Contents lists available at ScienceDirect Applied Catalysis A, General journal homepage: www.elsevier.com/locate/apcata Structure-dependent catalytic properties of mesoporous cobalt oxides in furfural hydrogenation Chinh Nguyen-Huy a,1 , Jihyeon Lee a,1 , Ji Hui Seo a , Euiseob Yang a , Jaekyoung Lee a , Keunsu Choi a , Hosik Lee b , Jae Hyung Kim a , Man Sig Lee d , Sang Hoon Joo a,c , Ja Hun Kwak a , Jun Hee Lee a, ⁎ , Kwangjin An a, ⁎ a School of Energy and Chemical Engineering, Republic of Korea b School of Mechanical and Nuclear Engineering, Republic of Korea c Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea d Korea Institute of Industrial Technology (KITECH), Ulsan, 44413, Republic of Korea ARTICLE INFO Keywords: Mesoporous Cobalt oxide Catalyst Furfural Selectivity ABSTRACT As the development of noble metal free catalysts became important in the biomass conversion, catalytic hy- drogenation of furfural (FAL) is investigated over ordered mesoporous cobalt oxide (m-Co 3 O 4 ). When m-Co 3 O 4 is reduced at 350 and 500 °C in hydrogen, the original crystal structure of Co 3 O 4 is changed to CoO and Co, respectively. Here we examine the effect of the structure, porosity, and oxidation state of m-Co 3 O 4 to identify catalytically active species for hydrogenation of FAL. Among cobalt oxide catalysts having different crystal structures and symmetry, m-CoO having p6mm symmetry exhibits the highest activity. In product selectivity, the CoO phase induces FAL hydrogenolysis by selective production of 2-methyl furan (MF), while the Co 3 O 4 and Co phases promote preferential hydrogenation of side chain (carbonyl group) of FAL to furfuryl alcohol. Density functional theory calculations also reveal that the adsorption of FAL on CoO(111) is higher than Co(111). Overall, these studies demonstrate that CoO as the most active phase is responsible for the high FAL conversion and the distinct pathway of FAL to MF. 1. Introduction Ordered mesoporous materials are widely used as catalysts as well as supports, due to their uniform and well-ordered pore structures with high surface area [1–3]. The structure, composition, and pore size are easily controlled depending on the target catalytic applications. Nano- casting is a novel method to prepare mesoporous materials, in which the final morphologies of various transition metal oxides are de- termined by the internal pore structure of the template [4–6]. For ex- ample, when internal voids of the mesoporous silica SBA-15 with in- terconnected hexagonal pore structures are filled with cobalt nitrate precursor in solution, a replica Co 3 O 4 with interconnected, hexagonally ordered wire-structures (p6mm) is generated by thermal anealing and subsequent removal of the silica mold [7,8]. When the template is changed to mesoporous silica KIT-6 with interconnected cubic pore structures, the Co 3 O 4 replica with cubic pore structures (Ia3d) is pro- duced instead. When the mesoporous oxides are further treated with hydrogen, reduced surfaces are provided with new species at different oxidation states [7,9]. Mesoporous cobalt oxides have been investigated as excellent catalysts for many reactions: oxidation of H 2 O, CH 4 , CO, and xylene [10–17]; oxygen evolution reaction [18–21]; desulfuriza- tion of H 2 S[22,23]; and hydrogenation of CO [24]. In a notable ex- ample, Gu et al. reported that ordered mesoporous CoO produced by H 2 reduction of the mesoporous spinel Co 3 O 4 exhibited unexpectedly high activity due to the presence of octahedrally coordinated Co 2+ species in rock-salt CoO [13]. As a major product of biomass decomposition, furfural (FAL) re- quires further upgrading to produce more stable products such as ga- soline/diesel pool or other useful chemicals [25–28]. To produce transportation fuels, there is a high demand for selective deoxygenation that preserves the CeC bonds while breaking the CeO bonds. From fundamental point of view, FAL hydrogenation has been widely exploited as a probe reaction, because of its distinct reaction pathways. FAL with both C]C and C]O double bonds is converted to furfuryl alcohol (FA), furan (FR), tetrahydrofuran (THF), 2-methylfuran (MF), and tetrahydrofurfuryl alcohol (THFA) over various novel metal https://doi.org/10.1016/j.apcata.2019.117125 Received 10 April 2019; Received in revised form 22 June 2019; Accepted 27 June 2019 ⁎ Corresponding authors. E-mail addresses: junhee@unist.ac.kr (J.H. Lee), kjan@unist.ac.kr (K. An). 1 These authors have contributed equally. Applied Catalysis A, General 583 (2019) 117125 Available online 29 June 2019 0926-860X/ © 2019 Elsevier B.V. All rights reserved. T