Search results for "Heterogeneous catalysis"

Photocatalytic oxidation of acetonitrile in gas–solid and liquid–solid regimes

2005

Il programma NON mi ha consentito di scaricare il PDF di questo articolo. Se lo volete ditemi come inviarlo ABSTRACT Photocatalytic degradation of acetonitrile was carried out in both gas–solid and liquid–solid regimes using two commercial TiO2 catalysts (Merck and Degussa P25). For the gas–solid regime, a continuous annular photoreactor was used. The influence on photodegradation kinetics of the gas flow rate and concentrations of acetonitrile, oxygen, and water was investigated. Acetonitrile degradation products detected in the gas phase included carbon dioxide and hydrogen cyanide. The same photoactivity was exhibited in the presence and in the absence of water vapour. The liquid–solid reg…

Cluster and Periodic Calculations of the Ethene Protonation Reaction Catalyzed by theta-1 Zeolite: Influence of Method, Model Size, and Structural Co…

2001

The protonation of ethene by three different acid sites of theta-1 zeolite was theoretically studied to analyze the extent and relevance of the following aspects of heterogeneous catalysis: the local geometry of the Bronsted acid site in a particular zeolite, the size of the cluster used to model the catalyst, the degree of geometry relaxation around the active site, and the effects related to medium- and long-range interactions between the reaction site and its environment. It has been found that while the reaction energy is very sensitive to the local geometry of the site, the activation energy is mainly affected by the methodology used and by electrostatic effects on account of the carbo…

Cu/P(4-PVP) stereochemistry in tetralin liquid-phase oxidation

2007

Abstract Cu/P(4-PVP) catalyst was used as catalyst for oxidation of tetralin in liquid phase. The catalyst was prepared by reaction of a Cu(II) salt with a 4-vinylpyridine-co-divinylbenzene polymer receptor and characterized by solid 1 H and 13 C NMR, XPS, FTIR, ESR spectroscopies, and by chemical reaction with pure tetralin. That information was used to gain insight into the stereochemistry of the active site needed to orient the reaction toward tetralone production. It was found that the Cu coordination with the pyridine was critical in influencing the peroxy-radical catalytic reaction, and that polyvinylpyridine was able to limit the autothermal oxidation. The active center is postulated…

Imidazolium-Functionalized Carbon Nanohorns for the Conversion of CO2 Unprecedented Increase of Catalytic Activity after Recycling

2017

Carbon nanohorns (CNHs) were selected as a novel catalytic platform for the design of imidazolium based hybrid materials able to promote the conversion of carbon dioxide into cyclic carbonates. Several heterogeneous catalysts were prepared using a one-step procedure based on the radical polymerization of various bis-vinylimidazolium salts in the presence of pristine CNHs. The as-synthesized materials were tested for the fixation of CO2 into epoxides. The excellent catalytic performances were evaluated in terms of turnover number and productivity. The versatility of the above hybrids was proved using several epoxides as substrate. Catalysts recyclability was successfully verified for several…

Effect of Pre-Reduction on the Properties and the Catalytic Activity of Pd/Carbon Catalysts: A Comparison with Pd/Al2O3

2013

The effect of pre-reduction in solution with chemical reagents on the catalytic performance and catalyst properties of Pd/carbon catalysts was systematically investigated with a multitechnique approach. The results are critically discussed in comparison to those recently obtained on analogous Pd/alumina catalysts. It was proved that the Pd phase on the carbon surface is characterized by a high mobility, opposite to what occurs on alumina. As a result, the Pd particles on carbon aggregate together during pre-reduction, with a consequent decrease in available metal surface. Pd particles remain aggregated also in reaction conditions; the decreased Pd dispersion negatively affects the catalyst …

Influence of Sodium on the Structure and HDS Activity of Co–Mo Catalysts Supported ON Silica and Aluminosilicate

2000

Abstract Structural changes and catalytic performances of hydrodesulfurization (HDS) Co–Mo catalysts, supported on amorphous aluminosilicate (ASA) and amorphous SiO 2 were investigated as a function of the amount of sodium ions added to the supports. The catalysts were prepared according to the incipient wet impregnation method using (NH 4 ) 6 Mo 7 O 24 as molybdenum precursor and CoCl 2 or Co(NO 3 ) 2 as cobalt precursor. Structural and morphological characterisations of the materials were performed with X-ray diffraction (XRD) and surface area measurements (BET). In the case of the ASA-supported catalysts, increasing the amount of sodium resulted in a gradual decrease of the catalyst surf…

Cross-Linked Polyamine from Imidazolium-Based Materials: A Simple Route to Useful Catalytic Materials

2018

Facile immobilization of copper(I) acetate on silica: A recyclable and reusable heterogeneous catalyst for azide–alkyne clickable cycloaddition react…

2019

Abstract The structurally well-defined copper(I) acetate was immobilized on silica gel via electrostatic interactions. The catalytic activity of the immobilized catalyst Cu(I)–SiO2 was examined in the click synthesis of 1,2,3-triazoles in water/ethanol at room temperature. The catalyst showed high catalytic activity and regioselectivity for the Huisgen [3+2] cycloaddition reaction between terminal alkynes and azides. The catalyst was recovered by simple filtration and reused for up to five times. The analysis of the local electrophilicity/nucleophilicity has been performed on the dinuclear copper–acetylide complex intermediate. Conceptual DFT (CDFT) analysis enabled the explanation of the f…

Synthesis and optimization of microwave-assisted exfoliated functionalized graphene as an efficient catalyst in biodiesel production

2018

In this study, the capability of functionalized graphene was investigated as heterogeneous catalyst in biodiesel production from vegetable oil. Graphene oxide was fabricated from graphite via carrier improved method, and its exfoliation was carried out by microwave radiation. The exfoliated sample was reduced and sulfonated, being analyzed by Fourier transform Infrared, Scanning Microscopy Transmission Electron Microscopy, X-ray diffraction and element mapping. The catalyst was employed in biodiesel production reaction and effective reaction parameters were studied. The optimized reaction temperature, time and catalyst percentage were 178 °C, 3 h and 1.9% respectively. It was observed that …

Hemicellulose hydrolysis catalysed by solid acids

2013

Depolymerising hemicellulose into platform sugar molecules is a key step in developing the concept of an integrated biorefinery. This reaction is traditionally catalysed by either enzymes or homogeneous mineral acids. We compared various solid catalysts for hemicellulose hydrolysis, running reactions in water, under neutral pH and relatively mild temperature and pressure (120°C and 10 bar) conditions. Sulphonated resins are highly active, but they leach out sulphonic groups. Sulphonated silicas are less active, but more stable. They have weakly and strongly bound sites and the strongly bound ones do not leach. Zeolites are moderately active and stable. Among them, H-ferrierite especially, d…