Impact of diverse active sites on MoS2 catalyst: Competition on active site formation and selectivity of thiophene hydrodesulfurization reaction

Hydrogenation Reaction Mechanisms on Ni-Doped MoS2 Catalysts: A Density Functional Theory Study of Sulfur Edge Engineering and Coregulated Electronic Effects

Precise modulation of local interatomic interactions affecting the electronic structure is an important method to control the catalytic activity and reaction pathways. In this study, we focused on the hydrogenation reaction of naphthalene and employed density functional theory calculations to investigate the specific influence of electronic effects triggered by the coregulation of Ni and sulfur edge engineering on the hydrogenation performance of Ni-doped MoS2 at different edge sulfur coverages (Ni-MoS2-X-θs). Our findings reveal that the interaction between Ni and S in the catalyst matrix material modifies the local electronic structure surrounding the sulfur atoms in the active site. Notably, Ni doping facilitates significant electron transfer, altering the charge and the electronic states at the catalyst edge. This, in turn, affects the adsorption capacity and reactivity of the catalyst, thereby reducing the energy barrier of the hydrogenation reaction. Furthermore, we paid particular attention to the modulation of catalytic activity and reaction pathways under the Eley-Rideal (E-R) mechanism. Interestingly, the sulfur coverage exhibited a nonlinear relationship with the adsorption and activation properties of the probe molecule. Typically, changes in the Mo edge sulfur coverage probability of Ni-MoS2-X-θs have a greater impact on the activation properties. Through comprehensive studies, we demonstrated that both compositional and structural factors must be considered when tailoring the catalytic performance. Importantly, adjusting the ratio of marginal sulfur atoms to metal atoms to 1:1 can effectively enhance the catalytic activity. This study provides valuable insights into the electronic effects regulating the hydrogenation reaction activity of MoS2-based catalysts. It also opens the way for the rational design of novel hydrogenation catalysts, offering a new strategy for optimizing the catalytic performance.

Theoretical study of the catalytic hydrodeoxygenation of furan, methylfuran and benzofurane on MoS2

Herein, we have studied the direct deoxygenation (DDO) (without prior hydrogenation) of furan, 2-methylfuran and benzofuran on the metal edge of MoS2 with a vacancy created under pressure of dihydrogen. For the three molecules, we found that the desorption of the water molecule for the regeneration of the vacancy is the most endothermic. Based on the thermodynamic and kinetic aspects, the reactivity order of the oxygenated compounds is furan ≈ 2-methylfuran > benzofuran, which is in agreement with literature. We present the key stages of the mechanisms and highlight the effects of substituents.

Support, composition, and ligand effects in partial oxidation of benzyl alcohol using gold–copper clusters

The effect of metallic composition, support, and ligands on catalytic performance using AuCu clusters in benzyl alcohol oxidation is investigated.

Treatment of landfill leachate evaporation concentrate by a modified electro-Fenton method

Landfill leachate evaporation concentrate (LLEC) is difficult to treat due to its complex pollutant composition, which involves large amount of organic matter and inorganic salts such as scaling ions. Because of its high conductivity and high chloride-ion content, this study employed the modified electro-Fenton method with a self-developed iron-loaded cathode to treat LLEC wastewater. The operating variables were optimized according to the response surface methodology where the chemical oxygen demand (COD) removal efficiency was considered as the response based on single-factor experiments. A second-order polynomial regression model was obtained, and an application experiment revealed that it could be applied to determine LLEC treatment conditions. The removal rates of COD and colour were 100% and 99.8%, respectively, under the optimal operating conditions of an initial pH of 6, electrode spacing of 1 cm and applied voltage of 9 V. Three-dimensional fluorescence spectroscopy demonstrated that the humic acid and fulvic acid pollutants were almost completely removed. Scanning electron microscopy and energy dispersive spectroscopy analysis showed that the iron catalyst was loaded in activated carbon pores and exhibited almost no consumption during the reaction, which effectively solved the problem of iron sludge precipitation caused by electro-Fenton oxidation technology. The atomic distribution in the crystal was also analyzed by X-ray diffraction. The specific energy consumption of electrochemical oxidation was 0.498 Wh·mg^-1 COD. The results indicate that the modified electro-Fenton technique with the proposed novel cathode is an effective method for treating LLEC.

Ultrasonication-assisted synthesis of 2D porous MoS2/GO nanocomposite catalysts as high-performance hydrodesulfurization catalysts of vacuum gasoil: Experimental and DFT study

In this study, a novel, simple, high yield, and scalable method is proposed to synthesize highly porous MoS₂/graphene oxide (M-GO) nanocomposites by reacting the GO and co-exfoliation of bulky MoS₂ in the presence of polyvinyl pyrrolidone (PVP) under different condition of ultrasonication. Also, the effect of ultrasonic output power on the particle size distribution of metal cluster on the surface of nanocatalysts is studied. It is found that the use of the ultrasonication method can reduce the particle size and increase the specific surface area of M-GO nanocomposite catalysts which leads to HDS activity is increased. These nanocomposite catalysts are characterized by XRD, Raman spectroscopy, SEM, STEM, HR-TEM, AFM, XPS, ICP, BET surface, TPR and TPD techniques. The effects of physicochemical properties of the M-GO nanocomposites on the hydrodesulfurization (HDS) reactions of vacuum gas oil (VGO) has been also studied. Catalytic activities of MoS₂-GO nanocomposite are investigated by different operating conditions. M9-GO nanocatalyst with high surface area (324 m²/g) and large pore size (110.3 Å), have the best catalytic performance (99.95%) compared with Co-Mo/γAl₂O₃ (97.91%). Density functional theory (DFT) calculations were also used to elucidate the HDS mechanism over the M-GO catalyst. It is found that the GO substrate can stabilize MoS₂ layers through weak van der Waals interactions between carbon atoms of the GO and S atoms of MoS₂. At both Mo- and S-edges, the direct desulfurization (DDS) is found as the main reaction pathway for the hydrodesulfurization of DBT molecules.

Epitaxial synthesis of Ni-MoS2/Ti3C2T x MXene heterostructures for hydrodesulfurization

Hierarchical structures of 2D layered Ti3C2T x MXene hold potential for a range of applications. In this study, catalysts comprising few-layered MoS2 with Ti3C2T x have been formulated for hydrodesulfurization (HDS). The support Ti3C2T x was derived from MAX phases (Ti3AlC2) via a liquid-phase exfoliation process, while MoS2 was obtained from synthesized aqueous ammonium tetrathiomolybdate (ATM). Furthermore, a series of catalysts with different architectures was synthesized by confinement of ATM and/or the promoter Ni in Ti3C2T x at different mole ratios, through a thermal conversion process. The synthesized MoS2/Ti3C2T x and Ni-MoS2/Ti3C2T x catalysts were characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction (TPR) measurements. The number of MoS2 layers formed on the Ti3C2T x support was calculated using Raman spectroscopy. The heterostructured few-layered MoS2/Ti3C2T x catalysts were applied in sulfur removal efficiency experiments involving thiophene. The active MoS2 sites confined by the Ti3C2T x enhanced hydrogen activation by proton saturation, and the electron charge stabilized the sulfur atom to facilitate hydrogenation reactions, leading to predominant formation of C4 hydrocarbons. The Ni-MoS2/Ti3C2T x showed the best activity at a promoter molar ratio of 0.3 when compared to the other catalysts. In particular, it is evident from the results that ATM and Ti3C2T x are potential materials for the in situ fabrication of hierarchical few-layered MoS2/Ti3C2T x catalysts for enhancing hydrodesulfurization activity in clean fuel production.