Highly efficient reversible hydrogenation of carbon dioxide to formates using a ruthenium PNP-pincer catalyst

The use of hydrogen as a fuel requires both safe and robust technologies for its storage and transportation. Formic acid (FA) produced by the catalytic hydrogenation of CO₂ is recognized as a potential intermediate H ₂ carrier. Herein, we present the development of a formate-based H₂ storage system that employs a Ru PNP-pincer catalyst. The high stability of this system allows cyclic operation with an exceptionally fast loading and liberation of H₂. Kinetic studies highlight the crucial role of the base promoter, which controls the rate-determining step in FA dehydrogenation and defines the total H₂ capacity attainable from the hydrogenation of CO₂. The reported findings show promise for the development of practical technologies that use formic acid as a hydrogen carrier. Like pinning down an ant: An Ru PNP catalyst provides unprecedented rates of CO₂ hydrogenation up to 1 100 000 h^-1 (turnover number >200 000) and excellent activity in the dehydrogenation of formic acid in DMF if used with the non-nucleophilic 1,8-diazabicyclo[5.4.0]undec-7-ene base. Unlike amine-based systems, this medium allows us to achieve high formate capacity together with rapid H₂ charging and release.