Journal of Catalysis 195, 31–37 (2000) doi:10.1006/jcat.2000.2968, available online at http://www.idealibrary.com on Origin of Cracking Functionality of Sulfided (Ni) CoMo/SiO 2 –ZrO 2 Catalysts M. S. Rana, B. N. Srinivas, S. K. Maity, G. Murali Dhar, 1 and T. S. R. Prasada Rao Catalysis Division, Indian Institute of Petroleum, Dehradun 248 005, India Received February 1, 2000; revised May 2, 2000; accepted June 17, 2000 DEDICATED TO PROFESSOR F. E. MASSOTH ON THE OCCASION OF HIS 75TH BIRTHDAY A systematic investigation of the hydrocracking activity of Mo, CoMo, and NiMo catalysts as a function of support composition, Mo content, and Co orNi content on supported ZrO 2 –SiO 2 catalysts of varying composition (Zr/Zr + Si = 0.0, 0.15, 0.30, 0.45, 0.70, 1.0) carried out in a microcatalytic reactor at 400 ◦ C and atmospheric pressure is presented. Varying the composition of the support, the Mo content, and the Co or Ni content was studied. Cumene crack- ing in the presence of hydrogen on the sulfided catalysts indicated that the supported molybdenum phase and the promoted counter- parts contribute significantly to the cracking functionality of the catalysts. From the studies based on SiO 2 and carbon supported catalysts it appears that it is unlikely that the observed high ac- tivities of supported MoS 2 and its promoted analogues are due to increased activity as a result of reduction in coke formation on the support surface. The creation of sulfhydryl groups and their role in generating the acid function are discussed. c  2000 Academic Press Key Words: CoMo catalysts; ZrO 2 –SiO 2 support; oxygen chemi- sorption; catalytic cracking functionality; hydroprocessing catalysts. 1. INTRODUCTION Sulfided Co–Mo and Ni–Mo hydroprocessing catalysts supported on various oxide supports were studied in rela- tion to hydrotreating and hydrocracking (1–4). These cata- lysts present hydrogenolysis, hydrogenation, and hydro- cracking functionalities (5, 6). While extensive studies have been carried out on the hydrogenolysis and hydrogenation functionalities of supported MoS 2 and WS 2 , there is only a small number of studies on the hydrocracking function- ality of these active components because it was generally believed that the hydrocracking functionality is related to the support only. The cracking functionality of the sup- port or the active component is generated by the acid sites present on the support or on the active component. There- fore, the question is whether the active component con- 1 To whom correspondence should be addressed. Fax: 091-135-671986. E-mail: gmurli@iip.res.in. tainsBrønsted acid sitesthat are strongenough to generate significant acidity compared to the supports. There have been a number of studies on the acidity of (Ni) CoMo/γ - Al 2 O 3 systems, the earliest of which focused on the acidity in the oxidicstate.These studiesrevealed that pure γ -Al 2 O 3 has Lewis acid sites only, while Mo/γ -Al 2 O 3 contains both Lewis and Brønsted acid sites (7, 8). Sulfidation or reduc- tion ofthese catalystsresulted in the disappearance ofthese Brønsted sites. However, Topsøe and Topsøe reported the presence of Brønsted acid sites in sulfided Mo/γ -Al 2 O 3 when pyridine was used at high temperatures (9). The ab- sence ofBrønsted sitesin other studieswasattributed to the activated nature of the adsorption of the probe molecule pyridine. Using dimethylpyridine as the probe molecule, Petit et al. (10) recently showed that Brønsted acid sites are indeed present on Mo, CoMo, and NiMo supported on γ - Al 2 O 3 and that the number of these sites increased due to the presence of H 2 S. There is always a significant concen- tration of H 2 S in industrial reactors; therefore, it is likely that the sulfided molybdenum phase has significant crack- ing functionality under actual reaction conditions. Catalytic reactions can be used not only to test the crack- ing functionality but also to test the acidity of the catalysts. Boorman et al. (11–13) studied acidity and cumene crack- ing activity on fluorinated CoMo/γ -Al 2 O 3 catalysts in ox- ide,reduced,and sulfided formsand concluded that sulfided catalysts are less active than the oxide forms. Massoth and co-workers (5, 6) studied the cracking of isooctene on var- ious supported Mo catalysts and found significant activ- ity for the cracking of isooctene to isobutene (14). Small amounts of cracking products were also observed during hexene hydrogenation on CoMo catalysts (15). Appreci- able dealkylation of m -diisopropylbenzene to cumene was also reported (5).Dealkylation of1-methylnaphthalene has been reported (16) to take place over Co-and Ni-promoted molybdenum catalysts. Significant cracking of isooctene was observed on silica-supported CoMo catalysts, which indicates that the sulfided CoMo active phase is the seat of hydrocracking activity; it is well known that SiO 2 surfaces 31 0021-9517/00 $35.00 Copyright c  2000 by Academic Press All rights of reproduction in any form reserved.