Border Reactivity of Polycyclic Aromatic Hydrocarbons and Soot Platelets Toward Ozone. A Theoretical Study

Abstract

PAH-based models, with an even or odd number of unsaturated carbon atoms and π electrons (even and odd PAHs for short), are selected to investigate, by molecular and periodic methods, their electron distribution and border reactivity toward ozone, and also to represent local features and edge reactivity of even or odd soot platelets. These results will contrast those previously collected for the internal positions of similar even (J. Phys. Chem. A 2005, 109, 10929.) or odd systems (J. Phys. Chem. A 2008, 112, 973.). Topologically different peripheral positions, representative of armchair and zigzag borders, exhibit different reactivity right from the beginning. Ozone attacks start off either to give primary ozonides by concerted addition or, nonconcertedly, to first produce trioxyl intermediates. Then, a variety of pathways are described, whose viability depends on both model and position. They can open the way to the possible formation of epoxide, aldehyde, and phenol groups (all entailing O(2) production) or ether (+CO(2)), lactone (+H(2)CO), and ketone functionalities. To sum up, functionalization, regardless of how achieved, can give a number of groups, most of which actually observed in PAH ozonization experimental studies. This picture can be matched up to the results on internal sites of our preceding papers, for which epoxidation was the only outcome. Most interestingly, formation of a ketone group may turn an even system into an odd one (and conversely) while involving production of HOO(•).

The gas‐phase ozonolysis reaction of methylbutenol: A mechanistic study

“…The selection of 3 O 2 rather than 1 O 2 is based on the calculation that the triplet state relative energy is more stable than the singlet by about 150 kJ mol −1 . This is in agreement with the work of Giordana et al that the triplet is somehow more stable than the singlet. It should be noted that the intersystem crossing point on the PES is at −147 kJ mol −1 ( PA4 and PB3 ) and −131 kJ mol −1 ( PB4 ).…”

“…This might be attributed to the lower steric factor in TS2A4 , where the O 2 is oriented away from the MBO structure, see IA1 in Figure . Giordana et al suggested the formation of epoxide + 3 O 2 from trioxyl diradical (formed from a nonconcerted ozone addition) via a barrierless activation energy. However, the higher determined energy of 27 kJ mol −1 at CBS‐QB3 in this work (Figure ) could be attributed to the geometry; in which both oxygens are attached to the C‐C bond.…”

“…This might be attributed to the lower steric factor in TS2A4, where the O 2 is oriented away from the MBO structure, see IA1 in Figure 6. Giordana et al [60] suggested the formation of epoxide Based on the recent work of Lin et al [62] , further reactions of the epoxide with atmospheric pollutants in the presence of nitrogen oxides (NO x = NO + NO 2 ) may lead to new gaseous products and likely formation of new aerosols, and thus affecting air pollution. Therefore, other reactions of epoxide with H 2 O, NH 3 , and SO 2 could be significant in aerosol formation.…”

Investigating repetitive reaction pathways for the formation of polycyclic aromatic hydrocarbons in combustion processes

“…9. Therefore, this work adds doubt on the general validity of the assumption that pyrene dimerization is the dominant particle inception pathway [84,88].…”

Hydrogen chloride adsorption on large defective PAHs modeling soot surfaces and influence on water trapping: A DFT and AIMD study

“…Thus, we use large PAH (C x H y ) molecules as a proxy to model the surface of the graphene-like platelets that form the BSUs constituting soot primary nanoparticles, as in previous works based on quantum chemical calculations. [37][38][39][40] Our results showed that the considered chlorine species can be either physisorbed or chemisorbed at the face or at the edge of the soot BSU, respectively. In addition, the theoretical characterization of the interaction of small water aggregates with the resulting chlorinated PAHs indicated that chlorine species may favor subsequent water adsorption on soot and, thus, participate in the hygroscopic behaviour of soot, for instance in smokes of industrial fires.…”