Amine‐Free Reversible Hydrogen Storage in Formate Salts Catalyzed by Ruthenium Pincer Complex without pH Control or Solvent Change

Abstract

Due to the intermittent nature of most renewable energy sources, such as solar and wind, energy storage is increasingly required. Since electricity is difficult to store, hydrogen obtained by electrochemical water splitting has been proposed as an energy carrier. However, the handling and transportation of hydrogen in large quantities is in itself a challenge. We therefore present here a method for hydrogen storage based on a CO2 (HCO3 (-) )/H2 and formate equilibrium. This amine-free and efficient reversible system (>90 % yield in both directions) is catalyzed by well-defined and commercially available Ru pincer complexes. The formate dehydrogenation was triggered by simple pressure swing without requiring external pH control or the change of either the solvent or the catalyst. Up to six hydrogenation-dehydrogenation cycles were performed and the catalyst performance remained steady with high selectivity (CO free H2 /CO2 mixture was produced).

Catalytic Dehydrogenation of Formic Acid with Ruthenium‐PNP‐Pincer Complexes: Comparing N‐Methylated and NH‐Ligands

“…Consequently, the behavior of complexes with N‐alkylated aliphatic pincer ligands has been scarcely investigated . Interestingly, Prakash and co‐workers reported the catalytic activity for formate dehydrogenation (DH) being independent of the N−H moiety of the pincer complex . Independently, our group presented a detailed mechanistic investigation of the Ru‐catalyzed methanol reforming .…”

Making a Splash in Homogeneous CO2 Hydrogenation: Elucidating the Impact of Solvent on Catalytic Mechanisms

“…The first order rate constant for conversion of HCO 3 − to CO 2 and HO − is 0.7 h −1 at room temperature, corresponding to Δ G ≠ =22.5 kcal mol −1 . For comparison, one the fastest reported catalysts for hydrogenation of NaHCO 3 , a ruthenium pincer complex, has TOF=1700 h −1 at 80 °C and 40 bar H 2 . The barrier for this catalytic TOF corresponds to Δ G ≠ ≈21 kcal mol −1 , which is similar to the barrier for HCO 3 − decomposition into CO 2 .…”

Hidrogén tárolása homogén katalitikus kémiai rendszerekben

“…Oláh György és munkatársai Ru(II)-pincer komplexeket használtak erre a célra 16 . Ezek közül 3 és 4 (3. ábra) mind a HCO 3 Na hidrogénezésére, mind a HCO 2 Na (+H 2 O) dehidrogénezésére alkalmasnak bizonyult tetrahidrofurán/víz elegyekben.…”

“…A reakciók viszonylag lassan, de a katalizátor aktivitásának lényeges csökkenése nélkül mentek végbe; hat hidrogénezés/dehidrogénezés ciklus során az összesített katalitikus ciklusszám (TON = átalakított szubsztrátum anyagmennyisége/katalizátor anyagmennyisége) 11 500 volt. Elvileg az ilyen tipusú Ru(II)-komplexek lehetõséget adnak hidrogén akkumulátorok megalkotására, azonban az említett közleményben 16 errõl a szerzõk nem számolnak be.…”

“…2) 15 . Conversely, for dehydrogenation of Na-formate (in THF-water mixtures) Ru(II)-pincer complexes, such as 3 (Fig 3) were synthetized 16 . Although the latter dehydrogenation reactions were relatively slow, 3 was capable of catalysis of bicarbonate hydrogenation, too, and this allowed construction of a dehydrogenation/hydrogenation cycle with the same catalyst for both half-reactions.…”