Isomerization reactions with sulfur-containing pentane over Metal/SO 42−/ZrO 2 catalysts

Abstract

The isomerization of the pentane that contains sulfur of 135 ppm as an ethylmethylsulfide was studied over Metal/SO 4 2−/ZrO 2 catalysts. Pd/SO 4 2−/ZrO 2 catalyst possessed stable isomerization activity and hydrodesulfurization (HDS) activity simultaneously, although the isomerization activity of Pt/SO 4 2−/ZrO 2 catalyst is weakened by the sulfur that is contained in the feed. Pd has the functions not only of the formation of carbenium ion from pentane but also of the desulfurization into H 2S from organic sulfur compounds. Pd seems to remain always in an activated state so that adsorbed sulfur can desorb promptly from the catalyst. The IR spectra of pyridine adsorbed on Metal/SO 4 2−/ZrO 2 catalysts were measured in order to analyze the reaction mechanism of sulfur-containing pentane. The IR spectra of pyridine adsorbed on spent Metal/SO 4 2−/ZrO 2 catalyst are obtained only on Lewis acid sites, although fresh catalysts are observed on both Brønsted acid sites and Lewis acid sites. This result shows that the isomerization reaction of pentane advances with the Lewis acid sites and the metal that causes the formation of carbenium ion. However, the Lewis acid sites are not observed with the Pt/SO 4 2−/ZrO 2 catalyst deactivated by sulfur. The sulfur adsorption on Pt causes the disappearance of the formation ability of atomic hydrogen, and carbon accumulates on the Lewis acid sites. On the other hand, the Pd/SO 4 2−/ZrO 2 catalyst keeps the Lewis acid sites even after the isomerization reaction of sulfur-containing pentane. The Lewis acid sites are not covered with carbon so that Pd has the functions of the desulfurization of sulfur compound and the supply of atomic hydrogen to SO 4 2−/ZrO 2. Therefore, the Lewis acid sites are the main active sites in the skeletal isomerization reaction of sulfur-containing pentane over Pd/SO 4 2−/ZrO 2 catalyst, and the sulfur tolerance of this catalyst can be explained by the hydrodesulfurization function of Pd and by the hydrogen supply to the Lewis acid sites.