Search results for "carbon"
showing 10 items of 6057 documents
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…
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…
From Mono- to Poly-Substituted Frameworks: A Way of Tuning the Acidic Character of C-c-H in o-Carborane Derivatives
2009
[EN] The incorporation of iodine atoms onto the boron vertices of the o-carborane framework causes, according to spectroscopic data, a uniform increase in the acidic character of the C-c-H (C-c= cluster carbon) vertices, whereas the incorporation of methyl groups onto the boron vertices of the o-carborane framework reduces their acidity. Methyl groups when attached to boron are electron-withdrawing in boron clusters, whereas iodine atoms bonded to boron act as electron donors. This has been proven on B-methyl and B-iodinated o-carboranes with NMR spectroscopy measurements and DFT calculations of natural bond orbital (NBO) charges. which show a Cumulative buildup of positive cluster only tot…
Reversible inhibition of CO2fixation by ribulose 1,5-bisphosphate carboxylase/oxygenase through the synergic effect of arsenite and a monothiol
2013
The activity of the photosynthetic carbon-fixing enzyme, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), is partially inhibited by arsenite in the millimolar concentration range. However, micromolar arsenite can fully inhibit Rubisco in the presence of a potentiating monothiol such as cysteine, cysteamine, 2-mercaptoethanol or N-acetylcysteine, but not glutathione. Arsenite reacts specifically with the vicinal Cys172-Cys192 from the large subunit of Rubisco and with the monothiol to establish a ternary complex, which is suggested to be a trithioarsenical. The stability of the complex is strongly dependent on the nature of the monothiol. Enzyme activity is fully recovered through …
Nature of cobalt active species in hydrodesulfurization catalysis: combined support and preparation method effects
2007
Abstract Co/γ-Al2O3, Co/SiO2, Co/MCM-41, Co/ASA and Co/S2 (amorphous aluminosilicate with Al/Si = 0.13 and with Al/Si ≈ 2, respectively) were prepared by the method of wet impregnation and by the method of precipitation in the presence of sodium carbonate. The samples were characterised by XPS, XRD and TPR. The catalytic activity was tested in the hydrodesulfurization of thiophene using a continuous flow reactor. Among the wet impregnated catalysts those supported on the amorphous and ordered mesoporous silica exhibited higher HDS activity as compared to the alumina containing supports. Particularly, the use of the mesoporous, high surface area MCM-41 support, determined the best performing…
Nitrous oxide emissions in a membrane bioreactor treating saline wastewater contaminated by hydrocarbons
2016
The joint effect of wastewater salinity and hydrocarbons on nitrous oxide emission was investigated. The membrane bioreactor pilot plant was operated with two phases: i. biomass acclimation by increasing salinity from 10 gNaCl L−1 to 20 gNaCl L−1 (Phase I); ii. hydrocarbons dosing at 20 mg L−1 with a constant salt concentration of 20 gNaCl L−1 (Phase II). The Phase I revealed a relationship between nitrous oxide emissions and salinity. During the end of the Phase I, the activity of nitrifiers started to recover, indicating a partial acclimatization. During the Phase II, the hydrocarbon shock induced a temporary inhibition of the biomass with the suppression of nitrous oxide emissions. The r…
Study by static SIMS, XPS and UPS of the adsorption of cyanogen on (100) Ni surfaces
2000
Abstract The interaction of cyanogen with (100) Ni surfaces at room temperature was studied using secondary ion mass spectrometry in a static mode, and photoemission spectroscopies (XPS and UPS). It has been shown that cyanogen is adsorbed on this nickel surface in a dissociative mode: atomic carbon and nitrogen are present on the surface as well as CN fragments. These adsorbed species have been characterized by XPS and UPS. Increasing the temperature in the 400 K range increases the rate of the dissociation reaction of CN into atomic carbon and nitrogen. Moreover carbon is found to dissolved into the bulk for temperatures as low as 475 K. No evidence has been found of a polymerized form of…
An unexpected ring carboxylation in the electrocarboxylation of aromatic ketones
2006
The electrocarboxylation of various aromatic ketones, carried out in N-methyl-2-pyrrolidone (NMP) in a diaphragmless cell equipped with a carbon cathode and an aluminium sacrificial anode, yielded, among the products, the target hydroxy acids, the corresponding alcohols and pinacols and, quite surprisingly, detectable amounts of substituted benzoic acids and cycloexene carboxylic acids. These compounds arise from a never reported before electrocarboxylation on the aromatic ring, respectively, for substitution of an aromatic hydrogen and from an addition reaction. For example, the electrocarboxylation of acetophenone gave rise to the substituted benzoic acids in ortho, para and meta position…
CO2 Fixation by Copper(II) Complexes of a Terpyridinophane Aza Receptor
2004
CO2 is fixed by a Cu2+ complex of a macrocyclic terpyridinophane ligand forming a carbamate group. Several features of the structure mimic the enzyme rubisco.
Promoting the activity and selectivity of high surface area Ni–Ce–O mixed oxides by gold deposition for VOC catalytic combustion
2011
Gold supported on nickel cerium oxide catalysts (Ni–Ce–O) have been studied for the total oxidation of propane, as a model for hydrocarbon volatile organic compound emission control. High surface area Ni–Ce–O catalysts were synthesized using a very simple evaporation method, where cerium and nickel salts were evaporated in the presence of a mixture of methanol and oxalic acid. Gold catalysts were prepared following a deposition–precipitation method. A very efficient catalyst for the oxidation of propane, in terms of both activity and selectivity, was obtained. This high activity has been related to the high surface area of the catalyst (and therefore to the presence of more active sites ava…