Gold Catalysts for Direct Propene Oxide Synthesis
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Supported gold nanoparticles (AuNPs) have been studied extensively for the direct epoxidation of propene with H2/O2 mixtures to yield propene oxide, an intermediate required to fabricate polyesters. Au/TiO2 catalysts achieve high selectivity, but catalyst deactivation and low hydrogen conversions are major limitations. In this research, we explore the possibility of achieving selective propene epoxidation with gold-based bifunctional catalysts. The gold-based catalysts consisted of gold nanoparticles and (transition)-metal complexes active in homogeneous propene oxidation. Afterward, the catalytic performance of gold-based bifunctional catalysts has been studied in the direct gas-phase oxidation of propene with H2/O2 mixtures. Analysis of the catalytic results proved that SiO2 supported gold-based bifunctional catalysts are highly active but lack selectivity towards propene oxide primarily due to limited intimacy between both supported metals. Secondly, we studied the stability of monometallic Au/TiO2 catalysts, which tend to deactivate quickly at 100°C due to the irreversible adsorption of propene oxide. Furthermore, we aimed to increase the catalytic performance by the formation of supported bimetallic nanoparticles on either TiO2 or Ti-SiO2. UV-Vis Spectroscopy, XRD and TEM were applied to study the structure of the bimetallic nanoparticles. However, these characterization techniques were insufficient to verify the structure of the supported bimetallic nanoparticles. We found that Au/Ti-SiO2 was the best performing catalysts for the oxidation of propene. Bimetallic supported nanoparticles negatively affected the catalytic performance compared to monometallic supportedcatalyst due to excessive particle growth, competitive adsorption and the formation of individual nanoparticles.