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采用密度泛函方法(B3LYP)在6-311+g(3df,2p)基组水平上,针对甲酸在超临界水中分解,研究了HCOOH+2H_2O反应和HCOOH+3H_2O反应的微观动力学机理。将理论计算结果与已有的实验结果对比发现,甲酸在超临界水中分解主要通过HCOOH+3H_2O反应机理进行,存在脱羧反应R(HCOOH+3H_2O)→d→TSd/e→e→TSe/P3→P3和脱羰反应R(HCOOH+3H_2O)→f→TSf/P4→P4两条主反应通道。利用传统过渡态理论(TST)计算得到两条主通道速控步骤在650～1500 K温度范围内的速率常数k_3和k_4,其表达式分别为k_3=2.99×10~(12)exp(-169.89 kJ·mol~(-1)/RT)s~(-1)和k_4=3.00×10~9exp(-159.01 kJ·mol~(-1)/RT)s~(-1)。
The kinetic mechanism of HCOOH + 2H 2 O reaction and HCOOH + 3H 2 O reaction was studied by density functional theory (B3LYP) at 6-311 + g (3df, 2p) group level for the decomposition of formic acid in supercritical water. Comparing the theoretical calculation results with the existing experimental results, it is found that the formic acid decomposes mainly in the supercritical water through the reaction mechanism of HCOOH + 3H_2O, and the decarboxylation reaction R (HCOOH + 3H_2O) → d → TSd / e → e → TSe / P3 → P3 and decarbonylation reaction R (HCOOH + 3H_2O) → f → TSf / P4 → P4 two main reaction channels. Using the traditional transient state theory (TST), the rate constants k_3 and k_4 in the speed control steps of the two main channels in the temperature range of 650 ~ 1500 K were calculated and the expressions were respectively expressed as k_3 = 2.99 × 10-12 exp (-169.89 kJ · mol -1 / RT) s ~ (-1) and k_4 = 3.00 × 10 ~ 9exp (-159.01 kJ · mol -1 / RT) s ~ (-1).