臭氧在烟气中氧化零价汞的量子化学研究

Quantum Chemical Study on Elemental Mercury Oxidation in Flue Gases by Ozone

利用量子化学方法计算研究了臭氧在烟气中氧化零价汞的微观反应机理,采用MP2/SDD计算方法优化得到反应物、过渡态、中间体及产物的几何构型,并通过振动分析与IRC分析确定反应过渡态和中间体,在QC ISD(T)/SDD水平上计算能量,同时进行零点能校正,计算了反应活化能,并采用经典过渡态理论(TST)计算反应的速率常数,拟算出反应的阿累尼乌斯表达式.结果表明,臭氧在烟气中产生的NO3、O3和NO2粒子对零价汞进行氧化的活化能分别为22.94 kJ/mol,53.34 kJ/mol和168.23 kJ/mol.通过活化能比较,得到3种粒子的氧化性强弱为:NO3>O3>NO2.在298 K下,将计算获得的反应速率常数与文献数据进行比较,结果吻合较好.

The microcosmic kinetic mechanism of reaction in the process of elemental mercury oxidation in flue gases by ozone was studied and discussed base on quantum chemistry in this paper. The geometry optimizations of reactants, transition states, intermediates and products were obtained by the quantum chemistry MP2 method at SDD basis function level. Both the transition states and intermediates were confirmed by vibration frequency analysis and intrinsic reaction coordinate （IRC） calculation. All molecule energies were calculated at QCISD（T）/SDD level and corrected with zero point energy. The activation energies were calculated. Also, The reaction rate constants were calculated from transition state theory 0 （TST）, and the Arrhenius expressions were numerated. Results show that, the reaction activation energies of the Hs oxidation by the NO3 , 03 and NO2 radicals, which are produced in the flue gas by ozone injection, are 22.94 kJ/mol, 53.34 kJ/mol and 168.23 kJ/mol respectively. The comparison of activation energies shows that the oxidation of NO3 is stronger than that of 03 and the oxidation of NO2 is weakest. The reaction rate constants calculated by quantum chemistry and TST were in good agreement with literature data.