Insights into Correlations among the Hydrodesulfurization, Hydrodenitrogenation, and Hydrogen Evolution Reactions over Molybdenum Phosphide Catalysts Modified by Cerium Oxide

A bulk MoP catalyst and a series of MoP catalysts modified by cerium oxide [Ce–MoP(x), where x represents the Ce/Mo molar ratio] were prepared by coprecipitation followed by in situ H2 temperature-programmed reduction. The addition of cerium oxide did not affect the electronic structure of MoP but decreased the MoP particle size and changed the morphology and the coordination state of MoP particles. The MoP catalyst was an aggregate of heterogeneously distributed pebble-like particles, while the Ce–MoP(x) catalysts were a mixture of pebble-like and rod-like particles. MoP only possessed a small amount of acid sites but showed almost no basicity. More acid sites and a large number of weak basic sites were found in Ce–MoP(0.4). The capacity of H2 adsorption on MoP was significantly enhanced by cerium oxide, which is related to their close proximity. We systematically studied the hydrodenitrogenation (HDN) of quinoline, the hydrodesulfurization (HDS) of dibenzothiophene (DBT), the desulfurization of 2-phenylcyclohexanethiol under both H2 and Ar, and the hydrogen evolution reaction (HER) under acidic conditions over these MoP catalysts to gain in-depth insights into the influences of cerium oxide on the catalytic performances of MoP and the correlations among HER and hydrotreating reactions. The introduction of cerium oxide, on the one hand, inhibited the HER and the hydrogen-related reactions over MoP (i.e., the hydrogenation, hydrogenolysis, and dehydrogenation reactions) but, on the other hand, facilitated the elimination reactions that do not need hydrogen. The results suggest that there is a correlation between the HER and the hydrogen-related reactions in the networks of quinoline HDN and DBT HDS. The correlation is discussed by considering the different H2 adsorption behaviors and the different coordination states of the MoP and Ce–MoP(x) catalysts.