Preparation of Highly Active Triflic Acid Functionalized SBA-15 Catalysts for the Synthesis of Coumarin under Solvent-Free Conditions

Highly acidic SBA-15 with different pore diameters has been prepared by functionalizing the mesoporous walls with different amounts of triflic acid (TFA). The structure of the SBA-15 before and after the functionalization with TFA was investigated by powder X-ray diffraction and nitrogen adsorption isotherms. The interaction of TFA with the surface silanol groups of SBA-15 and the acidity of the materials have been investigated by FTIR spectroscopy and temperature-programmed desorption of ammonia, respectively. The characterization results reveal that the mesoporous structure of the SBA-15 is retained even after the loading of TFA in the mesochannels and that the TFA molecules are bonded with the surface silanol groups of the SBA-15 supports. The acidity of the materials increases with increasing amount of TFA from 5 to 20 wt%. These functionalized, highly acidic materials are found to be highly active in the synthesis of coumarin and the catalytic efficiency was found to correlate with the total acidity or the amount of TFA in the porous channels of the SBA-15 catalysts. It has also been found that the activity of the TFA-functionalized SBA-15 in the synthesis of coumarin is much higher than that of different zeolites, pure mesoporous silica SBA-15, and other mesoporous catalysts used in this study.