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Light-Driven, Iron-Based Catalytic System Generates Hydrogen from Formic Acid

Boddien
A sustainable and reversible energy storage cycle based on hydrogen storage in, and release from, formic acid. Credit: ACS, Boddien et al.Click to enlarge.

A team of researchers in Germany report on the first light-driven, iron-based catalytic system for hydrogen generation from formic acid in a paper published online 15 June in the Journal of the American Chemical Society.

Formic acid (HCO2H, 4.4 wt % hydrogen) is one of the major products formed in biomass processing such as fermentation, pyrolysis, and supercritical reactions; it can undergo selective decomposition to hydrogen and carbon dioxide in the presence of a catalyst. Furthermore, Boddien et al. note, in addition to hydrogen generation, “a sustainable and reversible energy storage cycle can be envisioned by storage of hydrogen in formic acid and release from it”.

Here, carbon dioxide is converted to formic acid or formate derivatives either electrochemically or by catalytic hydrogenation. The resulting products are liquid at ambient conditions and can thus be handled, stored, and transported easily.

—Boddien et al.

A number of investigations have studied noble-metal based heterogeneous and homogeneous catalyst systems for hydrogen release from HCO2H have been studied, with some “remarkable results...in recent years”, according to the authors. However,

An actual goal in organometallic catalysis is the replacement of noble metal-based catalysts, such as ruthenium, iridium, palladium, and rhodium, with nonprecious metal catalysts such as iron compounds. Until now, no homogeneous non-noble metal catalyst system is known for selective hydrogen generation from formic acid under ambient conditions. [Emphasis original.] Herein, we report that simple iron carbonyl phosphine complexes allow for this transformation in the presence of visible light.

—Boddien et al.

The researchers showed that by application of a catalyst formed in situ from inexpensive Fe3(CO)12, 2,2':6'2"-terpyridine or 1,10-phenanthroline, and triphenylphosphine, hydrogen generation is possible under visible light irradiation and ambient temperature. Visible light is needed for both, creating an active system and driving the catalytic cycle. Hydrogen evolution can be easily triggered by switching on and off the light source.

Depending on the kind of N-ligands significant catalyst turnover numbers (>100) and turnover frequencies (up to 200 h-1) are observed, which are the highest known to date for nonprecious metal catalyzed hydrogen generation from formic acid.

—Boddien et al.

Resources

  • Article Albert Boddien, Björn Loges, Felix Gärtner, Christian Torborg, Koichi Fumino, Henrik Junge, Ralf Ludwig and Matthias Beller (2010) Iron-Catalyzed Hydrogen Production from Formic Acid. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja100925n

Comments

sulleny

Interesting progress in the use of non-noble metal catalysts. But still a hard path to generate large volumes of the most abundant element in the universe. There are far more sound methods of obtaining H2 from earth's vast resources.

Combined with low cost, high efficient FCs, the hydrogen energy carrier will free us from the century old "grid" concept.

Engineer-Poet

I had a vision of someone grinding up ants of genus Formica to get the raw material for hydrogen...

The enthalpy of combustion of formic acid is slightly less than that of hydrogen (-254.6 kJ/mol vs. -286 kJ/mol), so the light actually contributes energy to the product (as opposed to just supplying activation energy which is then dissipated as heat). Unfortunately, it's not a big gain.

Now, if someone invents a light-driven process which converts CO2+H2O to HCOOH + 1/2 O2, this will really be something.

richard schumacher

E-P, that's perfect: Corn sugar can be converted into ants even more efficiently than it can be made into ethanol. Cars will carry tanks of ants to generate H2 on-board for fuel cells as needed. Service stations can swap out depleted ant tanks for fresh ones within minutes. Each station can grow corn on the roof and maintain ant farms in the space formerly occupied by gasoline tanks.

Henry Gibson

Eliminate organic materials in landfills. Heat up all such organic materials with heat from nuclear reactors to supercritical temperatures and hydrogen will be formed and easily separated from CO2. Nuclear reactors can easily generate supercritical water temperatures if they are cooled by fluids other than water even heavy oils.

Eventually the process for using nuclear heat for the thermo-chemical production of cheap hydrogen will be perfected. Until then Hydrogen is to be made by the much more expensive high temperature electrolysis. ..HG..

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