Influence of formic acid and iron oxide nanoparticles on active hydrogenation of PAHs by hot compressed water. Isotope tracing study.

• Isotope tracing technique was applied to study the role of HCW as an active H-donor for hydrogenation of PAHs. • Compared to lone HCW, addition of formic acid and iron oxide NPs displays superior activity in hydrogenation of PAHs. • Hydrogenation from HCW only cape the double-bond carbon which belongs to the PAHs rings (C H), instead of single-bond carbon (C H). • The mechanisms of contribution of HCW during the conversion of PAHs were described. Use of hot compressed water (HCW) as a reaction medium to enhance conversion efficiency of polyaromatic hydrocarbons (PAHs) to lighter products is an important topic in green chemistry, where hydrogenation and ring opening of PAHs are crucial for tar removal and heavy oil upgrading with less coke. In this study, the influence of HCW on the conversion of coronene (super benzene) as model molecule of PAHs with 7-ring is examined. A series of agents, such as cheap iron oxide NPs (α-Fe 2 O 3) as an oxygen-donor, formic acid (CHOOH) as hydrogen-donor, and their physical mixtures, are used. Pure deuterium oxide (D 2 O) is also applied instead of H 2 O to track the hydrogenation from HCW. The influences of water density; reaction temperature, reaction time, and amount of catalyst loading on conversion of coronene and yield of coke are studied. The reaction in the presence of D 2 O as control experiment shows minor H/D exchange during the reaction process stating that water itself has no effect on hydrogenation of coronene. In the presence of agents (iron oxide, formic acid and their mix), however, outstanding synergistic effect occurs and water could be used as a green and efficient medium for hydrogenation and enhancing the conversion of coronene. In summary, the isotope tracing experiments reveals that hydrogenation from HCW only cape the double-bond carbon which belongs to the PAHs rings (C H), instead of hydrogenation of created alkyl groups with single-bond carbon (C H). This issue indicates the strong impact of active hydrogen from condensation reaction on hydrogenation of PAHs, which elaborated at the cost of made coke. [ABSTRACT FROM AUTHOR]