Research PaperPd0.09Ce0.91O2-δ: A sustainable ionic solid-solution precatalyst for heterogeneous, ligand free Heck coupling reactions

- Pd0.09Ce0.91O2-δ was prepared using a simple and rapid single step solution combustion method.
- A highly efficient and heterogeneous protocol for the Heck cross-coupling reactions was developed.
- A wide variety of olefins and aryl halides were employed as starting materials.
- The catalysts could be reused for at least three times without any significant change in its in activity.

A quick and easy method for the preparation of Pd2+ metal ion substituted in ceria, Pd0.09Ce0.91O2-δ solid solution oxide, is described. The Pd0.09Ce0.91O2-δ solid solution oxide was fully characterized by XRD, ICP-OES, BET, XPS, SEM, EDX, TEM, TGA and Raman spectroscopy. All characterization techniques strongly suggested that Pd2+ was successfully incorporated into the lattice structure of ceria. The effect of the reaction conditions on the catalytic properties of the Pd0.09Ce0.91O2-δ solid solution catalyst initially was studied in detail with the model Heck reaction of iodobenzene and methylacrylate to obtain optimum reaction conditions. The Pd0.09Ce0.91O2-δ solid solution catalyst then afforded substituted alkenes in good to excellent yields under these optimum reaction conditions. Steric and electronic effects were also studied, and were found to influence the catalytic activity. Characterization of the used catalyst suggests that Pd2+ in Pd0.09Ce0.91O2-δ is reduced in situ to Pd0 when employed in the Heck cross-coupling reactions. The catalyst was easily recovered by centrifuge and reused three times without significant loss of catalytic efficiency.