CoII Cryptates Convert CO2 into CO and CH4 under Visible Light

Abstract

Three Co^II octaazacryptates, with different substituents on the aromatic rings (Br, NO₂ , CCH), were synthesised and characterised. These and the already published non-substituted cryptate catalysed CO₂ photoreduction to CO and CH₄ under blue visible light at room temperature. Although CO was observed after short irradiation times and a large range of catalyst concentrations, CH₄ was only observed after longer irradiation periods, such as 30 h, but with a small catalyst concentration (25 nm). Experiments with ¹³ C labelled CO₂ showed that CO is formed and reacts further when the reaction time is long. The CCH catalyst is deactivated faster than the others and the more efficient catalyst for CH₄ production is the one with Br. This reactivity trend was explained by an energy decomposition analysis based on DFT calculations.

Keywords: carbon dioxide; cryptates; methane; photoreduction; visible light.