Carlos E. Gigola

Characterization of Pd and PdPbα-Al2O3 catalysts. A TPR-TPD study

Low loaded (< 0.5 wt.-%) palladium on α-Al2O3 catalysts were prepared using palladium acetylacetonate as a chemical precursor. Temperature programmed reduction studies (TPR) indicate that in the initial oxidized state a fraction of palladium exhibits a strong interaction with the alumina support. Hydrogen treatments remove the interaction allowing the formation of palladium particles that upon reoxidation stabilize the palladium as PdO1.4. Bimetallic PdPb catalysts were obtained by reacting the palladium catalysts with tetra-n-butyl lead. Hydrogen and carbon monoxide desorption studies (TPD) have shown that progressive lead addition suppresses the dissociative adsorption of hydrogen as well as the multiple coordinated forms of carbon monoxide. For hydrogen, the TPD spectra supports the existence of an ensemble effect upon alloying. On the other hand the increased adsorption strength of multiple coordinated carbon monoxide suggested the presence of a ligand effect. Another important effect of lead on the TPD of carbon monoxide is the inhibition of carbon dioxide formation. The role of lead in improving the selectivity of alkynes hydrogenation reactions is discussed.