Search results for "Supported catalysts"
showing 10 items of 17 documents
Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenatio…
2020
[EN] A Nb-containing siliceous porous clay heterostructure (PCH) with Nb contents from 0 to 30 wt %) was prepared from a bentonite and used as support in the preparation of supported NiO catalysts with NiO loading from 15 to 80 wt %. Supports and NiO-containing catalysts were characterised by several physicochemical techniques and tested in the oxidative dehydrogenation (ODH) of ethane. The characterisation studies on Nb-containing supports showed the presence of well-anchored Nb(5+)species without the formation of Nb(2)O(5)crystals. High dispersion of nickel oxide with low crystallinity was observed for the Nb-containing PCH supports. In addition, when NiO is supported on these Nb-containi…
Hydrogenolysis of hydroxymatairesinol on Y derived catalysts: a computational study
2010
Hydrogenolysis of 7-hydroxymatairesinol (HMR) to matairesinol (MAT) occurs on palladium supported acidic catalysts. HMR has three stereochemical centres and naturally exists as a mixture of two diastereoisomers, namely RRR-HMR and SRR-HMR. The latter is significantly more reactive than the former, in the reaction above. In order to elucidate the hydrogenolysis mechanism, simple surface events involving HMR derivatives on aluminated faujasite (H-Y) fragments were simulated by quantum chemical calculations. The metallic function of a Pd/H-Y acidic catalyst was also mimicked by a minimal palladium cluster. Stereochemical evidences pointed already out that water β-elimination on the epimeric ce…
Carbons from second generation biomass as sustainable supports for catalytic systems
2018
In this study activated carbons were produced from the wood of three different wood species (pine, birch, spruce). The resulting activated carbons were characterized in bulk for ash content, carbon content (elemental analyses), specific surface area, and pore size distribution, and at the surface by measuring the autogenerated pH and studying their structure by XPS. All the samples presented high surface areas and appeared to be mesoporous materials (mesopores >80%). The carbons were then used as support for AuPt nanoparticles and tested in the liquid phase oxidation of glycerol (GLY) and in the hydrogenation of levulinic acid (LA), two important chemicals from cellulose-based biomass. The …
Recyclable Catalyst Reservoir: Oxidation of Alcohols Mediated by Noncovalently Supported Bis(imidazolium)-Tagged 2,2,6,6-Tetramethylpiperidine 1-Oxyl
2013
Bis(imidazolium)-tagged 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) catalysts were adsorbed on different supports such as silica gel, silica gel modified with highly cross-linked polymeric imidazolium networks, and highly cross-linked polymeric imidazolium networks entrapping magnetic particles. These systems provided a convenient tool for the oxidation of both primary and secondary alcohols working as recyclable reservoirs for the bis(imidazolium)-tagged TEMPO catalysts. By using EPR spectroscopy it was demonstrated that the catalyst was released as the corresponding oxoammonium salt in the solution during the recycling step, thus promoting the oxidative process in a homogeneous fashion. …
Sol–gel material as a support of organometallic catalyst for ethylene polymerization
2008
Abstract The sol–gel procedure was applied to obtain powdery materials with different structures and morphology. It was possible to produce almost non-porous silica powder, with an extremely low surface area (ca. 4 m 2 /g) and very high uniformity of spherical particles as well as materials with various uniformity of particles and different porosity, most likely associated with increasing pore volume. Dependent on the properties of the carrier, the resulting supported vanadium catalysts (VOCl 3 /AlEt 2 Cl) showed significant differences concerning activity and stability. It was confirmed that improved hydrophobicity of the carrier’s surface may be useful and improve the activity of the syst…
Effect of silica-type sol–gel carrier’s structure and morphology on a supported Ziegler–Natta catalyst for ethylene polymerization
2006
Abstract Silica xerogels with different structures and morphology, synthesized using a sol–gel procedure, were used as a carrier of vanadium catalysts (VOCl 3 /AlEt 2 Cl) for ethylene polymerization. Two techniques of catalyst synthesis were applied: slurry impregnation and gas-phase adsorption and the relevant polymerization methods were then employed. The effect of the carrier structure and morphology on the vanadium loading in the catalysts, the catalyst’s activity and kinetic stability were investigated.
Carbon dioxide conversion to dimethyl carbonate: The effect of silica as support for SnO2 and ZrO2 catalysts
2011
International audience; Abundant in nature, CO2 poses few health hazards and consequently is a promising alternative to phosgene feedstock according with the principles of Green Chemistry and Engineering. The synthesis organic carbonates from CO2 instead of phosgene is highly challenging as CO2 is much less reactive. As part of our ongoing research on the investigation of catalysts for dimethyl carbonate (DMC) synthesis from methanol and CO2, we herein report results aimed at comparing the catalytic behavior of new SnO2-based catalysts with that of ZrO2. Silica-supported SnO2 and ZrO2 exhibit turnover numbers which are an order of magnitude higher than those of the unsupported oxides. Tin-b…
New Hybrid Organic-inorganic Multifunctional Materials Based on Polydopamine-like Chemistry
2021
Taking inspiration from the chemistry of dopamine, a simple and economic synthetic approach toward the synthesis of a series of silica-based polydopamine-like materials has been developed. Mild conditions and easy manipulation are the strongest aspects of this methodology. Such hybrid materials were successfully used as recyclable catalysts for Knoevenagel reactions.
Highly Loaded Multi-Walled Carbon Nanotubes Non-Covalently Modified with a Bis-Imidazolium Salt and their Use as Catalyst Supports
2016
The surfaces of multi-walled carbon nanotubes (MWCNTs) were non-covalently modified using two bis-imidazolium dibromide derivatives having phenyl or pyrene groups. Due to the presence of the two pyrene groups the bis(pyren-1-ylmethylimidazolium) dibromide derivative was immobilised at a loading of about 15-16 wt %, whereas only <3 wt % of the phenyl derivative was immobilised. The presence of the two imidazolium cations helped the immobilisation of tetrachloropalladate ions after exchange with bromide ions. Tetrachloropalladate was used as pre-catalyst in several Suzuki-Miyaura carbon-carbon cross-coupling reactions in water or water/ethanol at 50 °C in only 0.1 mol % and compared with the …
Gas-phase hydrogenation of propionitrile on copper-lanthanide oxides
2009
Abstract The hydrogenation of propionitrile on copper-lanthanide oxide catalysts (2Cu·CeO 2 and 4Cu·Ln 2 O 3 (Ln = La, Pr, Nd)) was studied in the gas phase. The activity of the catalysts varies with the lanthanide in the order 2Cu·CeO 2 > 4Cu·Pr 2 O 3 > 4Cu·La 2 O 3 ≥ 4Cu·Nd 2 O 3 , while the activation energies varies in the opposite order, except for 2Cu·CeO 2 . The main product was the primary amine, n -propylamine. The formation of the unstable imine CH 3 CH 2 N CHCH 3 as a major product over 2Cu·CeO 2 seems to be consistent with the acidity of the catalyst. The catalysts were more selective than conventional copper impregnation catalysts, Cu (10 wt.%) on SiO 2 , La 2 O 3 or CeO 2 ,…