexes for Enantioselective Epoxidation of Unfunctionalised Olefins

Heterogeneous Mn(III) chiral salen complexes are prepared through covalent attachment of salen ligand on silica gel via chloropropyl spacer and subsequent complexation with manganese. The complexes are well characterized by IR, UV/VIS, TGA and elemental analysis. Epoxidation of unfunctionalised prochiral olefins by Mn(III) chiral salen complexes using iodosobenzene and m-CPBA as the terminal oxidants and NMO as a co-oxidant was achieved with good yields albeit low enantiomeric excess.     

Synthesis of multiwalled carbon nanotubes on Al2O3 supported Ni catalysts in a fluidized‐bed

Multiwalled carbon nanotubes (MWNTs) were synthesized on Al₂O₃ supported Ni catalysts from C₂H₂ and C₂H₄ feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/U_mf), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized‐bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by‐product. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Fe-Mo/MgO催化剂CVD法制备碳纳米管

研究了Fe-Mo／MgO催化剂裂解乙炔制备碳纳米管的反应条件。结果表明,反应气氛对碳纳米管的生长具有明显的影响,在Hz或Ar气氛下,所得碳纳米管的质量较差,而在N2-H2(1：1体积比)和Ar-H2(5．5：1体积比)气氛下乙炔裂解可制得纯度好、收率较高的碳纳米管。电镜观察发现在Ar-H2气氛下所制备碳纳米管的直径(平均直径为18nm)明显小于在N2-H2气氛下所制备碳纳米管(平均直径为30nm),这便于通过反应气氛的调节来控制碳纳米管的直径。用Fe-Mo／MgO做催化剂、乙炔为碳源,Ar-H2反应气氛下．850℃左右、反应30min所得碳纳米管的质量、产率最佳。     

A Temperature Window for the Synthesis of Single-Walled Carbon Nanotubes by Catalytic Chemical Vapor Deposition of CH4 over Mo2-Fe10/MgO Catalyst

A temperature window for the synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of CH₄ over Mo₂-Fe₁₀/MgO catalyst has been studied by Raman spectroscopy. The results showed that when the temperature is lower than 750 °C, there were few SWCNTs formed, and when the temperature is higher than 950 °C, mass amorphous carbons were formed in the SWCNTs bundles due to the self-decomposition of CH₄. The temperature window of SWCNTs efficient growth is between 800 and 950 °C, and the optimum growth temperature is about 900 °C. These results were supported by transmission electron microscope images of samples formed under different temperatures. The temperature window is important for large-scale production of SWCNTs by catalytic chemical vapor deposition method.     

Structural study of β‐SiC(001) films on Si(001) by laser chemical vapor deposition

β‐SiC thin films have been epitaxially grown on Si(001) substrates by laser chemical vapor deposition. The epitaxial relationship was β‐SiC(001){111}//Si(001){111}, and multiple twins {111} planes were identified. The maximum deposition rate was 23.6 μm/h, which is 5‐200 times higher than that of conventional chemical vapor deposition methods. The density of twins increased with increasing β‐SiC thickness. The cross section of the films exhibited a columnar structure, containing twins at {111} planes that were tilted 15.8° to the surface of substrate. The growth mechanism of the films was discussed.     

Reusable Chiral Dicationic Chromium(III) Salen Catalysts for Aminolytic Kinetic Resolution of trans‐Epoxides

A series of new recyclable chiral dicationic chromium(III) salen complexes 1 – 10 bearing different substituents, viz., hydrogen, methyl, tert‐butyl, triphenylphosphinomethyl, triethylaminomethyl, methylimidazolium, methylpyridinium, methyl‐N,N‐dimethylpyridinium at the 3,3′‐ and 5,5′‐ positions of the salen unit with (1S,2S)‐(+)‐1,2‐diaminocyclohexane, (1S,2S)‐(−)‐1,2‐diphenyl‐1,2‐diaminoethane, and (S)‐(−)‐1,1′‐binaphthyl‐2,2′‐diamine collars have been synthesized and characterized by various physico‐chemical methods. These complexes were used as catalysts for the highly enantioselective aminolytic kinetic resolution of racemic trans‐epoxides with different anilines as nucleophiles at room temperature. With the use of catalyst 3 , anti‐β‐amino alcohols were obtained in excellent yields (>99% with respect to the nucleophile) and enantioselectivities (ee>99%) with the concomitant recovery of corresponding epoxides in high optical purity (ee up to >99%) and quantitative yields in 12 h. The catalyst 3 is recyclable in the aminolytic kinetic resolution process and worked well up to six cycles with retention of enantioselectivity.     

Degradability Enhancement of Poly(Lactic Acid) by Stearate-Zn(3)Al LDH Nanolayers

Recent environmental problems and societal concerns associated with the disposal of petroleum based plastics throughout the world have triggered renewed efforts to develop new biodegradable products compatible with our environment. This article describes the preparation, characterization and biodegradation study of poly(lactic acid)/layered double hydroxide (PLA/LDH) nanocomposites from PLA and stearate-Zn₃Al LDH. A solution casting method was used to prepare PLA/stearate-Zn₃Al LDH nanocomposites. The anionic clay Zn₃Al LDH was firstly prepared by co-precipitation method from a nitrate salt solution at pH 7.0 and then modified by stearate anions through an ion exchange reaction. This modification increased the basal spacing of the synthetic clay from 8.83 Å to 40.10 Å. The morphology and properties of the prepared PLA/stearate-Zn₃Al LDH nanocomposites were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TGA), tensile tests as well as biodegradation studies. From the XRD analysis and TEM observation, the stearate-Zn₃Al LDH lost its ordered stacking-structure and was greatly exfoliated in the PLA matrix. Tensile test results of PLA/stearate-Zn₃Al LDH nanocomposites showed that the presence of around 1.0–3.0 wt % of the stearate-Zn₃Al LDH in the PLA drastically improved its elongation at break. The biodegradation studies demonstrated a significant biodegradation rate improvement of PLA in the presence of stearate-Zn₃Al LDH nanolayers. This effect can be caused by the catalytic role of the stearate groups in the biodegradation mechanism leading to much faster disintegration of nanocomposites than pure PLA.     

Improvement in growth yield of single-walled carbon nanotubes with narrow chirality distribution by pulse plasma CVD

A pulse plasma chemical vapor deposition (CVD) technique was developed for improving the growth yield of single-walled carbon nanotubes (SWNTs) with a narrow chirality distribution. The growth yield of the SWNTs could be improved by repetitive short duration pulse plasma CVD, while maintaining the initial narrow chirality distribution. Detailed growth dynamics is discussed based on a systematic investigation by changing the pulse parameters. The growth of SWNTs with a narrow chirality distribution could be controlled by the difference in the nucleation time required using catalysts comprising relatively small or large particles as the key factor. The nucleation can be controlled by adjusting the pulse on/ofF time ratio and the total processing time.     

Layered-Double-Hydroxide-Supported Pd(TPPTS)2Cl2: A New Heterogeneous Catalyst for Heck Arylation of Olefins

The Pd(TPPTS)₂Cl₂ (TPPTS: triphenylphosphine trisulfonate, sodium salt) complex is immobilized on layered double hydroxides by the ion-exchange method. This heterogeneous catalyst is successfully used in Heck arylation of olefins. The catalyst can be recycled several times with almost consistent activity.     

Fast preparation of (111)‐oriented β‐SiC films without carbon formation by laser chemical vapor deposition from hexamethyldisilane without H2

(111)‐oriented β‐SiC films were prepared by laser chemical vapor deposition using a diode laser (wavelength: 808 nm) from a single liquid precursor of hexamethyldisilane (Si(CH₃)₃–Si(CH₃)₃, HMDS) without H₂. The effects of laser power (P_L), total pressure (P_tot) and deposition temperature (T_dep) on the microstructure, carbon formation and deposition rate (R_dep) were investigated. β‐SiC films with carbon formation and graphite films were prepared at P_L ≥ 170 W and P_to ≥ 1000 Pa, respectively. Carbon formation strongly inhibited the film growth. β‐SiC films without carbon formation were obtained at P_tot = 400‐800 Pa and P_L = 130‐170 W. The maximum R_dep was about 50 μm·h^?1 at P_L = 170 W, P_tot = 600 Pa and T_dep = 1510 K. The investigation of growth mechanism shows that the photolytic of laser played an important role during the depositions.     

Characterization of Photoluminescent (Y1–xEux)2O3 Thin Films Prepared by Metallorganic Chemical Vapor Deposition

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y₂O₃ (Y_{1– x} Eu _x )₂O₃ thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y_{1– x} Eu _x )₂O₃ thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl–3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 10³ Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y₂O₃, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y_{1– x} Eu _x )₂O₃ was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect.     

动态动力学拆分法制备(S)-(+)-呋虫胺

以(±)-四氢呋喃-3-甲醇与(D)-(+)-10-樟脑磺酰氯反应生成四氢呋喃-3-甲基樟脑磺酸酯,通过动态动力学拆分法得到单一构型四氢呋喃-3-甲基樟脑磺酸酯晶体,将晶体用解离剂解离得到(S)-(+)-四氢呋喃-3-甲醇,ee值99,收率85%,进一步与1,5-二甲基-2-硝基亚胺六氢-1,3,5-三嗪反应得到(S)-(+)-呋虫胺。     

Preparation of (110)-oriented SrTiO3 film on quartz glass by laser chemical vapor deposition

SrTiO₃ (STO) film was prepared on quartz glass by laser chemical vapor deposition at a deposition temperature (T_dep) ranged from 760 to 1104 K. Effect of the T_dep on the orientation, crystallinity, texture, and microstructure of the STO film was investigated. As the T_dep was increased, the preferred orientation of the STO film tended to be (110)-orientated with corresponding texture coefficient (TC) on the (110) reflection enhanced from 2.3 to 6; meanwhile, the full width at half maximum of the ω-scan on the (110) reflection decreased from 0.85° to 0.59°. The (110)-oriented grains were in wedge shape about 60 × 150 nm in size, which tended to be flat at an elevated T_dep of 1104 K.     

Enantioselective Synthesis of Chiral β‐Aryloxy Alcohols by Ruthenium‐Catalyzed Ketone Hydrogenation via Dynamic Kinetic Resolution (DKR)

A highly efficient enantioselective synthesis of chiral β‐aryloxy alcohols by the {RuCl₂[(S)‐SDP][(R,R)‐DPEN]} [(S_a,R,R)‐ 1a ; SDP=7,7′‐bis(diarylphosphino)‐1,1′‐spirobiindane; DPEN=trans‐1,2‐diphenylethylenediamine] complex‐catalyzed asymmetric hydrogenation of racemic α‐aryloxydialkyl ketones via dynamic kinetic resolution (DKR) has been developed. Enantioselectivities of up to 99% ee with good to high cis/anti‐selectivities (up to>99:1) were achieved.     

Epitaxial growth of 3C–SiC on Si(111) and (001) by laser CVD

Epitaxial 3C–SiC films have been deposited on Si(111) and Si(001) substrates via laser CVD with deposition rate of 12.32 and 15.56 μm/h, respectively. The activation energy of 3C–SiC on Si(111) and Si(001) was 80 and 160 kJ/mol, and the root mean square (RMS) roughness (w) as a function of the film thickness (h) follows power laws of w~h^0.31 and w~h^0.06, respectively. The growth mechanisms of epitaxial 3C–SiC films on Si(111) and Si(001) was investigated based on the structural analysis and roughness evolution.     

Cooperative Activation in the Hydrolytic Kinetic Resolution of Epoxides by a Bis‐Cobalt(III)salen‐Calix[4]arene Hybrid

A chiral, bimetallic cobalt(III)salen‐calix[4]arene hybrid structure was prepared and tested in the hydrolytic kinetic resolution (HKR) of racemic epoxides. Kinetic studies have revealed that the two catalytic units on the upper rim of the calixarene scaffold are able to activate the reactants in a cooperative and primarily intramolecular mode. High enantioselective behaviour was observed and besides, a higher stability was found for the bimetallic catalyst as compared to a monometallic reference complex.     

Effects of buffer layer materials and process conditions on growth mechanisms of forming networks of SWNTs by microwave plasma chemical vapor deposition

This study investigates the growth mechanism of IC compatible processes and to the feasibility of synthesizing networks of single-walled carbon nanotubes (SWNTs) at lower temperatures (610 °C) on Si wafer using microwave plasma chemical vapor deposition (MPCVD) with CH₄ and H₂ as source gases. The effects of the buffer layer materials (ZnS–SiO₂, Al₂O₃, AlON, and AlN ) and process conditions on growth of carbon nanostructures with Co as catalyst were also examined, where the buffer layers and Co catalyst were deposited in sequence by physical vapor deposition (PVD), followed by H-plasma pretreatment before deposition of carbon nanostructures. Additionally, the morphologies and bonding structures of carbon nanostructures were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and Raman Spectroscopy. Analytical results demonstrate that networks of SWNTs are more favorable to be synthesized by selecting proper buffer layer material (e.g., AlON), and under higher temperatures, thinner catalyst thickness (e.g., 5 nm) and lower CH₄ / H₂ ratio (e.g., 5 / 100 sccm/sccm). The networks of SWNTs can be fabricated at temperatures as low as 610 °C by manipulating these parameters. In conclusion, the growth mechanism determines the conditions for the formation of nano-sized extrusions on catalyst particles surface.