Activity of CoMo/g-Al 2 O 3 as a catalyst in hydrodesulfurization: effects of Co/Mo ratio and drying condition Y.S. Al-Zeghayer a , P. Sunderland b , W. Al-Masry a , F. Al-Mubaddel a , A.A. Ibrahim a , B.K. Bhartiya c , B.Y. Jibril a, * a Chemical Engineering Department, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia b Department of Chemical Engineering, The University of Leeds, Leeds LS2 9JT, UK c Saudi Aramco, Riyadh, Saudi Arabia Received 1 July 2004; received in revised form 2 December 2004; accepted 9 December 2004 Available online 26 January 2005 Abstract A series of g-alumina-supported cobalt–molybdenum hydrodesulfurization catalysts have been prepared with different ratios of cobalt to molybdenum (0.0–1.0) and under different drying temperatures (323, 373 and 423 K). The active components ions were loaded on the alumina via an incipient wetness impregnation method. The catalysts were converted to active sulfide form using dimethyldisulfide. Hydrodesulfurization (HDS) of dibenzothiophene (DBT) was tested at 550–683 K and 10 atm. Samples of the catalysts were characterized using SEM and XPS techniques. Changes in grain sizes and binding energy due to the cobalt–molybdenum interactions have been observed. The catalyst activities based on dibenzothiophene conversion rate constants and product (biphenyl BP and cyclohexylbenzene CHB) distributions, depended strongly on the Co/Mo ratios. CHB/BP ratio as high as 0.2 was obtained for Co/Mo of 0.2–0.4, while for higher Co/Mo ratios, no CHB was observed. The ratio of about 0.4 exhibited the highest rate constant. The drying temperature was found to improve the activities, with the lowest temperature showing the best performance in terms of dibenzothiophene degree of conversion. Such results suggest that cobalt and molybdenum are associated in a fixed proportion and that their distribution on the support surface, which in turn improves catalyst performance, could be modified by the catalyst preparation conditions. # 2004 Elsevier B.V. All rights reserved. Keywords: CoMo/g-Al 2 O 3 catalysts; Cobalt/molybdenum ratios; Hydrodesulfurization; Dibenzothiophene; Dimethyldisulfide; Co/Mo ratio; Drying condition; SEM; XPS 1. Introduction Sulfur reduction from gasoline using catalytic hydro- desulfurization (HDS) is a routine operation in petroleum refining processes. In this operation, sulfur-containing compounds such as thiophenes, dibenzothiophenes and mercaptans are removed. The removal is necessary in order to minimize the polluting effects of sulfur-containing gases such as SO 2 that may be released to the atmosphere. In addition, many catalysts employed in the refining down- stream operations could be poisoned by sulfur. This causes frequent shutdown and other operational difficulties. Perhaps the most important challenge presented by sulfur is its environmental degradation. This has made it necessary for the US Environmental Protection Agency (EPA) to review the allowable sulfur content of fuels, flue gases and other petroleum products. Recently, new guidelines have been established that, for instance, restrict the amount of sulfur allowed in diesel fuels to 1.3  10 2 g/dl 3 by the year 2010 [1]. This requires reduction of about 97% of the current level. Achieving this limit will require major improvement or redesign of the catalysts employed for HDS. Alumina-supported CoMo catalysts have been well established for hydrodesulfurization of oil fractions. The structures of both precursor and final catalysts have been extensively studied and the nature of the active sites has been proposed [2]. Studies were done on increasing the dispersion www.elsevier.com/locate/apcata Applied Catalysis A: General 282 (2005) 163–171 * Corresponding author. Tel.: +966 14676897; fax: +966 14678770. E-mail address: baba@ksu.edu.sa (B.Y. Jibril). 0926-860X/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2004.12.021