Metal phthalocyanines and imidazolium bromide Copolymers supported on multi-walled carbon nanotubes: a “lego-like” assembly of hybrid bifunctional materials applied for CO2 conversion

Abstract

The present study explores the development of hybrid heterogeneous bifunctional catalysts supported on multi-walled carbon nanotubes (MWCNT) for CO2 valorization in the synthesis of cyclic carbonates. These materials integrate both nucleophilic species (imidazolium bromide) and Lewis acid species (magnesium, copper, and zinc phthalocyanines), revealing improved catalytic activity through synergistic effects. MWCNT are employed as support enhancing the accessibility of active sites and the overall catalytic performance. Three different metalphthalocyanines with imidazole moieties (MgPC-Im4, CuPC-Im4 and ZnPC-Im4) were covalently anchored onto MWCNT through an atom economic polymerization process, resulting in new bifunctional materials (MPC@MWCNT) in which the polymeric network fully covers the nanotubes longitudinally. Comprehensive characterization of the hybrids by using different techniques confirmed the successful synthesis of these materials. Catalytic testing of the MPC@MWCNT materials in epoxide-CO2 cycloaddition reactions revealed that the MgPC@MWCNT hybrid exhibited superior catalytic activity compared to its unsupported counterpart, highlighting the benefits of the MWCNT as support (TON = 8050 vs TON = 7120), reaching very high TON values (up to 19920) at very low catalytic loadings (0.004-0.0013 mol% based on metal content). Importantly, this study introduces a simple yet effective novel method for covalently attaching high amounts of metal-phthalocyanines onto MWCNT. Potentially, the "lego-like" approach of this method allows for the creation of diverse materials with different metal centres, enabling access to a number of different applications in the field of Materials Science.