Drying, ageing and reducibility of Ru catalysts obtained via deposition-precipitation: the hidden role of water

Ruthenium catalysts prepared by deposition–precipitation (DP) contain highly hydrated oxidized Ru species whose structure and evolution remain difficult to define. Here, Ru catalysts supported on alumina and two activated carbons were investigated to clarify how support chemistry and water content affect the Ru phase formed by DP. HR-TEM, O K-edge NEXAFS, H2-TPR and CO chemisorption reveal marked support-dependent differences in Ru aggregation, local oxygen coordination, reducibility and site accessibility. On alumina, hydrated Ru oxy-hydroxide species coexist with RuO2-like local domains, whereas carbon supports stabilize predominantly hydroxylated and structurally disordered Ru environments. Post-synthesis drying and ageing progressively alter these properties through dehydration, with markedly different consequences depending on the support. On alumina, water removal promotes structural consolidation and RuO2-like ordering, making the Ru(IV) → Ru(III) → Ru(0) reduction sequence kinetically resolvable while decreasing the population of accessible Ru sites. On activated carbons, dehydration mainly affects site accessibility without inducing comparable RuO2-like ordering. Catalytic transfer hydrogenolysis of diphenyl ether (DPE) provides a first catalytic assessment of these differences: DPE conversion follows the same trend as CO-accessible Ru sites, while aromatic yield does not increase proportionally with activity because consecutive hydrogenation is also promoted. These results identify water as a transient structural component of DP-derived Ru catalysts and show that drying and storage history are integral to controlling their reducibility, site accessibility and catalytic behavior.