Molecular Catalysis 441 (2017) 28–34 Contents lists available at ScienceDirect Molecular Catalysis j o ur nal ho me page: www.elsevier.com/locate/mcat Editor’s choice paper Selective hydrodeoxygenation of guaiacol to phenolics over activated carbon supported molybdenum catalysts Zhe Cai a , Fumin Wang a,∗ , Xubin Zhang a,∗ , Rosine Ahishakiye b , Yi Xie a , Yu Shen a a School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China b School of International Education, Tianjin University, Tianjin 300072, PR China a r t i c l e i n f o Article history: Received 24 April 2017 Received in revised form 22 July 2017 Accepted 29 July 2017 Keywords: Hydrodeoxygenation Guaiacol Molybdenum Reaction pathways a b s t r a c t Activated carbon-supported molybdenum dioxide catalyst and molybdenum carbide catalyst were pre- pared by reduction in hydrogen with different temperatures. Hydrodeoxygenation (HDO) of guaiacol was investigated in 3 MPa initial H 2 pressure with these two catalysts. Phenolics were detected as the main products when catalyzed by molybdenum dioxide catalyst. Through analyzing the HDO selectiv- ity of guaiacol and the intermediates including 1,2-dihydroxy-3-methylbenzene, catechol, phenol and anisole, the HDO reaction pathways of guaiacol over Mo-based catalysts were proposed. In the first stage, transalkylation and breaking of three C O bonds take place to produce 1,2-dihydroxy-3-methylbenzene, catechol, phenol and anisole, whereafter cresol, phenol, toluene and benzene are produced. Furthermore, the effects of reaction temperatures and solvents on HDO of guaiacol were investigated. Using tetralin as solvent, in 3 MPa initial H 2 pressure and at 573 K, the conversion of guaiacol reached 98% with phenolics as the major product and the selectivity was greater than 91% after three hours of reaction time. © 2017 Elsevier B.V. All rights reserved. 1. Introduction For the nonrenewable property and continuous consumption of fossil energy, there is an urgent need for renewable energies. Bio- oils can be produced via the pyrolysis of lignocellulosic biomass which is regarded as ideal green energy sources [1]. The pyroly- sis oils are complex mixtures containing arboxylic acids, ketones, aldehydes, carbohydrates, aldehydes, furans and so on [2,3]. The pyrolysis oils are too high oxygen content to be used as fuel addi- tions, so they must be dealed with a hydrodeoxygenation process to reduce the oxygen content and increase energy value [4,5]. Thus, two-stage upgrading strategy was proposed in which the pyrolysisi oil was produced from pyrolysis of biomass and then hydrodeoxy- genation is performed to decrease the oxygen content [6]. Lignin is a very complex polymer with components includ- ing of coniferyl, sinapyl, and p-coumaryl alcohol [7]. For the study of hydrogenation of pyrolysis oils, guaiacol which is a small molecule with similar functional groups has been often studied as a model compound because of its three different oxygen-carbon bonds: C(sp3)–OAr (methoxy group), C(sp2)–OMe and C(sp2)–OH (hydroxyl) with the bond energies about 247, 356 and 414 kJ/mol, ∗ Corresponding authors. E-mail addresses: wangfumin@tju.edu.cn (F. Wang), tjzxb@tju.edu.cn (X. Zhang). respectively [8,9]. These three bonds are present in a large number of functional groups of lignin. Initial HDO catalysts referenced to the hydrodesulfurization (HDS) catalysts and the hydrodenitrogenation (HDN) catalysts [10]. Commercial sulfided NiMo and CoMo catalysts supported over acti- vated alumina were applied in the research of HDO [11], while catalysts supported on activated carbon, silica, zeolite, zirconia were investigated also for this process [12,13]. Van Ngoc Bui et al. [13] reported the support effect for CoMoS catalysts on HDO activity and selectivtity where zirconia allowed very high catalytic activi- ties and selectivity towards C arom -O hydrogenolysis. However, the sulfide catalysts are easy to be deactivated for the loss of sulfur species and the oxidation of the sulfur species to sulphate and sulphur may be introduced into product stream. [14] Early studies of noble metal catalysts have shown that such cat- alysts have a good activity on HDO of guaiacol. [4,9,15,16] Jingbo Mao et al. showed gold nanoparticles supported on TiO 2 exhibited remarkable selectivity to phenolics from guaiacol hydrodeoxy- genation [17]. Two major pathways to form phenol are proposed, (1) demethoxy of guaiacol and (2) hydrogenation of C(sp3)–OAr bond to form catechol and hydrodehydroxylation of catechol to form phenol followed. Recently, novel non-sulfurized and non-noble metal catalysts have been widely studied, including Ni, Mo, Co, Cu, Mn, W, and the like. The carbides [18], phosphides [19] and nitrides [20] of http://dx.doi.org/10.1016/j.mcat.2017.07.024 2468-8231/© 2017 Elsevier B.V. All rights reserved.