Synthesis of Solid Catalysts with Spatially Resolved Acidic and Basic Molecular Functionalities

A synthetic procedure was developed to prepare dual acid–base catalysts on a single platform. Mesoporous SBA-15 was derivatized using known grafting chemistry via the following steps: (1) addition of Boc-protected 3-aminopropyltriethoxysilane; (2) controlled use of UV/ozonolysis to selectively remove the exterior groups; (3) decoration of the exterior sites freed in Step 2 with 3-mercaptopropyltriethoxysilane; (4) selective oxidation of the mercaptan groups to sulfonic acid; and (5) pyrolytic deprotection of the amine. The resulting catalysts contain sulfonic acid functionality on the external surfaces and entrance of the pores and amino groups deep inside those pores, at coverage ratios that can be controlled by tuning the exposure time during the UV/ozonolysis step. The samples were fully characterized by 29 Si and 13 C solid-state NMR, infrared absorption spectroscopy, acid–base titrations, and N 2 adsorption isotherms measurements, and they were successfully tested for the promotion of a cascade Henry reaction. Optimum performance was seen with the catalyst having an overall 1:2 acid:base molar ratio.