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Pd(II)/Al₂O₃ and Pd(0)/Al₂O₃, containing 0.6% of palladium were characterized by EDX, SEM and XRD methods and used as catalysts of the Heck coupling of bromobenzene with butyl acrylate at 140 °C in molten [Bu₄N]Br salt. Monoarylated (trans-PhCH = CHC(O)OBu) (1) and diarylated (Ph₂C = CHC(O)OBu) (2) products were obtained in amounts dependent on kind of base present in the system (Scheme 1). During the reaction palladium was partially leached from the support forming [Bu₄N][PdBr₄] complex that catalyze Heck reaction or undergo readsorption on Al₂O₃. These soluble palladium complexes are partially reduced to Pd soluble nanoparticles which can also be anchored on Al₂O₃ giving active catalyst of Pd(0)/Al₂O₃ type. Reduction of Pd(II) to Pd(0) during catalytic process at the presence of bases (NaHCO₂, NaHCO₃, NaOAc, Cs₂CO₃) was studied by XPS method and the total reduction was …