(569de) Effect of Confinement of MFI Zeolites on Pd Catalysts for the Semi-Hydrogenation of Acetylene

The semi-hydrogenation of acetylene to ethylene is an industrially relevant reaction as it is required to remove trace acetylene impurities from ethylene feedstocks prior to polyethylene production. While the hydrogenation of acetylene to ethylene is facile, making its removal via hydrogenation feasible, the undesirable subsequent hydrogenation of ethylene is as well. For this reason, catalysts which selectively hydrogenate acetylene to ethylene are desirable. In this work, Pd catalysts synthesized within the cages of MFI-type zeolites, via a one-pot hydrothermal technique, show a significant selectivity enhancement (~20% increase) compared to their unconfined counterparts (e.g. Pd/SiO₂) at similar acetylene conversions (Fig 1a). To confirm confinement, the shape selective hydrogenation of nitroarenes was used (Fig 1b). To probe the effect of confinement on geometry, HR-TEM and PXRD will be utilized to determine if zeolites cause a reduction in average particle size. To analyze the effect of confinement on Pd oxidation state, XPS data of the Pd 3d region will indicate the degree of charge transfer to the framework through the shifting of Pd peaks to lower binding energies. This will be related to the Si/Al ratio (acidity) to determine the relationship between support acidity, Pd oxidation state (charge transfer), and selectivity. Additionally, acidity can influence both the reaction and deactivation mechanisms. The ability of the surface to dissociate H₂, a key step in the mechanism, will be evaluated through a H₂-TPR in which the peak temperature of H-species desorption can be correlated to “ease” of activation and support acidity. Time on stream data will be analyzed to show the deactivation rate of each catalyst and its dependence on support acidity. Taken together, this talk will demonstrate how the properties of Pd catalysts can be modulated inside the confinements of MFI framework, and develop structure-activity-stability relationships for the semi-hydrogenation of acetylene inside zeolite confinement.