Towards uranium catalysts

Abstract

Researchers worldwide have identified a large number of compounds with high hydrogen capacity that can fulfill these gravimetric and volumetric requirements.Unfortunately, the majority of these compounds fail to fulfill the thermodynamic and kinetic requirements for on-board storage systems. Alane has the gravimetric (10.1 mass% H 2 ) and the volumetric (149 kg H 2 /m 3 ) density needed to meet the 2010 DOE goals. In addition, rapid hydrogen release from alane can be achieved using only the waste heat from a fuel cell or a hydrogen internal combustion engine. 9 The main drawback to using alane in hydrogen storage applications is unfavorable hydriding thermodynamics. The direct hydrogenation of aluminium to alane requires over 10 5 bars of hydrogen pressure at room temperature as shown in equation(1). This impractically of using high hydriding pressure has precluded alane from being considered as a reversible hydrogen storage material. The other possible electrochemical reaction is having AlH -4 ion react with the aluminium anode to form alane. In this reaction route, the evolution of hydrogen is suppressed and the reaction is expected to consume the Al electrode as in equation (5) Experimental observations confirm that the anode is indeed consumed as shown in voltage experiments were performed. During these experiments, the current was steady and increased slightly with time. The electrochemical production of alane is not slowed by the formation of AlH 3 . In contrast to previous reports, no perception of alane is observed and the alane produced by our method is completely dissolved in solution as a THF adduct. 17During electrolysis, dendritic material was deposited on the platinum counter electrode.This material was collected and determined to be Na 3 AlH 6 from XRD data.Experiments were conducted to determine the feasibility of plating sodium at the platinum cathode as an alternative to NaH formation in the fueling cycle. The platinum cathode and aluminium anode potentials were -2.89 V and -1.31 V respectively. Plating of Na metal was observed at the cathode while alane was produced at the aluminium anode.Reacting sodium with aluminium from used alane under pressurized hydrogen will regenerate the starting material NaAlH 4 leading to a reversible cycle.In addition to determining the electrochemical processes for producing AlH 3 , recovering AlH 3 from the solution is a major step of this cycle. The separation of alane from AlH 3 •Et 2 O is well established and affords pure AlH 3 . [10][11][12] However, separation of the AlH 3 •THF adduct is more complicated because it decomposes when heated under vacuum.Therefore, adducts such as triethylamine (TEA) were added to the reaction product to stabilize the alane during purification. Adduct free alane is recovered by heating the neat liquid AlH 3 •TEA en vacuo.Alane recovered from the electrochemical cells was characterized by powder X-ray diffraction, Raman spectroscopy, and thermal gravimetric analyzer (TGA). Powder X-ray diffraction patterns data for two different...

Cleaving Off Uranyl Oxygens through Chelation: A Mechanistic Study in the Gas Phase

“…[1][2][3][4][5] In spite of its apparent chemical inertness, UO 2 2+ has recently caught growing attention for the tantalizing prospect of activating its remarkably stable metal-oxygen double bonds. 6 Nevertheless, the activation and functionalization of UO 2 2+ still remain challenging and elusive. In the condensed phase, a few examples of apparent activation and functionalization of the highly stable U=O bonds have been proposed recently, with notably the reductive silylation and coordination by a Lewis acid such as B(C 6 F 5 ) 3 or an alkali metal.…”

Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials

“…The new generation of nuclear reactors is designed to supply more electricity than previous technologies, but produce radioactive waste, which must be safely handled. This provides motivation for scientists to study the fundamental and applied properties of actinide systems in connection with their synthesis [2][3] , oxidation 4 , corrosion 5 , reprocessing 6 and migration 7 , stability at extreme conditions [8][9] , environmental impact 10 and disposal of nuclear waste 11 . Obviously, the development of new and beneficial use of depleted uranium may extend the application beyond the nuclear industry [6][7]12 .…”

Reductive disproportionation of nitric oxide mediated by low-valent uranium

“…[1][2][3][4] Initial theoretical studies of the coordination of NO to U III complexes suggested that distinct reaction pathways with NO are accessible to uranium and the early actinides, based on their oxophilicity and low-reduction potentials. 5 In light of both long-standing and recent evidence that uranium can be an efficient catalyst for important small molecule reactions, such as N 2 , CO 2 , and H 2 O reduction, [6][7][8][9][10][11][12] the potential complementary reactivity of uranium with NO may offer unique solutions for NO reduction. However, the investigation of low-valent early actinide reductive disproportionation of NO has been limited by the lack of appropriate coordination chemistry to isolate the reaction products and to identify the relevant redox chemistry of the actinides with NO.…”