Green Chemistry PAPER Cite this: Green Chem., 2017, 19, 3654 Received 17th May 2017, Accepted 4th July 2017 DOI: 10.1039/c7gc01477e rsc.li/greenchem Hydrodeoxygenation of cellulose pyrolysis model compounds using molybdenum oxide and low pressure hydrogen† Michael W. Nolte, a Alireza Saraeian a and Brent H. Shanks * a,b A molybdenum oxide catalyst in a low pressure hydrogen atmosphere was used for the hydrodeoxygenation (HDO) of pulsed injections of cellulose pyrolysis model compounds to examine reaction products. Higher catalyst loadings (≥20 : 1 catalyst : cellulose injection) in the HDO reactor were found to preferentially produce alkanes, while at lower loadings (≤10 : 1 catalyst : cellulose injection) alkene selectivity was increased. However, as the amount of catalyst was decreased, the pyrolysis vapors were not completely deoxygenated. The HDO of monofunctional oxygenated C 4 compounds found hydroxyl groups to be the most readily reacted and ether linkages to be the most recalcitrant. In general, the reactivity towards deoxygenation of the tested oxygen-containing functional groups was observed to be C–OH > CvO>C–OC. Several cellulose pyrolysis model compounds were also tested, including methyl glyoxal, glycolaldehyde, furfural, 5-hydroxy- methylfurfural, and levoglucosan, and found the same general trend to occur, except for levoglucosan, which was totally reacted and did not yield any oxygenated low molecular weight compounds despite containing two ether linkages. Across the compounds, the general reaction pathway was observed to include carbonyl/ alcohol hydrogenation/dehydrogenation, deoxygenation, and alkene isomerization and hydrogenation. 1. Introduction Interest in producing renewable fuels and chemicals from lignocellulosic biomass continues due to concerns over climate change, energy security, dwindling petroleum reserves, and political mandates among others. 1–6 Biomass represents an attractive feedstock, which could be converted through a variety of different routes to produce society’s fuels and chemi- cals. Among the various conversion strategies, fast pyrolysis is a promising technology that is able to rapidly convert solid, lower density biomass primarily into a denser liquid bio-oil. However, bio-oil contains high amounts of oxygen (∼40 wt%), water (20–30 wt%), and acids (pH 2–3), as well as reactive species that polymerize with time leading to an increase in vis- cosity, average molecular weight, and possible phase instability. 7–12 Therefore, in order to utilize the existing refin- ery infrastructure for bio-oil processing, these adverse pro- perties would need to be addressed. Upgrading bio-oil could be accomplished by selectively removing certain target molecules. For example, Zhang et al. used a calcium carbonate adsorbent for the vapor phase removal of the carboxylic acids. 13 However, to utilize existing hydrocarbon capital infrastructure, significant deoxygenation of the bio-oil is needed. Through extensive deoxygenation, a more stable, non-corrosive, less viscous, petroleum-miscible hydrocarbon product with a higher heating value could be obtained. Two main approaches have been explored to catalytically deoxygenate biomass pyrolysis oil. 14 The first strategy involves condensing the pyrolysis vapors as bio-oil and subsequently hydrotreating the bio-oil to stabilize the oil or fully deoxygen- ate it to form hydrocarbons. Comprehensive reviews on bio-oil hydrotreating have been recently published, 15,16 though in short, hydrotreating condensed bio-oil presents some notable difficulties. The high reactivity of some bio-oil compounds and their ability to polymerize necessitated the use of multiple upgrading steps operated at different temperatures. Although, even with multiple temperature stages, heavy tar or coke for- mation could plug the reactor resulting in high pressure drops. In addition, each upgrading stage usually employed high pressures of >1000 psi and in some cases high yields of CO, CO 2 , and coke were obtained at the expense of product yield. The catalysts that have been tested include noble metals, which may be cost-prohibitive to use industrially, and tran- † Electronic supplementary information (ESI) available. See DOI: 10.1039/ C7GC01477E a Department of Chemical and Biological Engineering, Iowa State University, Ames, IA, 50011, USA. E-mail: bshanks@iastate.edu; Fax: +1 515 294 2689; Tel: +1 515 294 1895 b Center for Biorenewable Chemicals (CBiRC), Iowa State University, Ames, IA, 50011, USA 3654 | Green Chem. , 2017, 19, 3654–3664 This journal is © The Royal Society of Chemistry 2017 Published on 07 July 2017. Downloaded by Iowa State University on 23/08/2017 02:40:24. View Article Online View Journal | View Issue