Mechanism and Kinetics\nof Ethanol–Acetaldehyde\nConversion to 1,3-Butadiene over Isolated Lewis Acid La Sites in Silanol\nNests in Dealuminated Beta Zeolite

Biomass-derived ethanol (EtOH) and acetaldehyde (AcH)\nconversion\nto 1,3-butadiene (1,3-BD) is an alternative process for 1,3-BD production.\nThe present investigation reports the preparation and characterization\nof isolated La sites introduced into the silanol nests in DeAlBEA\nas well as detailed studies of the mechanism and kinetics for the\nconversion of an EtOH–AcH mixture to 1,3-BD. La sites supported\non DeAlBEA are found to be present as (SiO)<sub>2</sub>La–OH\ngroups that are H-bonded with adjacent Si–OH groups, possessing\nhigh C–C coupling activity and stability, superior to state-of-the-art\nY-DeAlBEA. La sites supported on silica (La-SiO<sub>2</sub>) with\na similar chemical structure but no H-bonding interaction with Si–OH\ngroups were prepared for comparison. Lewis acid La sites promote AcH\naldol condensation, and the activity of such sites is nearly identical\nfor both La-DeAlBEA and La-SiO<sub>2</sub>. The rate of C<sub>4</sub> product formation increases by a factor of 4.8 upon addition of\nEtOH to the feed of AcH over La-DeAlBEA, whereas that over La/SiO<sub>2</sub> remains unchanged. Investigation of the mechanism and kinetics\nof AcH aldol condensation and EtOH–AcH conversion to 1,3-BD\nrevealed two C–C bond forming pathwaysAcH aldol condensation\nby Lewis acid La sites and direct coupling of EtOH–AcH over\nH-bonded (SiO)<sub>2</sub>La–OH···HO–Si\nsites. This study provides important information about the role of\nthe local environment of isolated Lewis acid sites and their effects\non the direct coupling of EtOH and AcH to form 1,3-BD.