Competitive hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline over unsupported MoS2 catalyst

• Quinoline and dibenzothiophene affected each other in the reactions toward the removal of their heteroatoms.
• The presence of H2S in the reaction feedstock of quinoline promotes the transformation to ortho-propylaniline.
• The hydrodenitrogenation reactions precede the hydrodesulfurization reactions.
• Dibenzothiophene may enhance the hydrodenitrogenation reaction of quinoline.

The hydrodesulfurization of dibenzothiophene and the hydrodenitrogenation of quinoline were investigated both individually and simultaneously as a mixture over an unsupported synthetic MoS2 catalyst. The reactions were carried out in a batch system under 3 MPa H2 at 340 °C. Investigations toward the effect of H2S on the hydrodenitrogenation reaction of quinoline revealed that H2S promoted the transformation of 1,2,3,4-tetrahydroquinoline (THQ1) to ortho-propylaniline (OPA), but had a considerable adverse impact on the transformation of OPA to propylbenzene and its derivatives (C9 products). The hydrodesulfurization of dibenzothiophene proceeded predominantly through a hydrogenation pathway to give cyclohexylbenzene. The hydrodesulfurization of dibenzothiophene was found to be completely inhibited during the initial stages of the reaction, when quinoline was added into the feedstock. The inhibition of the reaction persisted until the quinoline was transformed to a sufficiently low level. Thereafter, the hydrodesulfurization of dibenzothiophene recovered and the reaction proceeded with only moderate inhibition. In contrast, the hydrodenitrogenation of quinoline was significantly enhanced by the presence of dibenzothiophene in the reaction feedstock. The THQ1 and C9 products were the main species obtained from the hydrodenitrogenation reaction of quinoline. The presence of dibenzothiophene enhanced the activity and selectivity toward C9 productions. These results suggested that at least two types of active site were involved in the reaction. Dibenzothiophene could interact with distinct coordinative unsaturated sites, and this could stabilize and increase the acidity of the potential active sites assumed to be responsible for the hydrodenitrogenation reactions.

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