Jotheeswari Kothandaraman

Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst

A highly efficient homogeneous catalyst system for the production of CH3OH from CO2 using pentaethylenehexamine and Ru-Macho-BH (1) at 125-165 °C in an ethereal solvent has been developed (initial turnover frequency = 70 h(-1) at 145 °C). Ease of separation of CH3OH is demonstrated by simple distillation from the reaction mixture. The robustness of the catalytic system was shown by recycling the catalyst over five runs without significant loss of activity (turnover number > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concentration (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using a homogeneous catalytic system.

Amine-free reversible hydrogen storage in formate salts catalyzed by ruthenium pincer complex without pH control or solvent change.

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).

CO2 capture by amines in aqueous media and its subsequent conversion to formate with reusable ruthenium and iron catalysts

Conversion of carbon dioxide (CO2) captured from industrial sources (e.g. flue gas of power plants) or even from ambient air to value-added chemicals/fuels through CO2 capture and utilization (CCU) as a possible strategy to mitigate anthropogenic CO2 emissions to the atmosphere is proposed. In this context, combining the CO2 capture and utilization steps to generate fuels instead of going through the intermediate desorption and compression of captured CO2 has started to attract considerable interest as a way to lower the energy demand for the CO2 recovery processes involved in usual carbon capture and storage/sequestration approach. The main focus of this study is CO2 capture in aqueous amine solutions and conversion of the in situ formed ammonium carbamate/bicarbonate/carbonate to ammonium formate. The amines selected for this process served the dual purpose of capturing CO2 and stabilizing the formate product. The captured CO2 was selectively converted to formate (up to 95% yield) using, among others, superbases, in the presence of Ru- and Fe-based pincer complexes under moderate reaction conditions (50 bar H2 at 55 °C). By performing a biphasic reaction (water/Me-THF), the catalyst was recycled for five consecutive cycles and a TON > 7000 was obtained for the formation of ammonium formate from captured CO2. Overall, a green and straightforward approach to produce formate from captured CO2 is presented here.

Regioselective deuteration of alcohols in D2O catalysed by homogeneous manganese and iron pincer complexes

We report a convenient and cost-effective protocol for the regioselective deuteration of primary and secondary alcohols using Earth abundant homogeneous first row transition metal pincer catalysts. D2O is utilized as both a deuterium source and a solvent, allowing for a benign inexpensive process. Depending on the metal selected (Mn or Fe), a high degree of deuterium incorporation was observed selectively either at the α and β position (Mn) or exclusively at the α position (Fe), for primary alcohols. This simple, efficient, and cost-effective protocol for alcohol C–H bond deuteration constitutes a powerful tool for the large scale synthesis of deuterated molecules.