Pranjal Kalita

Synthesis of superacid-functionalized mesoporous nanocages with tunable pore diameters and their application in the synthesis of coumarins.

Here we demonstrate for the first time the preparation of a triflic acid (TFA)-functionalized mesoporous nanocage with tunable pore diameters by the wet impregnation method. The obtained materials have been unambiguously characterized by XRD, N(2) adsorption, FTIR spectroscopy, and NH(3) temperature-programmed desorption (TPD). From the characterization results, it has been found that the TFA molecules are firmly anchored on the surface of the mesoporous supports without affecting their acidity. We also demonstrate the effect of the pore and cage diameter of the KIT-5 supports on the loading of TFA molecules inside the pore channels. It has been found that the total acidity of the materials increases with an increase in the TFA loading on the support, whereas the acidity of the materials decreases with an increase in the pore diameter of the support. The acidity of the TFA-functionalized mesoporous nanocages is much higher than that of the zeolites and metal-substituted mesoporous acidic catalysts. The TFA-functionalized materials have also been employed as the catalysts for the synthesis of 7-hydroxy-4-methylcoumarin by means of the Pechmann reaction under solvent-free conditions. It has been found that the catalytic activity of the TFA-functionalized KIT-5 is much higher than that of zeolites and metal-substituted mesoporous catalytic materials in the synthesis of coumarin derivatives. The stability of the catalyst is extremely good and can be reused several times without much loss of activity in the above reaction.

Inclusion of size controlled gallium oxide nanoparticles into highly ordered 3D mesoporous silica with tunable pore diameters and their unusual catalytic performance

Here we demonstrate for the first time a novel nanosieve approach for tuning the size, shape, dispersion and the quantity of the gallium oxide nanoparticles inside a mesoporous silica support with a three dimensional porous structure, high surface area, and large pore volume (KIT-6). It was found that the size and shape of the gallium oxide nanoparticles in the pore channels of the KIT-6 can be controlled by simply tuning the pore diameter of the support. The obtained gallium oxide/KIT-6 nanocomposites with different gallium oxide contents have been characterized by several characterization techniques such as powder XRD, SAXS, nitrogen adsorption, UV-Vis, FT-IR, HRSEM and HRTEM. XRD, HRTEM and nitrogen adsorption results reveal that the mesostructural order of the KIT-6 materials was not affected even after the encapsulation of ca. 30 wt% gallium oxide nanoparticles. UV-Vis results reveal that bandgap of the materials can be controlled by simply changing the concentration of the gallium oxide or varying the pore diameter of the support. The above catalytic materials have been also successfully employed for the benzylation of benzene and other aromatic compounds. The role of the pore diameter of the support, the loading of the metal oxide nanoparticles and other reaction parameters affecting the activity of the catalysts has been clearly demonstrated. It has been found that gallium oxide supported KIT-6 materials are highly stable and active, and show superior performance over other metal substituted mesoporous and zeolite materials with a high substrate conversion and a high product selectivity in the alkylation of benzene under the optimized reaction conditions.

A facile synthesis of alkylated nitrogen heterocycles catalysed by 3D mesoporous aluminosilicates with cage type pores in aqueous medium

Friedel–Crafts alkylation of nitrogen heterocycles such as indoles and pyrroles with epoxides has been efficiently carried out using cage-type mesoporous aluminosilicates as recyclable catalysts in water under environmentally benign and mild conditions.

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.