Hydrodesulfurization of thiophene on Ru/Al2O3 catalyst - Effect of Ru particle size on activity and selectivity

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 surfa ce Ru and sulfur species. The HDS reaction was carried out at 400 degrees C and atmospheric pressure using a pulse microreactor or a single-pass, diff erential reactor. The Ru/Al2O3 catalyst was pretreated by three different m ethods: oxidized in air and subsequently reduced in H-2 (Ru-OR), reduced in hydrogen (Ru-R), and sulfided in 10% H2S/H-2 (Ru-S). There are volcano-typ e curves for hydrogen adsorption with a maximum at pretreatment temperature of 300 degrees C, i.e., for the Ru-OR300 acid Ru-S300 catalysts. The Ru-S3 00 a with the greatest hydrogen uptakes of these catalysts offered the high est HDS activity. Ru particle size increased with the amounts of (S-2)(2-) and S-2 anions for the Ru-S catalyst, indicating that extensive sulfidation of the Ru/Al2O3 catalyst st 400 degrees C brought about the formation of l arge particles of ruthenium sulfide. The HDS activity increased with the nu mber of small Ru particles, and also with decreasing amount of (S-2)(2-) an d S2- anions. There is a good relationship between the amount of strongly c hemisorbed hydrogen and the XPS peak area of Ru metal (Ru 3d(5/2)). This in dicated that smaller Ru metal panicles with strongly chemisorbed hydrogen a re responsible for the HDS of thiophene on the Ru/Al2O3 catalyst. The amoun t 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 incre asing Ru particle size, which was associated with the content of (S-2)(2-) and S2- anions;. From these results, it was concluded that the HDS of thiop hene takes place on corner and edge sites of small metallic Ru particle and the hydrogenation of thiophene occurs on a large Ru particle with (S-2)(2- ) and S2- anions.