Reducibility of Unsupported and Al ₂ O ₃ -Supported RuO ₂ Catalysts: When Ru Oxide Challenges Ru Metal in Hydrogenation

The reducibility of Ru-based catalysts plays a central role in defining their activity in hydrogenation, yet their behavior during reduction remains elusive, especially for oxidic precursors. Here, we unveil how oxide-derived ruthenium phases can rival, and even surpass, metallic Ru in hydrogenation catalysis. Using a combination of H2-temperature-programmed reduction (H2-TPR), synchrotron X-ray total scattering, and Ru K-edge X-ray absorption spectroscopy, we track the reduction dynamics of unsupported and Al2O3-supported RuO2 catalysts synthesized via deposition-precipitation. Chemometric analysis (PCA/MCR) reveals a two-step reduction pathway via a Ru2O3 intermediate, modulated by the structural disorder and hydration of the initial RuOx(OH)y phase. Unexpectedly, the amorphous and hydrated oxidic phase in the unsupported system exhibits good hydrogenation performance at a mild temperature (50 °C), outperforming its crystalline and reduced counterparts. These findings challenge the conventional view that metallic Ru is the sole active species and suggest that structural disorder, hydration, and redox flexibility can offer alternative routes to efficient supported catalysis. Our integrated approach redefines the design rules for Ru-based hydrogenation catalysts, emphasizing the hidden potential of unconventional oxidic precursors.