Capture of CO2 from N2 and CH4 over a wide temperature range on a robust MOF with Brønsted acidic and Lewis basic dual functional sites

Abstract

The need to mitigate the greenhouse effect and decrease environmental pollution has become an increasingly essential driving force for carbon dioxide (CO₂) capture from natural gas or flue gas, especially under high-temperature conditions associated with post-combustion processes. Herein, we successfully designed and synthesized a novel porous three-dimensional (3D) MOF (termed CUMT-1) embedded with free Brønsted acidic –COOH and Lewis basic triazolyl as well as dual functional sites for the separation of post-combustion relevant CO₂/N₂ or CO₂/CH₄ mixtures. CUMT-1a (activated CUMT-1) demonstrated an excellent CO₂ adsorption uptake of 4.6 mmol g⁻¹ and CO₂/CH₄ (53.1) and CO₂/N₂ (10.2) selectivities at 298 K. Impressively, such a great adsorption capacity could also be maintained at higher temperatures of 313 and 333 K to accommodate post-combustion processes. Breakthrough experiments verified that CUMT-1a could effectively produce high-purity N₂ and CH₄ (≥99.99%) as well as CO₂ (≥99.5%) from CO₂/CH₄, CO₂/N₂ or CO₂/CH₄/N₂ mixtures in a single adsorption–desorption cycle over a broad range of ratios and temperatures (273–333 K). Stability experiments and continuous adsorption/breakthrough studies revealed the outstanding reusability and stability of CUMT-1a. Molecular simulations further disclosed the crucial role of triazolyl and free –COOH groups in the excellent CO₂ capture and separation capabilities.