Incarceration of Iodine in a Pyrene-Based Metal-Organic Framework

A pyrene-based metal-organic framework (MOF) SION-8 captured iodine (I-2) vapor with a capacity of 460 and 250 mg g(MOF)(-1) at room temperature and 75 degrees C, respectively. Single-crystal X-ray diffraction analysis and van-der-Waals-corrected density functional theory calculations confirmed the presence of I-2 molecules within the pores of SION-8 and their interaction with the pyrene-based ligands. The I-2-pyrene interactions in the I-2-loaded SION-8 led to a 10(4)-fold increase of its electrical conductivity compared to the bare SION-8. Upon adsorption, >= 95 % of I-2 molecules were incarcerated and could not be washed out, signifying the potential of SION-8 towards the permanent capture of radioactive I-2 at room temperature

First-principles study of the paths of the decomposition reaction of LiBH4

A clear description of the paths of thermal decomposition of complex borohydrides represents a crucial step forward to their utilisation as a reservoir of hydrogen and hence as materials for solid state hydrogen storage. We present in this work a theoretical study of the possible paths of decomposition of LiBH4 by means of density functional theory approach. Our first-principles calculations showed the possibility to form linear chains of tetraborate of lithium in the residue of decomposition, among other thermodynamically competitive reactions. Their analytical formula LiBHx agreed with the quantitative analysis already reported by Schlesinger and co-workers in the 1940s. The structure showed the formula unit Li4B4H10, and the analytical formula LiBH2.5, of which the Gibbs free energy of formation was -111.76 kJ mol-1. The lattice stability was confirmed by the phonon calculations, which revealed all positive normal modes. Comparatively, the formation of lithium dodecaborate(12) is presented and discussed. The calculated standard Gibbs free energy of the decomposition reactions considered in the present work were in the range (158,286) kJ mol-1 of LiBH4 decomposed. © 2010 Taylor and Francis

Synthesis Mechanism of Alkali Borohydrides by Heterolytic Diborane Splitting

Similar to alane in alanates, borane species are assumed to be the mass transport intermediate in the hydrogen storage reaction MH + B + 3/2H2 MBH4 with M = Li and Na. One possible substep of this reaction is the interaction of diborane with the alkali hydride. In this paper, we unravel the synthesis mechanism of alkali borohydrides by solid-gas reaction of alkali hydrides and diborane gas by H/D isotope labeling of the reaction educts (e.g., LiD + B2H 6). The labeling enables us to trace the hydrogen/deuterium atoms in the borohydride product by Raman scattering and in the gas by infrared spectrometry measurements. We conclude that, during the LiBH4 synthesis from LiH, the entire BH4- unit is transferred from the diborane to the Li+ cation. This provides clear evidence for the heterolytic splitting of diborane on alkali hydrides and implies exchange of BH4- with H- ions of the underlying hydride. The detection of Li-H bonds at the surface of newly formed LiBH4 confirms the importance of H- defects for the synthesis of borohydrides. © 2010 American Chemical Society

Renewable energy storage via CO2 and H-2 conversion to methane and methanol: Assessment for small scale applications

This study analyses the power to methane - and to methanol processes in the view of their efficiency in energy storage. A systematic investigation of the differences on the two production systems is performed. The energy storage potential of CO2 to methanol and methane is assessed in a progressive way, from the ideal case to the actual simulated process. In ideal conditions, where no additional energy is required for the reaction and CO2 is fully converted into products, energy storage is 8% more efficient in methanol than methane. However, the Sabatier reaction can be performed with a lower degree of complexity compared to the CO2 to methanol reaction. For this reason, the methanol production process is analysed in detail. The influence of the process configuration and the energy requirements for the various necessary unit operations is investigated, and an efficiency ranking among the various alternatives is obtained. Single stage, recycle and cascade reactors are compared and assessed in terms of energy requirements for the operation and energy storage in the product. For small scale applications, the cascade reactor is the most suitable process technology, because it does not require additional energy and allows high yield to methanol. With the current technology, we demonstrate that a hybrid process, including both the CO2 hydrogenation to methanol and methane, is the most effective method to achieve a high conversion of renewable energy to carbon-based fuels with a significant fraction of liquid product

Hydrogen: the future energy carrier

Since the beginning of the twenty-first century the limitations of the fossil age with regard to the continuing growth of energy demand, the peaking mining rate of oil, the growing impact of CO2 emissions on the environment and the dependency of the economy in the industrialized world on the availability of fossil fuels became very obvious. A major change in the energy economy from fossil energy carriers to renewable energy fluxes is necessary. The main challenge is to efficiently convert renewable energy into electricity and the storage of electricity or the production of a synthetic fuel. Hydrogen is produced from water by electricity through an electrolyser. The storage of hydrogen in its molecular or atomic form is a materials challenge. Some hydrides are known to exhibit a hydrogen density comparable to oil; however, these hydrides require a sophisticated storage system. The system energy density is significantly smaller than the energy density of fossil fuels. An interesting alternative to the direct storage of hydrogen are synthetic hydrocarbons produced from hydrogen and CO2 extracted from the atmosphere. They are CO2 neutral and stored like fossil fuels. Conventional combustion engines and turbines can be used in order to convert the stored energy into work and heat. © 2010 The Royal Society