The detailed investigation of heavy oil catalytic upgrading is important because heteroatom-containing compounds are detrimental to refining processes and the environment. Atmospheric residues (ARs) with different compositions were hydrotreated in two plug-flow reactors in series to study the reactivity of various species over the commercial catalysts at the molecular level. A 15-T Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with atmospheric pressure photoionization (APPI) was applied to determine the molecular composition without chemical derivatization. Here, we examined the changes in bulk and molecular composition of two different ARs. The catalytic reactivity of the ARs was determined with respect to the relative abundance of the double bond equivalent (DBE) distribution dependent on carbon number for each class, such as hydrocarbon, sulfur, and nitrogen species. Reactivities and reaction routes of hydrocarbon, sulfur, and nitrogen species were discussed in detail at the molecular level.
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