Hydrodesulfurization of Thiophene on Ru/Al<sub>2</sub>O<sub>3</sub> Catalyst

Abstract

The activity and selectivity of pretreated 0.49% Ru/Al2O3 catalysts used in hydrodesulfurization (HDS) of thiophene were studied, in terms of surface properties such as, hydrogen and CO adsorption, Ru particle size, and surface Ru and sulfur species. The HDS reaction was carried out at 400°C and atmospheric pressure using a pulse microreactor or a single-pass, differential reactor. The Ru/Al2O3 catalyst was pretreated by three different methods: oxidized in air and subsequently reduced in H2 (Ru-OR), reduced in hydrogen (Ru-R), and sulfided in 10% H2S/H2 (Ru-S). There are volcano-type curves for hydrogen adsorption with a maximum at pretreatment temperature of 300°C, i.e., for the Ru-OR300 and Ru-S300 catalysts. The Ru-S300 with the greatest hydrogen uptakes of these catalysts offered the highest HDS activity. Ru particle size increased with the amounts of (S2)2- and S2- anions for the Ru-S catalyst, indicating that extensive sulfidation of the Ru/Al2O3 catalyst at 400°C brought about the formation of large particles of ruthenium sulfide. The HDS activity increased with the number of small Ru particles, and also with decreasing amount of (S2)2- and S2- anions. There is a good relationship between the amount of strongly chemisorbed hydrogen and the XPS peak area of Ru metal (Ru 3d5/2). This indicated that smaller Ru metal particles with strongly chemisorbed hydrogen are responsible for the HDS of thiophene on the Ru/Al2O3 catalyst. The amount of CO desorbed from metallic Ru was well related to the HDS activity. On the other hand, the hydrogenation of butenes to butane increased with increasing Ru particle size, which was associated with the content of (S2)2- and S2- anions. From these results, it was concluded that the HDS of thiophene takes place on corner and edge sites of small metallic Ru particle and the hydrogenation of thiophene occurs on a large Ru particle with (S2)2- and S2- anions.