*3.1. Catalysts Synthesis*

Two supports, namely Ce0.5Zr0.5O2 (CZOm) and ZrO2 (ZOm), were prepared by *w*/*o* microemulsion technique as described elsewhere [28] and were calcined at 750 ◦C for 5 h with a heating ramp of 2 ◦C/min. In the case of ZrO2 support, the microemulsion was heated to 70 ◦C for 30 min at the end of the synthesis in order to destroy the micelles.

The catalysts were prepared by reactive deposition of the Rh4(CO)12 cluster over the selected supports, namely CZOm and ZOm. In a typical experiment, the required amount of carbonyl cluster (0.6% of atomic Rh wt/wt of support) was dissolved in degassed n-hexane (10 mL) and added dropwise to a degassed n-hexane slurry of the desired support kept under CO atmosphere; the obtained slurry was then stirred for 24 h. The completion of the synthesis was evidenced by the discoloration of the solution and its IR analysis, which showed no peaks related to Rh4(CO)12 (νCO at 2075 (vs), 2069 (vs) 2044 (m) and 1885 (s) cm<sup>−</sup><sup>1</sup> in n-hexane).The solvent was thus removed in vacuum at room temperature. The catalyst was then stored under CO atmosphere and removed only to be pelletized and charged in the reactor, then readily kept under nitrogen flow and heated up to 500 ◦C. In order to provide a catalyst with a lower amount of Rh, the sample was diluted with bare CZOm or ZOm by 12 times, obtaining a catalyst with a loading of Rh of 0.05% (wt/wt of catalyst). In the case of reduced catalysts, the temperature was lowered to 200 ◦C then hydrogen (10% in nitrogen) was fluxed over the catalysts, while the temperature was again increased to 500 ◦C. After 15 h the hydrogen flux was stopped, and reactivity tests were carried out.
