Search results for " carbonate"
showing 10 items of 381 documents
The influence of water and of alkali promotor on the carbon number distribution of fischer-tropsch products formed over iron catalysts
1987
The carbon number distribution of Fischer-Tropsch products formed over an alkalized precipitated iron catalyst has been studied as a function of the water vapor pressure of the synthesis gas. The carbon number distribution of formed hydrocarbons is characterized by a bimodal Schulz-Flory distribution of growth probabilities P1 ≈ 0.6 and P2 ≈ 0.87 attributed to unpromoted and promoted (alkalized) sites on the catalyst surface. Promoted sites are more stable with respect to oxidation (deactivation) by water than unpromoted sites. The growth probability of unpromoted sites decreases with increasing ratio P/P — Studies using Mossbauer spectroscopy have shown that iron foils treated with water c…
Asymmetric Hydrogenation of Nonfunctionalized Olefins in Propylene Carbonate—Kinetic or Thermodynamic Control?
2011
Iridium-catalyzed hydrogenations of nonfunctionalized olefins in propylene carbonate as the solvent allow efficient catalysis with much higher enantioselectivities in comparison with dichloromethane which is usually employed for these reactions. Experimental and computational studies of the hydrogenation of 1-methylene-1,2,3,4-tetrahydronaphthalene have been performed to understand the limitation for this reaction.
Snapshots of calcium carbonate formation – a step by step analysis
2017
Abstract Recent advances in our understanding of CaCO3 nucleation from solution have provoked new and challenging questions. We have studied CaCO3 formation using precipitation by carbonate ester hydrolysis which ensures precipitation from a strictly homogeneous solution state and allows “titrating” carbonate to a solution with a given Ca2+ concentration on a timescale suited for kinetic studies. Nucleation and crystallization were traced by combining dynamic light scattering (DLS) and transmission electron microscopy (TEM). DLS served as in situ technique to identify the nucleation time, to monitor particle size evolution, to discriminate different precipitation mechanisms and to validate …
The role of distannoxanes in the synthesis of dimethyl carbonate from carbon dioxide
2003
Abstract The synthesis, characterization, and reactivity of 1,3-dimethoxytetrabutyldistannoxane were investigated in connection to the mechanism of the selective synthesis of dimethyl carbonate from CO2 and methanol. A new distannoxane, 1-methoxy-3-methylcarbonatotetrabutyldistannoxane, resulting from a 1:1 adduct with CO2 was isolated and characterised by volumetry, multinuclear NMR and IR spectroscopies. When this compound was submitted to 20 MPa of CO2 at 423 K in toluene no dimethyl carbonate was formed, conversely to dibutyldimethoxystannane. However, when methanol was the solvent, dimethyl carbonate was selectively produced. A promoting effect of Si(OCH3)4 was evidenced through methox…
Cr(VI)/Cr(III) and As(V)/As(III) Ratio Assessments in Jordanian Spent Oil Shale Produced by Aerobic Combustion and Anaerobic Pyrolysis
2011
With the increase in the awareness of the public in the environmental impact of oil shale utilization, it is of interest to reveal the mobility of potentially toxic trace elements in spent oil shale. Therefore, the Cr and As oxidation state in a representative Jordanian oil shale sample from the El-Lajjoun area were investigated upon different lab-scale furnace treatments. The anaerobic pyrolysis was performed in a retort flushed by nitrogen gas at temperatures in between 600 and 800 °C (pyrolytic oil shale, POS). The aerobic combustion was simply performed in porcelain cups heated in a muffle furnace for 4 h at temperatures in between 700 and 1000 °C (burned oil shale, BOS). The high loss-…
Tratamiento psicofarmacológico del trastorno bipolar en América Latina
2011
Objective: This study assessed the treatment preferences among Latin-American psychiatrists for their bipolar disorder patients and if these preferences reflect the current guidelines. Methods: We designed a survey comprised of fourteen questions. All the questions were aimed at the treatment of bipolar I patients only. We distributed the survey by hand or e-mail to psychiatrists in eight different countries: Argentina, Brasil, Colombia, Costa Rica, Ecuador, México, Perú and Venezuela. Between May 2008 and June 2009, we were able to gather 1143 surveys. Results: As the initial choice of treatment for a bipolar patient who debuts with mania, 61.3% choose a combination of an atypical antipsyc…
A Km-scale Cretaceous slope in western Sicily (Italy)
2017
Cretaceous slopes are well known from many regions of the world, since they are among the most prone depositional systems to host hydrocarbons. As far as Italy, in spite of fully described examples as the Majella and Gargano escarpments, detailed sedimentological and biostratigraphic studies from Sicily are not available, although the presence of slope carbonates of Cretaceous age in northwestern Sicily, is mentioned in several papers dealing with regional geology or geological mapping. The Cretaceous slope carbonates from this area, i.e. the San Vito Lo Capo Peninsula, belong to several thrust sheets of the Maghrebian chain. The stratigraphic setting in these tectonic units allows to recon…
Biomineralisations in crustaceans: storage strategies
2004
Abstract Crustaceans are a remarkable group of animals because of their ability to elaborate cyclically two kinds of calcified biomineralisations: an unstretchable exoskeleton (or cuticle) and also, for many species, depending of the way of life of the considered animal, transitory calcium deposits. They are in consequence subjected to a cyclic life and notably, to a periodical balance between two sources of calcium, exogenous and/or endogenous. The storage structures, essentially composed of calcium carbonate precipitated within a proteinaceous organic matrix, are very diversified. The calcium carbonate of the cuticle of most of the species is under a crystalline state and/or an amorphous …
POSS-Al-porphyrin-imidazolium cross-linked network as catalytic bifunctional platform for the conversion of CO2 with epoxides
2023
Two heterogeneous catalysts were prepared with the aim of following the promising path of CO2 fixation into epoxides. The synthetic procedure involves a radical copolymerization of an octavinylsilsesquioxane as inorganic core building block and tetrastyrylporphyrin aluminum chloride monomer (TSP-AlCl) in presence (POSS-TSP-AlCl-imiBr) or in absence (POSS-TSP-AlCl) of a bis-vinylimidazolium bromide salt (bis-imiBr), in order to investigate if the bifunctional heterogeneous material can display better catalytic performance than the separate species. All the solids were fully characterized and tested in the synthesis of cyclic carbonates starting from CO2 and several epoxides. The synergic coo…
Oleochemical carbonates: A comprehensive characterization of an emerging class of organic compounds
2022
Dialkyl carbonates (DAC) with short-medium alkyl length - oleochemical carbonates – are attracting attention because of their appealing properties, including low viscosity, flammability, toxicity, environ- mental impact and wide range of applications: lubricants, personal care, fuel additives etc. However, not much is known concerning their chemical physical properties and, more importantly, on the nature of microscopic correlations that eventually determine bulk performances. In view of this paucity, we pre- sent a large exploration of a series of chemical physical properties of a set of DACs ranging from dimethyl up to didodecyl carbonate. This study extends previously determined database…