Unraveling the Role of Surface Termination in Ni₂P(001) for the Direct Desulfurization Reaction of Dibenzothiophene (DBT): A Density Functional Theory (DFT) and Microkinetic Study

Abstract

Achieving ultradeep desulfurization of transportation fuels dictates the removal of the last fragments of sulfur present in bulky refractory molecules such as dibenzothiophene (DBT). Improving the hydrodesulfurization (HDS) performance of the next-generation Ni 2 P catalyst is crucial; however, it is still unclear how a DBT direct desulfurization (DDS) reaction proceeds on different surface terminations of this material. This work aims at elucidating the influence of Ni 3 P-, Ni 3 P 2 -, and partially sulfided Ni 3 P 2 (Ni 3 PS)-terminated surfaces of the Ni 2 P(001) crystal on the DDS reaction of DBT using density functional theory (DFT) computations. The scission of the first C−S bond in DBT was found to be kinetically hindered compared to the second C−S bond cleavage over the three surfaces owing to the highly stable structure of adsorbed DBT compared to the C 12 H 9 SH intermediate. Notably, the overall DBT desulfurization process is thermodynamically favorable only on the Ni 3 PS surface, due to the presence of the active phosphosulfide (Ni−P−S) phase. Microkinetic modeling was conducted to probe the reaction orders, apparent activation energy, and rate-controlling steps as a function of temperature. Notably, the ring-opening step of DBT, via the first C−S bond cleavage, is the rate-controlling step on Ni 3 P and Ni 3 PS surfaces, which is rationalized by the high energy barrier of this step. The activation energy of the reaction over the surfaces followed the order Ni 3 P < Ni 3 PS < Ni 3 P 2 . Compared to the bare Ni 3 P 2 surface, the lower activation energy on the Ni 3 PS surface is explained by the destabilization effect of the reaction intermediates on the latter. Thus, the partially sulfided Ni 3 P 2 provides a better model for the DBT desulfurization process than the fresh Ni 3 P 2 surface.

Unraveling the Structure and Surface Chemistry of the Phosphosulfide Phase Formed on Ni2P under Hydrodesulfurization Reaction Conditions: A DFT Study

“…Their results indicated that up to 50% of the surface phosphorus can be replaced by sulfur and suggested that the Ni 3 PS surface stoichiometry is an accurate representation of the actual active phase of Ni 2 P under HDS reaction conditions. In this regard, Elmutasim et al studied the direct desulfurization (DDS) reaction of dibenzothiophene on the Ni 3 P 2 and partially sulfided Ni 3 PS terminations using DFT calculations. The authors found that the overall dibenzothiophene desulfurization process is thermodynamically favorable only on the Ni 3 PS surface, due to the presence of the active phosphosulfide phase.…”

Direct deoxygenation reaction of oxygenated model compounds by biomass pyrolysis on the Ni5P4(001) surface: a computational study

“…23 According to the literature, the bond-creation reaction may exhibit a high kinetic barrier when the reacting species are strongly bonded to the substrate. 33,52,54,55 Therefore, the higher kinetic barrier of the rst hydrogenation step can be explained by the high stability of the benzyne intermediate, as shown in Fig. 9.…”

“…A higher activation energy of 0.24 eV was reported for H 2 dissociation on Ni 2 P(001), indicating that the dissociation is more favorable on Ni 5 P 4 (001) in comparison to Ni 2 P(001). 52 This is an exothermic step, releasing a reaction energy of −0.14 eV. It can be inferred that, unlike the parallel orientation, this perpendicular orientation of phenol enables a higher extent of OH interaction with the Ni 5 P 4 (001) surface and more facile dissociation of the O-H bond in phenol.…”