A ruthenium-based complex, ethylenediaminetetraacetato ruthenate [Ru-EDTA(H2O)(-)1was found to be an efficient homogeneous catalyst to activate carbon monoxide as well as water molecule in hydration of CO. It was investigated at moderate pressures (5-20 atm) and at 10-40 degrees C for direct conversion of CO to formic acid (FA). In typical catalytic experiments conducted in a pressure reactor of 300 ml capacity, 75 x 10(-3) M of FA was found to be formed at 10 atm CO pressure and 40 degrees C. The kinetics of the (i) complexation of CO with I and (ii) hydration of CO to formic acid reactions were investigated in detail by studying the rate of formation of intermediate Ru-EDTA-CO complex 2 and the rate of formation of FA, respectively as a function of the concentration of the catalyst 1, CO pressure, reaction temperature, ionic strength and pH. The rate of formation of FA was found to be first order with respect to the concentration of 1 and CO pressure, independent of pH and ionic strength, and dependent on temperature, in agreement with the Arrhenius equation. Similar kinetic profile and temperature dependence were observed for formation of complex 2 also. Activation parameters evaluated from temperature dependence were found to be favorable for the formation of 2 and the CO hydration product FA. Based on kinetic and experimental results, a mechanism for the hydration of CO to formic acid is suggested. (c) 2005 Elsevier B.V. All rights reserved.