Journal of Molecular Catalysis A: Chemical 388–389 (2014) 47–55 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical jou rn al hom epage: www.elsevier.com/locate/molcata Selective conversion of m-cresol to toluene over bimetallic Ni–Fe catalysts Lei Nie, Priscilla M. de Souza 1,2 , Fabio B. Noronha 1,2 , Wei An 3 , Tawan Sooknoi 4 , Daniel E. Resasco ∗ School of Chemical, Biological, and Materials Engineering, The University of Oklahoma, Norman, OK 73019, USA a r t i c l e i n f o Article history: Received 12 May 2013 Received in revised form 17 September 2013 Accepted 21 September 2013 Available online 12 October 2013 Keywords: Ni–Fe/SiO2 Hydrodeoxygenation Cresol Biomass Tautomerization a b s t r a c t The catalytic conversion of m-cresol in the presence of H 2 has been investigated on SiO 2 -supported Ni, Fe, and bimetallic Ni–Fe catalysts at 300 ◦ C and atmospheric pressure. Over the monometallic Ni catalyst, the dominant product is 3-methylcyclohexanone while 3-methylcyclohexanol and toluene appear in smaller amounts, even at high conversions. By contrast, on Fe and Ni–Fe bimetallic catalysts, the dominant prod- uct is toluene while the hydrogenation products (3-methylcyclohexanone and 3-methylcyclohexanol) are practically negligible in the entire range of conversions. To explain these differences, we have proposed a deoxygenation path that starts with the tautomer- ization of m-cresol to an unstable ketone intermediate (3-methyl-3,5-cyclohexadienone). The fate of this intermediate is determined by the ability of the catalyst to either hydrogenate the carbonyl group or the ring. The former would mostly occur on Fe and Ni–Fe catalysts that contain an oxophilic metal (Fe), while the latter would occur on Ni, which has a higher affinity for the aromatic ring. Hydrogenation of the carbonyl group produces a very reactive unsaturated alcohol (3-methyl-3,5- cyclohexadienol), which can be easily dehydrated to toluene. This would explain the high selectivity of Fe and Ni–Fe to toluene. By contrast, hydrogenation of the ring would result in 3-methylcyclohexanone, which can be further hydrogenated to 3-methylcyclohexanol. On supports that contain acid sites, which are active for dehydration, the formation of toluene would occur via dehydration of the alcohol and sub- sequent dehydrogenation. On the catalysts investigated in this work, dehydration of the corresponding alcohol does not occur, so the only path to toluene is via hydrogenation of the carbonyl of the unstable ketone intermediate. In addition, to the products mentioned above, xylenol is also observed in significant yields, which indicate that transalkylation of m-cresol is another reaction path occurring on these catalysts. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Phenolics are abundant components of the liquid product (bio- oil) obtained from the fast pyrolysis of biomass. They derive from both pyrolytic decomposition of lignin and condensa- tion/aromatization of small oxygenates. They can represent an important building block for potential production of fuels and ∗ Corresponding author. Tel.: +1 405 325 4370; fax: +1 405 325 5813. E-mail address: resasco@ou.edu (D.E. Resasco). 1 Permanent address: Depto de Engenharia Química/Instituto Militar de Engen- haria, Prac ¸ a Gal. Tiburcio, 80, CEP 22290-270, Rio de Janeiro, Brazil. 2 Permanent address: Instituto Nacional de Tecnologia (INT), Laboratório de Catálise, sala 518, Av. Venezuela 82, CEP 20081-312, Rio de Janeiro, Brazil. 3 Permanent address: Chemistry Department, Brookhaven National Laboratory, P.O. Box 5000, Upton, NY 11973-5000, USA. 4 Permanent address: King Mongkut’s Institute of Technology Ladkrabang, Cha- longkrung Road, Ladkrabang, Bangkok 10520, Thailand. chemicals from biomass. However, following the primary conver- sion step, an effective catalytic upgrading step is needed in the production of useful products [1–6]. As we have previously pointed out [7], the upgrading process should not only minimize the oxy- gen content in the product, but also maximize carbon retention. As a result, conventional hydrotreating, the most common and effec- tive method that has been tested for hydrodeoxygenation [8,9] may not be the optimum path for upgrading of bio-oil with max- imum carbon efficiency. We have recently investigated different paths, including ketonization, aldol condensation, aromatization and alkylation to accomplish the formation of C C bonds before deoxygenation, which maximizes the liquid fuel yield and carbon efficiency [10–12]. Several groups have investigated the use of sulfided catalysts (e.g., CoMo, NiMo) typically used in conventional hydrotreating for the deoxygenation of biomass-derived feedstocks [13]. These catalysts require addition of H 2 S to remain stable and active; how- ever, sulfidation is not required in the HDO of biomass-derived 1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molcata.2013.09.029