The crucial role of water clusters (H2O)n (n = 0–5) on the catalytic oxidation of AsH3: An accurate theoretical investigation

Abstract

The removal of AsH3 is typically accomplished by catalytic oxidation process. In the process, the existence of water molecules plays a crucial role on the removal efficiency, but prior studies have not thoroughly investigated the role of water in reaction mechanism, due to lack of experimental and computational techniques. In this study, the role of explicit water molecules on the AsH3 catalytic oxidation AsH3+O2+nH2O (n=0–5) was investigated using Density Functional Theory (DFT) method at B3LYP/6-311+G (d,p) level. The addition of (H2O)n (n=1–5) shows promoting catalytic effect on the oxidation process by reducing the reaction barrier energy of 3.27–10.70kcal/mol compared to the reaction without water molecule (16.44kcal/mol). One explicit H2O addition shows best catalytic effect on the oxidation process. The decreasing order of reaction energy barrier is 0H2O>(H2O)5>(H2O)4>(H2O)2>(H2O)3>H2O. Natural bond orbital (NBO) analysis was also conducted to confirm the bond-breaking and bond-making processes. Furthermore, reaction rate constants (kTS) of six catalytic oxidation reactions from 293K to 433K have been calculated to determine the catalytic role of water clusters. The values of kTS increase progressively with increasing temperature in the six reaction paths (n=0–5). Three water addition is most kinetically favourable among the six reactions.