Vasile I. Pârvulescu

Heterogeneous Gold Catalysts for Efficient Access to Functionalized Lactones

A novel class of heterogeneous gold catalysts supported on zeolite beta-NH4+ was prepared by the deposition-precipitation method. This new class of catalyst showed interesting catalytic activities for the intramolecular cycloisomerization of gamma-acetylenic carboxylic acids leading to functionalized gamma-alkylidene gamma-butyrolactones. Analysis of the supported gold species with in situ X-ray photoelectron spectroscopy (in situ XPS) suggests that cationic Au (possibly AuIII) can play an important role in such reactions. The high discrepancy in catalyst stability in favor of the Au supported on the zeolite system over bulk Au2O3 is explained by 1) the size of the particles and 2) the reversibility of the redox deactivating process (AuIII-->AuI) in the presence of oxygen for the supported system. The efficiency of this system allowed reaction under mild heterogeneous conditions. The potential for catalyst recycling was also highlighted.

Preparation and characterisation of mesoporous zirconium oxide

Mesoporous zirconium oxides were obtained using the polymeric sol-gel procedure. The synthesis was carried out in the presence of two series of surfactants, namely, N(C-n)(4)Br and N(CH3)(3)CnBr, with n = 8-18, and C-n, the linear alkyl chain. Hydrolysis of zirconium isopropoxide was carried out both under acid and base catalysis, and also using acetylacetone (acac) as a stabiliser. In order to obtain information on the sol-gel procedure in the above conditions, the composition parameters: Zr/H2O and Zr/surfactant ratios were modified in a rather wide interval. Mesoporous textures were obtained, with surface areas and pore size distributions depending on the synthesis conditions. The evolution of the sol-gel process and the resulting oxides were characterised with several tools: nitrogen adsorption-desorption isotherms, TG-DTA, XRD. SAXS, FTIR, C-13-CP/MAS NMR, and XPS measurements. The results showed that the phase structure of ZrO2 is sensitive to the composition parameters, and confirmed that in the presence of surfactants, the synthesis occurred via a scaffolding mechanism

Size tunable gold nanorods evenly distributed in the channels of mesoporous silica.

Uniformly distributed gold nanorods in mesoporous silica were synthesized in situ by performing a seed-mediated growth process in the channels of SBA-15 which functions as a hard-template to confine the diameter of gold nanorods. By changing the amount of gold precursor, gold nanorods were prepared with a fixed diameter (6-7 nm) and tunable aspect ratios from 3 to 30. Transmission electron microscope and electron tomography were utilized to visualize the gold nanorods supported on one piece of SBA-15 segment and showed a fairly uniform 3-dimensional distribution of gold nanorods within the SBA-15 channels. The longitudinal plasmon resonances of the gold nanorods/SBA-15 composites analyzed by diffuse reflectance UV-vis spectra were found to be tunable depending on the length of gold nanorods. No significant decrease in surface area and/or pore size of the composite was found after growth, indicating the growth process did not disrupt the open mesoporous structure of SBA-15. The combination of the tunable size of the nanorods and their 3-dimensional distribution within the open supporting matrix makes the gold nanorods/SBA-15 composites interesting candidates to systematically study the influence of the aspect ratio of gold nanorods on their properties and potential applications, i.e., catalyst, optical polarizer, and ultrasensitive medical imaging technique.

Visible-light C–heteroatom bond cleavage and detoxification of chemical warfare agents using titania-supported gold nanoparticles as photocatalyst

Gold nanoparticles supported on TiO2 effect the detoxification of soman and VX nerve gases and yperite vesicant agent at room temperature upon visible light illumination.

A polynuclear complex, {[Cu(bpe)2](NO3)}, with interpenetrated diamondoid networks: synthesis, properties and catalytic behavior

A polynuclear complex {[Cu(bpe)2](NO3)} (1), with five-fold interpenetrated diamondoid nets, was synthesized following a hydrothermal procedure, starting from a copper(II) salt, Cu(NO3)2·2.5H2O, and using a molar ratio Cu(NO3)2 : monoethanolamine : bpe : H2O of 1 : 3 : 1 : 500. The well stirred mixture was introduced into a Teflon-lined stainless steel autoclave, heated at 423 K, and kept at this temperature for 3 days. Red single crystals containing complex 1 were fully characterized by chemical analysis, FTIR, single-crystal X-ray diffraction, powder XRD, DR-UV-Vis, TG–heat flow analysis, sorption isotherms of N2 at 77 K, and X-ray photoelectron spectroscopy (XPS). The characterization results indicated that these crystals corresponded to a copper–organic network with a microporous-like structure in which part of the channels are blocked by water molecules and nitrate ions. The synthesis led to a structure in which all the Cu ions were well stabilized as a Cu(I) species, although the precursor was a Cu(II) compound. This structure exhibits remarkable properties: high thermal stability and capacity to totally exchange NO3− anions, without causing any damage to the microporous texture. The catalytic behavior was investigated in NO decomposition and NO reduction with hexane in the presence of O2, revealing very interesting and high catalytic activity. Cu was well preserved in a Cu(I) state after the catalytic tests, which provided new information about the mechanism of NO reaction on copper.

Synergism of Activated Carbon and Undoped and Nitrogen‐doped TiO2 in the Photocatalytic Degradation of the Chemical Warfare Agents Soman, VX, and Yperite

Efficient photocatalytic decomposition of chemical warfare agents is a process that may find application in emergency situations or for the controlled destruction of chemical warfare stockpiles. A series of heterogeneous photocatalysts comprising TiO2-activated carbon or N-TiO2-activated carbon composites exhibit excellent photocatalytic activity to effect the complete decomposition of yperite, soman, and VX in high concentrations. The remarkable photocatalytic activity arises from the synergism between adsorption on active carbon and photoactivity by titania. Nitridation makes the composite also active under visible-light irradiation.

Gold imidazolium-based ionic liquids, efficient catalysts for cycloisomerization of γ-acetylenic carboxylic acids

Ionic liquid stabilized gold(III) chloride is shown to be a very active catalyst in the cyclization of sterically hindered and unhindered acetylenic carboxylic acid substrates even in the absence of a base.

Novel Pd heterogeneous catalysts for cycloisomerisation of acetylenic carboxylic acids

The Pd-TPPTS complex (TPPTS - trisodium salt of 3,3′,3′′-phosphanetriyl benzenesulfonic acid) and PdCl42− salt heterogenised onto Zn2AlNO3 layered double hydroxide (LDH) using an ion-exchange procedure, have been shown to be efficient green catalysts in the cycloisomerisation reaction of acetylenic carboxylic acids to the corresponding 5-membered heterocycles.

Band gap effect on the photocatalytic activity of supramolecular structures obtained by entrapping photosensitizers in different inorganic supports

Different metallophthalocyanines and 2,4,6-triphenylpyrylium (TP+) ions were entrapped in different inorganic supports such as Y zeolite, mesoporous MCM-41, TiO2-SiO2 and SiO2 following a specific protocol. The resulting supramolecular structures were characterized by chemical analysis and diffuse reflectance UV-vis measurements. The determination of the band gap on the basis of UV-vis measurements showed that the host is not a spectator in this process and an electronic interaction occurs that lowers the band gap of the support. The XPS measurements were performed with an in situ X-ray photoelectron spectrometer, which can be operated at pressures of up to 1 mbar at the sample. They indicated that the formation of the supramolecular structure generates a stable environment, in which the oxidation state of the metal can still be influenced by reaction of the metal center with gas molecules. The photocatalytic tests carried out in photodecomposition of dipropyl sulfide showed a good correlation between the band gap values and the photocatalytic activity for metallophthalocyanine complexes. It is remarkable that the triphenylpyrylium ion follows the same trend observed for metallophthalocyanines, although it is a different type of photosensitizer.

Direct oxidation of amines to nitriles in the presence of ruthenium-terpyridyl complex immobilized on ILs/SILP

The immobilization of a ruthenium complex (Ru2Cl4(az-tpy)2) within a range of supported ionic liquids ([C4C1im]Cl, [C4C1im][NTf2], [C6C1im]Cl, [C4C1pyrr]Br, [C4C1im]Br, [C4C1pyrr]Cl) dispersed silica (SILP) operates as an efficient heterogeneous catalyst in oxidation of long chain linear primary amines to corresponding nitriles. This reaction follows a “green” route using a cheap and easy to handles oxidant (oxygen or air). The conversion was found to be strongly influenced by the alkyl chain length of the amine substrate and the choice of oxidant. No condensation reaction was observed between the starting amines and the selectivity to nitrile is 100%. Moving from a composition of 20 atm N2/5 atm O2 to 5 atm N2/20 atm O2 led to enhancements in the conversion (n-alkylamines) and selectivity (benzonitrile) which have been correlated with an increase of the solubilized oxygen. This was further supported by using different inert gas (nitrogen, helium, argon)/oxygen mixtures indicating that the O2 solubility in the SILP system, has an important effect on conversions and TON in this reaction using SILP catalysts. Experiments performed in the presence of CO2 led to a different behaviour due to the formation of amine-CO2 adducts. The application of the Weisz–Prater criterion confirmed the absence of any diffusional constraints.