Search results for " Heterogeneous Catalysis"
showing 10 items of 23 documents
Bismuth-Catalyzed Growth of SnS2 Nanotubes and Their Stability
2009
Interesterification of rapeseed oil catalysed by a low surface area tin (II) oxide heterogeneous catalyst
2018
Abstract The interesterification of rapeseed oil was performed in a batch reactor using for the first time low surface area massive tin(II) oxide as heterogeneous catalyst and methyl acetate as acyl acceptor. The effect of reaction temperature, methyl acetate to oil molar ratio and catalyst loading on the performances of the process were investigated. Yields in fatty acid methyl esters (FAMEs) and triacetin (TA) up to 90% and 70% respectively, were achieved after 4 h of reaction time at 483 K in the presence of 0.69 mol of SnO per mole of rapeseed oil using a methyl acetate to oil molar ratio of 40. Quite interestingly, the catalyst performances improved when water was added to the reaction…
Heterogeneous vs Homogeneous Palladium Catalysts for Cross-Coupling Reactions
2012
A large number of immobilized-Pd-catalysts for cross-coupling reactions have been introduced in the last decade. Are the observed catalyzed reactions truly heterogeneous or are they homogeneous due to leached palladium? This account critically addresses the leaching issue by selectively referring to some of the newly developed catalytic systems in an attempt to evaluate said systems based on uniform criteria. The report is concluded by identifying the relevant chemical and structural challenges in the field.
Heterogeneously catalyzed Suzuki-Miyaura conversion of broad scope
2012
The reaction tolerates a broad range of functional groups in the coupling partners and is usually performed in solution under homogeneous conditions at T ¢ 60 uC using 2–3 mol% catalytic amounts. The catalyst is often a Pd(0) complex with triarylphosphane ligands. 2 The catalytic cycle (Scheme 2) begins with the oxidative addition of an aryl halide to a Pd(0) species formed in situ to form an arylpalladium(II) halide intermediate. 3 Chloroarenes, especially nonactivated aryl chlorides, are notoriously less reactive due to the stability of the C–Cl bond (the relative reactivity of Ar–X is correlated to the respective bond dissociation energy: Ph–Cl: 96 kcal mol 21 ,P h–Br: 81 kcal mol 21 ,P …
Multifunctional halloysite and hectorite catalysts for effective transformation of biomass to biodiesel
2023
Halloysite surface was modified with tetrabutylammonium iodide, and then the obtained nanomaterial was used as support for ZnO nanoparticles. After characterization, the nanomaterial was used as a catalyst for fatty acid methyl esters (FAMEs) production. The recyclability of the nanomaterial was also investigated, and the optimization of reaction conditions by the design of experiments approach was performed as well. In addition, the synthesized nanomaterial was tested as a catalyst for FAME production from a series of waste lipids affording biodiesel in moderate to good yields (35–95%), depending on the matrix. To fully exploit the feasibility of clay minerals as catalysts in biodiesel for…
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 …
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…
Advances in organic and organic-inorganic hybrid polymeric supports for catalytic applications
2016
In this review, the most recent advances (2014–2016) on the synthesis of new polymer-supported catalysts are reported, focusing the attention on the synthetic strategies developed for their preparation. The polymer-supported catalysts examined will be organic-based polymers and organic-inorganic hybrids and will include, among others, polystyrenes, poly-ionic liquids, chiral ionic polymers, dendrimers, carbon nanotubes, as well as silica and halloysite-based catalysts. Selected examples will show the synthesis and application in the field of organocatalysis and metal-based catalysis both for non-asymmetric and asymmetric transformations.
Single-Walled Carbon Nanotube–Polyamidoamine Dendrimer Hybrids for Heterogeneous Catalysis
2016
We report the synthesis and catalytic properties of single-walled carbon nanotube-polyamidoamine dendrimers hybrids (SWCNT-PAMAM), prepared via a convergent strategy. The direct reaction of cystamine-based PAMAM dendrimers (generations 2.5 and 3.0) with pristine SWCNTs in refluxing toluene, followed by immobilization and reduction of [PdCl4](2-), led to the formation of highly dispersed small palladium nanoparticles homogeneously confined throughout the nanotube length. One of these functional materials proved to be an efficient catalyst in Suzuki and Heck reactions, able to promote the above processes down to 0.002 mol % showing a turnover number (TON) of 48 000 and a turnover frequency (T…
Controlling the molecular diffusion in MOFs with the acidity of monocarboxylate modulators.
2021
The catalytic performance of metal-organic frameworks (MOFs) is related to their physicochemical properties, such as particle size, defect-chemistry and porosity, which synthetic control can be potentially achieved by coordination modulation. By combining PXRD, 1HNMR, FT-IR, N2 uptake measurements we have found insights that the different types of defects (missing linker or missing clusters consequence of the spatial distribution of missing linkers, and the combination of both) could be controlled by the type of modulator employed. We show that the molar percent of defects, either as missing linkers or as part of missing cluster defects, is related to the modulator’s acidity and subse…