There have been numerous efforts to incorporate dioxygen into chemical processes because of its economic and environmental benefits. The conversion of dioxygen to water is one such example, having importance in both biology and fuel cell technology. Metals or metal complexes are usually necessary to promote this type of reaction and several systems have been reported. However, mechanistic insights into this conversion are still lacking, especially the detection of intermediates. Reported herein is the first example of a monomeric manganese(II) complex that can catalytically convert dioxygen to water. The complex contains a tripodal ligand with two urea groups and one carboxyamidopyridyl unit—this ligand creates an intramolecular hydrogen-bonding network within the secondary coordination sphere that aids in the observed chemistry. The manganese(II) complex is five-coordinate with an N4O primary coordination sphere; the oxygen donor comes from the deprotonated carboxyamido moiety. Two key intermediates were detected and characterized: a peroxo-manganese(III) species (1). The formulation of 1 was based on spectroscopic and analytical data, including an X-ray diffraction analysis. Reactivity studies showed dioxygen was catalytically converted to water in the presence of reductants, such as diphenylhydrazine and hydrazine. Water was confirmed as a product in greater than 90% yield. A mechanism was proposed that is consistent with the spectroscopy and product distribution, in which the carboxyamido group switches between a coordinated ligand and a basic site to scavenge protons produced during the catalytic cycle. These results highlight the importance of incorporating intramolecular functional groups within the secondary coordination sphere of metal-containing catalysts.

The Pacific Northwest National Laboratory (PNNL) is evaluating the performance of adsorption materials to extract uranium from natural seawater. Testing consists of measurements of the adsorption of uranium and other elements from seawater as a function of time using flow-through columns and a recirculating flume to determine adsorbent capacity and adsorption kinetics. The amidoxime-based polymer adsorbent AF1, produced by Oak Ridge National Laboratory (ORNL), had a 56-day adsorption capacity of 3.9 ± 0.2 g U/kg adsorbent material, a saturation capacity of 5.4 ± 0.2 g U/kg adsorbent material, and a half-saturation time of 23 ± 2 days. The ORNL AF1 adsorbent has a very high affinity for uranium, as evidenced by a 56-day distribution coefficient between adsorbent and solution of log KD,56day = 6.08. Calcium and magnesium account for a majority of the cations adsorbed by the ORNL amidoxime-based adsorbents (61% by mass and 74% by molar percent), uranium is the fourth most abundant element adsorbed by mass and seventh most abundant by molar percentage. Marine testing at Woods Hole Oceanographic Institution with the ORNL AF1 adsorbent produced adsorption capacities 15% and 55% higher than those observed at PNNL for column and flume testing, respectively. Variations in competing ions may be the explanation for the regional differences. Hydrodynamic modeling predicts that a farm of adsorbent materials will likely have minimal effect on ocean currents and removal of uranium and other elements from seawater when farm densities are <1800 braids/km2. A decrease in uranium adsorption capacity of up to 30% was observed after 42 days of exposure because of biofouling when the ORNL braided adsorbent AI8 was exposed to raw seawater in a flume in the presence of light. No toxicity was observed with flow-through column effluents of any absorbent materials tested to date. Toxicity could be induced with some non-amidoxime based absorbents only when the ratio of solid absorbent to test media was increased to part per thousand levels. Thermodynamic modeling of the seawater−amidoxime adsorbent was performed using the geochemical modeling program PHREEQC. Modeling of the binding of Ca, Mg, Fe, Ni, Cu, U, and V reveal that when binding sites are limited (1 × 10–8 binding sites/kg seawater), vanadium heavily outcompetes other ions for the amidoxime sites. In contrast, when binding sites are abundant, Mg and Ca dominate the total percentage of metals bound to the sorbent.

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Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in Marginal Abatement Cost Curves in General Equilibrium: The Influence of World Energy Prices SummaryMarginal abatement cost curves (MACCs) are one of the favorite instruments to analyze the impacts of the implementation of the Kyoto Protocol and emissions trading. As shown in this paper one important factor that influences MACCs are energy prices. This leads to the question of how to define MACCs in a general equilibrium context where the overall abatement level world wide influences energy prices and thus national MACCs. We first discuss the mechanisms theoretically and then use the CGE model DART to quantify the effects. The result is, that changes in energy prices resulting from different world wide abatement levels do indeed affect the national MACCs. Also, we compare different possibilities of defining MACCs -of which some turn out to be robust against changes in energy prices while others vary considerably.

A cap-and-trade system is a market-based approach to controlling pollution/emissions where the regulating authority sets an overall emissions cap, or limit. This cap is divided into allowances, which give the holder the right to emit one unit of emissions (e.g., 1 ton of carbon dioxide), and distributed among the market participants. Allowances can be traded freely, and every market participant is required to surrender one allowance per unit of verified emissions.

A non-oxido V(v) complex with glutaroimide-dioxime (H3L), a ligand for recovering uranium from seawater, was synthesized from aqueous solution as Na[V(L)2]·2H2O, and the structure determined by X-ray diffraction.

In this paper we empirically investigate potential determinants of allowance (EUA) price dynamics in the European Union Emission Trading Scheme (EU ETS) during Phase II. In contrast to previous papers, we analyze a significantly longer time series, place particular emphasis on the importance of price variable selection, and include an extensive data of renewable energy feed-in in Europe. We show (i) that results are extremely sensitive to choosing different price series of potential determinants, such as coal and gas prices, (ii) that EUA price dynamics are only marginally influenced by renewable energy provision in Europe, and iii) that EUA prices currently do not reflect marginal abatement costs across Europe. We conclude that the expectation of a more mature allowance market in Phase II cannot be confirmed. In this paper we empirically investigate potential determinants of allowance (EUA) price dynamics in the European Union Emission Trading Scheme (EU ETS) during Phase II. In contrast to previous papers, we analyze a significantly longer time series, place particular emphasis on the importance of price variable selection, and include an extensive data of renewable energy feed-in in Europe. We show (i) that results are extremely sensitive to choosing different price series of potential determinants, such as coal and gas prices, (ii) that EUA price dynamics are only marginally influenced by renewable energy provision in Europe, and iii) that EUA prices currently do not reflect marginal abatement costs across Europe. We conclude that the expectation of a more mature allowance market in Phase II cannot be confirmed.

Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Abstract: In the past years biofuels have received increased attention since they were believed to contribute to rural development, energy security and to fight global warming. It became also clear, though, that bioenergy cannot be evaluated independently of the rest of the economy and that national and international feedback effects are important. Computable general equilibrium (CGE) models have been widely employed in order to study the effects of international climate policies. The main characteristic of these models is their encompassing scope: Global models cover the whole world economy disaggregated into regions and countries as well as diverse sectors of economic activity. Such a modelling framework unveils direct and indirect feedback effects of certain policies or shocks across sectors and countries. CGE models are thus well suited for the study of bioenergy/biofuel policies. One can currently find various approaches in the literature of incorporating bioenergy into a CGE framework. This paper intends to give an overview of existing approaches and to critically assess their respective power. Grouping different approaches into categories and highlighting their advantages and disadvantages is important for giving a structure to this rather recent and rapidly growing research area and to provide a guidepost for future work. Terms of use: Documents in EconStor may IntroductionIn the context of energy security and climate protection, bioenergy is ascribed high importance. Especially biofuels have received increased attention since they are able to replace fossil energy in the transport sector. They are therefore seen as a special option since the transport sector is contributing an increasing share to global carbon emissions and since other renewable energy sources usually only replace fossil fuels in the electricity sector (wind, hydro, photovoltaics) or in the provision of heat (wood pellets, geothermal energy, solar thermal energy). Currently, only Brazil is able to produce bioethanol from sugar cane at sufficiently low costs to be competitive with conventional fuels. But for the reasons just explained, bioenergy and biofuels are part of several climate and energy policy packages in several countries and supported by quotas, tax exemptions or direct production subsidies which has resulted in a growing production and consumption of biofuels worldwide. Plans to further increase the use of bioenergy are already on the table. In Europe, the "Renewable...