Heterogeneous reactions between NO2 and anthracene adsorbed on SiO2 and MgO

The heterogeneous reactions of NO2 with anthracene adsorbed on SiO2 and MgO were investigated under dark conditions at 298 K using DRIFTS, GCMS, and UV–Vis. The pseudo-first-order rate constants of anthracene on SiO2 and MgO were obtained by fitting the exponential decay of adsorbed PAH concentrations versus reaction time. The reaction on SiO2 was almost two times faster than on MgO when the concentration of NO2 was 3.69 × 1012 molecules cm−3. Both 9-nitroanthracene and 9,10-anthraquinone were the products of the nitration of anthracene adsorbed on SiO2 whereas 9,10-anthraquinone was the only product formed by NO2 reaction with anthracene adsorbed on MgO. These results suggest that mineral oxides not only control the reaction kinetics of PAHs with NO2 but also alter the reaction pathway for the heterogeneous reaction of PAHs with NO2. The difference in the heterogeneous reactivity of NO2 with anthracene adsorbed on SiO2 and MgO was ascribed to the formation of HNO3 on SiO2, which can catalyze the nitration of PAHs by NO2. Due to the formation of nitro-anthracene and oxy-anthracene, the heterogeneous reactions of NO2 with anthracene also altered the optical properties of the mineral oxides on which anthracene were adsorbed.

Research highlights
► Heterogeneous reaction of anthracene with NO2 depends on the nature of substrate.
► Reactions rate of anthracene with NO2 on SiO2 is higher than that on MgO.
► HNO3 formed on SiO2 leads to higher reactivity and formation of 9-nitroanthracene.