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.