Active phase of dispersed MoS2 catalysts for slurry phase hydrocracking of vacuum residue

Stability of MoS2 Nanocatalysts for the Slurry-Phase Catalytic Hydrogenation of Anthracene

The stability of both the structure and activity of MoS2 nanocatalysts is crucial for minimizing the catalyst cost of the slurry-phase (SP) catalytic hydrogenation. MoS2-GP and MoS2-SP catalysts were, respectively, obtained by gas-phase (denoted as GP) and SP aging of fresh MoS2 catalysts. The MoS2-SP catalyst demonstrated a comparable catalytic hydrogenation activity to that of the fresh MoS2 catalyst, which is about 1.7 times of that for the MoS2-GP catalyst. After 12 cycles of the MoS2-SP catalyst, the obtained Cy12 catalyst demonstrates a retention of 92.0% of its initial catalytic activity. The MoS2-SP catalyst exhibits an impressive stability of catalytic hydrogenation. The MoS2-SP catalyst exhibits average stacking layers of 3.3 and an average slab of 5.2 nm and exposes 14.0% of active sites. The MoS2-SP catalyst can serve as a highly active and stable catalyst for catalytic hydrogenation. This finding can offer valuable insights into the stability of the hydrogenation catalyst in SP hydrogenation technology.

Constructing layer-by-layer self-assembly MoS2/C nanomaterials by a one-step hydrothermal method for catalytic hydrogenation of phenanthrene

Layer-by-layer self-assembly MoS2/C nanomaterials are constructed through the electrostatic adsorption between MoS2 nuclei with positive charge and C nuclei with negative charge using a facile one-step hydrothermal method. The layer-by-layer self-assembly MoS2/C catalysts with high exposure of catalytic hydrogenation active sites exhibit enhanced catalytic performance in phenanthrene hydrogenation.

Single-Atom Catalysts for Hydrogen Activation

Selective hydrogenation is one of the most important reactions in fine chemical industry, and the activation of H₂ is the key step for hydrogenation. Catalysts play a critical role in selective hydrogenation, and some single-atom catalysts (SACs) are highly capable of activating H₂ in selective hydrogenation by virtue of the maximized atom utilization and the highly uniform active sites. Therefore, more research efforts are needed for the rational design of SACs with superior H₂ -activating capabilities. Herein, the research progress on H₂ activation in typical hydrogenation systems (such as alkyne hydrogenation, hydroformylation, hydrodechlorination, hydrodeoxygenation, nitroaromatics hydrogenation, and polycyclic aromatics hydrogenation) is reviewed, the mechanisms of SACs for H₂ activation are summarized, and the structural regulation strategies for SACs are proposed to promote H₂ activation and provide schemes for the design of high-selectivity hydrogenation catalysts from the atomic scale. At the end of this review, an outlook on the opportunities and challenges for SACs to be developed for selective hydrogenation is presented.

Atomic coordination structural dynamic evolution of single-atom Mo catalyst for promoting H2 activation in slurry phase hydrocracking

Development of efficient catalysts with high atomic utilization and turnover frequency (TOF) for H₂ activation in slurry phase hydrocracking (SPHC) is crucial for the conversion of vacuum residue (VR). Herein, for the first time, we reported a robust and stable single atoms (SAs) Mo catalyst through a polymerization-pyrolysis-in situ sulfurization strategy for activating H₂ in SPHC of VR. An interesting atomic coordination structural dynamic evolution of Mo active sites was discovered. During hydrocracking of VR, the O atoms that coordinated with Mo were gradually replaced by S atoms, which led to the O/S exchange process. The coordination structure of the Mo SAs changed from pre-reaction Mo-O₃S₁ to post-reaction Mo-O₁S₃ coordination configurations, promoting the efficient homolytic cleavage activation of H₂ into H radical species effectively. The evolved Mo SAs catalyst exhibited robust catalytic hydrogenation activity with the per pass conversion of VR of 65 wt%, product yield of liquid oils of 93 wt%, coke content of only 0.63 wt%, TOF calculated for total metals up to 0.35 s^-1, and good cyclic stability. Theoretical calculation reveals that the significant variation of occupied Mo 4d states before and after H₂ interaction has a direct bearing on the dynamic evolution of Mo SAs catalyst structure. The lower d-band center of Mo-O₁S₃ site indicates that atomic H diffusion is easy, which is conducive to catalytic hydrogenation. The finding of this study is of great significance to the development of high atom economy catalysts for the industrial application of heavy oil upgrading technology.

The Effect of MoS2 Active Site Dispersion on Suppression of Polycondensation Reactions during Heavy Oil Hydroconversion

In this work, the composition, structural and morphological features, and particle size of the active phase of the catalyst (MoS2), synthesized in-situ during the heavy oil hydroconversion performed in continuous flow reactor on lab-scale pilot flow unit at T = 450 °C, P = 6.0–9.0 MPa, V = 1.0 h−1, H2/feed = 1000 nL/L, catalyst concentration C (Mo) = 0.01–0.08%wt have been studied. It has been shown that MoS2 formed during hydroconversion is represented by nanosized particles stabilized by polycondensation products as a result of strong adsorption and aggregation with the components of the hydroconversion reaction medium. The influence of morphological characteristics of catalyst nanoparticles on the feed conversion, the yield of gaseous and liquid products, and the quality of distillate fractions, as well as the yield of polycondensation products, have been studied. It has been established that an increase in MoS2 active site dispersion, both due to a decreased plate length and lower stacking numbers in MoS2 cluster, enhances hydroconversion effectivity, particularly, in suppressing polycondensation reactions.

Effects of the NiFe2O4 nanoadditive on the performance and emission characteristics of diesel engines: ultrasonic green synthesis by T3 hormone

NiFe₂O₄ nanosheets were successfully synthesized via combined ultrasonic and combustion methods using triiodothyronine (T3) hormone as a biotemplate. Isodiesel and heavy diesel were selected as feedstocks to evaluate the ultrasound-assisted catalytic oxidation process. In this study, we focused on high performance of diesel engine with NiFe₂O₄ nanosheets. Various conditions such as catalyst dosage, hydrogen peroxide dosage, frequency range and catalyst morphologies of NiFe₂O₄ were investigated to achieve optimized conditions. High levels of sulfur compounds (98%) were removed using NiFe₂O₄ catalysts under determined conditions (1.0 g L⁻¹ catalyst, O/S mole ratio = 2, frequency = 40 kHz and morphology of the nanocatalyst = nanosheets). The nickel ferrite nano additive was mixed with isodiesel and heavy diesel using an ultrasonicator device to achieve better stability. The results indicated that under the optimum amount (1% w/v), the NiFe₂O₄ nanostructure is the best additive to reduce NO_x, CO, HC and smoke emission in diesel engines. Moreover, a change in the flash point and viscosity of diesel fuels was observed with the addition of nanosheets. NiFe₂O₄ could be recycled 3 times without a significant decrease in catalyst activity.

In the present study, nanocrystals are synthesized by the ultrasonic method in different morphologies with T3 hormone as a template. Different parameters are investigated for the synthesis of nanostructures.

Insight into the Microstructure and Deactivation Effects on Commercial NiMo/γ-Al2O3 Catalyst through Aberration-Corrected Scanning Transmission Electron Microscopy

Atom-resolved microstructure variations and deactivation effects on the commercial NiMo/γ-Al2O3 catalysts were revealed by aberration-corrected scanning transmission electron microscope (Cs-STEM) equipped with enhanced energy dispersive X-ray spectroscopy (EDS). Structural information parallel to and vertical to the electron beam provides definitive insight toward an understanding of structure–activity relations. Under the mild to harsher reaction conditions, “fragment” structures (like metal single atoms, metal clusters, and nanoparticles) of commercial NiMo/γ-Al2O3 catalysts, gradually reduces, while MoS2 nanoslabs get longer and thinner. Such a result about active slabs leads to the reduction in the number of active sites, resulting in a significant decrease in activity. Likewise, the average atomic ratio of promoter Ni and Ni/(Mo + S) ratio of slabs decrease from 2.53% to 0.45% and from 0.0788 to 0.0326, respectively, by means of EDS under the same conditions stated above, reflecting the weakening of the promotional effect. XPS result confirms the existence of NixSy species in deactivated catalysts. This could be ascribed to the Ni segregation from active phase. Furthermore, statistical data give realistic coke behaviors associated with the active metals. With catalytic activity decreasing, the coke on the active metals regions tends to increase faster than that on the support regions. This highlights that the commercial NiMo/γ-Al2O3 catalyst during catalysis is prone to produce more coke on the active metal areas.