Silica-supported chitosan–platinum complex catalyst for hydrosilylation reactions

Silica-supported chitosan–platinum complex was prepared and characterized by ICP-AES, FT-IR, and XPS, respectively. The complex as catalyst was found to display high catalytic activity in the hydrosilylation reaction of allyl glycidyl ether with triethoxysilane for the first time. It can be recovered by simple filtration and reused for six times without significant loss of activity.     

Dehydration of glycerol with silica–phosphate-supported copper catalyst

Research on Chemical Intermediates - Silica–phosphate-supported copper catalyst was prepared by neutralization of sodium silicate with orthophosphoric acid followed by the addition of copper...     

Kinetics of thiophene hydrodesulfurization over a supported Mo–Co–Ni catalyst

In this study, the kinetics of thiophene (TH) hydrodesulfurization (HDS) over the Mo–Co–Ni-supported catalyst was investigated. Trimetallic catalyst was synthesized by pore volume impregnation and the metal loadings were 11.5 wt % Mo, 2 wt % Co, and 2 wt % Ni. A large surface area of 243 m²/g and a relatively large pore volume of 0.34 cm³/g for the fresh Mo–Co–Ni-supported catalyst indicate a good accessibility to the catalytic centers for the HDS reaction. The acid strength distribution of the fresh and spent catalysts, as well as for the support, was determined by thermal desorption of diethylamine (DEA) with increase in temperature from 20 to 600 °C. The weak acid centers are obtained within a temperature range between 160 and 300 °C, followed by medium acid sites up to 440 °C. The strong acid centers are revealed above 440 °C. We found a higher content of weak acid centers for fresh and spent catalysts as well as alumina as compared to medium and strong acid sites. The catalyst stability in terms of conversion as a function of time on stream in a fixed bed flow reactor was examined and almost no loss in the catalyst activity was observed. Consequently, this fact demonstrated superior activity of the Mo–Co–Ni-based catalyst for TH HDS. The activity tests by varying the temperature from 200 to 275 °C and pressure from 30 to 60 bar with various space velocities of 1–4 h^?1 were investigated. A Langmuir–Hinshelwood model was used to analyze the kinetic data and to derive activation energy and adsorption parameters for TH HDS. The effect of temperature, pressure, and liquid hourly space velocity on the TH HDS activity was studied.     

Ce-promoted Fe–Cu–ZSM-5 catalyst: SCR-NO activity and hydrothermal stability

Research on Chemical Intermediates - Fe–Cu–ZSM-5 and Ce–Fe–Cu–ZSM-5 solids prepared using solid-state ion exchange method (SSIE) were tested in the NH3–SCR of NO...     

Low temperature carbon monoxide catalytic oxidation at the Pd/Ce–Zr–Al–Ox catalyst

The homogeneous chemical composition ceria–zirconia–alumina (Ce–Zr–Al–O_x) nano-alloy were successfully synthesized by surfactant-assisted parallel flow co-precipitation method and applied as supports for low temperature CO oxidation. The experiment conditions were studied in detailed. At 0.92 wt% Pd loading, 30,000 ppm CO could be completely oxidized to CO₂ at 30 °C at a WHSV of 4,380 ml g^?1 h^?1 over the Pd/Ce–Zr–Al–O_x (n_Ce:n_Zr = 3:1) catalyst. Pd/Ce–Zr–Al–O_x catalysts were systematical studied by mean of BET, XRD and TEM analysis. XRD characterization showed that zirconium element entered into cubic structure of ceria and leaded to structure distortion. Addition of aluminum increased specific surface area of ceria–zirconia solid solution substantially. The average pore diameter of Ce–Zr–Al–O_x support palladium catalysts were the key impact factor for CO oxidation. When the Pd/Ce–Zr–Al–O_x catalysts had highly dispersed palladium nanoparticles, large average pore diameter, suitable surface area and pore volume, the activity of CO oxidation was the best.     

Preparation of onion-like Pd–Bi–Au/C trimetallic catalyst and their application

This paper describes the preparation of dispersed onion-like Pd–Bi–Au/C catalyst with average diameter of 13 nm obtained by consecutive chemical reduction of precursor gold, bismuth and palladium salts in aqueous solution and immobilization on active carbon. High-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments were performed to analyze the structure and to characterize the Pd–Bi–Au/C catalyst. The onion-like morphology is composed of high content of gold inner core, a Bi-rich intermediate layer and a Pd-rich external layer. The catalytic activity of the catalyst was subsequently investigated and they were found to be efficient catalysts for the aerobic liquid phase oxidation. The results showed that the catalytic activity of Pd–Bi–Au/C was higher than that of Pd–Au/C bimetallic catalyst, indicating that bismuth plays an important role in synergistic effect between gold and palladium.     

Imidazolium supported palladium–chloroglycine complex: recyclable catalyst for Suzuki–Miyaura coupling reactions

1-Glycyl-3-methyl imidazolium chloride–palladium(II) complex [[Gmim]Cl–Pd(II)] was found to be a catalyst for the Suzuki–Miyaura reaction with excellent yields with high turnover number (6.5 × 10²–9.4 × 10²).     

Phase equilibria in solvent mixture–ion exchange resin catalyst systems

Phase equilibria for solvent mixtures and strong acidic ion exchange resins in H⁺ form are investigated. Experimental data on ternary non-reactive solvent–solvent–polymer systems as well as reactive multicomponent systems are presented for moderately and highly cross-linked poly(styrene-co-divinylbenzene) (PS-DVB) resins. Esterification of acetic acid with ethanol is used as a model reaction. The data are correlated with a combination of thermodynamic models derived for polymer solutions and gels. Independently determined data is used whenever possible with a goal of reducing cross-correlations between the model parameters. The limitations of the thermodynamic modeling approach for solvent–ion exchange resin systems are discussed. It is shown that, due to glass transition of the polymer matrix, the underlying assumptions are not entirely valid in low dielectric constant media and at high cross-link densities.     

Electrocatalytic performance of PdCo–C catalyst for formic acid oxidation

PdCo–C catalyst was synthesized through a simple simultaneous reduction reaction with sodium borohydride in aqueous solution. Inductive coupled plasma emission spectrometer (ICP) and X-ray diffraction (XRD) technologies had been used to characterize the PdCo–C catalyst and proved that the amount of Co was 1.5 wt%, PdCo alloy was formed and possessed face-centered cubic (fcc) crystalline structure, and the average particle size was about 5.1 nm. The electrochemical tests (cyclic voltammetry (CV) and chronoamperometry (CA)) showed that the addition of Co could significantly improve the electrocatalytic activity and stability. The enhancement of electrocatalytic activity and stability was mainly ascribed to the interaction between Pd and additive Co, which facilitated the oxidation reaction of formic acid in direct pathway.     

Catalytic enantioselective cycloadditions: a readily available Diels–Alder catalyst

A highly selective Diels–Alder catalyst has been prepared from a commercially available tetrahydronaphthalene diol. Stereocontrol is enhanced by introduction of a planar chiral arene chromium tricarbonyl group.     

Oxidative dehydrogenation of ethane over a Mo–V–Nb–Te–O mixed-oxide catalyst in a cyclic mode

The oxidative dehydrogenation of ethane (ODE) into ethylene over a Mo–V–Nb–Te–O mixedoxide catalyst in a cyclic mode with alternate feeding of ethane and air has been investigated. The amount of oxide-phase oxygen involved in the reaction has been estimated by titrating the oxygen of the active phase of the catalyst with ethane. The reactivity of this oxygen increases with an increasing temperature. The amount active oxygen involved in ODE at 360–400°C is 0.2–0.6 mmol/g.     

Scission of C–O and C–C linkages in lignin over RuRe alloy catalyst

The performance of lignin depolymerization is basically determined by the interunit C–O and C–C bonds.Numerous C–O bond cleavage strategies have been developed, while the cleavage of C–C bond between the primary aromatic units remains a challenging task due to the high dissociation energy of C–C bond.Herein, a multifunctional Ru Re alloy catalyst was designed, which exhibited exceptional catalytic activity for the cleavage of both C–O and C–C linkages in a broad range of lignin model compounds(β...     

Short-time isoprene polymerization under the action of a titanium–magnesium catalyst

The short-time polymerization of isoprene under the action of a TiCl₄/MgCl2?i-Bu₃Al heterogeneous catalyst has been investigated. Pulse mixing of the catalyst and monomer in a cylindrical tubular reactor with a certain length followed by ethanol injection has made it possible to carry out polymerization for 0.1?0.7 s. In the first 0.3 s, when there is a considerable rise in the activity of the catalyst, living polymerization of isoprene takes place. In this period, polyisoprene has up to 95% trans-1,4 units. Extending the polymerization time to 0.7 s diminishes the average molar mass of polyisoprene, broadens its molar mass distribution, and decreases the concentration of trans-1,4 units to 83%. The data of this study have been analyzed on the basis of the kinetic continuity of the polymer chain initiation and growth.     

Ligand-free C–N bond formation in aqueous medium using a reusable Cu–Mn bimetallic catalyst

A general ligand-free protocol has been described for the recyclable and reusable Cu–Mn catalyzed C–N bond forming cross coupling reaction of arylboronic acids with various amines to form N-arylated amine products in aqueous medium affording excellent yields under ambient conditions, in 3–4 h.     

Deactivation of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the reaction of oxidative ethane dehydrogenation

The operational stability of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the oxidative dehydrogenation of ethane (ratio of C₂H₆: O₂ = 3: 1) is studied in a flow reactor at temperatures of 340–400°C, a pressure of 1 atm, and a WHSV of the feed mixture of 800 h^?1. It is found that the selectivity toward ethylene is 98% at 340°C, but the conversion of ethane at this temperature is only 6%; when the temperature is raised to 400°C, the conversion of ethane is increased to 37%, while the selectivity toward ethylene is reduced to 85%. Using physical and chemical means (XPS, SEM), it is found that the lack of oxidant in the reaction mixture leads to irreversible changes in the catalyst, i.e., reduced selectivity and activity. Raising the reaction temperature to 400°C allows the reduction of tellurium by ethane, from the +6 oxidation state to the zerovalent state, with its subsequent sublimation and the destruction of the catalytically active and selective phase; in its characteristics, the catalyst becomes similar to the Mo–V–Nb–O system containing no tellurium.     

Low-generation carbosilane dendrimers as core for starpolymers using a Ru–ROMP catalyst

Synthesis of new metathesis initiators by coupling Ru-complexes to low generation carbosilane dendrimers (G0–Ru, G1–Ru). These initiators show a very high activity for the ROMP of NBE. Using these dendrimer complexes, multi-arm starpolymers can be developed in a controlled manner.     

Domino aziridine ring opening and Buchwald–Hartwig type coupling-cyclization by palladium catalyst

Highly important trans-3,4-dihydro-2H-1,4-benzoxazine moieties were easily synthesized by domino aziridine ring opening with o-bromophenols and o-chlorophenols followed by the palladium catalyzed coupling-cyclization (intramolecular C_(aryl)–N_(amide) bond formation) with good to excellent yields.     

Biogenous iron oxide-immobilized palladium catalyst for the solvent-free Suzuki–Miyaura coupling reaction

Iron oxide produced by iron-oxidizing bacteria, Leptothrix ochracea, (biogenous iron oxide: BIO) was used as a support for immobilized palladium catalysts with organic cross-linkers. Palladium immobilized on BIO bearing imidazolium chloride delivered the desired biaryl products in sufficient yields in the Suzuki–Miyaura coupling reactions under solvent-free conditions and could be reused several times without significant loss of catalytic activity. It is shown that BIO can be exploited as a useful support for immobilization of palladium and the BIO-immobilized palladium catalyst effectively promotes the solvent-free Suzuki–Miyaura coupling reactions.     

Bulk production of multi-wall carbon nanotube bundles on sol–gel prepared catalyst

A method to grow multi-wall carbon nanotube bundles in a high yield (weighing over 15 times the catalyst) is developed and a plausible explanation for the formation and high yield of the bundles is suggested. The Co–Mo–Mg–O catalyst used in the experiment is prepared by a sol–gel technique, molybdenum being doped into the catalyst through oxidation and diffusion at 750 °C. Small changes to the catalyst preparation lead to the growth of single-wall carbon nanotubes (SWNTs). Our work is an exploitation of the high performance of the solid catalyst in the synthesis of novel nanomaterials.