On the sulfur-aided metal-support interaction in [formula omitted] catalysts

Abstract

The SMSI behavior displayed by sulfated Pt Al 2 O 3 Cl catalysts with relatively low sulfur content has been explained by the alternative reactions ▪ or ▪ Redox reaction (2) would be sulfur catalyzed, giving the so-called sulfur-aided SMSI. In this paper the SMSI behavior displayed by sulfided samples with only irreversibly held sulfur ( S Pt = 0.20–0.35 ) was studied by the changes in H 2 and O 2 chemisorption, infrared spectroscopy, temperature-programmed reduction and H 2S desorption at increasing temperatures. The changes in the 1380-cm −1 band (SO 2− 4 on the carrier) and in the 2060-cm −1 band (CO adsorption on Pt in linear form) were used to investigate the effects of the high-temperature reduction treatment. The TPR profiles of sulfated aluminas showed only one reduction peak at 650–680 °C; the presence of Pt gave rise to a low-temperature peak which appeared at 450–500 °C. Such a peak shifted to lower temperatures when the Pt content was increased. The data showed that the SMSI behavior of sulfated Pt Al 2 O 3 Cl samples is better explained in terms of redox reaction (1). During the HTR treatment Pt cata-lyzes the reduction of sulfate ions. The H 2S formed is adsorbed on the metal so that the H 2 chemisorption is suppressed by the S blockage of the surface. Subsequent oxidation treatment causes oxidized S species in the metal surface to migrate back to the support. The metallic fraction is regenerated and, as a consequence, the H 2 chemisorption capacity is restored.