Showing papers in "Journal of Molecular Catalysis A-chemical in 2004"
TL;DR: In this article, a roadmap for the literature values of density, viscosity, melting and glass transition temperatures, thermal stability, empirical solvent parameters, absorption, toxicity, surface tension, heat capacity, and thermal conductivity is provided.
Abstract: Ionic liquids are good solvents for catalytic reactions. The rational selection of the appropriate ionic liquid solvent for a particular reaction requires general knowledge of the properties of ionic liquids, and the details of some properties of the specific ionic liquid solvents being considered. The solvent properties of ionic liquids that are relevant to catalysis are discussed, and sources of the values of those properties for ionic liquids are identified. A roadmap for the literature values of density, viscosity, melting and glass transition temperatures, thermal stability, empirical solvent parameters, absorption, toxicity, surface tension, heat capacity, and thermal conductivity is provided.
745 citations
TL;DR: Olefin metathesis opens up new industrial routes to important petrochemicals, oleochemicals, polymers, and specialty chemicals, such as polymers as discussed by the authors.
Abstract: Olefin metathesis opens up new industrial routes to important petrochemicals, oleochemicals, polymers, and specialty chemicals. Industrial applications of the olefin metathesis reaction known until 1997 have been described elsewhere, including processes that have not been commercialized and processes that are no longer commercial [1]. Here we will discuss the present situation.
736 citations
TL;DR: In this paper, the photocatalytic activity of those catalysts was investigated for the liquid phase photocatatlytic degradation of active yellow XRG dye diluted in water under UV and visible light irradiation.
Abstract: Iron-ion-doped anatase titanium (IV) dioxide (TiO2) samples were prepared by hydrothermal hydrolysis and crystallization in octanol-water solution. The samples were characterized by X-ray diffraction, BET-specific surface area determination, UV-Vis diffuse reflectance spectroscopy and electron paramagnetic resonance spectroscopy. UV-Vis diffuse reflectance spectra showed a slight shift to longer wavelengths and an extension of the absorption in the visible region for almost all the ion-doped samples, compared to the non-doped sample. The photocatalytic activity of those catalysts was investigated for the liquid phase photocatatlytic degradation of active yellow XRG dye diluted in water under UV and visible light irradiation. It was found that the catalysts doped with FeCl3 have better catalytic activity for photodegradation of XRG than those doped with FeCl2. The amount of doped iron ion plays a significant role in affecting its photocatalytic activity and iron doped with optimum content can enhance photocatalytic activity, especially under visible light irradiation.
508 citations
TL;DR: In this article, the effect of annealing temperature on the morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2 was studied by means of TEM, XRD, DTG, DSC, BET and ESR.
Abstract: Nanotubed titanic acid (H2Ti2O4(OH)2) was prepared from nanotubed sodium titanate (Na2Ti2O4(OH)2) by an ion exchange reaction in a pH=1 HCl solution. The effect of annealing temperature on the morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2 was studied by means of TEM, XRD, DTG, DSC, BET and ESR. The results showed that nanotubed H2Ti2O4(OH)2 is thermally unstable. Its dehydration consists of two steps. In the first-step dehydration, single-electron-trapped oxygen vacancies (SETOVs) were generated. Accompanying the second-step dehydration, the transition of crystal form from orthorhombic system to anatase took place, at the same time the nanotubes broke. At T>300 °C, when the SETOV concentration greatly increased, the interaction between SETOV happened. (VOo)x formed could play the role of recombination center of photogenerated e−–h+ and make the photocatalytic behavior of TiO2 (anatase, obtained from 500 °C-treated nanotubed H2Ti2O4(OH)2) to become bad.
307 citations
TL;DR: In this article, the reaction of phenol photocatalytic oxidation in the presence of illuminated TiO2 was investigated and the concentration of catechol, hydroquinone and p-benzoquinone along with phenol in the course of the photoreaction was determined.
Abstract: Six hydroxylated aromatic compounds, p-benzoquinone and four aliphatic compounds were detected as intermediates of the reaction of phenol photocatalytic oxidation in the presence of illuminated TiO2. The concentration of catechol, hydroquinone and p-benzoquinone was determined quantitatively along with that of phenol in the course of the photoreaction. The reactions of TiO2-photooxidation of phenol and its primary intermediates—dihydroxybenzenes show 1st order behaviour. The use of initial reaction rates for kinetic studies is recommended because of many competitive reactions in illuminated suspensions of titanium dioxide. A possible mechanism of phenol full mineralisation is presented.
286 citations
TL;DR: A large number of attempts at the selective oxidation of alkanes may be classified into three basic types: high-temperature heterogeneous catalysis, biological/biomimetic catalysis and organometallic activation.
Abstract: A large number of attempts at the selective oxidation of alkanes may be classified into three basic types: high-temperature heterogeneous catalysis, biological/biomimetic catalysis, and organometallic activation. In this essay I discuss mechanistic similarities and differences between the three approaches, and their implications for the best opportunities for achieving desired selective transformations.
279 citations
TL;DR: In this article, the photocatalytic oxidation of phenol and chlorophenols was studied in the presence of ZnO in a batch reactor configuration illuminated with a 6 W low pressure mercury lamp.
Abstract: The photocatalytic oxidation of phenol and chlorophenols were studied in the presence of ZnO in a batch reactor configuration illuminated with a 6 W low pressure mercury lamp. The variables studied include catalyst usage, solution pH and phenol concentration. The degradation rate of phenol was favourable in the neutral pH range. However, o-chlorophenol and p-chlorophenol undergo degradation at a faster rate at lower pH values. The disappearance of phenols in each case approximately obeyed first-order kinetics with the apparent first-order decay constant increasing with decreasing solute concentration. Total organic carbon analysis indicated complete mineralisation of phenols on ZnO surface.
261 citations
TL;DR: The use of homogeneous catalysts that activate and functionalize the CH bonds of unactivated hydrocarbons is of particular interest from a scientific as well as an economic viewpoint as discussed by the authors.
Abstract: The development of selective, energy efficient direct alkane oxidation chemistry could lead to a new paradigm in materials and energy technologies in the 21st century that is environmentally and economically superior and allow the vast reserves of natural gas to be employed directly as feedstocks for fuels and chemicals. The use of homogeneous catalysts that activate and functionalize the CH bonds of unactivated hydrocarbons is of particular interest from a scientific as well as an economic viewpoint. This results from the strong potential for these catalysts to carry out oxidative hydrocarbon conversions with high atom and energy efficiency and under mild conditions. Despite the large body of work on the CH activation reaction that has been produced over the last three decades, to date relatively few catalyst systems that are based on this approach have been developed that allow the functionalization of hydrocarbons and there are still large gaps in our fundamental knowledge of how to rationally design such catalysts. Addressed in this paper are some of the key challenges and approaches to the de novo, rational development of the next generation of organometallic, alkane functionalization catalysts based on the CH activation reaction with emphasis on our own research.
231 citations
TL;DR: In this article, the role of transition metal complexes is overviewed for the iron, copper and chromium compounds, for which photoreactivity is of crucial environmental importance, and examples of different photocatalytic behaviours are presented in some details.
Abstract: The role of transition metal complexes is overviewed for the iron, copper and chromium compounds, for which photoreactivity is of crucial environmental importance. Attention is paid to these complex systems, in which metal centres are photoreduced by organic matter under solar irradiation and re-oxidized by molecular oxygen, i.e. to the systems, that play a part in the environmental photocatalysis. The photoreduction is accompanied by simultaneous oxidation of organic matter, which plays a role of ligand and/or sacrificial electron donor. Under favourable conditions a complete photodegradation of the organic pollutants can be achieved. The general mechanisms are analysed and examples of different photocatalytic behaviours are presented in some details. The systems are more sophisticated due to concurrent generation of active oxygen species, such as the O 2 − , HO 2 , OH , H 2 O 2 , and HO 2 − , which are involved in the redox reactions of the photocatalytic cycling and influence the pollutant degradation. Beside the monometallic cycles, the mixed metal systems can function in nature. The cooperation between the photocatalytic cycles of two metals can abate diverse environmental pollutants, but their efficiency can be either higher or lower in comparison with that of the sum of single cycles.
214 citations
TL;DR: In this article, high specific surface areas (77-244m 2 /g) were obtained for Titania-zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 ¼ ) by the sol-gel method.
Abstract: Titania–zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m 2 /g) were obtained. Acidity determined by NH 3 -TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH 3 /g for TiO 2 to 1226–1456 μmol NH 3 /g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO 2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO 2 rich region, amorphous material in the mixed oxide 50–50 TiO 2 –ZrO 2 and tetragonal and monoclinic crystalline phases in the ZrO 2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density.
210 citations
TL;DR: Chitosan-stabilized Pt (chi-Pt) or Pd (chiPd) colloidal nanoparticles catalyst prepared with various chitosans-metal molar ratios and reducing agents were characterized as mentioned in this paper.
Abstract: Chitosan-stabilized Pt (chi-Pt) or Pd (chi-Pd) colloidal nanoparticles catalyst prepared with various chitosan–metal molar ratios and reducing agents were characterized. Chitosan could stabilize Pt and Pd with minimum chitosan:M ratio of 5:1 and 2:1 respectively. The finest and well-dispersed particles of chi-Pt or chi-Pd were obtained when methanol or NaBH 4 were used as the reducing agents. Chi-Pt and chi-Pd reduced by hydrazine gave aggregated particles in all chitosan molar ratios. Chitosan could control particle size of Pt or Pd to within 1.9–2.2 nm when CH 3 OH or NaBH 4 was used as the reducing agents. Palladium or Platinum catalysis on cyclooctene hydrogenation gave cyclooctane. Hydrogenation of octene catalyzed by chi-Pd gave octane, 2-octene and 3-octene while chi-Pt prepared by methanol reduction showed 99.99% selectivity and conversion to octane. The catalytic activity of chi-Pt was higher than chi-Pd for both the hydrogenations.
TL;DR: ZEON as discussed by the authors developed isoprene extraction technology from C5 fraction of naphtha successfully and developed unique products using residual 1,3-PDE and DCPD components.
Abstract: Since its establishment in 1950, ZEON Corporation has contributed to the advancement of Japanese industry, as a chemical company focused on the manufacture of synthetic rubber. Some of our specialty rubber products hold 40–70% of the worldwide market share. ZEON’s exclusive technology is the source of a number of breakthroughs and continues to contribute to today’s polymer industry. In order to maintain the position as a leading company in synthetic rubber business, ZEON strategically planned industrialization of polyisoprene rubber to compete with natural rubber. The main raw material for polyisoprene rubber is isoprene monomer, which was not yet available on the market. ZEON had to first develop isoprene extraction technology from C5 fraction of naphtha successfully. The issue then was C5 fraction contained only 10–15% of isoprene monomer. In order to reduce the total isoprene monomer cost, we had to utilize other components. The components are 1,3-pentadiene (1,3-PDE), dicyclopentadiene (DCPD), and others. So along with polyisoprene business, we launched the 1,3-PDE resins business and DCPD resins business for adhesives and traffic paints in 1970. To fully utilize these extracted components, we still had to develop unique products using residual 1,3-PDE and DCPD. Our cyclo-olefin polymer business was born from this basic strategy to fully utilize those components. This report discusses the development and current status of cyclo-olefin polymer and its precision molding business, including optical film business, realized by the ZEON’s comprehensive utilization of C5 fraction.
TL;DR: In this paper, an anatase-type TiO2 photocatalyst with adsorptive property of activated carbon fibers was developed by a molecular adsorptiondeposition (MAD) method followed by calcination in a stream of Ar gas.
Abstract: Activated carbon fibers (ACFs) supported TiO2 Photocatalyst was successfully prepared by a molecular adsorption-deposition (MAD) method followed by calcination in a stream of Ar gas. The photocatalyst developed was characterized by SEM, XRD, XPS, BET surface area and UV-vis adsorption spectroscopy. SEM observation showed TiO2 was deposited on almost each carbon fiber with a coating thickness of about 100 nm, and the space between adjacent fibers was remained unfilled to allow UV light to penetrate into the felt-form photocatalyst to a certain depth. Anatase-form TiO2 was uniquely developed even as calcination temperatures rose up to 900degreesC. Tight contact of thin TiO2 coating to carbon fibers surfaces was supposed to suppress phase transformation of TiO2 from anatase to rutile, and to keep high crystallinity of anatase. As confirmed by XRD and XPS examinations, the micrographic structure and surface properties of ACFs had not been damaged by the deposition process and calcination at high temperatures. The present photocatalyst showed high photocatalytic reactivity in photodegradation of highly concentrated methylene blue (MB) solutions. The comparative experiments indicated the photocatalyst produced had a combined effect of photocatalytic reactivity of anatase-type TiO2 with adsorptive property of activated carbon fibers. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed. (C) 2004 Elsevier B.V. All rights reserved.
TL;DR: In this article, the anti-bacterial activity of the catalysts were determined qualitatively by testing the presence of coliforms in water after contacting with the catalyst, using a Readycult reagent.
Abstract: The present work highlights the high efficiency of silver nano-particles deposited over activated carbon, by electro-chemical deposition method, in controlling microorganisms in water. The anti-bacterial activity of the catalysts were determined qualitatively by testing the presence of coliforms in water after contacting with the catalyst, using a Readycult reagent. The catalytic characteristics of these materials are obtained by SEM (scanning electron microscopy), XRD (X-ray diffraction) and TPR (temperature programmed reduction). TPR results clearly indicate the presence of metallic silver in the dried catalyst prepared by electro-chemical deposition method and the presence of silver oxide and/or nitrate precursors in the catalysts prepared by impregnation method. SEM results indicate the presence of Ag particles in nanometer size. Comparison of the anti-bacterial activity of the Ag/C catalyst prepared by electro-chemical deposition method with that of the Ag/C catalyst prepared by conventional impregnation technique indicate that lower amount of former is sufficient in controlling the microorganism which is not the case with the latter. The main advantage of Ag/C catalyst prepared by electro-chemical deposition is that no pretreatment conditions like reduction are required for deactivation of microorganism in water, which is not the case with the catalysts prepared by impregnation technique.
TL;DR: In this paper, the authors investigated the catalytic activity, long-term stability and the reasons for deactivation of a nanosize gold-supported Au/TiO2 in CO oxidation.
Abstract: The activity, long-term stability and the reasons for deactivation of a nanosize gold- supported Au/TiO2 in CO oxidation were investigated. Characterization of the catalyst sample was made by XPS, FTIR, TEM, BET, “depletive” oxidation and TPD instrumental methods. In spite of the experimentally proved very high activity at temperatures below 213 K, the catalyst exhibited a gradual decrease in initial activity. Two main reasons for the catalyst deactivation were found: (i) capability to adsorb CO and accumulate it as carbonates, this deactivation is reversible and after heating the catalyst surface is restored by CO2 evolution; (ii) agglomeration of Au particles, which causes irreversible, however weak deactivation.
TL;DR: In this paper, a bifunctional nucleophile-electrophile catalyst system of tetradentate Schiff-base aluminum complexes ((Salen)AlX) in conjunction with a quaternary ammonium salt (n-Bu4NY) in the absence of any organic solvent is presented.
Abstract: Chemical fixation of carbon dioxide to cyclic carbonates proceeds effectively under extremely mild temperature and pressure by using a bifunctional nucleophile–electrophile catalyst system of tetradentate Schiff-base aluminum complexes ((Salen)AlX) in conjunction with a quaternary ammonium salt (n-Bu4NY) in the absence of any organic solvent. Electrophilicity of central Al3+ ion and the steric factor of substituent groups on the aromatic rings of (Salen)AlX (electrophile), and nucleophilicity and leaving ability of the anion Y− of n-Bu4NY (nucleophile) have a great effect on the catalytic activity of the bifunctional catalyst.
TL;DR: In this article, the size of synthesized Ag nanoparticles is reported, which decreases with increasing stabilizer: AgNO 3 molar ratio, decreased with increasing amount of methanolic NaOH added until an optimum amount was reached, and decreased with small amount of HCl added but increased rapidly on further addition, increasing the concentration of water in the reducing agent increased the particles size nearly linearly.
Abstract: The parameters influencing the size of synthesized Ag nanoparticles are reported. The particles size decreased with increasing stabilizer: AgNO 3 molar ratio, decreased with increasing amount of methanolic NaOH added until an optimum amount was reached, and decreased with small amount of methanolic HCl added but increased rapidly on further addition. The reducing activity of the reducing agent influenced the particle size significantly. In addition, increasing the concentration of water in the reducing agent increased the particles size nearly linearly. PVP is a better stabilizer than β-CD to prevent aggregation of small particles. Microwave irradiation for 20 s at output power of 700 W produced smaller and more narrowly distributed Ag particles than conventional heating method.
TL;DR: In this paper, the preparation of catalysts in situ, supported catalysts, and tungsten-based catalysts is discussed. But the main focus of this paper is on olefin metathesis studies.
Abstract: Recent advances in olefin metathesis studies include the preparation of catalysts “in situ,” supported catalysts, and tungsten-based catalysts, and observation of molybdacyclobutane complexes, molybdacyclopentane complexes, base-free methylene complexes, and ethylene complexes such as Mo(N-2,6-Cl2C6H3)(CH2CH2)[rac-Biphen](Et2O).
TL;DR: In this paper, the use of Sn(3-hydroxy-2-methyl-4-pyrone) 2 (H 2 O) 2 ) as catalysts in the transesterification reaction of different alkyl-chain triglycerides and alcohols was reported.
Abstract: This article reports the use of Sn(3-hydroxy-2-methyl-4-pyrone) 2 (H 2 O) 2 ( 1 ), Pb(3-hydroxy-2-methyl-4-pyrone) 2 (H 2 O) 2 ( 2 ), and Zn(3-hydroxy-2-methyl-4-pyrone) 2 (H 2 O) 2 ( 3 ) as catalysts in the transesterification reaction of different alkyl-chain triglycerides and alcohols. The methanolysis of native oils from Brazilian’s Savannah and Amazonian regions, such as Andiroba ( Carapa guianensis ), Babassu ( Orbignia sp. ), Cumaru ( Dipteryx odorata ), Palm tree ( Elaeis sp. ), Piqui ( Caryocar sp. ), and Soybean oil as well as the alcoholysis of Soybean oil with several alcohols (ethanol, propanol, iso -propanol, n -butanol, terc -butanol and cyclo -hexanol) was studied. Activities of the tin and lead pyrone complexes were observed in all the alcohol studies. For linear alcohols, the reaction activities decrease with increasing carbonic chain length. It was also shown that the catalytic activities are higher when vegetable oil with short chain fatty acids or with a high unsaturated degree and short and linear chain alcohols are used.
TL;DR: Titania-supported tungsten and vanadia oxides with different W and V loadings and calcined at different temperatures have been prepared by the sol-gel method and characterized as mentioned in this paper.
Abstract: Titania-supported tungsten and vanadia oxides with different W and V loadings and calcined at different temperatures have been prepared by the sol–gel method and characterized. Large amount of tungsten (9%; w/w) provides thermal stability to WO3/TiO2 systems upon addition of vanadia. It is found that WO3 and V2O5 crystallites are formed when their concentrations are higher than those corresponding to three monolayers. DTA analyses have shown that the presence of V2O5 crystallites is not essential for the transformation of titania anatase into rutile. High reactivity in limited temperature range (225–350 °C) has been observed for the catalyst with 8% (w/w) V2O5 with a high formation of N2O amount during the SCR reaction. The catalyst with 3% (w/w) V2O5 exhibits a slight lower reactivity but with a high selectivity to N2 preserved in all working temperature.
TL;DR: In this paper, a regioselective one-pot synthesis of 2-aryl benzimidazoles, benzoxazoles and benzthiazoles has been achieved in excellent isolated yields under ambient conditions using the ionic liquids, 1-butylimidazolium tetraflouroborate ([Hbim]BF4) and 1,3-di-nbutylamidazolate tetrafluoroborate ([bbim] BF4) as reaction media and promoters.
Abstract: A regioselective one-pot synthesis of 2-aryl benzimidazoles, benzoxazoles and benzthiazoles has been achieved in excellent isolated yields under ambient conditions using the ionic liquids, 1-butylimidazolium tetraflouroborate ([Hbim]BF4) and 1,3-di-n-butylimidazolium tetrafluoroborate ([bbim]BF4) as reaction media and promoters. There was no need for the use of an additional catalyst normally employed in the methodologies reported so far.
TL;DR: In this article, a simple synthesis procedure for the immobilization of propyl thiol groups on silica is investigated using various concentrations of 3-mercapto propyl trimethoxy silane (3-MPTS) in the range of 5-40%.
Abstract: A simple synthesis procedure for the immobilization of propyl thiol groups on silica is investigated using various concentrations of 3-mercapto propyl trimethoxy silane (3-MPTS) in the range of 5–40%. The thiol group functionalised silicas (SiO2–SH) were then oxidized to Bronsted sulphonic acid silica materials (SiO2–SO3H) using aqueous H2O2 as oxidizing agent. The surface structures of the functionalized catalysts were analyzed by a series of characterization techniques like elemental analysis, FTIR, TG-DTA, Surface area measurements, XPS, 13 C CP MAS NMR and 29 Si MAS NMR. The 13 C CP MAS NMR analyses confirm that disulphide species are not formed under the present preparation condition of catalysts. The acidity of the synthesized catalysts were further confirmed by the temperature programmed desorption of ammonia. The catalytic activity of the sulphonic acid functionalized silicas was evaluated in the liquid phase acetalization of ethyl acetoacetate with ethylene glycol and in the acetylation of anisole with acetic anhydride. The catalysts were found to be active in the acetalization reaction, which needs mild acidic sites, while the acetylation reactions gave lower activity, probably it needs stronger acid sites. A 30 wt.% SO3H loaded silica (SiO2–SO3H30) was recycled two times in the acetalization of ethyl acetoacetate and no major change in the conversion of EAA and selectivity to fructone is seen, which further argue against the possibility of leaching of the anchored sulphur containing species during reactions.
TL;DR: In this article, the addition reactions of aliphatic acids with olefins to give corresponding esters have been investigated using SO 3 H-functionalized ionic liquids as dual catalyst-solvent.
Abstract: Addition reactions of aliphatic acids with olefins to give corresponding esters have been investigated using SO 3 H-functionalized ionic liquids as dual catalyst–solvent. The isolation of the desired products could be achieved via simple decantation and ionic liquids could be reused continuously after dried in vacuum (5–12 mmHg) at ca. 80 °C.
TL;DR: In this paper, the Fischer esterification of acetic acid utilizing task specific ionic liquid (TSIL) 1 and ethanol revealed an interesting trend when comparing overall conversions with the level of reuse.
Abstract: Initial studies involving the Fischer esterification of acetic acid utilizing task specific ionic liquid (TSIL) 1 and ethanol revealed an interesting trend when comparing overall conversions with the level of reuse. A rise in product yield was observed up to the third recycling of the ionic liquid (IL) medium. Post-run analyses revealed that the TSIL remained unchanged and the by-products of the reaction, acetic acid and water, were being retained. Use of TSILs in the Fischer esterification reaction was both high yielding and programmable if the proper ratio of both water and reagents to immobilized medium was observed.
TL;DR: In this article, a 14-membered hexaaza macrocyclic ligand was obtained by the one-pot template reactions of formaldehyde and ethylenediamine with alkyl and benzyl amine within the cavities of zeolite Y by a two-step process in the liquid phase.
Abstract: Copper(II) complexes with 14-membered hexaaza macrocyclic ligand “1,3,6,8,10,13-hexaaza cyclotetradecane, 1,8-dimethyl-“[Cu((Me) 2 [14]aneN 6 )](ClO 4 ) 2 ” 2 ; 1,8-diethyl-“[Cu((Et) 2 [14]aneN 6 )](ClO 4 ) 2 ” 3 ; 1,8-dibuthyl-“[Cu((Bu) 2 [14]aneN 6 )](ClO 4 ) 2 ” 4 ; and 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane“[Cu((benzyl) 2 [14]aneN 6 )](ClO 4 ) 2 ” 5 ”, have been prepared by the one-pot template reactions of formaldehyde and ethylenediamine with alkyl and benzyl amine within the cavities of zeolite Y. These complexes were entrapped in the supercage of zeolite Y by a two-step process in the liquid phase: (i) inclusion of a Cu(II) precursor complex, [Cu(en) 2 ] 2+ -NaY 8 , and (ii) in situ one-pot template reaction of the copper(II) precursor complex with the formaldehyde and amine. The new materials “[Cu((Me) 2 [14]aneN 6 )]-NaY 9 , [Cu((Et) 2 [14]aneN 6 )]-NaY 10 , [Cu((Bu) 2 [14]aneN 6 )]-NaY 11 , [Cu((Benzyl) 2 [14]aneN 6 )]-NaY 12 ” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV-Vis, XRD, BET, DRS). Analysis of the data indicates that the Cu(II) complexes are encapsulated in the NaY zeolite supercages and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. By comparing the performance of the heterogeneous system with the neat complex in the oxidation of tetrahydrofurane (THF) using hydrogen peroxide as oxygen donor, a protection effect of the matrix over the active center was evidenced by a higher conversion and product selectivity. Encaged complexes yield mainly tetrahydrofurane-2-ol (THF-2-ol) and insignificant amount of tetrahydrofurane-2-one (THF-2-one), while with their homogeneous counterparts, selectivity’s to THF-2-one are higher.
TL;DR: In this paper, post-treatment of reduced copper catalyst with alkaline solution is effective in improving the selectivity to ethyl acetate in the dehydrogenative dimerization of ethanol.
Abstract: Post-treatment of reduced copper catalyst, which contains Zn, Zr, and Al, with alkaline solution is effective in improving the selectivity to ethyl acetate in the dehydrogenative dimerization of ethanol. The treatment with Na2CO3 and K2CO3 greatly suppressed the formation of by-products such as butanone and 2-butanol, and resulted in the improvement of the selectivity to ethyl acetate. The suppression of butanone and 2-butanol is caused by the neutralization of surface acid sites that are active for the dehydration from 1,3-butanediol, into which acetaldol is hydrogenated. These acid-sites are formed after reduction of the Cu-Zn-Zr-Al-O mixed oxide precursor, and thus the post-treatment is effective. We also discuss the reaction routes in the side reactions.
TL;DR: In this article, two commercially available acid-activated montmorillonite clay catalysts, K5 and K10, have been characterised by ammonia adsorption microcalorimetry at 150°C.
Abstract: Two commercially available acid-activated montmorillonite clay catalysts, K5 and K10, have been characterised by ammonia adsorption microcalorimetry at 150 °C. The adsorption capacities and molar enthalpies of adsorption have been interpreted in terms of the concentration and strength of surface acid sites. Clays exchanged with Al3+, Fe3+ and Na+ have been examined. Catalytic activities have also been measured, in liquid phase reactions in swelling and non-swelling solvents, and in reactions catalysed by Bronsted and by Lewis acid sites. The relationships between ammonia adsorption characteristics and catalytic activities have been determined. It has been shown that anhydrous ammonia is able to access all acid sites on the clay surface, including those in the residual clay interlayer regions which would normally only be accessible in the presence of a swelling solvent. Ammonia adsorption on clays exchanged with Fe3+, where Lewis acidity is maximised, is more extensive and with a higher molar enthalpy of adsorption than on clays maximised for Bronsted acidity. It is concluded that ammonia can be satisfactorily used as a probe of surface acidity when Bronsted acidity dominates but, if there is significant Lewis acidity, ammonia adsorption data is difficult to interpret.
TL;DR: In this article, the authors reported on the olefin polymerization behavior of phenoxy-imine ligated Zr, Ti, and V complexes 1−10 with MgCl2/RmAl(OR)n systems.
Abstract: This contribution reports on the olefin polymerization behavior of phenoxy-imine ligated Zr, Ti, and V complexes 1–10 with MgCl2/RmAl(OR)n systems. Zr complexes 1–4 combined with MgCl2/RmAl(OR)n display strikingly high ethylene polymerization activities; indeed, they are some of the highest reported activities for methylalumoxane (MAO)- and borate-free olefin polymerization catalysts (max. 1819 kg-PE/(mmol-cat h), 0.9 MPa ethylene pressure, 50 °C). In addition, when Ti complexes 5–7 are combined with MgCl2/RmAl(OR)n they exhibit high ethylene polymerization activities (max. 36.3 kg-PE/(mmol-cat h), 0.9 MPa ethylene pressure, 50 °C) and produce polyethylenes with narrow molecular weight distributions (Mw/Mn) and ethylene–propylene copolymers with homogeneous structures, representing the first examples of MAO- and borate-free, highly active single-site catalyst systems. The activities exhibited by the Zr and Ti complexes with MgCl2/RmAl(OR)n are superior or comparable to those obtained with MAO cocatalyst systems. Moreover, V complexes 9 and 10 in association with MgCl2/RmAl(OR)n demonstrate high activities at elevated temperatures (9: 75 °C, 65.1 kg-PE/(mmol-cat h), atmospheric ethylene pressure) and are the first reported examples of highly active, thermally robust single-site V-based olefin polymerization catalysts. All of the polyethylenes formed from the MgCl2/RmAl(OR)n systems display good polymer morphology, indicating that complexes 1–10 are heterogenized on the surface of the MgCl2/RmAl(OR)n. These results suggest that MgCl2/RmAl(OR)n not only works as an excellent cocatalyst, but is also a good support for phenoxy-imine ligated Zr, Ti, and V complexes.
TL;DR: In this paper, the properties of polymer-stabilized aqueous colloids of silver sulfide were studied and the nature and energies of optical transitions responsible for the absorption of visible light by the colloidal nanoparticles were determined.
Abstract: Optical properties of polymer-stabilized aqueous colloids of silver sulfide were studied. Nature and energies of optical transitions responsible for the absorption of visible light by silver sulfide nanoparticles were determined. Catalytic properties of Ag 2 S nanoparticles in methylviologen reduction by sodium sulfide were examined. It was shown that this reaction is reversible, the equilibrium caused by a reverse reaction between the product of direct catalytic process – sulfur (polysulfide anions) and cation-radical of methylviologen. It was found that Ag 2 S nanoparticles can catalyze reduction of Ag + ions by various reductants, in particular, hydroquinone or sodium sulfite, with the formation of silver particles having characteristic plasmon absorption bands in the visible spectral domain. Effect of the conditions of Ag + catalytic reduction on the shape and intensity of plasmon resonance bands of metallic silver were studied, schematic mechanism of this reaction was proposed. It was shown that at the irradiation of solutions containing Ag 2 S nanoparticles, Ag + cations and a reducing agent with the light corresponding to the fundamental absorption band of nanoparticulate silver sulfide, the rate of Ag + catalytic reduction increased whereas kinetic features of catalytic reaction and characteristics of plasmon resonance absorption bands of silver nanoparticles changed. A mechanism of photochemical activation of the catalytic reduction of silver ions with the participation of Ag 2 S nanoparticles was proposed.
TL;DR: In this paper, a degradation mechanism based on ethanol reaction with photogenerated holes is proposed, and different surfacial OH distributions determine ethanol-catalyst interactions. But no deactivation of these catalysts was observed during the experimental time period (6h).
Abstract: Ethanol degradation by TiO2 and TiO2 doped with Fe, Pd and Cu has undergone FTIR spectroscopic study. Ethanol interaction with bare-TiO2 and Fe-TiO2 yields the formation of ethoxides on the catalyst surface that can readily be oxidised to acetates by radicals O2 − and OH. Conversely, ethanol interaction with Pd-TiO2 and Cu-TiO2 generates an intermediate species between ethanol and ethyleneglycol. Acetate-producing oxidation of these latter species is inhibited because electrons that form radicals O2 − are captured by the respective metallic oxides. In these catalysts a degradation mechanism based on ethanol reaction with photogenerated holes is proposed. Also, different surfacial OH distributions determine ethanol–catalyst interactions. Furthermore, ethanol degradation has been studied in a gaseous continuous flow system. Exhaust gases have been analysed by means of GC and FTIR. These experiments demonstrate that bare-TiO2 and Fe-TiO2 degrade ethanol to provide only acetaldehyde and their catalytic activity progressively decays over time. On the contrary, Pd-TiO2 and Cu-TiO2 have produced ethyleneglycol in addition to acetaldehyde. No deactivation of these catalysts was observed during the experimental time period (6 h).