Infrared and x-ray photoelectron spectroscopy study of chloride effect in palladium catalysts.

INFRARED AND X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF CHLORIDE EFFECT IN PALLADIUM CATALYSTS. Chloride poisoning is known as having an inhibitor effect in the activity of metal catalysis. In this work in situ infrared spectroscopy (FTIR) of adsorbed carbon monoxide and x-ray photoelectron spectroscopy (XPS) were used to investigate the effect of chloride presence in the electronic metal density in the d subshell of palladium dispersed on alumina. The chloride poisoning effect was interpreted as an electronic effect since a weak back-bunded Pd-CO was formed due to the decrease in the electronic density of the d subshell of palladium, which could be also detected by the higher Pd 3d(5/2) binding energy in the chloride presence. A similar poisoning effect was also observed for chloride free Pd/Al2O3 reduced at 500 degreesC, and it was interpreted based on the interaction of metal with the alumina surface. The use of molybdena/alumina binary system as support, yield a contrary effect due to the metal-support interaction.