Hydrodeoxygenation of Acetophenone over Supported Precious Metal Catalysts at Mild Conditions: Process Optimization and Reaction Kinetics Celeste Gonza ́ lez, Pablo Marín, Fernando V. Díez, and Salvador Ordó ñ ez* Department of Chemical and Environmental Engineering, University of Oviedo, Facultad de Química, Julia ́ n Clavería 8, Oviedo 33006, Spain ABSTRACT: Bio-oils obtained by pyrolysis of lignocellulose feedstocks must be upgraded to reduce the oxygen content, improving their quality as biofuels. Catalytic hydrotreatment has been proposed to reduce the oxygen content of biofuels and meet the standard requirements. Acetophenone is interesting as a model compound for the study of hydrodeoxygenation of pyrolysis bio-oils, which contain aromatic ketones. In this work, acetophenone gas-phase hydrodeoxygenation over precious metal (Pt, Pd, Ru, and Rh) supported catalysts has been studied in a fixed-bed reactor (space time, W/F = 0.75-1.0 kg cat s mol tot -1 ). The influence of the catalyst active phase and operating conditions (pressure of 0.5-1.5 MPa and temperature of 275- 375 °C) on the catalyst stability and activity and product distribution was studied. For the optimum pressure (1.0 MPa) and 275 and 375 °C, a reaction kinetic model based on the reaction scheme has been proposed and fitted to the experimental data obtained at different space velocities (W/F =0-1.5 kg cat s mol tot -1 ). 1. INTRODUCTION The development of cleaner and renewable fuels is growing as a result of the environmental hazards and possible shortage of traditional fossil fuels. In this context, biomass constitutes an energy resource widely available around the world. The use of lignocellulose materials as feedstock to produce biofuels increases the yield of the biomass conversion, in comparison to traditional biofuels (bioethanol and lipid biodiesel), whose manufacture requires the use of a very small and edible (starches and lipids) fraction of this biomass. 1 One of the proposed schemes for upgrading lignocellulosic feedstocks is based on biomass pyrolysis followed by a chemical upgrading of the resulting oil. Pyrolysis is a thermal decomposition of the biomass that produces a pyrolysis oil (bio-oil), formed by a complex mixture of hydrocarbons, with a high oxygen content. Some oxygenated functional groups appearing in bio-oils are carboxyl, carbonyl (acetone and aldehyde), alcohol, and ester. 2-4 The oxygen content in bio-oils is usually 35-40%, 5 while in heavy petroleum fuel oil, the oxygen content is only 1%. 6 The presence of oxygenated compounds deteriorates the properties of bio-oils as biofuels, increasing viscosity, acidity, and instability, decreasing volatility and energy density, etc. 7 Upgrading of bio-oils is aimed to decrease their oxygen content, improving the properties of the resulting biofuel. Two types of upgrading catalytic processes have been proposed: cracking and hydrogenation. Catalytic hydrogenation and, most specifically, hydrodeox- ygenation (HDO) is based on the reaction with hydrogen at a high temperature and pressure in the presence of a catalyst, leading to bio-oil constituents. 8-10 Conventional hydrotreating catalysts, such as CoMo/Al 2 O 3 and NiMo/Al 2 O 3 , are used at an industrial scale in hydrotreating petroleum fractions for the simultaneous elimination of sulfur, oxygen, and nitrogen. 10 The use of these catalysts for hydrotreating of bio-oils has been extensively studied: optimization of catalyst formulation and operating conditions (typically 250-400 °C and 3.0-20.0 MPa) 8,11,12 and also kinetic studies. 13-17 These catalysts are used in sulfided form, which considerably outperforms the oxidic form in HDO of bio-oils, and hence, the reaction must be carried out in the presence of sulfur. The sulfur content of bio-oil is too small to produce enough H 2 S during hydro- treating, and for this reason, an external source of H 2 S is required to maintain the catalyst in a stable sulfided form. 8 This is an important drawback of hydrotreating catalysts for bio-oil HDO. Recently, precious metal-based catalysts, e.g., Pt 18 and Ru, 19-21 have been proposed and studied as an alternative to conventional hydrotreating catalysts. 22,23 The most important advantage of precious metal catalysts is the high activity, even at a low pressure and temperature, which would result in smaller reactors and economic advantages. Studies with model compounds are useful for determining the activity and stability of catalysts used in HDO of bio-oils and also for understanding the reaction kinetics. The composition of pyrolysis bio-oils is rather complex, formed by different families of compounds with concentration varying according to the biomass feedstock or the processing conditions. Compounds often used as models for bio-oils are guaiacol (2-methoxyphenol), ethyl phenol, or anisole (methox- ybenzene), among others. These compounds are representative of lignin precursor molecules. 8 The composition of bio-oils also accounts for acids, esters, ketones, etc. These compounds, with a higher oxidation state, require a higher degree of HDO. In this work, the focus is set on ketones (around 27 wt % of the crude bio-oil 24 ) and particularly acetophenone, which is selected as the model compound. 25,26 Acetophenone is a simple aromatic ketone, representative of other more complex ketones Received: September 16, 2015 Revised: November 10, 2015 Published: November 23, 2015 Article pubs.acs.org/EF © 2015 American Chemical Society 8208 DOI: 10.1021/acs.energyfuels.5b02112 Energy Fuels 2015, 29, 8208-8215