Catalytic performance and elution of Pd in the Heck reaction over zeolite-supported Pd cluster catalyst

摘要

The Heck reaction was carried out in N,N-dimethylacetamide (DMAc) solvent with Pd-supported zeolites as catalysts. Particular attention was paid to the influence of pretreatment conditions and the kind of zeolites on the catalytic activity and the elution of Pd. Pd2+ ion-exchanged zeolites exhibited relatively high activity in the reaction. However, a considerable amount of Pd was dissolved in the solvent. Deposition of agglomerated Pd-0 was observed after the reaction, suggesting the dissolved Pd2+ species was reduced with DMAc during reaction. Pd-0-loaded zeolites were prepared by the reduction of Pd oxide/zeolites with H-2. Among Pd-0-loaded catalysts, Pd-0/H-Y exhibited high activity. The dissolution of Pd was significantly suppressed over Pd-0/H-Y, as indicated by ICP analysis of the solution. The recycled use of Pd-0/H-Y was possible through oxidation and successive reduction with H-2. The growing process of Pd clusters in H-Y was followed by energydispersive XAFS (partly Quick XAFS) during temperature-programmed reduction in diluted H-2. It was found that stable Pd-13 clusters that interacted with Bronsted acid sites were generated in the pore of H-Y. The Pd-13 clusters were ascribed to the active and insoluble species in the Heck reaction. (c) 2005 Published by Elsevier Inc.