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Pore architecture of catalyst supports is an important factor facilitating accessibility of reactants to catalytic sites. This holds the key to improving catalytic activities. Amongst various catalytic reactions, supported Pd nanoparticles-catalyzed C–C cross-coupling reactions have been attracting a great deal of attention in the last decade. Although various supports have been examined, applications of hierarchically porous monolithic materials have never been reported, mainly because of difficulties in multistep synthesis of catalysts. We herein report a novel on-site reduction-based methodology using hierarchically porous hydrogen silsesquioxane (HSQ) monoliths for one-step synthesis of Pd nanoparticles-embedded monoliths (Pd@HSQ). Characterization of these monoliths evidences the on-site reduction, i.e. formation of Pd nanoparticles and conversion of Si–H present in the monolith to Si–O∼. Fast, quantitative reduction of Pd2+ to Pd(0) to form supported Pd nanoparticles is achieved with preservation of the porous structure of the original monolith, which makes this material attractive as a catalyst for C–C cross-coupling reactions. The obtained Pd@HSQ catalyst has been employed in the Mizoroki–Heck cross-coupling reaction. High accessibility of reactant molecules, undetectable leaching of Pd nanoparticles and easy separation of the monolith from liquid media provide high catalytic activity, reusability and easy handling. [ABSTRACT FROM AUTHOR]

A facile synthesis of a new class of reactive porous materials is reported: hierarchically porous hydrogen silsesquioxane (HSiO1.5, HSQ) monoliths with well-defined macropores and mesopores. The HSQ monoliths are prepared via sol-gel accompanied by phase separation in a mild condition, and contain micrometer-sized co-continuous macropores and high specific surface area reaching up to 800 m2 g−1 because of the small mesopores. A total preservation of Si-H, which is always an issue of HSQ materials, is confirmed by 29Si solid-state NMR. The HSQ monolith has then been subjected to reduction of noble metal ions to their corresponding metal nanoparticles in simple aqueous solutions under an ambient condition. The nanoparticles produced in this manner are immobilized on the HSQ monolith and are characterized by X-ray diffraction (XRD) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Both the bare HSQ and nanoparticles-embedded HSQ are promising as heterogeneous catalysts, exhibiting reusability and recyclability. [ABSTRACT FROM AUTHOR]

Novel Pd nanoparticles embedded hydrogen silsesquioxane monoliths are prepared using an on-site reduction methodology and successfully applied as catalyst in the title reaction. [ABSTRACT FROM AUTHOR]