Anja Kammer

Efficient Hydrogen Production from Alcohols under Mild Reaction Conditions

Today more than 80% of the energy consumed worldwide is based on fossil fuels. It is undisputable that the resulting CO 2 release has unwanted environmental consequences, such as global warming. In addition, fossil fuels are inherently limited. Therefore, developing a benign, unlimited energy system based on renewable resources represents one of the major challenges for the future. Among the different concepts for alternative energy carriers, the development of a “hydrogen-economy” has been proposed. In this respect in recent years, the use of biomass for hydrogen production has attracted much attention. Here, the dehydrogenation of bioalcohols and carbohydrates shows high potential. In the past, significant progress for this process has been achieved by using heterogeneous catalysts.

Water Oxidation with Molecularly Defined Iridium Complexes: Insights into Homogeneous versus Heterogeneous Catalysis

Molecularly defined Ir complexes and different samples of supported IrO(2) nanoparticles have been tested and compared in the catalytic water oxidation with cerium ammonium nitrate (CAN) as the oxidant. By comparing the activity of nano-scaled supported IrO(2) particles to the one of organometallic complexes it is shown that the overall activity of the homogeneous Ir precursors is defined by both the formation of the homogeneous active species and its conversion to Ir(IV)-oxo nanoparticles. In the first phase of the reaction the activity is dominated by the homogeneous active species. With increasing reaction time, the influence of nano-sized Ir-oxo particles becomes more evident. Notably, the different conversion rates of the homogeneous precursor into the active species as well as the conversion into Ir-oxo nanoparticles and the different particle sizes have a significant influence on the overall activity. In addition to the homogeneous systems, IrO(2)@MCM-41 has also been synthesized, which contains stabilized nanoparticles of between 1 and 3 nm in size. This latter system shows a similar activity to IrCl(3)⋅xH(2)O and complexes 4 and 5. Mechanistic insights were obtained by in situ X-ray absorption spectroscopy and scanning transmission electron microscopy.

Exploring the Reactivity of Nickel Pincer Complexes in the Decomposition of Formic Acid to CO2/H2 and the Hydrogenation of NaHCO3 to HCOONa

The nickel‐catalyzed decomposition of formic acid to yield molecular hydrogen and the nickel‐catalyzed hydrogenation of bicarbonate as a carbon dioxide mimic have been examined. Well‐defined nickel complexes modified by a PCP‐pincer ligand, especially nickel hydride and nickel formate complexes, revealed catalytic activity with turnover numbers of up to 626 (decomposition) and 3000 (hydrogenation). Thus, a formal hydrogen storage and release cycle performed by a well‐defined nickel catalyst was accomplished.

Dual functionality of formamidine polymers, as ligands and as bases, in ruthenium-catalysed hydrogen evolution from formic acid

In the present study, the ruthenium-catalysed decomposition of formic acid to yield hydrogen has been examined. A ruthenium complex modified polyformamidine network was used as a solid catalyst. As a dual support the polyformamidine acts both as a ligand and as a base for the activation of formic acid.

Highly Efficient Base-Free Dehydrogenation of Formic Acid at Low Temperature

The ruthenium complex [RuH2 (PPh3 )4 ] is a competent catalyst for the selective dehydrogenation of formic acid (FA) at low temperature. It tolerates water and shows excellent performance (TOF up to 36 000 h-1 at 60 °C). Remarkably, no basic additives are necessary to obtain such high activity and the defined complex is stable for up to 120 days, making this system one of the most effective formic acid dehydrogenation catalysts known to date.

Diferrate [Fe2(CO)6(μ‐CO){μ‐P(aryl)2}]− as Self‐Assembling Iron/Phosphor‐Based Catalyst for the Hydrogen Evolution Reaction in Photocatalytic Proton Reduction—Spectroscopic Insights

This work is focused on the identification and investigation of the catalytically relevant key iron species in a photocatalytic proton reduction system described by Beller and co-workers. The system is driven by visible light and consists of the low-cost [Fe3 (CO)12 ] as catalyst precursor, electron-poor phosphines P(R)3 as co-catalysts, and a standard iridium-based photosensitizer dissolved in a mixture of THF, water, and the sacrificial reagent triethylamine. The catalytic reaction system was investigated by operando continuous-flow FTIR spectroscopy coupled with H2 gas volumetry, as well as by X-ray absorption spectroscopy, NMR spectroscopy, DFT calculations, and cyclic voltammetry. Several iron carbonyl species were identified, all of which emerge throughout the catalytic process. Depending on the applied P(R)3 , the iron carbonyl species were finally converted into [Fe2 (CO)6 (μ-CO){μ-P(R)2 }]- . This involves a P-C cleavage reaction. The requirements of P(R)3 and the necessary reaction conditions are specified. [Fe2 (CO)6 (μ-CO){μ-P(R)2 }]- represents a self-assembling, sulfur-free [FeFe]-hydrogenase active-site mimic and shows good catalytic activity if the substituent R is electron poor. Deactivation mechanisms have also been investigated, for example, the decomposition of the photosensitizer or processes observed in the case of excessive amounts of P(R)3 . [Fe2 (CO)6 (μ-CO){μ-P(R)2 }]- has potential for future applications.