Gold nanoparticles (AuNPs) have attracted enormous attention due to their unique catalytic activities, which are not revealed in bulk gold. Reactions catalyzed by AuNPs include alcohol oxidation, nitroarene reduction, hydrogenation of quinolone compounds and carbon-carbon cross coupling reactions. The major advantage of colloidal AuNPs over supported AuNPs is the greater catalytic activity and selectivity. Colloidal catalysts also catalyze reactions under mild conditions and have significant advantages over supported catalyst in the field of chiral catalysis. Advantages of supported catalysts are the reusability and recovery of the catalyst by simple mechanical methods like centrifugation, filtration and sedimentation. Supported catalysts are preferred over colloidal catalyst at industrial scales when used in a continuous reactor system on a stationary support. In this work, an in-depth comparison of the catalytic activity and available catalytic sites of colloidal AuNPs and the same AuNPs supported on titania has been performed. The model AuNP catalyzed reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH<sub>4</sub>) has been used to study the reaction kinetics by simple UV-Vis spectroscopy. A systematic study of the different gold nanoparticles loading onto the titania support and the dependence of available catalytically active sites have been carried out through a simple organothiol adsorption method which can be easily characterized by a bench top UV-Vis spectrophotometer with great accuracy. This provides a direct method of characterization of both colloidal and heterogeneous catalysts leading to direct comparison of the two systems. We have also examined the effect of support on the catalytic activity of the AuNP from the same experiments. The results have been compared with regular chemisorption analysis of heterogeneous catalysts. STEM and HR-TEM has been used to characterize the morphology of the AuNP on the titania support and EDX analysis has been used to confirm the successful immobilization of the AuNP onto the support. In this work we have also characterized the effect of annealing on the size and morphology of the supported gold nanoparticle.

Comparative characterization of catalytic properties of colloidal and supported gold nanoparticle catalysts by ligand adsorption method

253rd National Meeting (2017)

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