Synthesis of NiMo catalysts supported on mesoporous Al2O3 with different crystal forms and superior catalytic performance for the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Modulating the Reaction Pathway of Ni2P/Al2O3 by Introducing Different Noble Metals for Hydrodesulfurization of Diesel

Regulating the reaction pathway of a hydrodesulfurization (HDS) catalyst to achieve ultradeep desulfurization of diesel is a low-energy-consumption yet effective strategy but remains a tricky challenge. Herein, we present a Ni2P/Al2O3 catalyst with mesoporous properties synthesized by a facile hydrothermal-temperature-programmed reduction and normal impregnation (TPRI) method, and then different precious metals with similar loadings were introduced to prepare M-Ni2P/Al2O3 (M = Pt, Pd) catalysts through incipient wetness impregnation. Their structures were analyzed by a series of characterization methods, and their catalytic performances were examined for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS. The correlation characterization results revealed that the kind of precious metals significantly affected the surface acidity and then the metal-support interaction (MSI) between Ni2P and Al2O3. Among them, the Pt-Ni2P/Al2O3 catalyst exhibits superior HDS activity with 88.5% 4,6-DMDBT conversion to Pd-Ni2P/Al2O3 (76.3%) and pristine Ni2P/Al2O3 (58.6%) catalysts under reaction conditions of 3.4 MPa, 340 °C, and LHSV = 4.8 h-1. This should be due to the introduction of Pt, which significantly facilitates the dissociation rate of H2 and the subsequent generation of more active hydrogen species than Pd, thereby promoting the formation of Brønsted acid sites, remarkably facilitating the isomerization (ISO) pathway, and markedly enhancing the 4,6-DMDBT HDS conversion of Pt-Ni2P/Al2O3. This work provides an efficient protocol to tame the reaction pathway and thereafter the catalytic performance of the HDS catalyst in the future.

One-pot solvothermal preparation of the porous NiS2//MoS2 composite catalyst with enhanced low-temperature hydrodesulfurization activity

The simple preparation of mesoporous NiS2//MoS2 composite catalyst through a one-pot solvothermal method is presented. The improvement of the specific surface area (220 m2/g) and the construction of the porous structure are realized by this method in the case of no support. The organics acts as a microscopic binder contribute to uniform stacking of MoS2 with NiS2 clusters. The composite structure including NiS2 and MoS2 was obtained (proved by XRD, XPS, TEM, IR, UV-vis and RAMAN) and changed the microelectronic environment of the active metal surface (DFT calculation). The mesoporous NiS2//MoS2 catalyst (Ni1Mo1-200) showed an excellent hydrodesulfurization performance of dibenzothiophene (DBT conversion: 78 % at 260 °C) and a high ratio of direct desulfurization pathway (SDDS/HYD = 16.6) at a low reaction temperature. By combining the characterization and theoretical calculation results, the advantages of this NiS2//MoS2 composite structure in synergistic catalysis was further confirmed.

Sulfidation of Supported Ni, Mo and NiMo Catalysts Studied by In Situ XAFS

Active sites in Mo-based hydrotreating catalysts are produced by sulfidation. To achieve insights that may enable optimization of the catalysts, this process should be studied in situ. Herein we present a comparative XAFS study where the in situ sulfidation of Mo/δ-Al2O3 and Ni/δ-Al2O3 is compared to that of δ-Al2O3 supported NiMo catalysts with different NiMo ratios. The study also covers the comparison of sulfidation of Ni and Mo using different oxide supports as well as the sulfidation conditions applied in the reactor. The XAFS spectra confirms the oxide phase for all catalysts at the beginning of the sulfidation reaction and their conversion to a sulfidized phase is followed with in situ measurements. Furthermore, it is found that the monometallic catalysts are less readily sulfidized than bimetallic ones, indicating the importance of Ni-Mo interactions for catalyst activation. Mo K-edge XAFS spectra did not show any difference related to the support of the catalyst or the pressure applied during the reaction. Ni K-edge XAFS spectra, however, show a more complete sulfidation of the Ni species in the catalyst when SiO2 is used as a support as compared to the Al2O3. Nevertheless, it is believed that stronger interactions with Al2O3 support prevent sintering of the catalyst which leads to its stabilization. The results contribute to a better understanding of how different parameters affect the formation of the active phase of the NiMo catalysts used in the production of biofuel.

Effect of Gallium as an Additive Over Corresponding Ni–Mo/γ-Al2O3 Catalysts on the Hydrodesulfurization Performance of 4,6-DMDBT

Experiments were carried out to research the different contents of Ga₂O₃ modification effects on the hydrodesulfurization (HDS) performance of 4,6-dimethyldibenzothiophene (4,6-DMDBT) catalyzed by the stepwise impregnation method. Characterization techniques such as XRD, BET, HRTEM, NH₃-TPD, and Py-FTIR were performed to determine the effects of each modification of the catalyst by Ga on the properties of the prepared supports and catalysts. The catalytic effect of gallium is reflected in the fact that the empty d-orbitals of Ga elements participate in the formation of molecular orbitals in the active center and change their orbital properties, thus generating a direct desulfurization active phase suitable for complex sulfides for endpoint adsorption. The characterization results indicated that the introduction of Ga₂O₃ with appropriate content (2 wt.%) promoted Ni and Mo species to disperse uniformly and doping of more Ni atoms into the MoS₂ crystals, which also increased the average stacking number and the length of MoS₂. As a result, more NiMoS active phases were favored to form in the system. The specific surface area and the amounts of acid sites were increased, facilitating the adsorption of reactant molecules and the HDS reactions. The HDS results also suggested the effects of Ga modification play a very important role in the catalytic performance of the corresponding catalysts. The catalyst Ga–Ni–Mo/Al₂O₃ exhibited the highest conversion rate towards 4,6-DMDBT HDS when the amount of Ga₂O₃ loading was 2 wt.% with an LHSV of 2.5 h⁻¹ at 290°C and Ga modification also can effectively improve the direct desulfurization (DDS) route selectivity in varying degrees.

Hierarchical Hybrid Supports and Synthesis Strategies for Hydrodesulfurization of Recalcitrance Organosulfur Compounds

It is undisputed that there is a paradigm shift in the global trend of crude oil towards being more sour and heavier than usual light sources. Consequently, the hydrotreating activity becomes a bottleneck with high content of S, N, metals and other impurities than expected. On the other hand, the price of petroleum products lately witnessed instability and fell to the lowest average price (<USD 20) in recent times. In the same vein, the regulation to control the emission of toxic compounds in the atmosphere become stricter as promulgated by various policymakers. In this sense, robust hydrotreating catalysts with characteristics efficient catalytic activity, selectivity and stability are highly desirable. Recently, different approaches have been used to improve and cushion the unprecedented effect emanated from economic, social and environmental challenges posed by heavy and sour crude sources, price instability of the refined products and regulation to lower the sulfur to minimum level or zero parts per millions (ppm). Importantly, the role of support in catalysis cannot be over emphasized, whilst the surface area and porosity, mechanical and thermal stability, dispersion of active metals, acidity/basicity have been greatly improved, the increased activity, stability and selectivity has been observed significantly. In this review, hybrid supports based on aluminosilicates (zeolitic types) and other notable supports from recent literatures were explored and discussed for Ni(Co)Mo(W) supported catalysts for hydrodesulfurization (HDS) activity of heavy organosulfur molecules. The emphasis on the hybrid supports' varied characteristics for HDS of organosulfur molecules, where there are necessities for fast diffusion of reactants and products, better dispersion of MoS₂ crystallites, high surface area and pore volume, and increased acidity of the catalysts are greatly emphasized. Furthermore, the progress made so far on different HDS active phases viz. noble metals, metal phosphides, intermetallic silicides, carbides and iron-zinc are highlighted in this write-up, irrespective of the support composition in the supported catalysts formulations. The need for application of predictive tools, like machine learning (ML) in the design and development of HDS catalysts, and performance evaluation of HDS activity towards achieving better catalytic operation was briefly highlighted. Finally, the review will serve as a summary of scientific efforts in this regards and bridge a gap for the newcomers to investigate the topic in a better way through proper selection and efficient catalysts design.

A hierarchical ZSM-22/PHTS composite material and its hydro-isomerization performance in hydro-upgrading of gasoline

The ZSM-22/PHTS (ZP) composite material assembled from a ZSM-22 zeolite crystal displayed a mesoporous structure. The CoMo/ZPA120 catalyst presented a good balance between HDS activity (95.2%) and lower ΔRON (−1.1).

Structural Screening and Design of Dendritic Micro-Mesoporous Composites for Efficient Hydrodesulfurization of Dibenzothiophene and 4,6-Dimethyldibenzothiophene

Novel dendritic micro-mesoporous TS-1/dendritic mesoporous silica nanoparticle (DMSN) composites (TD) were assembled by TS-1 nanocrystals with ultrasmall particle size and strong acidity. TS-1 seeds and DMSNs were composited via the Ti-O-Si chemical bond, which stimulate the generation of Brønsted (B) and Lewis (L) acids. The spillover d-electrons produced by the Ti element of TS-1 seeds produced a spillover of d-electrons, which could interact with the surface of MoS₂ phases, thereby reducing Mo-S interactions and create sulfur vacancies that are favorable for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) reactions. The increased amount of B&L acid of NiMo/TD-2.0 with cetyltrimethylammonium bromide/sodium salicylate molar ratio of 2.0 played an important role in facilitating the hydrogenation (HYD) route of DBT HDS and the isomerization (ISO) route of 4,6-DMDBT HDS, which is more favorable for the reduction of steric hindrance of DBT and 4,6-DMDBT reactants in the HDS reaction process. The NiMo/TD-2.0 catalyst exhibited the highest turnover frequency (TOF) value and HDS reaction rate constant (k_HDS) of DBT and 4,6-DMDBT due to its ultrasmall particle size, uniform spherical dendritic morphology, strong B&L acidity, and good stacking degree.

The Influence of Pore Structure and Acidity on the Hydrodesulfurization of Dibenzothiophene over NiMo-Supported Catalysts

A series of mesoporous materials of SBA-16 were in situ incorporated into ZSM-5 crystallites via a two-step self-assemble method, and hydrodesulfurization (HDS) catalysts were prepared on the corresponding ZSM-5/SBA-16 (ZS) composites. The characterization results indicated that ZSM-5 nanoseeds were fabricated into the silica framework of the ZS composites, and the three-dimensional Im3m cubic structure of SBA-16 was retained simultaneously. In addition, the ZS series materials possessed open pores and large surfaces, which would facilitate the diffusion of reactants in the mesoporous channels. Moreover, the introduction of ZSM-5 seeds into composites could enhance the acidities of supports. As a result, the NiMo/ZS series catalysts exhibited high activities for DBT HDS processes. The NiMo/ZS-160 catalyst exhibited the highest catalytic efficiency (96.5%), which was apparently attributed to the synergistic contributions of the physicochemical properties of ZS supports and the dispersion states of active metals. Correspondingly, DBT HDS reactions over the NiMo/ZS series catalysts mainly proceeded via a hydrogenation desulfurization route that benefitted from the enhanced acidities especially the total Brønsted acid.

Promoting effects of SO42− on a NiMo/γ-Al2O3 hydrodesulfurization catalyst

SO₄²⁻ anchors to a NiMo/γ-Al₂O₃ catalyst, weakening the metal–support interactions, inhibiting MoS₂ aggregation, increasing the number of Ni–Mo–S sites, and thus improving its activity and stability.

Ultradeep hydrodesulfurization of fuel over superior NiMoS phases constructed by a novel Ni(MoS4)2(C13H30N)2 precursor

Ni(MoS₄)₂(C₁₃H₃₀N)₂ was synthesized and adopted for preparing a NiMoS/γ-Al₂O₃ hydrodesulfurization catalyst, and the as-prepared catalyst exhibits superior 4,6-dimethyldibenzothiophene hydrodesulfurization activity.

An overview of conventional and alternative technologies for the production of ultra-low-sulfur fuels

Environmental concerns have given a great deal of attention for the production of ultra-low-sulfur fuels. The conventional hydrodesulfurization (HDS) process has high operating cost and also encounters difficulty in removing sulfur compound with steric hindrance. Consequently, various research efforts have been made to overcome the limitation of conventional HDS process and exploring the alternative technologies for deep desulfurization. The alternative processes being explored for the production of ultra-low-sulfur content fuel are adsorptive desulfurization (ADS), biodesulfurization (BDS), oxidative desulfurization (ODS), and extractive desulfurization (EDS). The present article provided the comprehensive information on the basic principle, reaction mechanism, workability, advantages, and disadvantages of conventional and alternative technologies. This review article aims to provide valuable insight into the recent advances made in conventional HDS process and alternative techniques. For deep desulfurization of liquid fuels, integration of conventional HDS with an alternative technique is also proposed.

Synthesis of Mesoporous γ-Al₂O₃ with Spongy Structure: In-Situ Conversion of Metal-Organic Frameworks and Improved Performance as Catalyst Support in Hydrodesulfurization

Over the past decades, extensive efforts have been devoted to modulating the textural properties, morphology and microstructure of γ-Al₂O₃, since the physiochemical properties of γ-Al₂O₃ have close correlations with the performance of hydrotreating catalysts. In this work, a spongy mesoporous γ-alumina (γ-Al₂O₃) was synthesized using Al-based metal-organic frameworks (Al-MOFs) as precursor by two-step pyrolysis, and this Al-MOF-derived γ-Al₂O₃ was used as hydrodesulfurization (HDS) catalyst support, to explore the effect of support on the HDS performance. Compared with industrial γ-Al₂O₃, the spongy alumina displayed well-developed porosity with relatively high surface area, large pore volume, and abundant weak Lewis acid sites. Based on catalyst characterization and performance evaluation, sulfurized molybdenum and cobalt molecules were able to incorporate and highly disperse into channels of the spongy mesoporous alumina, increasing the dispersion of active catalytic species. The spongy γ-Al₂O₃ was also able to enhance the diffusion efficiency and mass transfer of reactant molecules due to its improved texture properties. Therefore, the corresponding catalyst presented higher activities toward HDS of dibenzothiophene (DBT) than that from industrial alumina. The spongy mesoporous γ-alumina synthesized by Al-MOFs provides a new alternative to further develop novel γ-alumina materials with different texture and various nanoporous structures, considering the diversity of MOFs with different compositions, topological structures, and morphology.

Towards active macro–mesoporous hydrotreating catalysts: synthesis and assembly of mesoporous alumina microspheres

Stable macro–mesoporous alumina formed via a pore-directing-agent-free molding process shows promise for the hydrotreatment of heavy oils.

Enhanced catalytic activity of monodispersed porous Al2O3 colloidal spheres with NiMo for simultaneous hydrodesulfurization and hydrogenation

Fabrication of monodispersed porous Al₂O₃ spheres with controlled morphologies.

Synthesis of ZSM-5/KIT-6 with a tunable pore structure and its catalytic application in the hydrodesulfurization of dibenzothiophene and diesel oil

Porous support materials were prepared by assembling primary and secondary ZSM-5 structural units into a well-ordered mesoporous framework. The materials possessed both ZSM-5 microporous building units and mesoporous structure were used as supports for the preparation of hydrodesulfurization (HDS) catalysts. The materials and their corresponding catalysts were characterized by XRD, FTIR, ²⁷Al MAS NMR, TEM, N₂ adsorption–desorption, Py-FTIR, H₂-TPR, Raman, and HRTEM techniques. The pore structures of the composite materials were modulated by adjusting the molar ratio of butanol/P123 (BuOH/P123) and then, the influences of BuOH/P123 on the catalytic performance in the HDS of dibenzothiophene (DBT) and diesel oil were systematically studied. The results showed that butanol has a big influence on the structure of the micro–mesoporous material, whereby different micro–mesoporous structures, such as the p6mm hexagonal structure or Ia3̄d cubic structure, were formed with different butanol addition amounts. The composite ZK-3 (BuOH/P123 = 100) possessed the best surface area and pore structure. Therefore, the NiMo/ZK-3 catalyst showed the highest catalytic activity in the HDS of DBT with a BP selectivity of 72.1% due to its excellent textural property, moderate MSI, relatively high B/L ratios, and highly dispersed NiMoS active phases. Moreover, the NiMo/AZK-3 catalyst exhibited excellent catalytic performance in the HDS of diesel oil.

Porous material with tunable pore structure ZSM-5/KIT-6 was prepared by adjusting the addition amount of n-butanol. NiMo/ZK-3 and NiMo/AZK-3 catalysts exhibit good catalytic performances in the HDS of DBT and diesel oil, respectively.

Synthesis of micro-mesoporous materials ZSM-5/FDU-12 and the performance of dibenzothiophene hydrodesulfurization

The micro-mesoporous materials ZF-x (ZSM-5-FDU-12, x = SiO₂/Al₂O₃) with different molar ratios of SiO₂/Al₂O₃ were synthesized by an in situ nano-assembly method with the ZSM-5 precursor serving as the silica source.