Hydrogen storage in the carbon dioxide/formic acid system, using homogeneous iron(II)-phosphine catalysts in aqueous solution

The valorization of carbon dioxide and its transformation into useful chemicals is essential as mankind consumes more and more fossil fuels, thus producing equivalent wastes. The storage of hydrogen, a promising energy carrier, is also of great interest in developing a sustainable future. Here, we present our results on aqueous phase formic acid (FA) dehydrogenation reaction using non-noble metal, iron based pre-catalysts. We have synthesized the m-trisulfonated-tris[2-(diphe nylphosphino)ethyl]phosphine sodium salt (PP3TS), a water soluble polydentate ligand. The catalysts, with iron (II), were formed in situ and were active in homogeneous catalytic, selective formic acid dehydrogenation resulting in H2 and CO2 from aqueous formic acid solutions. This required no organic co-solvents, bases or any additives. Manometry, multinuclear NMR and FT-IR techniques were used to follow the dehydrogenation reactions, calculate kinetic parameters, and analyze the gas mixtures for purity. The iron (II) catalyst is entirely selective and the H2 and CO2 gas mixture is 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. The reverse reaction, the direct CO2 hydrogenation using an iron (II) phosphine catalyst is also presented here. In water, using the same iron (II) catalyst precursor with PP3TS as the ligand, up to 0.5 M of formic acid can be produced without any additives, i.e. in acidic aqueous solutions. These results were obtained at room temperature and under hydrogen and carbon dioxide pressures. The system is not sensitive to oxygen or air exposure. Therefore, his carbon dioxide reduction and formic acid dehydrogenation cycle can be repeated several times without the loss of the catalyst activity. Hydrogen is regarded as one of the future energy carriers. Using this Fe(II)-PP3TS catalyst, a reversible hydrogen storage system can be realized by a battery-like charge/discharge mechanism. This allows for a clean storage of energy in the form of formic acid as well as the safe delivery of hydrogen gas to proton exchange membrane fuel cells

Additive free, room temperature direct homogeneous catalytic carbon dioxide hydrogenation in aqueous solution using an iron(II) phosphine catalyst

The negative consequences of the global warming require an important reduction of CO2 emission; and the valorization of the carbon dioxide, its transformation into useful chemicals is essential. We present here our studies on the direct CO2 hydrogenation reaction, yielding formic acid. In water, for the first time, an Fe(II) catalyst using meta-trisulfonated-tris[2-(diphenyl-phosphino)-ethyl]phosphine (PP3TS) ligand, has been found active in CO2 reduction. In homogeneous catalytic reactions, without any addi- tives, at room temperature, under hydrogen and carbon dioxide gas pressures up to 0.5 M of formic acid is obtained, in acidic aqueous solutions. The same catalyst is active also in the reverse reaction, under dif- ferent reaction conditions, i.e. at low pressure and high temperature. The CO2 reduction and formic acid dehydrogenation catalytic cycle has been repeated several times; without deactivation of the catalyst, it is not sensitive to oxygen/air. The Fe(II)-PP3TS complex could be a suitable catalyst in a chemical hydro- gen storage/delivery system

Hydrogen Storage in the Carbon Dioxide - Formic Acid Cycle

This year Mankind will release about 39 Gt carbon dioxide into the earth's atmosphere, where it acts as a greenhouse gas. The chemical transformation of carbon dioxide into useful products becomes increasingly important, as the CO2 concentration in the atmosphere has reached 400 ppm. One approach to contribute to the decrease of this hazardous emission is to recycle CO2, for example reducing it to formic acid. The hydrogenation of CO2 can be achieved with a series of catalysts under basic and acidic conditions, in wide variety of solvents. To realize a hydrogen-based charge-discharge device ('hydrogen battery'), one also needs efficient catalysts for the reverse reaction, the dehydrogenation of formic acid. Despite of the fact that the overwhelming majority of these reactions are carried out using precious metals-based catalysts (mainly Ru), we review here developments for catalytic hydrogen evolution from formic acid with iron-based complexes

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