Formic Acid Catalyzed Gas-Phase Reaction of H2O with SO3 and the Reverse Reaction: A Theoretical Study

Authors

  • Dr. Bo Long ,

    Corresponding author
    1. College of Computer and Information Engineering, Guizhou University for Nationalities, Guiyang, 550025 (China), Fax: (+86) 8513610344
    2. Department of Physics, Guizhou University, Guiyang, 550025 (China)
    • College of Computer and Information Engineering, Guizhou University for Nationalities, Guiyang, 550025 (China), Fax: (+86) 8513610344
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  • Prof. Zheng-wen Long,

    1. Department of Physics, Guizhou University, Guiyang, 550025 (China)
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  • Prof. Yi-bo Wang,

    Corresponding author
    1. Key Laboratory of Guizhou High Performance Computational Chemistry, Department of Chemistry, Guizhou University, Guiyang, 550025 (China)
    • Key Laboratory of Guizhou High Performance Computational Chemistry, Department of Chemistry, Guizhou University, Guiyang, 550025 (China)
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  • Dr. Xing-feng Tan,

    1. College of Photo-Electronics, Chongqing University of Posts and Telecommunications, Chongqing, 400065 (China)
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  • Dr. Yu-hua Han,

    1. Department of Physics, Guizhou University, Guiyang, 550025 (China)
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  • Prof. Chao-yun Long,

    1. Department of Physics, Guizhou University, Guiyang, 550025 (China)
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  • Prof. Shui-jie Qin,

    1. Department of Physics, Guizhou University, Guiyang, 550025 (China)
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  • Prof. Wei-jun Zhang

    1. Laboratory of Environment Spectroscopy, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031 (China)
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Abstract

The formic acid catalyzed gas-phase reaction between H2O and SO3 and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc-pv(T+d)z and CCSD(T)//MP2/aug-cc-pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H2O with SO3 is lowered through formic acid catalysis from 15.97 kcal mol−1 to −15.12 and −14.83 kcal mol−1 for the formed H2O⋅⋅⋅SO3 complex plus HCOOH and the formed H2O⋅⋅⋅HCOOH complex plus SO3, respectively, at the CCSD(T)//MP2/aug-cc-pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to −3.07 kcal mol−1 from 35.82 kcal mol−1 with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO3+H2O reaction with formic acid is 105 times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H2SO4 reaction is about 10−13 cm3 molecule−1 s−1 in the temperature range 200–280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO3 and H2SO4 in atmospheric chemistry.

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