Computational screening of metal-substituted HKUST-1 catalysts for chemical fixation of carbon dioxide into epoxides

Abstract

Developing high-performance catalysts for the chemical fixation of CO₂ into epoxides remains an ongoing hot yet challenging issue in the field of catalysis. Metal–organic frameworks (MOFs) represent an attractive type of catalyst candidate for this reaction due to their remarkable properties including large surface area, high stability, open channels, and permanent porosity. Although the Cu-HKUST-1 MOF has recently been shown to exhibit good activity towards CO₂ fixation, and a series of other isostructural analogues, i.e., M-HKUST-1 (M = Mo, Cr, Fe, Ru and Zn), have even been synthesized, there is no theoretical investigation on CO₂ cycloaddition catalyzed by both the parent and metal-substituted HKUST-1, to the best of our knowledge. In this work, with the attempt to design powerful catalysts, we computationally screened a series of M-HKUST-1 systems (M = Mo, Cr, Ti, Cu, W, Sc, Fe, Ru, Zn, Cd, and V) in the presence of quaternary ammonium salts (TBAX, X = F, Cl, Br, and I) for catalytic activity toward the synthesis of cyclic carbonates from propylene oxide (PO) and CO₂. Of these, several M-HKUST-1 systems (M = Cr, W, Fe, Zn, and Cd) were predicted to exceed the performance of the original Cu-HKUST-1 reported experimentally for CO₂ chemical conversion based on the rate-limiting energy barrier. In particular, W-HKUST-1 was predicted to be the most promising catalyst within the screened M-HKUST-1 series. In addition, for Cu-HKUST-1, the catalyst system containing Br⁻ is more efficient than the one containing F⁻, Cl⁻ and I⁻. The proton attachment energy of the X⁻ anion is a suitable descriptor for screening promising co-catalytic materials for the specific reaction. The present computational investigation would greatly enrich the CO₂–PO reaction catalyzed by M-HKUST-1/TBAX, and provide a valuable guideline for the design of more powerful MOFs/IL catalysts.