Mechanistic details of C[sbnd]O bond activation in and H-addition to guaiacol at water-Ru cluster interfaces.

Graphical abstract Highlights • Guaiacol hydrodeoxygenation proceeds via competing C O cleavage and H-addition routes. • Rapid, initial H* addition to guaiacol leads to common, partially-saturated reactive intermediate. • Partially-saturated reactive intermediate undergoes kinetically relevant C O cleavage or H-addition. • Selectivity ratio of C O cleavage to H-addition increases linearly with *-to-H* coverage ratio. • Initial H* addition on guaiacol is reversible and leads to H-D exchange on the benzylic ring. Abstract Catalytic pathways of guaiacol and hydrogen (H 2) reactions on dispersed Ru clusters in the aqueous medium and the associated kinetic requirements for C OCH 3 bond cleavage and H-addition steps are established based on kinetic and isotopic investigations. Time-dependent kinetic measurements in a gradientless semi-batch reactor reveal that guaiacol reacts with H 2 via two independent routes of C OCH 3 bond cleavage and H-addition; the former leads to phenol, cyclohexanone, cyclohexanol, and cyclohexane and latter to 2-methoxy-cyclohexanol. During catalysis, an adsorbed guaiacol undergoes a single, quasi-equilibrated H-adatom (H*) addition on its aromatic ring, forming a partially-hydrogenated intermediate, before the sequential kinetically relevant C OCH 3 cleavage or H* addition steps on Ru cluster surfaces nearly saturated with deprotonated guaiacol. Increasing the H* coverage promotes the overall turnovers but decreases the selectivity towards the C OCH 3 bond cleavage, because H* addition event not only activates guaiacol but also promotes H-addition without breaking its C O bond. [ABSTRACT FROM AUTHOR]