Atmospheric degradation mechanism of benzyl peroxy radical: A theoretical study

2022

ACS Earth Space Chem.

The present work represents the reaction mechanism and kinetics study of the 4-methyl-3-penten-2-one initiated by OH radicals. The geometries of all stationary points are optimized at the M06-2X/6-311+ +G(d,p) level of theory, and the energy values are refined by making single point energy calculation at the CCSD(T)/6-311++G(d,p) level of theory to construct an energy-level diagram. By employing conventional transition state theory along with a tunneling coefficient, the overall rate constants are calculated in the temperature range of 180−360 K and can be summarized by a modified Arrhenius three-parameter fit expression: k (T) = 6.72 × 10 −20 × T 2.5 × exp (2056.4/T) cm 3 molecule −1 s −1 . The rate constant obtained at 298 K is found to be 1.02 × 10 −10 cm 3 molecule −1 s −1 , which is in good agreement with the experimental data. In the atmosphere, the major oxidation products of the title reaction are acetone, methyl glyoxal, (CH 3 ) 2 COHC(O)H, CO 2 , and formaldehyde, which are in accordance with experimental detection. The atmospheric lifetime of 4-methyl-3-penten-2-one initiated by OH radicals and the impact of products on tropospheric chemistry have been provided in the paper.

Section: Methodssupporting

confidence: 83%

Theoretical Investigations of the OH-Initialized Oxidation of 4-Methyl-3-Penten-2-One in the Atmosphere

2022

ACS Earth Space Chem.

“…By recombination of IM6 with NO 2 , the Nitrate1 or Nitrate1A [CH 3 OC(ONO 2 )HCHOHC(O)CH 3 ] will be formed readily via an exergonic process (Δ E = −136.71 and −125.05 kJ/mol, respectively). The reaction mechanism of nitrate formation proposed in this paper is consistent with that of CH 3 ONO 2 , and PhCH 2 ONO 2 . With the migration of H from −CH group (Nitrate1) to the adjacent O-atom of −NO 2 group, products P5 [CH 3 OC(O)CHOHC(O)CH 3 ] + HONO will be formed via TS–Nitrate1-P5 by overcoming a barrier of 146.70 kJ/mol.…”

Section: Resultsmentioning

confidence: 99%

“…In high concentration NO environment, IM3 combines with a NO radical into two conformations, IM4 and IM4A [CH 3 OC(OONO)HCHOHC(O)CH 3 ], and these two processes are strongly exothermic by 75.65 and 82.02 kJ/mol, respectively. After that, IM4 and IM4A can directly dissociate into alkoxy radicals IM6 plus NO 2 through a barrierless O–O bond cleavage process. − The bond dissociation energies of IM4 and IM4A are 26.77 and 33.14 kJ/mol, respectively, implying that IM4 and IM4A could easily form IM6 + NO 2 .…”

Section: Resultsmentioning

confidence: 99%

Kinetics, Products, and Mechanisms Study of the Atmospheric Degradation of (E)-4-Methoxy-3-buten-2-one with Hydroxyl Radicals

2023

ACS Earth Space Chem.

High-level ab initio calculations have been conducted to investigate the mechanisms and kinetics of the oxidation of (E)-4-methoxy-3-buten-2-one by hydroxyl radicals (OH) in the atmosphere. Potential energy diagrams have been constructed at the CCSD(T)/6-311++G(d,p)//BH&HLYP/6-311++G(d,p) level of theory to characterize the overall reaction mechanism. Transition-state theory, in combination with Eckart tunneling, is employed to calculate the rate coefficients for the title reaction over the 180−360 K temperature range. Rate coefficients can then be fitted to a modified form of the Arrhenius equation: k = 2.00 × 10 −13 × exp(1960.4/T) cm 3 molecule −1 s −1 . The room temperature rate coefficient is calculated to be 1.41 × 10 −10 cm 3 molecule −1 s −1 , which matches well with the experimentally reported ones. The kinetic results imply that the reaction for OH radicals with (E)-4-methoxy-3-buten-2-one mainly leads to the formation of two hydroxyalkyl radicals by the initial addition of OH radicals to the >C�C< double bond. Under NO x -contaminated atmospheric environments, the hydroxyalkyl radicals can undergo further reactions to give various products such as methyl formate, methyl glyoxal, 2-hydroxy-2-methoxyacetaldehyde, peroxyacetyl nitrate (PAN), CO 2 , and a variety of peroxyalkyl nitrates and organic nitrates, which are in qualitative agreement with the experimental observations. A discussion on the atmospheric implications is also presented.

“…Under the irradiation of ultraviolet lamp, the photogenerated electrons and hydroxyl radicals are generated, which act on the methyl of toluene to dehydrogenate and generate hydrogen radicals (H•) and benzyl radicals (PhCH 2 •) that further react with O 2 in the system to generate benzyl peroxy radicals (PhCH 2 O•). The coupling product of PhCH 2 O 2 is unstable and decomposes to benzyl alcohol that continue to be oxidized to form benzaldehyde (Feng et al 2019).Phenol is produced when methyl groups on toluene are substituted by hydroxyl radicals. The substituted methyl and benzyl generate phenylacetaldehyde under the action of free radicals, and phenylacetaldehyde is further oxidized to phenylacetic acid under the synergistic effect of ultraviolet light and O 2 .…”

Section: Analysis Of Intermediate Productsmentioning

confidence: 99%

Synergistic effect of adsorption and photocatalysis for the degradation of toluene by TiO2 loaded on ACF modified by Zn(CH3COO)2

Sun

et al. 2021

Preprint

Activated carbon fiber (ACF) was modified by Zn(NO3)2, ZnCl2 and Zn(CH3COO)2), respectively, and then TiO2 was loaded on the modified ACFs. The adsorption and photocatalysis performance were explored through the removal of toluene, and TiO2/ACF-Ac modified by Zn(CH3COO)2) with the best toluene performance was selected. The characterization results indicated that TiO2 was mainly loaded on the surface with large amount of oxygen-containing functional groups in anatase phase. The photoelectric chemical experiment results demonstrated that the modified ACFs remarkably improved the charge transmission and the separation efficiency of electrons and holes, and enhanced the utilization rate of sunlight. The adsorption saturation time reached 40 hours and photodegradation rate was 70%. The direct desorption of generated small molecule substances such as H2O and CO2 from the surface of the composites can achieve the in-situ regeneration of the adsorbent. Overall, the bifunctional catalysts provide a prospective way for the treatment of VOCs.