Evolution of Carbonate-Intercalated γ-NiOOH from a Molecularly Derived Nickel Sulfide (Pre)Catalyst for Efficient Water and Selective Organic Oxidation.

The development of a competent (pre)catalyst for the oxygen evolution reaction (OER) to produce green hydrogen is critical for a carbon-neutral economy. In this aspect, the low-temperature, single-source precursor (SSP) method allows the formation of highly efficient OER electrocatalysts, with better control over their structural and electronic properties. Herein, a transition metal (TM) based chalcogenide material, nickel sulfide (NiS), is prepared from a novel molecular complex [NiII (PyHS)4 ][OTf]2 (1) and utilized as a (pre)catalyst for OER. The NiS (pre)catalyst requires an overpotential of only 255 mV to reach the benchmark current density of 10 mA cm-2 and shows 63 h of chronopotentiometry (CP) stability along with over 95% Faradaic efficiency in 1 m KOH. Several ex situ measurements and quasi in situ Raman spectroscopy uncover that NiS irreversibly transformed to a carbonate-intercalated γ-NiOOH phase under the alkaline OER conditions, which serves as the actual active structure for the OER. Additionally, this in situ formed active phase successfully catalyzes the selective oxidation of alcohol, aldehyde, and amine-based organic substrates to value-added chemicals, with high efficiencies.

Alumina-Based Bifunctional Catalyst for Efficient CO2 Fixation into Epoxides at Atmospheric Pressure.

The quest toward sustainability and decarbonization demands the development of methods for efficient carbon dioxide capture and utilization. The nonreductive CO2 fixation into epoxides to prepare cyclic carbonates has gained attention in recent years. In this work, we report the development of guanidine hydrochloride-functionalized γ alumina (γ-Al2O3), prepared using green solvents, as an efficient bifunctional catalyst for CO2 fixation. The resulting guanidine-grafted γ-Al2O3 (Al-Gh) proved to be an excellent catalyst to prepare cyclic carbonates from epoxides and CO2 with high selectivity. The nitrogen-rich Al-Gh shows increased CO2 adsorption capacity compared to that of γ-Al2O3. The as-prepared catalyst was able to carry out CO2 fixation at 85 °C under atmospheric pressure in the absence of solvents and external additives (e.g., TBAI or KI). The material showed negligible loss of catalytic activity even after five cycles of catalysis. The catalyst successfully converted many epoxides into their respective cyclic carbonates under the optimized conditions. The gram-scale synthesis of commercially important styrene carbonates from styrene oxide and CO2 using Al-Gh was also achieved. Density functional theory (DFT) calculations revealed the role of alumina in activating the epoxide. This activation facilitated the chloride ion to open the ring to react with CO2. The DFT studies also validated the role of alumina in stabilizing the electron-rich intermediates during the course of the reaction.