Journal of Catalysis 190, 191–198 (2000) doi:10.1006/jcat.1999.2742, available online at http://www.idealibrary.com on Hydrodesulfurization and Hydrogenation Reactions on Noble Metal Catalysts I. Elucidation of the Behavior of Sulfur on Alumina-Supported Platinum and Palladium Using the 35 S Radioisotope Tracer Method Toshiaki Kabe, 1 Weihua Qian, Yosiki Hirai, Li Li, and Atsushi Ishihara Department of A pplied Chemistry, Tokyo University of A griculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan Received August 6, 1999; revised October 20, 1999; accepted October 25, 1999 Hydrodesulfurization (HDS) reactions of 35 S-radioisotope- labeled dibenzothiophene (DBT) were carried out overa series of γ - Al 2 O 3 -supported noble-metal-containing catalysts at 5.00 MPa and at 260 and 280 ◦ C. The amount of sulfur (S TOTAL ) accommodated on the catalyst and the amount of labile sulfur (S 0 ) participating in the reaction were determined using a direct method, the 35 S ra- dioisotope pulse tracer method, which has recently been developed by the authors. It was observed that both S TOTAL and S 0 increased linearly with an increase in active metal loading. At the same time, it was found that the sulfided test noble metal catalysts corresponded to a S/Pt (Pd) ratio of 0.25 and that almost all the labile sulfur on these catalysts was mobile in the HDS reaction. Further, the activ- ities of both HDS and hydrogenation reactions over the bimetallic catalyst (Pt–Pd) were higher than those of the monometallic cata- lysts tested together, whereas the synergetic effects observed on the Pt–Pd catalyst were not as significant as in typical Co–Mo catalyst cases. c  2000 Academic Press Key Words: noble metal catalyst; hydrodesulfurization; hydro- genation; 35 S radioisotope tracer method; platinum; palladium. 1. INTRODUCTION The growing knowledge about the aromatics contained in diesel fuels with respect to their adverse effects causing undesired emissions in exhaust gases and resultant health hazards has led to limitations on the use of these aromat- ics around the world. Under such circumstances, refiners are required to develop new catalysts capable of higher hydrogenation activity in order to meet the emission stan- dardsthat have been made more stringent each year.Noble metal catalysts such as γ -Al 2 O 3 -supported platinum and palladium catalysts are known to be highly active in the hydrogenation ofaromatics.Cooper et al. reported that un- der moderate conditions, a γ -Al 2 O 3 -supported platinum 1 To whom correspondence should be addressed. catalyst can saturate 60–70% of the aromatics occurring in Kuwait heavy gas oil (HGO) (1). However, one of the major problems associated with the use of platinum and palladium is their high sensitivity to the sulfur compounds that are usually present in hydrogenation feedstocks (2–4), and it is often taken as a fact that the feedstocks normally need a severe hydrotreating pretreatment to attain sulfur concentration reductions below a few parts per million (5). Thus, noble metal catalysts will be of limited use because ofsuch severe pretreatment unlesstheyare proven to with- stand the sulfur tolerance problems involved. Recent stud- ies show that the addition of a second transition metal may effectively improve the activity of these catalysts and their tolerance to sulfur (6–11).It hasalso been reported that the sulfur tolerance of a noble metal catalyst can be increased with the use of zeolite as a support (6, 12–16). The sulfur poisoning was attributed to the fact that the adsorption of H 2 S decreases the metal–support interaction, and thereby promotesthe platinum migration which eventuallyleadsto the increase in platinum particle size (9, 17). Meanwhile, recent studies show that some noble metal catalysts may not be as sensitive to sulfur as has generally been recog- nized (18–21). Therefore, we feel that it is worth while to investigate the fundamental catalytic features of the noble metal catalysts of our interest. Before our present study, radioactive 35 S-labeled diben- zothiophene ([ 35 S]DBT) was synthesized, and its hy- drodesulfurization (HDS) reaction was carried out accord- ing to the 35 S radioisotope pulse tracer method (RPTM) over sulfided Mo-based catalysts under practical HDS conditions (22–26). The hydrogenation (HYD) activity of phenanthrene (PHE) over monometallic and bimetal- lic catalysts—Pt/Al 2 O 3 , Pd/Al 2 O 3 , and Pt–Pd/Al 2 O 3 —was then investigated in the presence of dibenzothiophene (DBT).Thebimetalliccatalyst(Pt–Pd/Al 2 O 3 ) showed some synergetic effects, but not as significant as in typical Co– Mo catalyst cases, whereas the former showed better 191 0021-9517/00 $35.00 Copyright c  2000 by Academic Press All rights of reproduction in any form reserved.