Mechanism of Catalytic Effect of Water Clusters on the Oxidation of Phosphine Gas

The mechanism of PH3 oxidation is investigated at B3LYP/6-311+g (d, p) level using density functional theory calculation with n = 0-6 water molecules addition. The corresponding geometric structure, energy surface profile are studied to determine the catalytic effect of water clusters. The results show that addition of water clusters into the system will be beneficial for the oxidation reaction to different extent. Four water molecules addition is the most favorable mode as it lowers the reaction barrier from 29.04 kcal (0H(2)O) to 12.40 kcal/mol. The energy barrier follows the order: 0H(2)O > (H2O)(5) > (H2O)(2) > (H2O)(6) > (H2O)(3) > (H2O)(4). Natural bond orbital (NBO) analysis shows that four water molecules addition has the largest second order stabilization energy of LP (O1) (O1 in H2O) -> sigma*(P-H1) and LP (O2) (O2 in H2O) -> sigma*(O3-H2), which facilitates proton transfer and formation of P-OH bond. In addition, the reaction rate constants k(TS) are simulated from 293 to 433 K. The result shows that four water molecules addition has best catalytic effect thermodynamically and kinetically.