First Principle Investigations of Bio-Oil Hydrodeoxygenation (HDO) over Ru/Ti02



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Biomass can be converted to bio-oil, which contains hundreds of oxygenated species that are detrimental to its use as transportation fuel. Hydrodeoxygenation (HDO) is a promising technology to reduce the oxygen content of bio-oil and improve its properties. From the many oxygenated compounds in real bio-oils we chose acetaldehyde, phenol, and m-cresol as model compounds to investigate reaction mechanisms and active sites on Ru/TiO2(110) using density functional theory (DFT). Acetaldehyde HDO was explored on Ru(0001), RuTiO2(110), 1 ML RuO2/TiO2(110), RuO2(110), TiO2(110), and Ru10/TiO2(110). HDO of the phenolic compounds, phenol and m-cresol, was investigated on Ru(0001), TiO2(110), and Ru10/TiO2(110). Our overall findings suggest that vacancy sites on TiO2(110) have high selectivity for the desired C-O bond cleavages steps, but the formation of vacancy sites is limited by hydrogen activation. In contrast, the metallic Ru(0001) surface activates hydrogen easily, but leads to undesired decarbonylation reactions for acetaldehyde and ring hydrogenation reactions for phenolic compounds. Our simulations show that the active site responsible for the desired direct C-O scission reaction is the Ru/TiO2 interface, which is supported by experimental evidence showing a linear relationship between the rate of m-cresol HDO and the perimeter of Ru clusters supported on TiO2. Furthermore, we have proposed a proton-assisted direct deoxygenation for phenol HDO, which is well agreement with isotopic labeling experiments performed by our collaborators. Finally, we hypothesize that the amphoteric nature of the metal-oxide support, i.e., its ability to accept and donate protons, is the key characteristic of an efficient HDO catalyst. The proton is provided through heterolytic bond cleavage across the Ru/TiO2 interface and subsequently assists in the C-O bond cleavage step in alcohols.



DFT, Hydrodeoxygenation, Bio-oil, Ru/TiO2


Portions of this document appear in: Nelson, Ryan C., Byeongjin Baek, Pamela Ruiz, Ben Goundie, Ashley Brooks, M. Clayton Wheeler, Brian G. Frederick, Lars C. Grabow, and Rachel Narehood Austin. "Experimental and theoretical insights into the hydrogen-efficient direct hydrodeoxygenation mechanism of phenol over Ru/TiO2." ACS catalysis 5, no. 11 (2015): 6509-6523.