(387g) Understanding the Role of Cu-O-Si Units in the Hydrogenation of Methyl Acetate on Cu/SiO2 Catalysts

The production of ethanol has received a lot of attention in recent years due to its application as a fuel. Hydrogenation of methyl acetate is potentially a more sustainable route for ethanol production compared to the common corn-to-ethanol pathway. Copper catalysts supported on silica are usually utilized for the selective production of ethanol and methanol. The state-of-the-art copper catalysts for this reaction are made using the ammonia evaporation method (AE). These catalysts made by AE have been shown to significantly improve activity compared to the catalysts made by the more conventional incipient wetness method. This has been attributed to the presence of smaller and more dispersed copper nanoparticles as well as the high ratio of Cu⁺/Cu⁰ in the reduced catalyst sample. The increased amount of Cu⁺ is attributed to the incomplete reduction of the Cu-O-Si units present in copper phyllosilicates formed during the AE synthesis. While these Cu-O-Si units are believed to be the source of high Cu⁺ content, to the best of our knowledge, there has been no direct proof for this in the literature. In this work, we seek to gain a fundamental understanding of the role of these Cu-O-Si units. We do this by systematically varying the units in the Cu/SiO₂(AE) sample by coating with a SiO₂ layer through the hydrolysis of tetraethyl orthosilicate (TEOS). Transmission Electron Microscopy (TEM) images of the Cu/SiO₂(AE) sample showed needle-like structures corresponding to the presence of copper phyllosilicates with abundant Cu-O-Si units. Preliminary reaction results show that the methyl acetate hydrogenation reaction had a lower activation energy on the coated catalyst as compared to the catalyst without coating. This suggests that the silica coating could be introducing more Cu-O-Si units needed to yield more Cu⁺ required for the reaction.