Chemical Equilibria in Formic Acid/Amine-CO2 Cycles under Isochoric Conditions using a Ruthenium(II) 1,2-Bis(diphenylphosphino)ethane Catalyst

The equilibrium position in formic acid/amine–CO2 systems has been examined as a function of pressure and tem- perature under isochoric conditions. The homogeneous ruthe- nium(II)-1,2-bis(diphenylphosphino)ethane catalyst was active in both reactions, that is, in formic acid cleavage producing pure hydrogen and CO2, as well as in carbon dioxide hydroge- nation under basic conditions. High yields of formic acid dehy- drogenation into H2 and CO2 are favored by low gas pressures and/or high temperatures, and H2 uptake is possible at elevat- ed H2–CO2 pressures. These results take us one step closer to the realization of a practical H2 storage–discharge device

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

Carbon Dioxide to Methanol: The Aqueous Catalytic Way at Room Temperature

Carbon dioxide may constitute a source of chemicals and fuels if efficient and renewable processes are developed that directly utilize it as feedstock. Two of its reduction products are formic acid and methanol, which have also been proposed as liquid organic chemical carriers in sustainable hydrogen storage. Here we report that both the hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized at ambient temperature and in aqueous, acidic solution, with an iridium catalyst. The formic acid yield is maximized in water without additives, while acidification results in complete (98%) and selective (96%) formic acid disproportionation into methanol. These promising features in combination with the low reaction temperatures and the absence of organic solvents and additives are relevant for a sustainable hydrogen/methanol economy

Investigation of Hydrogenation of Formic Acid to Methanol using H2 or Formic Acid as a Hydrogen Source

Production of methanol (MeOH) from CO2 is strongly desired as a key chemical feedstock and a fuel. However, the conventional process requires elevated temperature and pressure, and high temperature restricts the productivity of MeOH due to equilibrium limitations between CO2 and MeOH. This paper describes the efficient hydro- genation/disproportionation of formic acid (FA) to MeOH by using iridium catalysts with electronically tuned ligands and by optimizing reaction conditions. An iridium complex bearing 5,5′-dimethyl-2,2′- bipyridine in FA hydrogenation achieved MeOH selectivity with H2 of up to 47.1% for FA hydrogenation under 4.5 MPa of H2 in the presence of H2SO4. The final concentration of MeOH of 3.9 M and a TON of 1314 were obtained in 12 M FA aqueous solution including 10 mol % of H2SO4 at 60 °C under 5.2 MPa of H2. Even under atmospheric pressure without introduction of external hydrogen gas, the FA disproportionation under deuterated conditions produced MeOH with 15.4% selectivity. Furthermore, the isotope effect and NMR studies revealed mechanistic insight into the catalytic hydrogenation of FA to MeOH

Carbon Dioxide to Methanol: The Aqueous Catalytic Way at Room Temperature

Carbon dioxide may constitute a source of chemicals and fuels if efficient and renewable processes are developed that directly utilize it as feedstock. Two of its reduction products are formic acid and methanol, which have also been proposed as liquid organic chemical carriers in sustainable hydrogen storage. Here we report that both the hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized at ambient temperature and in aqueous, acidic solution, with an iridium catalyst. The formic acid yield is maximized in water without additives, while acidification results in complete (98%) and selective (96%) formic acid disproportionation into methanol. These promising features in combination with the low reaction temperatures and the absence of organic solvents and additives are relevant for a sustainable hydrogen/methanol economy

Method for producing methanol from carbon dioxide and hydrogen gas in homogeneously catalyzed reactions and in an aqueous medium

The invention relates to a method for producing methanol from hydrogen and carbon dioxide gas in homogeneously catalyzed reactions, composed of the carbon dioxide hydrogenation reaction to formic acid and the formic acid disproportionation reaction into methanol, both being conducted in aqueous media at mild conditions (temperature in the range from 20 to 100 °C, total hydrogen and carbon dioxide gas pressure up to 100 bar)

Homogeneous Catalysis for Sustainable Hydrogen Storage in Formic Acid and Alcohols

Hydrogen gas is a storable form of chemical energy that could complement intermittent renewable energy conversion. One of the main disadvantages of hydrogen gas arises from its low density, and therefore, efficient handling and storage methods are key factors that need to be addressed to realize a hydrogen-based economy. Storage systems based on liquids, in particular, formic acid and alcohols, are highly attractive hydrogen carriers as they can be made from CO2 or other renewable materials, they can be used in stationary power storage units such as hydrogen filling stations, and they can be used directly as transportation fuels. However, to bring about a paradigm change in our energy infrastructure, efficient catalytic processes that release the hydrogen from these molecules, as well as catalysts that regenerate these molecules from CO2 and hydrogen, are required. In this review, we describe the considerable progress that has been made in homogeneous catalysis for these critical reactions, namely, the hydrogenation of CO2 to formic acid and methanol and the reverse dehydrogenation reactions. The dehydrogenation of higher alcohols available from renewable feedstocks is also described. Key structural features of the catalysts are analyzed, as is the role of additives, which are required in many systems. Particular attention is paid to advances in sustainable catalytic processes, especially to additive-free processes and catalysts based on Earth-abundant metal ions. Mechanistic information is also presented, and it is hoped that this review not only provides an account of the state of the art in the field but also offers insights into how superior catalytic systems can be obtained in the future

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)

Homogenous catalytic hydrogenation of bicarbonate with water soluble aryl phosphine ligands

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Hydrogen Production by Selective Dehydrogenation of HCOOH Catalyzed by Ru-Biaryl Sulfonated Phosphines in Aqueous Solution

The selective dehydrogenation of aqueous solutions of HCOOH/HCOONa to H₂ and CO₂ gas mixtures has been investigated using RuCl₃·3H₂O as a homogeneous catalyst precursor in the presence of different monoaryl-biaryl or alkyl-biaryl phosphines and aryl diphosphines bearing sulfonated groups. All catalytic systems were used in water without any additives and proved to be active at 90 °C, giving high conversions and good TOF values. As an alternative Ru­(II) metal precursor, the known dimer [Ru­(η⁶-C₆H₆)­Cl₂]₂ was also tested as in situ catalyst with selected phosphines as well as an isolated Ru­(II)-catalyst with one of them. By using high-pressure NMR (HPNMR) techniques, indications on the nature of the active species involved in the catalytic cycles were obtained