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摘要: 应用量子化学密度泛函理论B3LYP方法，研究了砷与氮氧化物（N2O、NO2和NO）的反应机理。全参数优化了各反应物、中间体、过渡态和产物的几何构型，通过频率分析证实中间体和过渡态的真实性，并通过内禀反应坐标（IRC）计算以进一步确定过渡态。为了得到更精确的能量信息，在B2PLYP水平下计算各结构的单点能，并通过动力学参数深入分析其反应机理。结果表明，砷与三种氮氧化物（N2O、NO2和NO）的反应能垒分别为78.45、2.58、155.85 kJ/mol。在298-1800 K，各反应速率随温度的升高而增大。由于砷与NO2的反应能垒较低，其反应速率大于1012 cm3/（mol·s），说明该反应容易发生且速率极快。砷与N2O和NO的反应，在298-900 K，反应速率随温度的升高明显增加；当温度进一步升高，其增加的趋势有所减缓。Abstract: The reaction mechanism between arsenic and nitrous oxides (N2O, NO2 and NO) was investigated by applying density functional theory in quantum chemistry. The geometries of reactants, intermediates, transition states and products for each reaction were optimized. Frequency analysis was applied to verify those geometries, and the authenticity of transition states were confirmed by intrinsic reaction coordinate analysis (IRC). The stationary points of the single point energy were calculated at B2PLYP level, and the kinetic analysis was conducted to further reveal the reaction mechanism. Results show that the energy barrier of the reactions between arsenic and nitrous oxides (N2O, NO2 and NO) is 78.45, 2.58 and 155.85 kJ/mol, respectively. The reaction rate increases in the range of 298-1800 K and keeps at a high level (>1012 cm3/(mol·s)), although the temperature has a tiny impact on the reaction of arsenic with NO2 as a result of a low energy barrier, indicating that the reaction is easy to take place. Furthermore, it is found that the rate of reaction between arsenic and N2O or NO has a rapid increase at 298-900 K, and then the rate increment becomes less with the further increase of temperature.
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Key words:
- coal combustion /
- arsenic /
- nitrous oxides /
- density functional theory /
- kinetics
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表 1 各反应物、生成物键长和键角的计算值及实验值
Table 1 Calculated and experimental bond lengths and bond angles
Species Bond length (r/nm)
Bond angle (θ/(°))Calculated value Exprimental value N2O r(N-O) 0.1184 0.1185[20] r(N-N) 0.1126 0.1127[20] θ(N-N-O) 180.00 180.00[20] N2 r(N-N) 0.1095 0.1098[20] NO2 r(N-O) 0.1194 0.1199[21] θ(O-N-O) 134.23 133.70[21] NO r(N-O) 0.1150 0.1151[22] AsO r(As-O) 0.1632 0.1624[23, 24] 
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表 2 反应通道各驻点的能量
Table 2 Stationary point energy of each reaction
Reaction B2PLYP/(a.u.) ZPE/(a.u.) Etot/(a.u.) Erel/(kJ·mol-1) (1) As+N2O -2420.19225 0.01125 -2420.18100 0 TS -2420.15981 0.00869 -2420.15112 78.45 AsO+N2 -2420.33202 0.00820 -2420.32382 -374.97 (2) As+NO2 -2440.60933 0.00882 -2440.60051 0 M -2440.68649 0.00904 -2440.67745 -202.01 TS -2440.68426 0.00779 -2440.67647 -199.43 AsO+NO -2440.69733 0.00727 -2440.69006 -235.11 (3) As+NO -2365.42302 0.00453 -2365.41849 0 M -2365.41799 0.00425 -2365.41374 12.47 TS -2365.35649 0.00211 -2365.35438 168.32 AsO+N -2365.38994 0.00247 -2365.38747 81.44
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表 3 不同温度As+N2O→AsO+N2的动力学参数值
Table 3 Kinetic parameters of the reaction As+N2O→AsO+N2 at different temperatures
T/K A/(cm3·mol-1·s-1) k/(cm3·mol-1·s-1) 298 6.48×1010 1.15×10-3 600 8.76×1010 1.30×104 900 1.05×1011 2.95×106 1200 1.19×1011 4.57×107 1500 1.29×1011 2.39×108 1800 1.37×1011 7.26×108
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表 4 不同温度As+NO2→AsO+NO的动力学参数值
Table 4 Kinetic parameters of the reaction As+NO2→AsO+NO at different temperatures
T/K A/(cm3·mol-1·s-1) k/(cm3·mol-1·s-1) 298 8.52×1012 3.02×1012 600 1.47×1013 8.80×1012 900 1.82×1013 1.29×1013 1200 2.03×1013 1.57×1013 1500 2.17×1013 1.77×1013 1800 2.27×1013 1.92×1013
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表 5 不同温度As+ NO→AsO+ N的动力学参数值
Table 5 Kinetic parameters of the reaction As+ NO→AsO+ N at different temperatures
T/K A/(cm3·mol-1·s-1) k/(cm3·mol-1·s-1) 298 1.02×1013 4.95×10-15 600 1.80×1013 4.88×10-1 900 2.31×1013 2.09×104 1200 2.66×1013 4.38×106 1500 2.92×1013 1.09×108 1800 3.11×1013 9.33×108
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表 6 反应动力学参数
Table 6 Kinetic parameters for each reaction
Reaction A/(cm3·mol-1·s-1) Ea/
(kJ·mol-1)As+N2O→AsO+N2 1.48×1011 78.45 As+NO2→AsO+NO 2.72×1013 2.58 As+NO→AsO+N 3.69×1013 155.85
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