Catalysis by palladium–rare-earth-metal (REPd3) intermetallic compounds: hydrogenation of but-1-ene, buta-1,3-diene and but-1-yne

Abstract

The hydrogenation reactions of but-1-ene, buta-1,3-diene and but-1-yne have been studied on a series of REPd₃ intermetallic compounds (RE = La, Ce, Pr, Nd, Sm) in a powdered form. Because the catalytic pretreatments were found to change activities and selectivities, bulk and surface characterisations were performed by XRD and XPS, before and after the catalytic tests. After 15 h pretreatment with H₂ at 573 K, these catalysts showed stable and reproducible activities and selectivities with characteristic changes throughout the series when compared to Pd/pumice catalysts. LaPd₃ was the most easily decomposed and its behaviour resembled that of a Pd/La₂O₃ catalyst. CePd₃ was only partly decomposed, the surface becoming partially transformed to metallic palladium and the catalytically active cerium compound, producing a highly active catalyst of low selectivity. Conversely, Pr(Nd,Sm)Pd₃ were not decomposed in the bulk and they were more selective than Pd/pumice. Typical trends in the hydrogenation rate ratios of but-1,3-diene to but-1-yne were also observed. Different electronic effects were proposed to explain the different catalytic behaviour of these palladium catalysts.