Abstract: The direct conversion of syngas to ethanol on the Rh_nNi_n/TiO₂ (n = 1, 2, 3, 4) catalyst has been investigated by using the density functional theory (DFT) and micro-kinetic methods, in order to elucidate the regulatory mechanism of Rh_nNi_n alloy cluster size-induced metal-support interaction on the catalytic performance of Rh_nNi_n/TiO₂ in the ethanol synthesis. The results indicate that Rh₁Ni₁/TiO₂ and Rh₃Ni₃/TiO₂ can significantly enhance the conversion of CO and the formation of C−C bond and meanwhile inhibit the generation of methane. Rh₁Ni₁/TiO₂ exhibits the highest ethanol production activity and relative selectivity. The electronic property analysis results suggest that Ni atoms on the alloy clusters and Ti and O atoms on the supports transfer the most charge to the Rh atoms on the Rh₁Ni₁/TiO₂ catalyst, which displays the strongest Rh-Ni interaction on the alloy clusters as well as the strongest interaction between the alloy clusters and the TiO₂ support, endowing Rh₁Ni₁/TiO₂ with the highest catalytic activity. In addition, the Ab-initio molecular dynamics (AIMD) simulations at 525 K show that the Rh₁Ni₁/TiO₂ catalyst has high thermal stability.