Search results for "Catalysis"
showing 10 items of 5944 documents
Cocrystal trimorphism as a consequence of the orthogonality of halogen- and hydrogen-bonds synthons.
2019
True trimorphic cocrystals, i.e. multi-component molecular crystals of identical composition that exhibit three polymorphic structures, are exceedingly rare and so far no halogen-bonded cocrystal system has been reported to exhibit trimorphism. Here we describe a unique example of a trimorphic cocrystal exhibiting both hydrogen and halogen bonds in which the differences between polymorphs reveal their orthogonality, evident by the apparently independent variation of well-defined hydrogen- and halogen-bonded motifs. peerReviewed
Improvement of catalytic activity over Cu--Fe modified Al-rich Beta catalyst for the selective catalytic reduction of NOx with NH3
2016
Copper and iron bimetal modified Al-rich Beta zeolites from template-free synthesis were prepared for selective catalytic reduction (SCR) of NOx with NH3 in exhaust gas streams. Comparing to the Cu-based and Fe-based mono-component Beta catalysts, Cu(3.0)-Fe(1.3)-Beta bi-component catalyst shows better low-temperature activity and wider reaction-temperature window. Over 80% of NO conversion can be achieved at the temperature region of 125–500 °C. Due to the synergistic effect of copper and iron evidenced by XRD, UV–Vis–NIR, EPR and XPS measurements, the dispersion state of active components as well as the ratio of Cu2+/Cu+ and Fe3+/Fe2+ were improved over Cu(3.0)-Fe(1.3)-Beta. Isolated Cu2+…
The role of H2O in the photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst
1999
Abstract Photocatalytic oxidation of toluene has been carried out in a gas–solid regime by using polycrystalline anatase TiO2 in a fixed-bed continuous reactor. Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was mainly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected. In the presence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of toluene to benzaldehyde was almost completely inhibited, and an irreversible deactivation of th…
Pumice-Supported Nickel Catalysts
1997
A series of nickel catalysts supported on pumice was prepared by precipitation and impregnation techniques. The influence of the calcination and reduction temperatures on the structural properties such as lattice parameters and particle dimensions of the oxide precursors and of the reduced catalysts was investigated by X-ray diffraction measurements. The effect of structural changes on the catalytic activity in the hydrogenation of carbon monoxide has been evaluated. The turnover frequencies, as well as product distributions, are discussed in terms of the influence of the support properties and of its interaction with the metal. Changes of the C2+yield over CH4yield ratio versus nickel disp…
DFT insights into the oxygen-assisted selective oxidation of benzyl alcohol on manganese dioxide catalysts
2020
Abstract The reactivity pattern of the MnO2 catalyst in the selective aerobic oxidation of benzyl alcohol is assessed by density functional theory (DFT) analysis of adsorption energies and activation barriers on a model Mn4O8 cluster. DFT calculations predict high reactivity of defective Mn(IV) sites ruling a surface redox mechanism, L-H type, involving gas-phase oxygen. Bare and promoted (i.e., CeOx and FeOx) MnOx materials with high surface exposure of Mn(IV) sites were synthesized to assess kinetic and mechanistic issues of the selective aerobic oxidation of benzyl alcohol on real catalysts (T, 333–363 K). According to DFT predictions, the experimental study shows: i) comparable activity…
Surface Study of Pumice Supported Nickel Catalysts Used in the Hydrogenation of CO
1998
A series of pumice supported nickel catalysts used in the CO hydrogenation reaction were characterised by X-ray photoelectron spectroscopy. Qualitative and quantitative analysis of the XPS peaks have shown the effect of the calcination conditions on the chemical state of the nickel before hydrogenation and the particle size of the metal after reduction. Calcination at high temperature determined enrichment of sodium ions on the surface of the support and also on the metal particles. After exposure to the gas mixture CO/H2, formation of nickel carbides and other carbon species was checked. The correlation found between the surface atomic ratio Na/Si and the activity and selectivity of the ca…
Catalytic activity of solvated and unsolvated lanthanide halides in Friedel–Crafts acylations
2000
Abstract Anhydrous lanthanide halides — chlorides and bromides — can act as homogeneous catalysts of Friedel–Crafts acylations. The catalytic activity is related to the solubility of these anhydrous salts. More soluble THF or dioxane (Diox.) neodymium and samarium adducts are more active catalysts.
Catalytic Activity of Char Obtained from Fast Pyrolysis in Esterification Reactions
2021
In this study different pathways for obtaining activated carbon with catalytical activity were analysed. Industrially fast pyrolysis is an efficient way of lignocellulosic biomass processing, since in this process various important high value chemicals are obtained. Biochar is obtained as the by-product in fast pyrolysis process from which activated carbon can be acquired with further chemical activation. Different methods for chemical activation of biochar were tested with the obtained activated charcoals being used as a catalyst in esterification reactions to evaluate their potential use as a heterogenic catalyst. Highest catalytical activity was observed when biochar was pre-treated with…
Investigation of Activities for Pt-M Bimetallic Nanoparticles Catalysts on the Oxygen Reduction Reaction
2015
Bi-metallic Pt3Ni/C and Pt3Co/C electrocatalysts were successfully synthesized by a solvent free chemical vapour deposition method with a narrow particle size distribution. The results showed that the electrochemical surface area was increased by adding the additional Ni or Co to a pure Pt catalyst. Pt3Ni/C catalyst exhibited a significant enhancement of oxygen reduction reaction activity. The catalysts were characterized by EDS, XRD, HRTEM and electrochemical activity was determined using cyclic voltammetry.
Studies of structural composition distribution heterogeneity in ethylene/1-hexene copolymers using thermal fractionation technique (SSA)
2005
Abstract Investigations into the compositional heterogeneity of ethylene/1-hexene copolymers obtained with various zirconocene/MAO catalysts, either homogeneous or supported on inorganic carriers such as a complex of magnesium chloride with tetrahydrofuran or methyl alcohol, were conducted. The dependence between metallocene structure, as well as catalyst immobilization, and the compositional heterogeneity of the related products was investigated. It was found that the heterogeneity of copolymers is determined by the metallocene catalyst structure. The amount of peaks on the DSC thermograms of copolymers and their division increase with the increase of bulkiness of the ligand in the catalyt…