Studies of the Interaction of Palladium Particles with Acid Sites of δ-Al2O3 and δ-Al2O3/Ni-HPCM Composite

Variations in the concentrations of oxide sites in the traditional δ-Al₂O₃ and composite δ-Al₂O₃/Ni-HPCM (highly porous permeable cellular material) supports before and after supporting the active component were studied in order to identify the reasons for the formation of different states of palladium species in these oxides. It was established that the contents of proton-donor OH groups and aproton Lewis sites were 316 and 575 mmol/g in δ-Al₂O₃ that was as high as 1.4 and 1.6 times, respectively, of those in δ-Al₂O₃/Ni- HPCM, while the quantities of Lewis sites with QCO ≥ 35.0 kJ/mol and OH fragments bonded to penta-coordinated aluminium cations in δ-Al₂O₃ were 1.8 times of those in alumina on Ni- HPCM. After supporting palladium, the loss in number of these sites in δ-Al₂O₃ was ca. 1.7 times of that in Pd/δ-Al₂O₃/Ni- HPCM. This fact can argue for a stronger interaction of palladium species with the surface of the traditional δ-Al₂O₃ and indicate a wider range of charge states of palladium in the Pd/δ-Al₂O₃ catalyst. The latter leads to a lower selectivity of hydrogenation of acetylene to ethylene in the presence of Pd/δ-Al₂O₃ compared to that in the presence of Pd/δ-Al₂O₃/Ni- HPCM.

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