Bifunctional Ni-Based Catalyst Supported on Plugged Hexagonal Templated Silica for Efficient CO2 Cycloaddition to Epoxides

Abstract The cycloaddition of carbon dioxide (CO2) to epoxides is an attractive route for sustainable chemical synthesis, yet many metal-based catalytic systems require co-catalysts, suffer from limited recyclability, or exhibit inefficient mass transport. Herein, we report a bifunctional heterogeneous catalyst (I−Ni-AP-PHTS) wherein nickel is coordinated to an imidazolium-functionalized salicylaldehyde ligand immobilized within plugged hexagonal templated silica (PHTS). The catalyst was constructed via stepwise surface functionalization and metal coordination while preserving the hierarchical pore architecture of the support. This work presents an engineered material solution for CO2 valorization, where the catalyst’s pore architecture is rationally designed to overcome mass-transfer limitations and enhance local reactant concentration. The I−Ni-AP-PHTS catalyst exhibits high activity for CO2 cycloaddition to styrene oxide, achieving 97% conversion and >99% selectivity under mild conditions (80 °C, 10 bar CO2) at a low catalyst loading (0.075 mol %). Notably, it significantly outperforms analogous systems based on conventional mesoporous silicas SBA-15 and hollow mesoporous silica, highlighting the potential critical role of the plugged pore architecture. This behavior is attributed to the combined influence of ordered pore architecture, reactant accessibility, and a possible confinement effect near the immobilized Ni/imidazolium active sites. Although the final catalysts display comparable equilibrium CO2 uptake, the PHTS architecture may provide a more favorable local catalytic environment under reaction conditions. The catalyst demonstrates broad substrate scope, converting various terminal epoxides into cyclic carbonates in excellent yields (85−98%), and retains activity over multiple cycles with minimal loss. These findings establish PHTS-supported bifunctional nickel catalysts as an effective platform for CO2 valorization and demonstrate that pore architecture engineering is a powerful strategy for designing high-performance heterogeneous catalytic materials.