The hydrolysis of formaldehyde [HCHO + H 2 O → H 2 C-(OH) 2 ] assisted by bimolecular acidic catalyst of X (X = H 2 SO 4 •••H 2 O and (H 2 SO 4 ) 2 ) under different concentrations of H 2 SO 4 and H 2 O was performed by quantum chemical calculations of CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/6-311++G(3df,3pd) and the master equation method. The calculated results show that the hydrolysis reaction of HCHO catalyzed by X can occur through both HCHO•••H 2 O + X (one-step reaction) and H 2 O•••X + HCHO (stepwise reaction) routes. The stepwise reaction assisted by H 2 SO 4 •••H 2 O is the most favorable reaction among all the hydrolysis reactions assisted by X, with its effective rate constant larger by at least 2 orders of magnitude. In comparison with the hydrolysis of HCHO without X, the favorable route for the hydrolysis of HCHO with H 2 SO 4 •••H 2 O can reduce the energy barrier by 32.0 kcal•mol −1 . Meanwhile, the energy barrier of this reaction is also lower by another 0.8−17.6 kcal•mol −1 than those of the hydrolysis reaction of HCHO assisted by H 2 SO 4 , HCOOH, HNO 3 , CH 3 COOH, H 2 O, and (H 2 O) 2 . From the viewpoint of the calculated effective rate constant k′, the hydrolysis of HCHO with H 2 SO 4 •••H 2 O {[H 2 SO 4 ] = 10 6 molecules•cm −3 and [H 2 O] at 40−100% relative humidity (RH) along with [H 2 SO 4 ] = 10 7 −10 8 molecules•cm −3 and [H 2 O] at 20−100% RH} is more effective than the hydrolysis reaction assisted by H 2 O, (H 2 O) 2 , HCOOH (0.01−10 ppbv), HNO 3 (10 9 −10 11 molecules•cm −3 ), and CH 3 COOH (1−5 ppbv) within the temperature range of 280−320 K. Under the same condition, the hydrolysis of HCHO with H 2 SO 4 •••H 2 O can compete well with the hydrolysis of HCHO assisted by H 2 SO 4 (10 6 −10 8 molecules•cm −3 ). Therefore, this work predicts that H 2 SO 4 •••H 2 O can play a significant role in the hydrolysis of HCHO in the condition of wet areas with relatively high H 2 SO 4 pollution.

The hydrolysis of formaldehyde (HCHO) assisted by bimolecular acidic catalysts of H2SO4●●●H2O and (H2SO4)2 under different concentrations of H2SO4 and H2O were performed by quantum chemical calculations and the Master Equation method. The calculated results show that H2SO4●●●H2O and (H2SO4)2 catalyzed hydrolysis reaction of HCHO can occur through both one-step route and stepwise process. Effective rate coefficients (kt′) within the temperature range of 280-320 K show that H2SO4●●●H2O assisted reaction via stepwise route exerts the strongest catalytic role in increasing the rate of the hydrolysis of HCHO among all the hydrolysis reactions with H2SO4●●●H2O and (H2SO4)2 with its effective rate coefficient larger by at least 1 order of magnitude. As compared with the naked hydrolysis of HCHO, the favorable route of the hydrolysis of HCHO with H2SO4●●●H2O can reduce the energy barrier by 32.0 kcal·mol-1. Meanwhile, this reaction is also lower by another 0.8-17.6 kcal·mol-1 than that with H2SO4, HCOOH, HNO3, CH3COOH, H2O and (H2O)2. The calculated kt′ also reveals that the hydrolysis of HCHO with H2SO4●●●H2O ([H2SO4] =108 molecules∙cm-3 and [H2O] at 20%-100% RH) is more effective than that with H2O and (H2O)2 within 280-320 K, and can compete well with the hydrolysis of HCHO in the presence of HCOOH (2-10 ppbv), HNO3 (1011 molecules●cm-3), CH3COOH (1-5 ppbv) within 280-320 K. So, this work predicts that H2SO4●●●H2O can play a significant role in the hydrolysis of HCHO in the condition of wet areas with relatively high H2SO4-polluted.