Computational investigation of N2O adsorption and dissociation on the silicon-embedded graphene catalyst: A density functional theory perspective

Exploring the Evolution Mechanism of Sulfur Vacancies by Investigating the Role of Vacancy Defects in the Interaction between H2S and the FeS(001) Surface

Vacancy defects are inherent point defects in materials. In this study, we investigate the role of Fe vacancy (V_Fe) and S vacancy (V_S) in the interaction (adsorption, dissociation, and diffusion) between H₂S and the FeS(001) surface using the dispersion-corrected density functional theory (DFT-D2) method. V_Fe promotes the dissociation of H₂S but slightly hinders the dissociation of HS. Compared with the perfect surface (2.08 and 1.15 eV), the dissociation energy barrier of H₂S is reduced to 1.56 eV, and HS is increased to 1.25 eV. Meanwhile, S vacancy (V_S) significantly facilitates the adsorption and dissociation of H₂S, which not only reduces the dissociation energy barriers of H₂S and HS to 0.07 and 0.11 eV, respectively, but also changes the dissociation process of H₂S from an endothermic process to a spontaneous exothermic one. Furthermore, V_Fe can promote the hydrogen (H) diffusion process from the surface into the matrix and reduce the energy barrier of the rate-limiting step from 1.12 to 0.26 eV. But it is very hard for H atoms gathered around V_S to diffuse into the matrix, especially the energy barrier of the rate-limiting step increases to 1.89 eV. Finally, we propose that V_S on the FeS(001) surface is intensely difficult to form and exist in the actual environment through the calculation results.

Effect of Impurity Atoms on the Adsorption/Dissociation of Hydrogen Sulfide and Hydrogen Diffusion on the Fe(100) Surface

In the actual environment, impurity atoms significantly affect the adsorption/dissociation of gas molecules on the substrate surface and in turn promote or impede the formation of subsequent products. In this study, we investigate the effects of three kinds of impurity atoms (H, O, and S) on the adsorption/dissociation of hydrogen sulfide (H₂S) and hydrogen (H) diffusion processes by using the density functional theory method. We found that impurity atoms can change the charge density distribution of the surface and thus affect the adsorption/dissociation process of H₂S. The existence of a H atom reduces the dissociation barrier of H₂S. The adsorption site of H₂S near the O atom is transferred from the bridge site to the adjacent top site and the first-order dissociation barrier of H₂S is 0.07 eV, which is prominently lower than that of the pristine surface (0.28 eV). The presence of a S atom transfers the adsorption site of H₂S to a farther bridge site and effectively affects the dissociation process of H₂S. Both O and S atoms hinder the dissociation process of HS. Moreover, the diffusion process of H atoms to the subsurface can be slightly impeded by the O atom. Our work theoretically explains the influence mechanism of impurity atoms on the adsorption/dissociation of H₂S and H diffusion behavior on the Fe(100) surface.

A DFT study of the adsorption energy and electronic interactions of the SO2 molecule on a CoP hydrotreating catalyst

The adsorption energy and electronic properties of sulfur dioxide (SO2) adsorbed on different low-Miller index cobalt phosphide (CoP) surfaces were examined using density functional theory (DFT). Different surface atomic terminations and initial molecular orientations were systematically investigated in detail to determine the most active and stable surface for use as a hydrotreating catalyst. It was found that the surface catalytic reactivity of CoP and its performance were highly sensitive to the crystal plane, where the surface orientation/termination had a remarkable impact on the interfacial chemical bonding and electronic states toward the adsorption of the SO2 molecule. Specifically, analysis of the surface energy adsorption revealed that SO2 on Co-terminated surfaces, especially in (010), (101) and (110) facets, is energetically more favorable compared to other low index surfaces. Charge density difference, density of states (DOS) and Gibbs free energy studies were also carried out to further understand the bonding mechanism and the electronic interactions with the adsorbate. It is anticipated that the current findings will support experimental research towards the design of catalysts for SO2 hydrodesulfurization based on cobalt phosphide nanoparticles.