Hybrid macroporous Pd catalytic discs for 4-nitroaniline hydrogenation: Contribution of the alginate-tetraalkylphosphonium ionic liquid support

Tetraalkylphosphonium ionic liquid (IL) was immobilized in a composite material made of alginate and cellulose fibers (to strengthen the gel) conditioned under the form of highly porous discs. These materials have been used for immobilizing Pd(II) by adsorption from HCl solutions. The metal reduction allows to prepare a catalytic material that was successfully used for the hydrogenation of 4-nitroaniline into p-phenylenediamine using formic acid as the hydrogen donor. The main objective of the study is to understand the contribution of the IL in the catalytic activity. The hydrogenation kinetics were compared for raw material (containing the IL) and for methanol-washed material (without IL) for 8 successive catalytic runs. The presence of the IL allows to stabilize Pd micro/nanoparticles and prevents their release to the solution.

Left panel: SEM photograph of macroporous catalytic disc (alginate + ionic liquid + Pd). Right panel: Comparison of kinetic profiles for 4-nitroaniline hydrogenation using IL-supported catalytic disc (top) and IL-free disc (bottom) for 8 successive cycles.Figure optionsDownload as PowerPoint slideHighlights
► Palladium is immobilized on macroporous ionic liquid-alginate composite material.
► The Pd//IL/Alginate catalytic discs are efficient for 4-nitroaniline hydrogenation.
► The catalytic discs can be used in dynamic continuous mode.
► The IL contributes to metal immobilization and to catalyst stability.
► After IL washing the catalyst rapidly looses catalytic efficiency when recycled.