Search results for " carbonate"

Using natural analogues to investigate the effects of climate change and ocean acidification on Northern ecosystems

2018

AbstractNorthern oceans are in a state of rapid transition. Still, our knowledge of the likely effects of climate change and ocean acidification on key species in the food web, functionally important habitats and the structure of Arctic and sub-Arctic ecosystems is limited and based mainly on short-term laboratory studies on single species. This review discusses how tropical and temperate natural analogues of carbonate chemistry drivers, such as CO2 vents, have been used to further our knowledge of the sensitivity of biological systems to predicted climate change, and thus assess the capacity of different species to show long-term acclimation and adaptation to elevated levels of pCO2. Natur…

Ca-rich carbonates associated with ultrabasic-ultramafic melts. Carbonatite or limestone xenoliths? A case study from the late Miocene Morron de Vill…

2016

The volcanic products of the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain) are known for being one of the few outcrops of leucitites in the entire circum-Mediterranean area. These rocks are important because aragonite of mantle origin has been reported as inclusion in olivine macrocrysts. We use petrographic observations, mineral compositions, as well as oxygen and carbon isotope ratios coupled with experimental petrology to understand the origin of carbonate phase in these olivine-phyric rocks. Groundmass and macrocryst olivines range from δ18OVSMOW of +4.8‰, typical of mantle olivine values, to +7.4‰, indicating contamination by sedimentary carbonate.…

Biomineralizations: insights and prospects from crustaceans.

2011

19 pages; International audience; For growing, crustaceans have to molt cyclically because of the presence of a rigid exoskeleton. Most of the crustaceans harden their cuticle not only by sclerotization, like all the arthropods, but also by calcification. All the physiology of crustaceans, including the calcification process, is then linked to molting cycles. This means for these animals to find regularly a source of calcium ions quickly available just after ecdysis. The sources of calcium used are diverse, ranging from the environment where the animals live to endogenous calcium deposits cyclically elaborated by some of them. As a result, crustaceans are submitted to an important and energ…

Biomineralization events in Recent volcanic and sedimentary settings: textural features and isotope signatures.

2008

Synthesis of recent stratigraphic data on bathonian to oxfordian deposits of the eastern Paris basin

2007

International audience

Probable root structures and associated trace fossils from the Lower Pleistocene calcarenites of favignana island, southern italy: dilemmas of interp…

2012

Two types of large, branched structures from the Lower Pleistocene (Calabrian) high-energy calcarenites of Favignana Island are described: Faviradixus robustus gen. et sp. nov. and Egadiradixus rectibrachiatus gen. et sp. nov. They may be interpreted as root structures of large plants, trees and trees or shrubs, respectively. The former taxon co-occurs with the marine animal trace fossils Ophiomorpha nodosa , Ophiomorpha isp., Thalassinoides isp. and Beaconites isp. The interpretation as root structures although tentative is probable and can be related to short emergence episodes for the formation of E . rectibrachiatus or to longer emergence, responsible for the discontinuity at the base o…

Direct electrochemical generation of organic carbonates by dehydrogenative coupling.

2018

Organic carbonates are an important source for polycarbonate synthesis. However, their synthesis generally requires phosgene, sophisticated catalysts, harsh reaction conditions, or other highly reactive chemicals. We present the first direct electrochemical generation of mesityl methyl carbonate by C–H activation. Although this reaction pathway is still challenging concerning scope and efficiency, it outlines a new strategy for carbonate generation.

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…

Design of POSS-Imidazolium Supported Hybrids for the Conversion of Carbon Dioxide into Cyclic Carbonates

2018

Nowadays, the design of heterogeneous catalysts for the conversion of CO2 into useful chemical products is attracting the attention of the scientific community. The catalytic processes involving carbon dioxide as C1 feedstock are of growing interest for the sustainable development.1 The synthesis of cyclic carbonates by coupling CO2 with epoxides is one of the most interesting pathways for the conversion of carbon dioxide in terms of both atom economy and final products applications. Moreover, ionic liquids emerged as one of the most active catalysts for the production of cyclic carbonates starting from CO2 and epoxides.2 Herein, a series of heterogeneous catalytic systems bearing imidazoli…

Imidazolium Based Cross-Linked Nanostructures from POSS molecular bricks for the Efficient Conversion of Carbon Dioxide

2019

Polyhedral oligomeric silsesquioxanes (POSS) have been employed as molecular bricks for the synthesis of imidazolium cross-linked networks as heterogeneous catalyst for the conversion of carbon dioxide into cyclic carbonates via reaction with epoxides. Two hybrid materials with different nucleophilic species (bromide and iodide) have been prepared and characterized by means of elemental analysis, 13C and 29Si solid state NMR, thermogravimetric analysis and IR spectroscopy. The solids were tested as the sole catalyst under metal- and solvent-free reaction conditions showing full selectivity toward the formation of cyclic carbonates and outstanding productivity values. Several epoxides were r…