The highly efficient, heterogeneous Ru-PPh3/Al2O3 catalysts with the different molar ratios of Ru and PPh3 (1:3, 1:6, 1:9, 1:12, 1:15) were prepared and employed in hydrogenation of CO2 to formic acid. It was demonstrated that the indispensable electron-donation ligand PPh3 increased the catalytic activity of Ru-PPh3/Al2O3 via providing electrons to the Ru center. Procedures of dihydrogen coordination and CO2 insertion into the Ru-H bond proceeded easily in the presence of the optimal quantity of the electron donor PPh3, the protonic additive KH2PO4 and the appropriate co-solvent. A favorable turnover frequency of up to 751 h(-1) was obtained over Ru-PPh3/Al2O3(1:9) with 0.63 wt% Ru loading using KH2PO4 and PPh3 as additives in the mixed solution of ethanol, trimethylamine, and H2O.