Carbon Nitride as a Catalyst Support for Ethylene Epoxidation

Ethylene oxide is a major industrial product that serves as a precursor to a wide range of commonly used everyday products: from polyesters to anti-freeze. It is produced via the selective oxidation of ethylene over silver containing catalysts. The current state of the art consists of only one type of catalyst: silver nanoparticles on -alumina. The main aim of the master’s thesis is to investigate the effect of using a nitrogen-rich catalyst support in the partial oxidation of ethylene, specifically using silver nanoparticles supported by graphitic carbon nitride (g-C3N4). Carbon nitride was synthesised via the thermal condensation of melamine. Impregnation of Ag nanoparticles on the g-C3N4 was carried out via incipient wetness impregnation using silver oxalate as the Ag precursor according to patent literature. Silver wt% loadings were carried out at 5%, 15% and 30%. Catalyst composition, structure and morphology analysis were carried out using DRIFTS, ATR-FTIR, XRD, XPS, BET physisorption, TEM and STEM. The catalysts were then assessed using a microreactor and gas chromatography to evaluate selectivity to ethylene oxide at similar conversions to then be compared to a standard benchmark catalyst: silver nanoparticles supported on -alumina (15wt% Ag). Catalytic performance testing revealed that the support on its own and 5 wt% Ag on g-C3N4 showed little to no conversion and zero selectivity towards ethylene oxide. While the 15%wt and 30 wt% samples demonstrated comparable selectivity at similar conversion to the benchmark sample, albeit requiring higher reaction temperatures and lower space velocities. To further understand the structure-reactivity relationship of the g-C3N4 supported catalysts operando DRIFTS (diffuse reflectance infra-red spectroscopy) and in-situ synchrotron XPS (X-ray photoelectron spectroscopy) were carried out. These studies identified a possible reaction intermediate for the production of the undesired reaction products water and CO2. However, no evidence of previously identified ‘active’ oxygen species were identified for both inactive and active Ag/g-C3N4 samples.