Periodic DFT Study on the Adsorption and Catalytic Desulfurization of Thiophene over VC(001) and VN(001) via Hydrogenation and Direct Pathways

Abstract

Periodic ab initio DFT calculations based on ultrasoft pseudopotentials and a plane-wave basis set were carried out to shed some light on the adsorption and reaction mechanisms of thiophene over vanadium carbide and vanadium nitride cubic face-centered (001) surfaces and its implications for hydrodesulfurization (HDS). Direct (DDS) and hydrogenating (HYD) routes were considered for further desulfurization reactions. Furthermore, to identify their role in the adsorption and desulfurization process, various initial configurations for the adsorption complexes were investigated. Our results suggest that ring hydrogenation does not necessarily lead to a preference for the HYD pathway of thiophene desulfurization. Moreover, surface and electronic effects due to adsorption were also evaluated. We have found that under ideal conditions, vanadium nitride and carbide surfaces present similar activity over desulfurization of thiophene, in qualitative agreement with experiments.

Adsorption and Desulfurization Mechanism of Thiophene on Layered FeS(001), (011), and (111) Surfaces: A Dispersion-Corrected Density Functional Theory Study

“…Similar high activation energy barriers and endothermicity have been reported for the direct desulfurisation pathway of thiophene on the ReS 2 (001) surface 24 and on transition-metal carbides and nitride. 8 , 75 On the ReS 2 (001) surface, 24 the breaking of the first and second C–S bonds needs to surmount activation energy barriers of 1.76 and 1.85 eV, respectively, whereas on the NbC(001) surface, 74 activation energy barriers of 1.74 and 1.82 eV have to be overcome. Similarly, on the VC(001) surface, 8 the scission of the first and second C–S bonds needs to overcome activation energy barriers of 1.49 and 1.88 eV, respectively.…”

“…8,75 On the ReS 2 (001) surface, 24 the breaking of the first and second C−S bonds needs to surmount activation energy barriers of 1.76 and 1.85 eV, respectively, whereas on the NbC(001) surface, 74 activation energy barriers of 1.74 and 1.82 eV have to be overcome. Similarly, on the VC(001) surface, 8 the scission of the first and second C−S bonds needs to overcome activation energy barriers of 1.49 and 1.88 eV, respectively.…”

“… 1 − 4 Natural petroleum contains different organosulfur compounds, where aromatic species like thiophene (C 4 H 4 S) are the least reactive, which makes them common impurities in transportation fuels. 5 The HDS process consists of the reaction of the sulfur-containing compound with hydrogen to form hydrocarbons and H 2 S. 6 − 8 The key step of the desulfurization process is the C–S bond cleavage, but it is not well-understood. 9 Gaining an improved understanding of the catalytic desulfurization process relies heavily on knowledge about the initial adsorption geometry, the nature of the active sites, and a model mechanism for the C–S bond dissociation process.…”

“…Direct desulfurisation (DDS) or catalytic hydrodesulfurization (HDS) of sulfur-containing organic molecules from petroleum is of considerable technological and fundamental interest because of increasingly stringent global environmental regulations on the maximum sulfur level in fuel. − Natural petroleum contains different organosulfur compounds, where aromatic species like thiophene (C 4 H 4 S) are the least reactive, which makes them common impurities in transportation fuels . The HDS process consists of the reaction of the sulfur-containing compound with hydrogen to form hydrocarbons and H 2 S. − The key step of the desulfurization process is the C–S bond cleavage, but it is not well-understood . Gaining an improved understanding of the catalytic desulfurization process relies heavily on knowledge about the initial adsorption geometry, the nature of the active sites, and a model mechanism for the C–S bond dissociation process. , As a reaction model of desulfurization, the adsorption and reaction of thiophene on various transition-metal surfaces has been studied to help understand the catalytic desulfurization mechanism and for testing the reactivity of aromatic compounds. − …”