Deep Hydrogenation Research Articles

On the circulation of hydrogen in the atmosphere and the Earth’s crust

A review of data on sources and sinks of hydrogen of various origins in the atmosphere and in the near-surface part of the Earth’s crust is given (only some cases we are talking about the crust as a whole). Based on the results of the consideration of this information, it was concluded that the influence of underground non-biogenic («geological») hydrogen on the content and balance of gas in the atmosphere, up to the stratosphere, is insignificant. The complexity of the experimental determination of the flow of geological hydrogen, free of biogenic and anthropogenic interference, the influence of the testable excavation, etc. is obvious. Probable sources of deep hydrogen are considered: the remains of magmatic gases (outside the areas of volcanism), metamorphic reactions, and radiolysis of water. The potential for significant H2 flow is only apparent in areas of currently activated faults. The data on the most powerful suppliers of geological hydrogen — modern active volcanoes and thermal fields are given. The gas circulation scheme of the Avachinsky volcano is built, based on the thermal model. The latter is controlled by data from geothermometers, the results of direct temperature measurements in deep wells, and a velocity model. The possibility of fumaroles carrying unchanged hydrogen from the magma chamber has been shown. The prospects for the formation of hydrogen deposits are estimated as uncertain. Magmatic and metamorphogenic gas in some areas is formed enough to accumulate a significant deposit over several tens of thousands of years. But the possibility of its preservation during this period or longer raises doubts. Hydrocarbon deposits without material input from great depths can lose reserves in much less time. Higher rocks permeability to hydrogen contributes to much greater gas leakage.

Intensification of catalytic transfer hydrogenation of fatty acid methyl esters by using ultrasound

Ultrasound was applied to intensity the catalytic transfer hydrogenation (CTH) of highly unsaturated fatty acid methyl esters (FAMEs) to realize the effective hydrogenation of FAMEs under mild conditions. Under the optimum reaction conditions of ultrasound-assisted CTH using La-doped nickel-boride amorphous alloy (Ni–La–B) as catalyst, sodium borohydride as hydrogen donor and water as solvent, a high conversion ratio of hydrogenation for polyunsaturated FAMEs could be easily realized at 35 °C at 120 min (ca. 78.66%). It was found that ultrasound presented a significant intensification effect on the CTH of FAMEs; different from the conventional and ultrasound approaches, by using ultrasound-assisted approach of CTH, deep hydrogenation could be avoided to a certain extent even under the high conversion ratio of hydrogenation, and the hydrogenated product with good performance was easily gained. The self-purification function of ultrasound on the catalyst played the most important positive effect on the intensification of CTH of FAMEs. Overall, the ultrasound-assisted approach played an effective process intensification on the CTH of FAMEs to produce high-quality products under mild conditions.

Ab initio study of the structure and relative stability of MgSiO4H2 polymorphs at high pressures and temperatures

Abstract Using particle swarm optimization with density functional theory, we identify the positions of hydrogen in a hypothetical Mg-end-member of phase egg (MgSiO4H2) and predict the most stable crystal structures with MgSiO4H2 stoichiometry at pressures between 0 and 300 GPa. The particle swarm optimization method consistently and systematically identifies phase H as the energetically most stable structure in the pressure range 10–300 GPa at 0 K. Phase Mg-egg has a slightly higher energy compared to phase H at all relevant pressures, such that the energy difference nearly plateaus at high pressures; however, the combined effects of temperature and chemical substitutions may decrease or even reverse the energy difference between the two structures. We find a new MgSiO4H2 phase with the P43212 space group that has topological similarities to phase Mg-egg and is energetically preferred to phase H at 0–10 GPa and 0 K. We compute the free energies for phase Mg-egg, phase P43212, and phase H at 0–30 GPa within the quasi-harmonic approximation and find that the effect of temperature is relatively small. At 1800 K, the stability field of phase P43212 relative to the other polymorphs increases to 0–14 GPa, while pure phase Mg-egg remains energetically unfavorable at all pressures. Simulated X-ray diffraction patterns and Raman spectra are provided for the three phases. Additionally, the crystallographic information for two metastable polymorphs with the P1 space group is provided. Our results have implications for the deep hydrogen cycle in that we identify two novel potential carrier phases for hydrogen in the mantles of terrestrial planets and assess their stability relative to phase H. We determine that further experimental and computational investigation of an extended compositional space remains necessary to establish the most stable dense hydrated silicate phases.

Catalytic cracking of n-heptane over Fe modified HZSM-5 nanosheet to produce light olefins

Aiming at the acid modification and stabilization of ordered mesopores in HZSM-5 nanosheet (NS) zeolite for catalytic cracking, two kinds of Fe-modified NS zeolite catalysts were prepared by incipient wetness impregnation (Fe/NS) and an in-situ hydrothermal synthesis method (Fe@NS, N-[3-(trimethoxysilyl)propyl]ethylenediamine complexed Fe as precursors). Fe modification conveyed a lower n-heptane cracking conversion by the Fe/NS catalyst because of the decreased total acid content compared with the parent NS catalyst. However, the decreased Brønsted to Lewis acid ratios by Fe modification restricted the deep hydrogen transfer of olefins, leading to an enhanced ethylene and propylene yields in the product. Furthermore, for Fe@NS catalyst, the highly dispersed FeOx between the nanosheet layers stabilized the mesopore arrangement, and the facilitated diffusion by highly connected channels further alleviated olefin consuming. At reaction temperature of 550 °C with a weight hourly space velocity of 8.64 h−1, a 41.8 wt% yield of light olefins (ethylene of 12.2 wt% and propylene of 29.6 wt%) by the Fe@NS catalyst was realized, which was 10.4% and 21.7% higher than that of the Fe/NS and parent NS catalysts, respectively. Moreover, Fe@NS also showed a good catalytic stability with a deactivation rate of only 4.37% after 18 h reaction.

Deep Hydrogenation Saturation of Naphthalene Facilitated by Enhanced Adsorption of the Reactants on Micro‐Mesoporous Pd/HY

AbstractDeep hydrogenation saturation of polycyclic aromatic hydrocarbons is of great importance for the production of valuable chemical products, but is hard due to the presence of hardly broken π bond. In this work, micro‐mesoporous HY supported Pd catalysts (Pd/HY‐a) have been prepared by a simple impregnation method following alkali treatment of pristine HY zeolite, which exhibited superior performance for the deep hydrogenation saturation of naphthalene. Pd/HY‐a was systematically characterized and compared with the Pd catalysts supported on pristine HY, ZSM‐5, SBA‐15, and Al2O3. In Pd/HY‐a, abundant mesoporous pore channels together with suitable B acid sites greatly facilitate the adsorption of the reactants (naphthalene and tetralin) and properly tune the electron state of loaded Pd. Therefore, efficient deep hydrogenation saturation of naphthalene has been achieved on Pd/HY‐a. Moreover, the kinetic behaviors of naphthalene hydrogenation on Pd/HY‐a were preliminarily investigated, in which the first‐order kinetic model fitted the experimental data well in the early reaction stage.

Thermodynamic assessment of the possibility of olivine interaction with deep-seated hydrogen

Olivine is one of the most widespread minerals of the Earth's upper mantle. It is widely accepted in the scientific community, that during olivine interaction with water large amounts of hydrogen are released. On the other hand, the idea of an accumulation of huge hydrogen amounts in the core and lower mantle of the Earth is becoming more and more popular now. In this paper, we attempt to assess the possible interaction of hydrogen rising from the depths with olivine in the upper mantle, which has not been done before. Program GEMS was used for modeling calculations. The influence of the hydrogen amount on the serpentinization process at T = 323.15 ÷ 593.15 K and P = 3⋅107 ÷ 3⋅108 Pa has been estimated. The initial composition of the system was set as 1 mol of olivine (Fe0.1Mg0.9SiO4). The amount of added hydrogen was set as 1, 500, and 5000 mol. The water was not specified as a composition of the initial system. The simulation showed that hydrogen can cause the serpentinization process, which indicates in favor of the hypothesis about deep hydrogen sources, although it is not 100% proof of this.

Enhancing light olefins and aromatics production from naphthenic-based vacuum gas oil: Process integration, techno-economic analysis and life cycle environmental assessment

Global excess capacity of lubricating oil and high-value added utilization of naphthenic-based heavy oil concerns have attracted tremendous attention. Enhancing the highly efficient transformation for polycyclic aromatic hydrocarbons (PAHs) rich in naphthenic-based vacuum gas oil to light olefins and aromatics could be a promising solution through systematic process integration. Four naphthenic-based heavy oil processing schemes, hydrotreating, hydrocracking, hydro-upgrading and deep catalytic cracking, and a novel deep hydrogenation coupled with the two stage risers of maximizing propylene process (DHTMP), are brought up. The process simulation and models are established for the processing schemes to gain detailed mass balance and energy consumption results. The operating parameters are optimized for the purpose of maximizing light olefins and aromatics. The economic and life cycle environmental assessment are conducted to determine the superiority of DHTMP process over other schemes. The DHTMP process realized full recovery and utilization of low-value light cycle oil and efficient transformation of PAHs to light olefins and aromatics. Moreover, the DHTMP process shows great performance from the techno-economic and life cycle environment aspect. The results in this study have great guiding significance to the process intensification of PAHs in vacuum gas oil converting to light olefins and aromatics products efficiently.

Influence of reference states on Jupiter’s dynamo simulations

Jupiter’s magnetic field is thought to be generated in its deep metallic hydrogen region through dynamo action, yet the detailed dynamic process remains poorly understood. Numerical simulations have produced Jupiter-like magnetic fields, albeit using different control parameters and reference state models. In this study, we investigate the influence of different reference state models, based on <i>ab initio</i> calculations and based on the polytropic equation of state. In doing so, we perform five anelastic convection dynamo simulations that can be divided into two groups. In each group, different reference states are used while other control parameters and conditions are set to be identical. We find the reference state model can be very influential for the simulations in which buoyancy force is dominant over the Lorentz force. In this regime, different dynamical outcomes can be attributed to the effective buoyancy force resulting from different reference states. For simulations in which the Lorentz force is dominant over the buoyancy force, however, dynamo actions tend to be insensitive to different reference state models. If Jupiter’s dynamo is in a strong field regime, i.e., the Lorentz force plays a dominant role, our numerical results suggest that Jupiter’s internal reference state, which remains poorly constrained, may play a minor role in the dynamo process of the planet.

Tuning product selectivity in CO2 hydrogenation over metal-based catalysts.

Conversion of CO2 into chemicals is a promising strategy for CO2 utilization, but its intricate transformation pathways and insufficient product selectivity still pose challenges. Exploiting new catalysts for tuning product selectivity in CO2 hydrogenation is important to improve the viability of this technology, where reverse water-gas shift (RWGS) and methanation as competitive reactions play key roles in controlling product selectivity in CO2 hydrogenation. So far, a series of metal-based catalysts with adjustable strong metal–support interactions, metal surface structure, and local environment of active sites have been developed, significantly tuning the product selectivity in CO2 hydrogenation. Herein, we describe the recent advances in the fundamental understanding of the two reactions in CO2 hydrogenation, in terms of emerging new catalysts which regulate the catalytic structure and switch reaction pathways, where the strong metal–support interactions, metal surface structure, and local environment of the active sites are particularly discussed. They are expected to enable efficient catalyst design for minimizing the deep hydrogenation and controlling the reaction towards the RWGS reaction. Finally, the potential utilization of these strategies for improving the performance of industrial catalysts is examined.

Long-term monitoring of natural hydrogen superficial emissions in a brazilian cratonic environment. Sporadic large pulses versus daily periodic emissions

In many basins, hydrogen-emitting structures are now observed, but the estimation of the H2 flow leading to their formation remains poorly constrained since all data show that the H2 emissions are variable in space and time. We present here the data of a long-term monitoring campaign with a high density of permanent hydrogen detectors installed in 2 structures in the Minas Gerais State (Brazil). Results show that two kinds of signals are recorded, large sporadic pulses that affect the H2 content of the soil for one or two days and smaller ones, with a daily periodicity, that last 6 h and during which the near surface soil concentration usually does not exceed 200 ppm. This last signal is very regular in frequency, less in amount, and the daily maximum happens around noon or in the early afternoon. We interpret the large pulses as evidences of a deep hydrogen flux, leaking either from a reservoir located in the subsurface, from an aquifer which is degassing or, although it seems unlikely, directly from the H2 generation area.The time correlation between the pulse and the increase of the daily signal suggests that this last one corresponds to the slow release of the gas that has been captured by the soil during its transport towards the surface. This daily signal is most likely influenced by external factors such as atmospheric pressure and sub-surface bacterial activity. In map view, the lack of correlation between the highest hydrogen concentrations over time suggests that the soil is very heterogeneous and that preferential pathways exist. The results confirm that long-term monitoring, over a few months, is mandatory to catch a certain number of high pulses and so to have a better estimation of the real flow. Data also suggests that sensors with a large concentration range should be used (from 10 to several 104 ppm). Even if quantification of leakage doesn't help to quantify the subsurface reserves, these new data allow a more precise evaluation of the quantity of H2 released in surface by these structures, few hundred of kilo per day, and confirm the high H2 prospectivity of this basin.

Quantitative investigation on deep hydrogen trapping in tempered martensitic steel

In this work, the correlation between different microstructural components and hydrogen trapping with high density in tempered niobium carbide (NbC)-precipitated martensitic steel was quantitatively investigated using a combination of electrochemical hydrogen permeation experiments and thermal desorption spectroscopy. The martensite lath and a high density of dislocations, which constitute the reversible hydrogen trapping sites, with a density of 2.24 × 1020 cm−3 in Fe-0.05C-1.10Mn-4.50Ni-0.50Cr-0.50Mo-0.05Nb wt.% martensitic steel. The dislocation with high density could disperse the hydrogen distribution. Furthermore, the uniformly distributed NbC nanoprecipitates, the high-angle grain boundaries, and the grain-boundary precipitates were found to act as irreversible hydrogen traps, with a density of 1.00 × 1020 cm−3. These deep hydrogen trapping sites could not only trap hydrogen irreversibly, but also can inhibit the accumulation of hydrogen. The interpretation of hydrogen trapping is significant to enhance the hydrogen embrittlement resistance of high-strength martensitic steels.

Atomic-scale investigation of deep hydrogen trapping in NbC/α-Fe semi-coherent interfaces

The precipitation of niobium carbide (NbC) is a superior approach to mitigating hydrogen embrittlement (HE). The role of the semi-coherent interface between NbC and α-Fe on hydrogen trapping and HE resistance in high-strength tempered martensitic steel was investigated in this study. High-resolution transmission electron microscopy observations are performed to reveal the atomic-scale crystallographic orientation relationship, atomic arrangements, and associated crystalline defects in the NbC/α-Fe semi-coherent interface. We observed the Kurdjumov–Sachs orientation relationship with (11¯1¯)NbC//(101)α−Feand [01¯1]NbC//[1¯11]α−Febetween the NbC and α-Fe phases. Noticeably, two sets of misfit dislocations with Burgers vectors of b(1)=ab/2[111]on (011¯)α-Fe planes and b(2)=ab/2[11¯1]on (110) α-Fe planes (ab is the lattice constant of α-Fe), which would be the deep hydrogen trapping sites, were characterized in the NbC/α-Fe semi-coherent diffuse interface. In addition, density functional theory-based first-principles calculations revealed that the deep binding energy between the NbC/α-Fe semi-coherent interface and hydrogen is 0.80 eV, which well matches the hydrogen desorption activation energy of 81.8 kJ/mol determined via thermal desorption spectroscopy experiments. These demonstrate that the nature of the deep hydrogen trapping sites of the NbC/α-Fe semi-coherent interface is the misfit dislocation core. Distinguished HE resistance was obtained and ascribed to the deep hydrogen trapping of uniformly dispersed NbC nanoprecipitates with an average diameter of 10.0 ± 3.3 nm. The strategy of deep hydrogen trapping in the NbC/α-Fe semi-coherent interface is beneficial for designing HE-resistant steels.

NbOPO4 Supported Rh Nanoparticles with Strong Metal-Support Interactions for Selective CO2 Hydrogenation.

Strong metal-support interactions (SMSI) could improve the performance of nanoparticle catalysts through the electronic and geometric modulation of the reducible metal oxide supports. Here, SMSI is demonstrated to occur for catalysts with non-oxide carrier, such as NbOPO4 -supported Rh nanoparticles, under reduction treatment at low temperature. During CO2 hydrogenation, this Rh/NbOPO4 catalyst with SMSI exhibits impressive CO selectivity at high CO2 conversion in a wide temperature range with hindered methanation. For example, over 98.9 % CO selectivity was obtained with 39.9 % CO2 conversion at 500 °C. Mechanism investigations demonstrate that the SMSI results in the formation of a metal-support interface with weaker CO adsorption than the metallic Rh sites, thus accelerating the CO desorption, which hinders deep hydrogenation. Rh nanoparticles with small diameter of about 1.1 nm is sinter-resistant with unchanged performance during a long-period test. This work might extend the investigation of SMSI from oxides to phosphate supports, which helps optimizing the selectivity and stability of metal nanoparticle catalysts.

Hydrodechlorination and deep hydrogenation on single-palladium-atom-based heterogeneous catalysts

Halophenols are widely present in wastewater and groundwater, which threaten global water safety and human health. Importantly, hydrodechlorination (HDC) via heterogeneous catalysis is efficient and environmentally friendly. To further improve the catalytic performance and atomic economy, Pd-based single atom catalysts (SACs) were prepared through electrostatic attraction and used in the catalytic HDC for the first time. By substituting different defect-rich supports, the coordination environments of atomically dispersed Pd-atoms were mediated with different catalytic performance. The results demonstrate that the Pd/CeO2 SACs have the highest HDC activity and remain stable during cycle tests. The moderately intensive metal-support interactions (MIMSI) effect was identified as a critical factor for the higher activity of SACs, unlike the traditional strong metal-support interaction effect. The HDC process on Pd SACs was further investigated by combining kinetic experiments with density functional theory calculations, which facilitated the recognition of HDC intermediates and an understanding of the reaction mechanism.

A new hydrous iron oxide phase stable at mid-mantle pressures

The amount of hydrogen stored in the Earth's interior is important for a range of issues, including the volatile incorporation during the Earth formation and the co-evolution of the atmosphere, the hydrosphere, and the interior. Recent experiments found titanium bearing ε-FeOOH in a hydrous basaltic system at 12–19 GPa and 1300 K. Pyrite-type FeOOH was found to be stable at pressures higher than 80 GPa. These discoveries suggest possible hydrogen storage in the mantle transition zone and in the mantle below 1800 km depths, respectively. However, it remains uncertain how the potential deep hydrogen storage can be connected to the shallower storage. Here, we report a new hydrous iron oxide (η-Fe12O18+x/2Hx, x≈2) stable at pressures between the stability fields of the ε- and the pyrite-type FeOOH. Our experiment also shows that the new η phase can exist together with the major lower mantle minerals including bridgmanite and periclase, making it an important hydrogen-bearing phase in the Earth's deep interior. Because of its limited H2O storage capacity, which is less than 1/6 of the storage capacity of the pyrite-type phase and the ε phase, the stability of the η phase would result in H2O loss during water transport in the mid mantle and therefore limit the amount of H2O potentially stored in the Fe–O–H system of the lower mantle. The large channel in the crystal structure of the η phase could provide potential storage sites for other volatile elements in the deep mantle.

Optimization and lumped kinetic model study of coal-based aerospace kerosene hydrogenation process

The effects of various factors on the hydrodegumming (HDG) of oil during the deep hydrogenation of coal-based aerospace kerosenee (CBAK) were studied by single factor experiment and response surface methodology (RSM) analysis on a fixed-bed hydrogenation unit with the existent gum content as the observation value. The results show that in order to achieve better HDG effect of CBAK, it must be carried out at high reaction temperature (T), high reaction pressure (P) and low liquid hourly space velocity (LHSV). The influence of various factors on the gum content of hydrogenated oil was analyzed by using the Design Expert software. The influence degree order was as follows: LHSV > P > T. At the same time, the process conditions of deep hydrogenation were optimized by simulation: P = 11.91 MPa, LHSV = 1.60 h−1, V(H2)/V(Oil) = 800, T = 619.84 K, under which the expected gum content was 0.26 mg (100 mL)−1. On this basis, according to the speed of CBAK-HDG reactivity, the existent gum in the raw material were divided into three lumps, which are high reactivity, medium reactivity, and slow reactivity, then the three lumped kinetic model of CBAK-HDG was established. The kinetic parameters of the model were calculated by Levenberg–Marquardt method, and the model was verified by the measured data. The experimental results show that the average relative error of the model is 8.28%, the predicted value is reliable and the extrapolation is quite good. The calculation results of the model parameters correspond to the results of RSM, which is consistent with the hydrogenation reaction law. The results of this study are expected to provide some theoretical basis and reference for the further study of coal-based space kerosene hydrofining process and the optimization of operation conditions of industrial units.

BUDHiES IV: Deep 21-cm neutral Hydrogen, optical, and UV imaging data of Abell 963 and Abell 2192 at z ≃ 0.2

ABSTRACT In this paper, we present data from the Blind Ultra-Deep H i Environmental Survey (BUDHiES), which is a blind 21-cm H i spectral line imaging survey undertaken with the Westerbork Synthesis Radio Telescope. Two volumes were surveyed, each with a single pointing and covering a redshift range of 0.164 &amp;lt; z &amp;lt; 0.224. Within these two volumes, this survey targeted the clusters Abell 963 and Abell 2192, which are dynamically different and offer unique environments to study the process of galaxy evolution within clusters. With an integration time of 117 × 12 h on Abell 963 and 72 × 12 h on Abell 2192, a total of 166 galaxies were detected and imaged in H i. While the clusters themselves occupy only 4 per cent of the 73 400 Mpc3 surveyed by BUDHiES, most of the volume consists of large-scale structures in which the clusters are embedded, including foreground and background overdensities and voids. We present the data processing and source detection techniques and counterpart identification based on a wide-field optical imaging survey using the Isaac Newton Telescope and deep ultraviolet (UV) Galaxy Evolution Explorer (GALEX) imaging. Finally, we present H i and optical catalogues of the detected sources as well as atlases of their global H i properties, which include integrated column density maps, position–velocity diagrams, global H i profiles, and optical and UV images of the H i sources.

Ruthenium Catalysts Templated on Mesoporous MCM-41 Type Silica and Natural Clay Nanotubes for Hydrogenation of Benzene to Cyclohexane

Mesoporous ruthenium catalysts (0.74–3.06 wt%) based on ordered Mobil Composition of Matter No. 41 (MCM-41) silica arrays on aluminosilicate halloysite nanotubes (HNTs), as well as HNT-based counterparts, were synthesized and tested in benzene hydrogenation. The structure of HNT core-shell silica composite-supported Ru catalysts were investigated by transmission electron microscopy (TEM), X-ray fluorescence (XRF) and temperature-programmed reduction (TPR-H2). The textural characteristics were specified by low-temperature nitrogen adsorption/desorption. The catalytic evaluation of Ru nanoparticles supported on both the pristine HNTs and MCM-41/HNT composite in benzene hydrogenation was carried out in a Parr multiple reactor system with batch stirred reactors (autoclaves) at 80 °C, a hydrogen pressure of 3.0 MPa and a hydrogen/benzene molar ratio of 3.3. Due to its hierarchical structure and high specific surface area, the MCM-41/HNT composite provided the uniform distribution and stabilization of Ru nanoparticles (NPs) resulted in the higher specific activity and stability as compared with the HNT-based counterpart. The highest specific activity (5594 h−1) along with deep benzene hydrogenation to cyclohexane was achieved for the Ru/MCM-41/HNT catalyst with a low metal content.

Deep mantle hydrogen in the pyrite-type FeO2–FeO2H system

The pyrite-type FeO2 and FeO2H were synthesized at the pressure-temperature conditions relevant to Earth’s deep lower mantle. Through the water-iron reaction, the pyrite-phase is a good candidate to explain the chemical heterogeneities and seismological anomalies at the bottom of the mantle. The solid solution of pyrite-type FeO2 and FeO2H, namely the FeO2Hx (0 ​≤ ​x ​≤ ​1), is particularly interesting and introduces puzzling chemical states for both the O and H atoms in the deep mantle. While the role of H in the FeO2–FeO2H system has been primarily investigated, discrepancies remain. In this work, we summarize recent progress on the pyrite-phase, including FeO2, FeO2H, and FeO2Hx, which is critical for understanding the water cycling, redox equilibria, and compositional heterogenicities in the deep lower mantle.

Preparation of highly active unsupported Ni–Si–Mo catalyst for the deep hydrogenation of aromatics

Abstract A mesoporous nickel-silicon-molybdenum composite oxide with the phase of ammonium nickel (or silicon) molybdate was synthesized by chemical precipitation and unsupported nickel-silicon-molybdenum sulfide catalysts with various Ni/Si ratios were obtained by sulfidation of the oxide precursors. The oxide precursors and unsupported sulfide catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPR, and HRTEM. The unsupported nickel-silicon-molybdenum sulfide catalysts were tested in the hydrogenation of naphthalene. It was found that the introduction of Si could increase the specific surface area and improve the pore structure of precursors, and reduce the reduction temperature of Mo species. The results of naphthalene hydrogenation showed that the introduction of Si could significantly improve the hydrogenation activity of the catalysts, especially the Ni9.5Si0.5Mo10 catalyst exhibited the highest aromatic hydrogenation activity at low temperature. Interestingly, it is found that the tetralin selectivity is 100% in the low temperature range (220–260 °C) over Si10Mo10 catalyst, which might be attractive in the production of tetralin and other industrial application.