An Overview of the Challenges and Progress of Synthesis, Characterization and Applications of Plugged SBA-15 Materials for Heterogeneous Catalysis

A new generation of SBA-15, plugged SBA-15, was initially synthesized in 2002 using extra silica precursors (Si/organic template molar ratios approximate to 80-140) in the gel mixture. The plugged SBA-15 materials possess short cylinders (length approximate to 20-100 nm), which are connected to neighbors by constricted entrances (windows) through the central axis. The gas adsorption-desorption isotherms of plugged SBA-15 materials present unique hysteresis loop Type H5 classification identified by IUPAC in 2015, which is related to certain pore structures containing open and plugged mesopores. The plugged SBA-15 has been used to support various types of catalysts, including metal complexes, metal nanocatalysts, and active metals by the incorporation in their framework demonstrating excellent (enantio)selectivity, stability against coke, and thermal stability. The plugged SBA-15 materials bear the other unique properties of the ship-in-the-bottle synthesis of, e.g., metal complexes that confine homogeneous catalysts, which is not possible by conventional SBA-15 due to leaching. In this mini-review, the challenges and progress of the synthesis in controlling the plugging and incorporation of metals and organic moiety in their framework, characterizing the short mesochannel dimensions (window and length sizes) by several advanced techniques and applying plugged SBA-15 materials in heterogeneous catalysis for challenging reactions, has been discussed.