Cite this: RSC Advances, 2013, 3, 12635 Received 21st March 2013, Accepted 19th June 2013 Hydrodeoxygenation of bio-oil over Pt-based supported catalysts: importance of mesopores and acidity of the support to compounds with different oxygen contents3 DOI: 10.1039/c3ra41405a www.rsc.org/advances Yuxin Wang,* ab Jinhu Wu a and Shengnian Wang* b The importance of the acidity and mesoporous structure to the hydrodeoxygenation activity of catalysts for bio-oil upgrading was investigated. By testing three model bio-oil compounds, we showed that catalysts with a strong acidity (e.g. ZSM-5) have a high hydrodeoxygenation activity, while the mesoporous struc- ture of the support can further improve the catalytic performance of ZSM-5. 1. Introduction Bio-oil shows promising potential as a feedstock of hydrocarbon products to help reduce the current global challenges of fossil fuel shortage, climate change and environmental problems. 1–3 However, its high corrosivity, poor thermal stability, and low heat capacity impede the wide acceptance of bio-oil in many industrial practices. 4 Such poor oil quality is caused, largely, by the high oxygen content of its many compounds (up to 40%). Currently, several approaches, including the catalytic pyrolysis of biomass, zeolite cracking, and hydrodeoxygenation, have been developed to reduce the oxygen content of bio-oil. The biomass pyrolysis process can directly convert biomass to aromatics, but with a low liquid yield. 5 The catalytic cracking of bio-oil with zeolites mainly eliminates oxygen in the form of CO, CO 2 and H 2 O, which results in serious coking problems. 6 Compared to these two deoxygena- tion processes, hydrogenation, a well-developed petroleum refin- ing technology, seems more desirable for bio-oil upgrading, because the oxygen in bio-oils can be efficiently removed as H 2 O during hydrogenation and most of the carbon is retained in the final hydrocarbon product, rather than resulting in coke on the catalyst. 7 In the traditional hydrogenation process, sulfided Co–Mo and Ni–Mo catalysts are commonly used to efficiently remove S, N, and O from oil. Under high temperature (.573 K) and high pressure (.8 MPa) conditions, saturated hydrocarbons can be mass produced. However, such harsh hydrotreating conditions are inappropriate for bio-oil hydrodeoxygenation. 8 Bio-oil would be quickly decomposed and polymerized under these conditions, resulting in a serious char–coke problem on the catalyst and a quick loss of its catalytic activity. Moreover, the low sulfur content of bio-oil compounds means it is not desired to use traditional sulfided catalysts for their hydrodeoxygenation. 9 Some recent studies have found that noble metal based catalysts showed a high hydrodeoxygenation activity at lower temperatures (473 K) and no need for a pre-sulfidisation, making them suitable for bio-oil deoxygenation. 10 However, further studies found that the physical and chemical properties of their support material play important roles in the catalytic activity of these catalysts. Various supports have been investigated, including alumina, silica, active carbon, and zeolites. 11–14 Their various acidities and pore structures produced different catalytic activities when hydrodeoxygenating bio-oil. For example, an early study showed that Pt clusters dispersed on zeolite had a much better catalytic activity than those on alumina or silica when hydrodeoxygenating phenol-type bio-oil compounds. 15 However, for large bio-oil molecules, such as phenolic oligomers and dibenzofuran (DBF), their catalytic activity was insufficient. Our early study demonstrated that when Pt was impregnated on mesoporous supports, the hydrodeoxygenation activity for DBF could be greatly improved. 16 These findings suggest that both the acidity and pore structure might be important for catalysts in bio-oil hydrodeoxygenation. Hence, we prepared Pt-based catalysts with three different support materials and explored the importance of the acidity and mesopores on the catalytic performance. Specifically, Pt supported on the conven- tional Al 2 O 3 (mesoporous support with weak acidity), zeolite ZSM- 5 (microporous support with strong acidity), and mesoporous zeolite ZSM-5 17 (MZSM-5 with hierarchical porosity and strong acidity), were used in the evaluation. Three common bio-oil compounds with various oxygen contents and molecular sizes, dibenzofuran (DBF, C 12 H 8 O with a 9 wt.% oxygen content, 0.87 6 0.50 nm molecule size), cresol (C 7 H 8 O with 15 wt.% oxygen content, 0.59 6 0.50 nm molecule size), and guaiacol (GUA, a Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao, Shandong 266101, P. R. China b Institute for Micromanufacturing, Louisiana Tech University, 911 Hergot Avenue, Ruston, Louisiana 71270, USA. E-mail: yxwang@latech.edu; swang@latech.edu 3 Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra41405a RSC Advances COMMUNICATION This journal is ß The Royal Society of Chemistry 2013 RSC Adv., 2013, 3, 12635–12640 | 12635 Published on 19 June 2013. Downloaded by Library of Chinese Academy of Sciences on 20/05/2014 08:30:15. View Article Online View Journal | View Issue