Sulfurization of $\text{Pt}\text{Al}{}_2\text{O}{}_3\text{Cl}$ catalysts

Abstract

Sulfur-platinum interaction was studied by ir spectroscopy of the coadsorbed CO, competitive hydrogenation reactions, and chemisorption of O₂, CO, and H₂, $\text{Pt}\text{Al}{}_2\text{O}{}_3$ catalysts of different metal loadings and mean particle size were used. Infrared spectra for variable coverages of sulfur and CO were obtained. The predeposited S on Pt caused an upward shift of v(CO) from 2068 to 2083 cm⁻¹; a superimposed band that shifted to the lower frequencies for decreasing CO coverages was detected. The $\text{k}{}_{\mathrm{T}}{}_{\mathrm{B}}$ values ($\text{k}{}_{\mathrm{T}}{}_{\mathrm{B}}$, ratio of the adsorption equilibrium constant) for the competitive hydrogenation of benzene and toluene were determined. It was found that the $\text{k}{}_{\mathrm{T}}{}_{\mathrm{B}}$ ratio increases from 4.2 for unsulfided samples to 6.0 for sulfided samples. On the other hand, the irreversibly held sulfur on the metal increased the ratio of the reversibly adsorbed H₂ to the total adsorbed H₂. These results are discussed considering electronic, geometric, and surface heterogeneity effects. A “localized” modification of the metal by the electron-acceptor properties of sulfur is advanced as a possible explanation.