Experimental and Theoretical Insights into the Hydrogen-Efficient Direct Hydrodeoxygenation Mechanism of Phenol over Ru/TiO₂

Abstract

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 D 2 O and DFT calculations to provide insight into the mechanism of the highly efficient HDO catalyst, Ru/TiO 2 . The data point to the importance of interface sites between Ru nanoparticles and the TiO 2 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 TiO 2 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.

Hydrogenation of Lactic Acid to 1,2‐Propanediol over Ru‐Based Catalysts

“…The higher reducibility of Ru/TiO 2 may be explained by the acid–base characteristics of the TiO 2 surface which can catalyze the dissociation of H 2 . Previous computational studies indicated the possibility of a heterolytic cleavage of H 2 at interfacial sites between Ru nanoparticles and basic bridging hydroxyl groups of the TiO 2 surface . For Ru/C, besides the main peak at 150 °C, two additional reduction features at 200 °C and in the 400–600 °C range were observed.…”

Water-assisted oxygen activation during selective oxidation reactions

“…Finally, a better mechanistic understanding of which oxygen species participate in desired and undesired oxidation pathways is required to improve selectivity and atom-efficiency. Besides catalytic oxidation reactions, water-mediated proton transfer has other farreaching implications, for instance, in catalytic hydrodeoxygenation of bio-oil [72], electrocatalysis [73][74][75], and any reaction using solid acid catalysts including zeolites [76,77]. Thus, we see numerous opportunities for innovative research on water-assisted catalysis in diverse areas that may ultimately lead to disruptive technologies.…”

Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces

“…[1] Such interfaces can form the basis of bifunctional catalysis,w here each material contributes its unique functionality to the active site.F or example,b ifunctional catalysts have shown promise for selective hydrodeoxygenation (HDO) of alcohols/aldehydes with aromatic substituents,adesirable path for production of fuels or chemicals from biomass ( Figure 1a). [4][5][6][7][8] Thei mportance of interfacial sites in catalysis suggests that catalyst design should emphasize novel methods for tailoring these interfaces that go beyond using the oxide as as imple catalyst carrier. [4][5][6][7][8] Thei mportance of interfacial sites in catalysis suggests that catalyst design should emphasize novel methods for tailoring these interfaces that go beyond using the oxide as as imple catalyst carrier.…”