Tailored Mn-based MOF with bimodal porosity for effective CO2 adsorption and catalytic valorization via cycloaddition reactions

Abstract

The development of multifunctional materials capable of capturing and converting CO₂ under mild conditions remains a major challenge in climate change mitigation. In this work, we report the synthesis and characterization of Mn-URJC-13, a novel manganese-based metal–organic framework (MOF) constructed from 4,4′-biphenyldicarboxylic acid and isonicotinic acid. The material displays bimodal porosity, with two distinct channels of approximately 4.6 and 9.1 Å, resulting in a BET surface area of 541 m²/g and pore volume of 0.198 cm³ /g. Mn-URJC-13 exhibits CO₂ adsorption capacities of 3.92, 3.37, and 2.02 mmol/g at 0, 25, and 45 °C, respectively. The isosteric heat of adsorption (Qₛₜ) is 24.1 kJ/mol, indicating a physisorption mechanism. These values are competitive with those of MOFs having higher surface areas, owing to the material’s optimized porosity and open Mn(II) sites. As a heterogeneous catalyst, Mn-URJC-13 promotes the cycloaddition of CO₂ to epoxides under mild conditions (room temperature, 12 bar CO₂), achieving up to 99 % conversion and > 99 % selectivity for propylene oxide, and 87 % conversion for epichlorohydrin. The catalyst remains structurally stable and recyclable, with only a slight decrease in activity over five consecutive cycles. Unlike many MOFs based on Zn, Cu, or Co, Mn-URJC-13 employs Mn(II), a less commonly explored metal in this context. This expands the range of catalytic MOFs and offers new insights into the design of sustainable, bifunctional materials for CO₂ capture and valorization.