Periodic DFT calculation for the formation of EPFRs from phenol on γ-Al2O3 (110): Site-dependent mechanism and the role of ambient water

The heterogeneous interfacial reaction on metal oxide surfaces in combustion and thermal processes is the crucial source of environmentally persistent free radicals (EPFRs). Al2O3 is one of the most abundant metal oxides in fine particulate matter (PM) encountered in combustion systems. In the present work, the detailed formation mechanism of EPFRs from phenol on the gamma-Al2O3 (110) surface with different hydration levels was investigated by periodic theoretical calculations. The results show that gamma-Al2O3 has stronger catalytic activity for the for-mation of EPFRs compared with other metal oxides including alpha-Al2O3. Furthermore, the heterogeneity of the gamma-Al2O3 (110) surface has an impact on the formation energy barrier of EPFRs, even on the reaction route itself. When introducing ambient water, the formation pattern of EPFRs at various surface sites transforms from a single type of pathway to a mixed reaction mode and then changes to an almost new mixed mode with elevated water coverage. The multiple roles of ambient water on catalytic dissociation reaction, which had been rarely inves-tigated in previous studies, was clarified. Although this work focuses on gamma-Al2O3, it is expected to foster a crucial re-examination and integration of conventional EPFRs formation mechanism on the other metal oxide surfaces already reported in the literature, providing a novel insights into the heterogeneous generation of atmospheric PM-associated EPFRs.

Automated summary

In this study, the formation mechanism of EPFRs from phenol on the gamma-Al2O3 surface was investigated using theoretical calculations. It was found that gamma-Al2O3 has strong catalytic activity for the formation of EPFRs. The introduction of ambient water changes the formation pattern and energy barrier of EPFRs, and the role of ambient water in catalytic dissociation reactions was clarified.