Design of periodic mesoporous organosilica catalyst bearing copper phthalocyanine and quaternary ammonium for CO₂ cycloaddition

The development of heterogeneous catalysts with high activity, stability, and co-catalyst-free operation remains a significant challenge for the sustainable conversion of CO₂ into value-added chemicals. Herein, we report a novel periodic mesoporous organosilica (PMO) heterogeneously functionalized with copper phthalocyanine (CuPc) and quaternary ammonium salts (CuPc-UQA₂-PMO). This catalyst integrates CuPc centers, hydrogen-bond-donating urea groups, and iodide-releasing quaternary ammonium moieties within a highly ordered mesoporous silica framework via covalent anchoring, creating a synergistic trinity active site. The resulting catalyst exhibits a well-defined spherical morphology, uniform element distribution, and a BET surface area of 714 m²·g^-1. Under cocatalyst-free conditions (100 ^oC, 2.0 MPa CO₂), CuPc-UQA₂-PMO achieves nearly 99% yield and 100% selectivity for propylene carbonate from the cycloaddition of CO₂ and propylene oxide. Density functional theory (DFT) calculations reveal the cooperative activation of epoxide by Cu²⁺ and urea, along with the availability of I^- species from the quaternary ammonium moieties for ring-opening initiation and the synergistic adsorption/polarization of CO₂ by the π-conjugated system and quaternary ammonium cation, significantly lowers the energy barrier (24.21 kcal·mol^-1 for the rate-determining step). Furthermore, the catalyst reveals excellent recyclability over five consecutive cycles without appreciable loss in activity or structural integrity, highlighting its great potential for practical applications in green carbon utilization.