Effects of SiO ₂ Support on the Formation of Active Sites in HfO ₂ /SiO ₂ Catalysts for the Conversion of Ethanol and Acetaldehyde to 1,3-butadiene

High Resolution Image Download MS PowerPoint Slide Efforts to improve the conversion efficiency of 1,3-butadiene (BD) synthesis from biomass feedstocks, such as bioethanol, have the potential to drive the development of sustainable chemical manufacturing processes. In this study, BD synthesis from ethanol and acetaldehyde was investigated over HfO 2 /SiO 2 catalysts prepared using different SiO 2 supports. Although BD yield strongly depended on the type of SiO 2 support, a consistent relationship between conversion and BD yield was observed for all catalysts. The determined activation energies of the HfO 2 /SiO 2 catalysts were nearly identical, regardless of the type of SiO 2 support, indicating that the nature of the active sites for BD synthesis is consistent across the catalysts. The amounts of Lewis acid sites in the catalysts, determined via pyridine adsorption, exhibited a linear relationship with both the BD synthesis reaction activity and the quantity of silanol (Si–OH) groups present in the SiO 2 supports. Dynamic nuclear polarization NMR further showed that BD yield increased with the concentration of Si–O–Hf species. These results demonstrate that the active sites for BD synthesis over HfO 2 /SiO 2 catalysts are Lewis acid sites, specifically Si–O–Hf species formed from interactions between Si–OH groups and Hf ions on the SiO 2 surface.