Effect of the acid-base properties of Pd-Ca/Al2O3 catalysts on the selective hydrogenation of phenol to cyclohexanone: FT-IR and TPD characterization

The effect of the addition of calcium as promoter on the acid-base properties of the Pd/Al2O3 system has been studied by FT-IR of pyridine, pyrrole and CO2 adsorbed and by TPD of CO2 in order to better clarify the role of calcium on the performance of palladium supported catalysts in the selective hydrogenation of phenol to cyclohexanone. The obtained results have shown that the addition of calcium causes a decrease in the acidity of the system, essentially in terms of amount of acid sites, and a corresponding increase in the number and strength of the basic sites. It has been suggested that the promoter enhances the catalytic performance of Pd/Al2O3 through a variation of the acid-base characteristics of the support leading to a modification of the electronic surroundings of Pd sites on which hydrogen is activated. (C) 1998 Elsevier Science B.V. All rights reserved.