Catalytic performance of zinc containing ionic liquids immobilized on silica for the synthesis of cyclic carbonates

Cycloaddition of carbon dioxide and epoxides was investigated using zinc halide based Lewis acidic ionic liquids (ILs) as catalysts. ILs such as 1-butyl-3-methylimidazolium bromide (BMImBr), 1-butylpyridinium bromide (BPyBr), tetra-n-butylammonium bromide (TBABr) were mixed with zinc halide and supported on silica gel to produce heterogeneous catalysts. Catalytic reaction tests demonstrated that the incorporation of zinc ions can significantly enhance the catalytic activity of the silica-supported ILs for the cycloaddition of CO₂ to epoxides in solvent-free conditions. BPyBr-ZnCl₂/SiO₂ showed the highest propylene carbonate yield of 98% when the reaction was carried out with 0.5 g of catalyst at 120 °C at 1.89 MPa of CO₂ pressure for 4 h. The immobilized zinc containing IL catalyst could be reused for at least four cycles without any considerable loss of its activity.     

Epitaxial nucleation model for chiral-selective growth of single-walled carbon nanotubes on bimetallic catalyst surfaces

An epitaxial nucleation model for single-walled carbon nanotube (SWCNT) growth on bimetallic catalysts surfaces is reported in support of experimental observations of chiral enrichment. We model the bimetallic catalyst surfaces as a 2D (1 1 1) surface consisting of Ni or a combination of Ni and Fe atoms, with varying average bond length between nearest neighbor atoms which corresponds to the crystal structure of the alloys. The energies associated with nanotube cap formation on these various surfaces are calculated using density functional theory (DFT). We find that certain cap chiralities, such as (8, 4), are more stably bound to a surface that resembles a Ni_0.27Fe_0.73 bimetallic catalyst, whereas other chiralities, such as (9, 4), are more stable on a pure Ni surface. These results help explain the predominance of certain chiralities on specific bimetallic catalysts and provide a potential route to controlling the chirality of as-grown SWCNTs.     

Unique vapor phase synthesis of 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine selectively over Co–Al-MCM-41

Cyclization of cyclopentanone, formaldehyde and ammonia in vapor phase gives 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine (HHDCP) and spiro[cyclopentane-1,8′-(1′,2′,3′,5′,6′,7′,8′,8′a) octahydrodicyclopenta[b,e]]pyridine (SCOHDCP) over zeolites HY, HZSM-5, Hβ and mesoporous Al-MCM-41 molecular sieves. The preliminary screening of catalysts clearly shows that Al-MCM-41 is more suitable for the vapor phase synthesis of HHDCP. As the NH₃-TPD profiles of Al-MCM-41 show wide range distribution of acid sites in the temperature range of 200–600 °C (weak–medium–strong), Al-MCM-41 is further modified with transition metal ions like V(V), Mn(II), Fe(III), Co(III), Cu(II), La(III) and Ce(III) to fine tune the acid sites. Correlation of activity and selectivity of transition metal modified Al-MCM-41 with the NH₃-TPD profiles show that though the conversions are high, selectivity of either HHDCP or SCOHDCP is a preference of acid site strength formed on metal ion modification. Interestingly Co²⁺ ion modification of Al-MCM-41 resulted distinctly into two sets of acid sites with T_max around 218 °C (weak–medium) and 673 °C (strong). The reaction is studied on Co–Al-MCM-41 by adsorbing pyridine at 300 °C. The typical acidity available on pyridine adsorbed Co–Al-MCM-41 around 300 °C is showing cyclization activity forming only HHDCP indicating that weak–medium acid sites are responsible for the formation of HHDCP. Based on the product distribution plausible reaction mechanism is proposed.     

Solvent free synthesis of chalcone and flavanone over zinc oxide supported metal oxide catalysts

Liquid phase Claisen–Schmidt condensation between 2′-hydroxyacetophenone and benzaldehyde to form 2′-hydroxychalcone, followed by intramolecular cyclisation to form flavanone was carried out over zinc oxide supported metal oxide catalysts under solvent free condition. The reaction was carried out over ZnO supported MgO, BaO, K₂O and Na₂O catalysts with 0.2 g of each catalyst at 140 °C for 3 h. Magnesium oxide impregnated zinc oxide was observed to offer higher conversion of 2′-hydroxyacetophenone than other catalysts. Further MgO impregnated with various other supports such as HZSM-5, Al₂O₃ and SiO₂ were also used for the reaction to assess the suitability of the support. The order of activity of the support is ZnO > SiO₂ > Al₂O₃ > HZSM-5. Various weight percentage of MgO was loaded on ZnO to optimize maximum efficiency of the catalyst system. The impregnation of MgO (wt%) in ZnO was optimized for better conversion of 2′-hydroxyacetophenone. The effect of temperature and catalyst loading was studied for the reaction.     

Synthesis,structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands

The chiral biaryl-based N₄-ligands, (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(pyrrol-2-ylmethyleneamino)-1,1′-binaphthyl (1H₂) and (S)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), can effectively stabilize the chiral rare earth metal chloride complexes such as 1-YCl(dme) (3) and 2-YCl(dme) (4), which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, treatment of 3 with half equiv of 1Na₂ in THF gives the binuclear complex 1-Y(thf)-1-Y(thf)-1 (5) in 70% yield. These complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides.     

Epoxidation of olefins catalyzed by molybdenum–siloxane compounds

The triphenylsiloxy complex MoO₂(OSiPh₃)₂ and a related polyhedral metallasiloxane formulated as [MoO₂(O₂SiPh₂)]_n have been tested as catalysts for the liquid phase epoxidation of cyclic olefins by tert-butylhydroperoxide at 55 °C. The initial activities increased in the order 1-octene < trans-2-octene < cyclododecene < cyclooctene and the corresponding epoxides were the only observed products. The best results were obtained without the addition of any co-solvents (other than decane), forming solid–liquid systems. Cyclooctene oxide was obtained in quantitative yield within 7.5 h of reaction, and the solid catalysts could be recycled without measurable loss of activity.     

New phenomenon in competitive hydrogenation of binary mixtures of activated ketones over unmodified and cinchonidine-modified Pt/alumina catalyst

Competitive hydrogenations of eight binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL), pyruvic aldehyde dimethyl acetal (PA) and trifluoroacetophenone (TFAP) on platinum/alumina catalysts unmodified (racemic hydrogenation) and modified by cinchonidine (chiral hydrogenation) were studied under the experimental conditions of the Orito reaction. Reaction rates of chiral and racemic hydrogenations were determined and relative adsorption coefficients were calculated. In the competitive chiral hydrogenation of EP + MBF, EP + TFAP and KPL + MBF binary mixtures a new phenomenon was observed: namely the EP and KPL are hydrogenated faster than MBF and TFAP, whereas in racemic one the MBF and TFAP are hydrogenated faster than EP or KPL. Effects of the activated ketones structure on their reactivity and the stability of the surface complexes are discussed. It was found that differences in rate enhancement are caused by the differences both in the adsorptivity and in the reactivity of adsorbed substrates and adsorbed intermediate complexes.     

Two new isomeric complexes containing a well-resolved 1D water morph and (6, 3)-connected framework through hydrogen bonding interactions

Two new isomeric complexes, namely {[Cu(fum)(tpy)] · 5H₂O}_n (1) and [Cu₂(fum)₂(tpy)₂] · 4H₂O (2), have been synthesized simultaneously from the reaction of Cu(fum) with tpy (where fum = fumarate, tpy = 2,2′:6′,2″-terpyridine) under mild condition. The crystal structures of complexes were determined by X-ray single-crystal diffraction. Complex 1 stabilizes in an unusual 1D water tape notated T4(2)10(2), which is directed by two chiral helical water chains; binuclear complex 2 represents a complicated (6, 3)-connected framework via supramolecular interactions. Additionally, complex 1 exhibits weak ferromagnetic behavior.     

A new lamellar solid trapping water clusters and intercalated organosulfonate guests

The synthesis and X-ray crystal structure of a lamellar framework with water clusters and organosulfonate guests trapped in the interlamellar region, [Co(H₂O)₂(4,4′-bpy)₂] · (ps)₂ · 10H₂O 1 (4,4′-bpy = 4,4′-bipyridine; Hps = pyridine-4-sulfonic acid), are presented. The structure is made up of cationic square-grid cobalt-4,4′-bipyridine layers with lamellar separation of ca. 8 Å, which is comparable to the hydrotalcite-like solids. The structure also contains intercalated charge-compensating ps⁻ anions and water molecules defining it a hydrotalcite analog.     

A chiral 3D polymer with right- and left-helices based on 2,2′-biimidazole: Synthesis,crystal structure and fluorescent property

A novel three-dimensional (3D) polymer [Cd₂(Hbiim)₄]_n (H₂biim = 2,2′-biimidazole) 1 was obtained through hydrothermal reaction and characterized by single crystal X-ray diffraction, and the fluorescent property was also determined. Compound 1 crystallizes in a monoclinic chiral space group P2₁ and contains two types of helical chains. Hbiim⁻ partially deprotonated of H₂biim exhibits two different coordination modes, which contributes greatly to the formation of the 3D chiral framework. Compound 1 exhibits blue fluorescence at 488 nm in the solid-state upon excitation at 430 nm.     

Three-dimensional fivefold interpenetrating microporous metal–organic framework based on mixed flexible ligands

The chiral diamondoidlike Cd(II) containing coordination polymer {[Cd(oba)(bib)]·2H₂O}_n (1) (oba = 4,4′-oxybis(benzoate), bib = 1,4-bis(2-methyl-imidazol-1-yl)butane) is reported; the 3D networks interpenetrate fivefold, nevertheless leave cavities capable of including sizable guest molecules. This compound also exhibits high thermal stability and blue-shift emission, and can be explored for potential blue luminescent materials.     

Thermogravimetric study on pyrolysis of biomass with Cu/Al2O3 catalysts

The Cu/Al₂O₃ catalysts of three different compositions (10, 20 and 30 wt.% Cu loading), have been investigated with regard to their catalytic effects on pyrolysis of paper biomass species (up to 800 °C) by thermogravimetric analysis (TGA) experiments. The results show that catalysts made devolatilization at lower (below 200 °C) and middle temperature (200–400 °C) regions in the pyrolysis of the biomass species, and the temperature reduction effects follow the order: 30 > 20 > 10 wt.% copper loading. Although the catalysts with 10 and 20 wt.% copper have shown almost similar activity, whereas dehydration reaction was enhanced almost 40% in the presence of 30 wt.% copper-loaded catalyst. At the same time, the amount of residue at the end of the reaction also decreased with increase in the copper loading from 10 to 30 wt.%. At higher temperatures (above 400 °C), the catalyst with greater copper loaded worked more nicely possibly due to the enhancement of the depolymerization reaction over dehydration of cellulose in presence of more basic catalysts. The catalysts were characterized by using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis and scanning electron microscopy (SEM). XRD results show the formation of CuAl₂O₄ spinel and Cu₂O phase in the catalysts.     

Chirality delivery through multiple and helical H-bonding from chiral coordination complex to its supramolecular architecture

The path of the chirality delivery in the crystalline and chiral nucleotide–Co(II) complex, [Co(GMP)(H₂O)₅]·3H₂O (GMP = guanosine-5′-monophosphate), has been studied based on X-ray single crystal diffraction analysis, liquid- and solid-state circular dichroism (CD) spectroscopy. The multiple and helical H-bonding is a distinctive way of chirality delivery from the discrete molecules to three-dimensional supramolecular architecture.     

Supported imidazole as heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO2

Imidazole anchored onto a silica matrix, by means of a propyl linkage, is found to be an effective heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO₂ in near quantitative yield. The versatility of this catalyst is demonstrated by using different substrates (epichlorohydrin, propylene oxide, butylene oxide and styrene oxide) for this cycloaddition reaction. These CO₂ insertion reactions were typically carried out in the temperature range of 343 to 403 K at 0.6 MPa CO₂ pressure under solvent-free conditions. Several spectroscopic methods were used to characterize the catalyst and study the integrity of the fresh and spent catalysts.     

Impact of nitrogen doping of carbon nanospheres on the nickel-catalyzed hydrogenation of butyronitrile

Three nickel catalysts supported on carbon and nitrogen-doped carbon nanospheres have been prepared by deposition-precipitation (DP) with urea (ca. 2% w/w). The nanospheres were prepared by thermal pyrolysis of benzene (CNS_B), aniline (CNS_A) and nitrobenzene (CNS_N) and characterized by transmission electron microscopy (TEM), N₂ adsorption–desorption, temperature-programmed oxidation (TPO), X-ray diffraction (XRD), elemental (CHN) analysis, X-ray photoelectron spectroscopy (XPS), temperature-programmed decomposition (TPD) and acid/base titrations, revealing different graphitic characteristics and different distribution of nitrogen (when present) functionalities. Upon Ni introduction, the catalysts were characterized by temperature-programmed reduction (TPR), XRD and TEM. Surface area weighted mean Ni particle diameters (post activation at 603 K) were in the range 10.5–18.2 nm. Ni particle size exhibited a big dependence on CNS nitrogen doping, where nitrogen introduction, essentially in the quaternary form, enhanced metal sintering by enriching the surface electron density of the support. The catalysts were tested in the gas phase hydrogenation of butyronitrile (T = 493 K). Extracted specific reaction rates in the steady state followed the sequence: Ni/CNS_B < Ni/CNS_A < Ni/CNS_N. When the active metal was physically mixed with the support, the following sequence was obtained: Ni + CNS_B < Ni + CNS_A < Ni + CNS_N. Our results demonstrate that doping carbon nanospheres with nitrogen strongly impacts on reactant adsorption and metal sintering, both critical aspects in the hydrogenation of nitriles. Selectivity was not sensitive to the support (or the physical mixture) employed and was in all cases close to 100% to the primary amine.     

Self-organization of nitrogen-doped carbon nanotubes into double-helix structures

Self-organization of nitrogen-doped carbon nanotube (N-CNT) double helices was achieved by chemical vapor deposition (CVD) with Fe–Mg–Al layered double hydroxides (LDHs) as the catalyst precursor. The as-obtained N-CNT double helix exhibited a closely packed nanostructure with a catalyst flake on the tip, which connected the two CNT strands on both sides of the flake. A mechanism for the self-organization of N-CNTs into double-helix structures with a moving catalyst head is proposed. Effective carbon/nitrogen sources, high-density active catalyst nanoparticles, space confinement, and the precise chiral match between the two CNT strands are found to be crucial for the N-CNT double helix formation. The morphologies of N-CNTs can be well tuned between bamboo-like and cup-stacked structures, and a CNT/N-CNT heterojunction can be constructed by changing the carbon feedstock from C₂H₄ to CH₃CN during CVD growth. N-CNT double helices with a length of 10–36 μm, a screw pitch of 1–2 μm, a CNT diameter of 6–10 nm, and a N-content of 2.59 at.% can be synthesized on the LDH catalysts by the efficient CVD growth.     

Two d10 coordination polymers based on 4,4′-(hexafluoroisopropylidene)diphthalic acid: Syntheses,structures and physical properties

Two novel coordination polymers, [Zn₂(FA)(4,4′-bipy)₂]·2H₂O (1) and Cd₂(FA)(2,2′-bipy) (2), (H₄FA = 4,4′-(hexafluoroisopropylidene)diphthalic acid, 4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine), have been synthesized under hydrothermal conditions, and their structures were determined by single-crystal X-ray diffraction. Polymer 1 features an unusual three-dimensional (3D) network with (4 · 6² · 8³)(4² · 6² · 8²) topology. Polymer 2 has a complicated 3D framework and crystallizes in non-centrosymmetric space group (Fdd2) belonging to polar point group (C_2v), which displays a strong SHG response and ferroelectric properties. Moreover, the luminescent properties of 1 and 2 have also been investigated.     

Template-assisted assembly of porous lanthanide coordination polymers with 2-aminoterephthalic acid

Porous lanthanide coordination polymers, {[Ln₂(atpt)₃(H₂O)₂] · 0.5(4,4′-bpy)(H₂O)}_n [Ln = Eu(1), Gd(2), Yb(3), H₂atpt = 2-aminoterephthalic acid, 4,4′-bpy = 4,4′-bipyridine] were obtained by hydro-solvothermal reaction, in which 4,4′-bpy acts as template. For the first time the nitrogen atom of an atpt ligand coordinates to metal ions in 1–3. The photophysical properties and thermal stability of 1 were investigated.     

Alkylimidazolium/alkylpyridinium octamolybdates catalyzed oxidation of sulfides to sulfoxides/sulfones with hydrogen peroxide

β-Mo₈O₂₆ based alkyl imidazolium and pyridinium salts of general formula [Bmim]₄Mo₈O₂₆ (Bmim = 1-butyl-3-methylimidazolium), [Hmim]₄Mo₈O₂₆ (Hmim = 1-hexyl-3-methylimidazolium), [Dhmim]₄Mo₈O₂₆ (Dhmim = 1.2-dimethyl-3-hexylimidazolium) and [Hpy]₄Mo₈O₂₆ (Hpy = 1-hexylpyridinium) have been used as catalysts for the oxidation of sulfides using 30% hydrogen peroxide as oxidant. The examined β-Mo₈O₂₆ salts prove to be highly active and are self-separating. A high selectivity towards either sulfoxides or sulfones can be nicely controlled by variation of the reaction conditions. In both cases, the catalysts can be recycled and reused for several times without significant loss of activity, representing a good stability of the catalysts.     

Hydrogen production via methanol steam reforming over Au/CuO,Au/CeO2, and Au/CuO–CeO2 catalysts prepared by deposition–precipitation

The production of hydrogen (H₂) with a low concentration of carbon monoxide (CO) via steam reforming of methanol (SRM) over Au/CuO, Au/CeO₂, (50:50)CuO–CeO₂, Au/(50:50)CuO–CeO₂, and commercial MegaMax 700 catalysts were investigated over reaction temperatures between 200 °C and 300 °C at atmospheric pressure. Au loading in the catalysts was maintained at 5 wt%. Supports were prepared by co-precipitation (CP) whilst all prepared catalysts were synthesized by deposition–precipitation (DP). The catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy (SEM). Au/(50:50)CuO–CeO₂ catalysts expressed a higher methanol conversion with negligible amount of CO than the others due to the integration of CuO particles into the CeO₂ lattice, as evidenced by XRD, and a interaction of Au and CuO species, as evidenced by TPR. A 50:50 Cu:Ce atomic ratio was optimal for Au supported on CuO–CeO₂ catalysts which can then promote SRM. Increasing the reaction time, by reducing the liquid feed rate from 3 to 1.5 cm³ h^?1, resulted in a catalytic activity with complete (100%) methanol conversion, and a H₂ and CO selectivity of ～82% and ～1.3%, respectively. From stability testing, Au/(50:50)CuO–CeO₂ catalysts were still active for 540 min use even though the CuO was reduced to metallic Cu, as evidenced by XRD. Therefore, it can be concluded that metallic Cu is one of active components of the catalysts for SRM.