Epoxidation of olefins using molecular oxygen as the oxidant catalyzed by supported Au-Ag bimetallic nanocatalysts

Abstract

The research above was aimed at developing a catalytic system for the epoxidation of the olefins using molecular oxygen as the oxidant. Ag, Au and Ag-Au catalysts of two different concentrations one double the concentration of the other were prepared using two methods. One was in the presence of the citrate reductant and the other by PEP and PVP. The Au nanoparticles were ruby-red, the Ag nanoparticles were yellow and Ag-Au nanoparticles were red. The citrate was not a good enough reductant for the preparation of Ag nanoparticles therefore the use of sodium borohydride which gave better results. The catalysts were characterized using the UV-Visible spectrophotometer (UV-17000 CE SHIMADZU) to produce absorption bands that were compared to literature values to confirm the presence of the nanoparticles (where the Ag nanoparticles ranged 400-500nm and the Au nanoparticles ranged 500-600nm). It was also observed that the Au nanoparticles were higher in concentration than the Ag nanoparticles in the heterogeneous catalyst. The schlenk line set-up was aligned with all the optimized reaction parameters for the oxidation and the products analyzed using the GC. The Au monocatalyst gave a conversion percentage of 4.47%, Ag-Au 26.67% and Ag-Au double concentration 40.66% after 24hours. Therefore, the Ag-Au catalyst at double concentration gave the best results in the reaction.