Search results for " Chemical engineering"
showing 10 items of 2965 documents
On the Complexation of Cu(II) and Cd(II) With Polycarboxyl Ligands. Potentiometric Studies With ISE-H+, ISE-Cu2+, and ISE-Cd2+
2009
The interaction of Cu2+ and Cd2+ ions with polyacrylates (PAA, 2 kDa and 100 kDa), polymetacrylate(PMA, 5.4 kDa), and alginate (AA, 70 kDa to 100 kDa) was studied by potentiometry, using ISE-Cu2+, ISE-Cd2+, and ISE-H+ electrodes. The investigations were performed in NaNO3 aqueous solutions, in the ionic strength range 0.10 e I (mol ·L-1) e 0.75, at T ) 298.15 K. The “diprotic-like model” was used to explain the acid-base behavior of the polycarboxylates under investigation (for this model, the monomeric unit of the polyelectrolyte is considered as a dicarboxylate). The results give evidence for the formation of the ML species in all the systems investigated. In addition, the MLH species was…
Dual stereocontrolled alkylation of aldehydes with polystyrene-supported nickel complexes derived from α-amino amides
2015
Nickel(II) complexes derived from α-amino amide ligands anchored to gel-type and monolithic polymers act as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes. Similar to the analogous homogeneous systems, dual stereocontrol in addition products can be achieved by controlling the stoichiometry of the immobilized nickel complex. Aromatic and aliphatic aldehydes were alkylated in good yields with enantioselectivities comparable to those obtained with the homogeneous analogues. These polymer-supported catalysts offer significant advantages as no metal leaching is observed and they can be easily recovered from the reaction mixture by simple filtration and…
The different catalytic behaviour in the propane total oxidation of cobalt and manganese oxides prepared by a wet combustion procedure
2013
Abstract Cobalt oxide and manganese oxide catalysts have been prepared through aqueous synthesis using a wet combustion procedure. These materials have been tested as catalysts for the total oxidation of propane. It has been observed a different catalytic behaviour between cobalt and manganese oxides although for both oxides a very high catalytic activity has been obtained. Cobalt oxides prepared by the wet combustion procedure are less reactive than a simple cobalt oxide prepared without the addition of organic acids. However, in the case of manganese oxide the use of organic acids highly increases the catalytic activity. The different catalytic behaviour has been related to the variation …
A step forward in the development of superoxide dismutase mimetic nanozymes: the effect of the charge of the surface on antioxidant activity
2019
Two binucleating hezaaza macrocycles containing a pyridinol spacer have been prepared and characterised. Protonation studies indicate the deprotonation of the phenol group at relatively low pH values with the concomitant occurrence of a keto-enolic equilibrium. These ligands readily form binuclear Cu2+ and Zn2+ complexes as denoted by potentiometric and spectroscopic studies. The binding of the metals yields to the ready deprotonation of the phenol with the stabilisation of the keto form that results in complexes of greater stabilities than the analogous ones containing pyridine as spacer instead of pyridine. Mixed Cu2+–Zn2+-complexes were also detected in aqueous solutions containing equim…
Removal of Fe(III) from synthetic wastewater into raw and modified clay: Experiments and models fitting
2017
Water pollution by heavy metal ions has become a serious environmental issue especially due to their toxicity and tendency to bioaccumulation. Natural smectite clay was treated using sulfuric acid ...
Enhanced Heterogeneous Catalytic Conversion of Furfuryl Alcohol into Butyl Levulinate
2014
We study the catalytic condensation of furfuryl alcohol with 1-butanol to butyl levulinate. A screening of several commercial and as-synthesized solid acid catalysts shows that propylsulfonic acid-functionalized mesoporous silica outperforms the state-of-the-art phosphotungstate acid catalysts. The catalyst is prepared via template-assisted sol-gel polycondensation of TEOS and MPTMS. It gives 96 % yield (and 100 % selectivity) of butyl levulinate in 4h at 110 °C. Reaction profiles before and after a hot filtration test confirm that the active catalytic species do not leach into the solution. The catalyst synthesis, characterization, and mode of operation are presented and discussed. Sour ca…
The reduction of molecular oxygen by iron porphyrins
2002
Abstract Molecular assemblies have been synthesised to reproduce the structure of the cytochrome c oxidase (C c O) active site and to explore the roles played by its different features. It was discovered that a single iron porphyrin, adsorbed at the surface of a graphite electrode, is a selective catalyst for the four-electron reduction of dioxygen to water, at pH 7. To cite this article: D. Ricard et al., C. R. Chimie 5 (2002) 33–36
Oxidative dehydrogenation of ethane: A study over the structure and robustness of Ni–W–O catalysts
2014
[EN] The robustness of one selected Ni-W-O catalyst has been studied in the oxidative dehydrogenation of ethane. This catalyst initially deactivates for the first 10 h online decreasing 15% of its catalytic activity compared to its initial stable catalytic activity. However from 10 to 60 h online the catalytic activity keeps almost stable. On the other hand, it has been shown that the Ni-W-O catalyst cannot tolerate an oxygen-free atmosphere (C-2 and He) as nickel oxide is transformed into metallic nickel. Methane and hydrogen as well as abundant coke were formed on the surface of the catalyst in these O-free conditions. However a re-calcination in air leads to the removal of coke, the cata…
AlTf-UVM-7—Highly active catalysts for the synthesis of long chain symmetrical ethers and non-ionic surfactant structures
2010
New Lewis acid AlTf-UVM-7 catalysts with bimodal pore system and different Si to Al ratios were prepared in a two-step synthesis in which triflic acid (Tf) was incorporated into previously synthesized mesoporous aluminum-containing silica. The Al incorporation inside the pore walls was carried out through the Atrane method. The characterization of the resulted catalysts showed that the triflic acid treatment step did not damage the texture or the structure of the catalysts. These materials were used as green catalysts for the etherification of fatty alcohols and the conversion of ethylene glycol (EG) with n-octanol resulting in mixtures of short ethoxylated structures with a large distribut…
Porous clays heterostructures as supports of iron oxide for environmental catalysis
2018
[EN] Porous Clays Heterostructures (PCH) from natural pillared clays (bentonite with a high proportion of montmorillonite) have been used as supports of iron oxide for two reactions of environmental interest: i) the elimination of toluene (a representative compound of one of the most toxic subsets of volatile organic compounds, aromatics) by total oxidation and ii) the selective oxidation of H2S to elemental sulfur. For both reactions these catalysts have resulted to be remarkably more efficient than similar catalysts prepared using conventional silica as a support. Thus, in the total oxidation of toluene it has been observed that the catalytic activity obtained using siliceous PCH is two o…