A Viable Hydrogen Storage and Release System Based on Cesium Formate and Bicarbonate Salts: Mechanistic Insights into the Hydrogen Release Step

Aqueous solutions of cesium formate and bicarbonate repre- sent an effective hydrogen storage–delivery couple that under- goes either release or take up of hydrogen in the presence of {RuCl2(mTPPTS)2}2 (TPPTS = triphenylphosphine trisulfonate) and excess mTPPTS ligand, with no other additives required. Cesium salt solutions offer the advantage of improved volu- metric and gravimetric H2 density compared to their sodium and potassium analogs, owing to their high water solubility. Details of the equilibrium between formate and bicarbonate, which constitutes an important parameter for the applicability of this H storage/release cycle, were determined. H production is readily tunable by controlling the operating pressure. This behavior was also rationalized through the identification of catalytic intermediates under various conditions. High con- centration formate and bicarbonate solutions were used during the tests and the bidirectional catalytic system could be recycled without loss of activity or replacement of solvent. A tentative mechanism is proposed for the formate dehydrogen- ation step. Among the identified hydride species, the penta- coordinated [RuH(H2O)(TPPTS)3] complex was indispensable for promoting the formate dehydrogenation reaction

High-pressure NMR spectroscopy: An in situ tool to study tin-catalyzed synthesis of organic carbonates from carbon dioxide and alcohols. Part 2 [1]

Dialkoxide diorganotin(IV) complexes are known to readily react with carbon dioxide under pressure and they are considered as suitable catalyst precursor models for the direct synthesis of organic carbonates. To gain a better understanding of CO2 insertion processes with Sn-OR bonds, the reactivity of n-Bu2Sn(OCH(CH3)(2))(2) (2) was investigated using high-pressure NMR (HP-NMR) spectroscopy. In deuterated solvents (isopropanol-d(8) and toluene-d(8)) under 50 bar of CO2 pressure at 80 degrees C, Sn-119{H-1} NMR experiments revealed the exclusive formation of an unprecedented tetraorganodistannoxane species, characterized as the bis[diisopropycarbonatotetrabutyldistannoxane] complex, {[n-Bu2Sn(OC(O)OCH(CH3)(2))(2)](2)O}(2) {7}(2). The formation of hemicarbonato ligands resulting from CO2 insertion was also confirmed by FT-IR and C-13 NMR spectroscopies. To the best of our knowledge, spectroscopic detection of the distannoxane species 7 is unprecedented. (C) 2015 Elsevier B.V. All rights reserved

Quantitative aqueous phase formic acid dehydrogenation using iron(II) based catalysts

We present here the results of our investigation on aqueous phase formic acid (FA) dehydrogenation using non-noble metal based pre-catalysts. This required the synthesis of m-trisulfonated-tris[2-(diphe nylphosphino)ethyl]phosphine sodium salt (PP3TS) as a water soluble polydentate ligand. New catalysts, particularly those with iron(II), were formed in situ and produced H2 and CO2 from aqueous FA solutions, requiring no organic co-solvents, bases or any additives. Manometry, multinuclear NMR and FT-IR tech- niques were used to follow the dehydrogenation reactions, calculate kinetic parameters, and analyze the gas mixtures for purity. The catalysts are entirely selective and the gaseous products are free from CO contamination. To the best of our knowledge, these represent the first examples of first row transition metal based catalysts that dehydrogenate quantitatively formic acid in aqueous solution

Regioselective Nitration and/or Halogenation of Iridabenzofurans through Electrophilic Substitution

Regioselective electrophilic substitution reactions of the iridabenzofurans [Ir(C7H5O{OMe-7})(CO)(PPh3)(2)]-[OTf] (1) and IrCl(C7H5O{OMe-7})(PPh3)(2) (2) provide a convenient route to mononitro-, dinitro-, and mixed nitro-/halo- substituted derivatives. Treatment of cationic 1 with copper(II) nitrate in acetic anhydride ("Menke" nitration conditions) gives the mononitrated iridabenzofuran [Ir(C7H4O{NO2-2}{OMe-7})(CO)(PPh3)(2)][O3SCF3] (3). Under the same conditions neutral 2 undergoes dinitration to form IrCl(C7H3O{NO2-2}{NO2-6}{OMe-7}) (PPh3)(2) (5). Simple substitution of the carbonyl ligand in 3 with chloride gives the neutral mononitro derivative IrCl(C7H4O{NO2-2}{OMe-7})(PPh3)(2) (4). Depending on the conditions employed, treatment of the iridabenzofurans 1 and 2 with Cu(NO3)(2) and either lithium chloride or lithium bromide in acetic anhydride gives either the mixed nitro-/halo-substituted iridabenzofurans IrCl(C7H3O{NO2-2}{Cl-6}(OMe-7})(PPh3)(2) (6) and IrCl(C7H2O{NO2-2}{NO2-4}{Cl-6}{OMe-7})(PPh3)(2) (7) or the simple halo-substituted iridabenzofurans [Ir(C7H4O-{Cl-6}{OMe-7}) (CO) (PPh3)(2)] [OTf] (8), [Ir(C7H4O{Br-6}1 OMe-7}) (CO) (PPh3)(2)] [OTf] (9), and IrBr(C7H3O{Br-2}{Br-6}{OMe-7})(PPh3)(2) (10). Bromination of 4 with pyridinium tribromide gives IrCl(C7H3O{NO2-2}{Br-6}{OMe-7})(PPh3)2 (11). The molecular structures of 3-7 and 11 have been obtained by X-ray crystallography

Heterogeneous Catalytic Reactor for Hydrogen Production from Formic Acid and Its Use in Polymer Electrolyte Fuel Cells

A proof-of-concept prototype of a medium-scale heterogeneous catalytic reactor for continuous production of hydrogen through formic acid (FA) dehydrogenation has been developed. A commercial proton exchange membrane (PEM) fuel cell (FC) fed with the resulting gas outflow (H2 + CO2) was applied to convert chemical energy to electricity. To implement an efficient coupling of the reactor and FC, research efforts in three interrelated areas were undertaken: 1) catalyst development and testing; 2) computer modelling of heat and mass transfer to optimize the reactor design and 3) study of compatibility of the reactor gas outflow with a PEM FC. During the catalyst development, immobilization of a homogeneous Ru – metatrisulphonated triphenylphosphine (mTPPTS) catalyst on different supports was performed and Ru-mTPPTS supported on phosphinated polystyrene beads demonstrated the best results. A validated mathematical model of the catalytic reactor with coupled heat transfer, fluid flow and chemical reactions was proposed for catalyst bed and reactor design. Measured reactor operating characteristics were used to refine modelling parameters. In turn, catalyst bed and reactor geometry was optimised during an iterative adaptation of the reactor and model parameters. In the final phase, PEM FC operating conditions and (H2+CO2) gas treatment were optimized to provide the best FC efficiency and lifetime. Stable performance of a commercial 100W PEM FC coupled with the developed reactor prototype was successfully demonstrated. The low CO concentration (below 5 ppm) in the reformate was insured by preferential oxidation (PROX)

Heterogeneous Catalytic Reactor for Hydrogen Production from Formic Acid and Its Use in Polymer Electrolyte Fuel Cells

A proof-of-concept prototype of a heterogeneous catalytic reactor has been developed for continuous production of hydrogen via formic acid (FA) dehydrogenation. A laboratory-type polymer electrolyte fuel cell (PEFC) fed with the resulting reformate gas stream (H₂ + CO₂) was applied to convert chemical energy to electricity. To implement an efficient coupling of the reactor and PEFC, research efforts in interrelated areas were undertaken: (1) solid catalyst development and testing for H₂ production; (2) computer modeling of heat and mass transfer to optimize the reactor design; (3) study of compatibility of the reformate gas fuel (H₂ + CO₂) with a PEFC; and (4) elimination of carbon monoxide impurities via preferential oxidation (PROX). During the catalyst development, immobilization of the ruthenium­(II)–<i>meta</i>-trisulfonated tri­phenyl­phosphine, Ru-<i>m</i>TPPTS, catalyst on different supports was performed, and this complex, supported on phosphinated polystyrene beads, demonstrated the best results. A validated mathematical model of the catalytic reactor with coupled heat transfer, fluid flow, and chemical reactions was proposed for catalyst bed and reactor design. Measured reactor operating data and characteristics were used to refine modeling parameters. In turn, catalyst bed and reactor geometry were optimized during an iterative adaptation of the reactor and model parameters. PEFC operating conditions and fuel gas treatment/purification were optimized to provide the best PEFC efficiency and lifetime. The low CO concentration (below 5 ppm) in the reformate was ensured by a preferential oxidation (PROX) stage. Stable performance of a 100 W PEFC coupled with the developed reactor prototype was successfully demonstrated