Biofuels DOI: 10.1002/ange.201108306 Upgrading Pyrolysis Oil over Ni/HZSM-5 by Cascade Reactions** Chen Zhao and Johannes A. Lercher* Bio-oil, produced by fast pyrolysis or liquefaction of ligno- cellulosic biomass, is an aqueous, highly oxofunctionalized (but nearly sulfur-free) mixture of light-to-medium hydro- carbons containing 15–30 wt % H 2 O. [1] Although it is consid- ered to be a promising basis for second-generation energy carriers, the corrosive nature, low vapor pressure, high viscosity, and instability of bio-oil limit its direct application. Currently, bio-oil is primarily used for generating heat, but it has a heating value of below 19 MJ kg À1 , as compared to 42– 44 MJ kg À1 for conventional fuel oil. [2] When it is directly burned in diesel engines, bio-oil has ignition difficulties owing to its low heating value, and the thermally unstable compo- nents leading to excessive coking. [3] In principle, the production of high-grade transportation fuels from bio-oil is feasible; hydrogenation and hydrodeox- ygenation (HDO) with sulfide catalysts such as cobalt- or nickel-doped molybdenum sulfides are currently used. How- ever, these sulfide catalysts contaminate the products by sulfur transfer, and the removal of this sulfur from the surface of the catalysts by a reverse Mars van Krevelen mechanism causes them to eventually deactivate. [4] An alternative approach, based on zeolites, simultaneously catalyzes several reactions, including dehydration, cracking, polymerization, deoxygenation, and aromatization at temperatures between 623 and 723 K. Under these reaction conditions, oxygenates are mostly converted into aromatic molecules and carbona- ceous deposits, while the yield to alkanes does not exceed 25 %. [5] As pyrolysis oil contains high concentrations of water along with the reactive oxygen-containing compounds, it is highly beneficial to convert the aqueous mixture under mild conditions with water-tolerant catalysts. The good solubility of hydrogen in water, as exemplified by the successful conversion of polyols [6] and terpenes, [7] and the phase separation between the aqueous phase and the hydrocarbons produced, are further advantages for this approach. Previ- ously we reported a catalytic system with dual functions, combining carbon-supported noble metal catalysts and min- eral/organic acids for the aqueous-phase hydrodeoxygenation of the phenolic fraction of bio-oil at 523 K, [8a,b] achieving quantitative yields of alkanes. The combination of Raney Ni as base metal and Nafion/SiO 2 as solid acid has subsequently been shown to also be an efficient and recyclable dual- functional catalyst combination. [8c] However, the high cost and difficulty of handling of such a catalyst prohibit scale-up for large-scale continuous processes. Recently, the bifunc- tional (metal/acid) catalysts have also been used for efficient hydrodeoxygenation of phenols in both ionic liquids [8d] and the gas phase ; [8e] notably, in the absence of water and only for individual model components. Herein, we report a new, stable, and widely applicable catalyst, zeolite HZSM-5 with a pore system containing a substantial fraction of Ni metal particles. This catalyst can quantitatively produce C 5 –C 9 hydrocarbons from paraffins, naphthenes, and aromatic molecules in a cascade reaction by hydrodeoxygenation of n-hexane-extracted crude bio-oil in the presence of substan- tial concentrations of water under mild reaction conditions (523 K, 5 MPa H 2 ). The crude bio-oil tested for this work is a red to black viscous liquid derived from thermal pyrolysis of pine trees (Netherlands BTG-BTL Company). The typical properties and composition of this pyrolysis oil are compiled in Table S1 of the Supporting Information. The composition of this oil can be roughly divided into water (15–30 wt %); water-soluble acetic acid, sugars, and polyols; and n-hexane-soluble organic molecules including phenols, ketones, aldehydes, and furans. The acetic acid, sugars, and polyols fraction can be efficiently used to generate H 2 through aqueous phase reforming (APR). [6] As lignocellulosic biomass consists of roughly 70 % cellulose and hemicellulose, and 1 mol glucose can generate 13 mol H 2 through APR, the H 2 produced by these components is sufficient for selective hydrodeoxygenation of the rest of the organic fraction to a hydrocarbon trans- portation fuel. With sugars and sugar derivatives remaining in the water phase, the n-hexane-soluble fraction of the bio-oil consisted mainly of furan and phenol, as well as ketone and aldehyde components, and accounted for approximately 40 % of the total carbon contained in the crude bio-oil, as determined by elemental analysis after solvent evaporation. The components of n-hexane-extracted bio-oil mainly include C 5 –C 6 substituted furans, ketones, and aldehydes derived from the deconstruction of cellulose and hemicellu- lose, as well as C 6 –C 9 substituted phenols derived from the deconstruction of lignin (Figure 1a). These compounds are substituted with alcohol, ketone, and ether functional groups, which tend to react to form larger molecules. [9] Hydrodeoxygenation of such a mixture, on Ni/HZSM-5 in a semibatch reaction for four hours at 523 K and 5 MPa H 2 with a stirring speed of 680 rpm, allowed us to quantitatively convert it to the corresponding C 5 –C 9 hydrocarbons. The organic part of the liquid phase included approximately 15 % of pentane, cyclopentane, and methylcyclopentane, as well as 85% of C 6 –C 9 cyclohexane with or without methyl, ethyl, or propyl groups, along with some isomerized cycloalkanes and aromatic molecules (Figure 1 b) and methanol. Only trace [*] Dr. C. Zhao, Prof. Dr. J. A. Lercher Catalysis Research Center and Department of Chemistry Technische Universität München, 85747 Garching (Germany) E-mail: johannes.lercher@ch.tum.de [**] This research was performed in the framework of the European Graduate School for Sustainable Energy. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201108306. A ngewandte Chemi e 1 Angew. Chem. 2012, 124,1–7  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü