In this work, a systematic study was carried out to determine the effect of TiO2 and precious metal (Ru) support on HDO phenols and to determine the activity and selectivity of catalysts against the DDO (Aromatics) pathway. The reaction was carried out in a batch reactor at 300 °C. Evaluation of the catalyst showed that ruthenium nanoparticles (~ 2 nm) supported by titanium dioxide (TiO2) produced significant activity and selectivity for phenol HDO. The main product of this reaction is benzene. Furthermore, the activity and selectivity observed during phenol deoxygenation via ruthenium catalyst were unstable. Therefore, a high pressure burette together with a 25 mL Parr reactor was used to test the activity and stability of the Ru/TiO2 catalyst by calculating the hydrogen consumption rate as a function of pressure. As the reaction progresses, the rate of hydrogen consumption decreases which indicates that the catalyst has deactivated over time.

This work characterized the surface chemistry of a number of different titania samples including four commercial anatase samples, an anatase sample that we synthesized, the pyrogenic titania samples P25 and P90, and a commercial rutile sample. X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), were used to identified surface species that might interfere with the acid/base properties of the surface hydroxyls. All commercial anatase samples were contaminated by sulfur, which diminished their effectiveness as metal oxide supports for heterogeneous catalysis and has implications for their utility as photocatalysts. Hydrogen-bonded surface hydroxyls remained after calcination up to 400 degrees C for all anatase samples, in contrast to rutile and the pyrogenic titania materials P25 and P90, in which they were eliminated. Ru(0) catalysts on titania without hydrogen-bonded surface hydroxyls showed enhanced C-O hydrogenolysis selectivity in the presence of water while Ru(0) catalysts on titania with hydrogen-bonded surface hydroxyls showed diminished selectivity in water, suggesting that surface hydrophilicity is important for this reaction. Heteroepitaxy between rutile RuO2 and rutile TiO2 is not essential for the creation of small evenly-spaced supported Ru(0) nanoparticles, which are important in many catalytic reactions. (C) 2019 Elsevier Ltd. All rights reserved.

Catalytic reduction of pyrolyzed biomass is required to remove oxygen and produce transportation fuels, but limited knowledge of how hydrodeoxygenation (HDO) catalysts work stymies the rational design of more efficient and stable catalysts, which in turn limits deployment of biofuels. This work reports results from a novel study utilizing both isotopically labeled phenol (which models the most recalcitrant components of biofuels) with D2O and DFT calculations to provide insight into the mechanism of the highly efficient HDO catalyst, Ru/TiO2. The data point to the importance of interface sites between Ru nanopartides and the TiO2 support and suggest that water acts as a cocatalyst favoring a direct deoxygenation pathway in which the phenolic OH is replaced directly with H to form benzene. Rather than its reducibility, we propose that the amphoteric nature of TiO2 facilitates H-2 heterolysis to generate an active site water molecule that promotes the catalytic C-O bond scission of phenol. This work has clear implications for efforts to scale-up the hydrogen-efficient conversion of wood waste into transportation fuels and biochemicals.