Heterogeneous catalysis is ubiquitous in refining and chemical industries as it enables the formation of desirable products with minimal energy consumption. Since catalysis is a surface process, (metal) nanoparticles (NPs) often constitute the catalyst active phase, which is stabilized by a high-surface-area support and possibly promoted by a second metal. In this work, we have designed AuRh NPs supported on rutile TiO2 nanorods as model catalysts for several reactions involving hydrogen. A simple colloidal co-reduction method using NaBH4 and polyvinyl alcohol (PVA) generates 3 nm-sized bimetallic NPs.[1] However, unlike their Au and Rh counterparts, the AuRh colloids are instable in solution, as monitored in situ by dynamic light scattering and liquid-phase TEM.[2] Thus, once formed the NPs must be readily immobilized on the support in order to avoid their further growth. The AuRh/TiO2 catalysts present synergistic nanoalloying effects in all the investigated processes: stronger oxidation resistance of Rh in air,[1] stronger sulfidation resistance of Rh during tetralin hydrogenation in the presence of H2S,[1] higher selectivity to oxygen-free products in the hydrodeoxygenation of guaiacol,[3] and higher performance in the selective hydrogenation of cinnamaldehyde.[2] The structures of the colloids and their evolutions after immobilization and thermal treatments in a hydrogen atmosphere relevant to the catalytic reactions have been investigated by aberration-corrected STEM, EDX, UV-Vis, CO-FTIR, XPS and XRD. Heating the catalysts to 350 °C eliminates the PVA and leads to the segregation of Au and Rh within the particles: the NPs adopt a Janus configuration with the Rh side in contact with the titania support.[1,4] Further heating to 700 °C leads to NP coalescence and formation of “Au ball-Rh cup” ~10 nm-sized particles.[4] DFT calculations on unsupported and supported clusters show that the observed restructuring is driven by the strong Au-Rh segregation tendency, the lower surface energy of Au with respect to Rh, and the stronger Rh-TiO2 bonding with respect to Au-TiO2.[4–6] References [1]Z. Konuspayeva, P. Afanasiev, T.-S. Nguyen, L. Di Felice, F. Morfin, N.-T. Nguyen, J. Nelayah, C. Ricolleau, Z. Y. Li, J. Yuan, G. Berhault, L. Piccolo, Phys. Chem. Chem. Phys. 2015, 17, 28112–28120. [2]Z. Konuspayeva, G. Berhault, P. Afanasiev, T.-S. Nguyen, S. Giorgio, L. Piccolo, Submitted. [3]T.-S. Nguyen, D. Laurenti, P. Afanasiev, Z. Konuspayeva, L. Piccolo, J. Catal. 2016, 344, 136–140. [4]L. Piccolo, Z. Y. Li, I. Demiroglu, F. Moyon, Z. Konuspayeva, G. Berhault, P. Afanasiev, W. Lefebvre, J. Yuan, R. L. Johnston, Sci. Rep. 2016, 6, 35226. [5]I. Demiroglu, Z. Y. Li, L. Piccolo, R. L. Johnston, Catal. Sci. Technol. 2016, 6, 6916–6931. [6]I. Demiroglu, Z. Y. Li, L. Piccolo, R. L. Johnston, Comput. Theor. Chem. 2017, 1107, 142–151.