Direct Desulfurization Pathway Research Articles

Regulating the coordination environment of surface alumina on NiMo/Al2O3 to enhance ultra-deep hydrodesulfurization of diesel

Herein, a set of NiMo/Al2O3 catalysts with distinct coordination state of surface alumina were design and prepared by a facile calcination strategy. Various characterization methods were employed to analyze the structural properties of NiMo/Al2O3 catalysts, and the catalytic performances of corresponding catalysts were tested for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The results indicate that the synthesized samples show uniform specific surface area (130 m2·g−1) and pore size (3.5 nm), but varying penta-coordinated aluminum content, which significantly influences the NiMo/Al2O3 catalysts’ surface acidity. Therein, NiMo/Al2O3-600 prepared by calcination at 600 °C exhibits the highest ratio of penta-coordinated aluminum species, which endows more abundant Brønsted acid than that of tetra- and hexa-coordinated aluminum counterparts, thereby substantially promoting the isomerization and direct desulfurization pathways of 4,6-DMDBT HDS, and thereafter considerably boosting the HDS performance of NiMo/Al2O3-600 with 94.5 % 4,6-DMDBT conversion, which is notably higher than that of NiMo/Al2O3-500 (74.4 %) and NiMo/Al2O3-700 (62.7 %).

MOF-derived CoP/C catalyst for efficient dibenzothiophene hydrodesulfurization

The design of an active and sulfur-resistant catalyst for dibenzothiophene (DBT) hydrodesulfurization (HDS) in crude oil purification is highly desirable but remains a grand challenge. Here, two carbon-supported cobalt phosphide catalysts Co2P/C and CoP/C, and a reference sample Co/C are successfully synthesized using a metal–organic-frameworks (MOFs) precursor. A P/Co ratio dependence on crystal phases is found, leading to the formation of two pure-phase cobalt phosphide catalysts CoP/C and Co2P/C. Catalyst evaluation in HDS of DBT shows that the CoP/C catalyst exhibits a higher activity and stability than Co2P/C and Co/C, giving a 93.7 % DBT conversion with 100 h stability under 3 MPa and 380 ◦C. Moreover, a 67.4 % biphenyl yield characterizes the dominance of the direct desulfurization (DDS) pathway. The obtained catalytic performance over the CoP/C catalyst is also superior to the published cobalt phosphide catalysts. Multiple characterization techniques co-evidence that the copious specific surface area, efficient electron transport from Co to P, high thermal stability of Co nanoparticles (NPs), and strong sulfur resistance account for the enhanced catalytic performance of CoP/C. The findings of this report suggest that phosphorus-modified cobalt over the carbon support can act as a promising catalyst for the HDS of DBT.

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.

Controllable synthesis of nanostructured nickel phosphosulfide by reduction of mixtures of Na4P2S6 and NiCl2 with low P/Ni ratios in hydrogen plasma

Transition-metal phosphides and phosphosulfides constitute a class of versatile and promising catalysts in the field of enery production. The preparation of nanostructured phosphides and phosphosulfides is chanllenging because the thermal reduction of phosphate precursors requires high temperatures. In the present work, nanostructured nickel phosphosulfide catalysts composed of Ni2P particles surrounded by a distinct sulfur-containing layer were prepared by reduction of mixtures of Na4P2S6 and NiCl2 in H2 plasma. The minimum P/Ni ratio needed for the formation of nickel phosphosulfide was between 4/7 and 2/3, and the input voltage of the plasma generator (Vin) should be higher than 40 V. The control of the particle sizes of the nickel phosphosulfide catalysts was realized by simply regulating Vin. Another minor factor affecting the particle size was H2 flow rate. The actual precursor for the formation of nickel phosphosulfide can be Ni2P2S6, which underwent fast reduction in H2 plasma to yield NiS. In the hydrodesulfurization of dibenzothiophene, the nanostructured nickel phosphosulfide catalyst exhibited higher activity and hydrogenation pathway (HYD) selectivity than the one with large particle size. The optimal P/Ni ratio of the nickel phosphosulfide catalysts was found to be 4/5, and the HYD pathway was more favored by the increase in the P/Ni ratio than the direct desulfurization pathway.

Elucidating the mechanisms of titanium–induced morphological and structural changes in catalysts on mesoporous Al2O3–TiOx mixed oxides: Effect of non–stoichiometric TiOx phase

In the present work, mesoporous Al 2 O 3 –TiO x composites with different titania loadings (4, 8 and 12 wt%) were synthesized to evaluate the effect of non-stoichiometric TiO x phases on the hydrodesulfurization (HDS) ability of the CoMo/Al 2 O 3 –TiO x catalysts. The activity of the catalysts was evaluated in the dibenzothiophene (DBT) HDS reaction carried out at 593 K, 5.5 MPa in a batch reactor. Regardless of the TiO x content, all sulfided CoMo Al 2 O 3 –TiO x catalysts were more active than the CoMo/Al 2 O 3 catalyst. For all catalysts, DBT HDS occurs mainly through the direct desulfurization (DDS) pathway (95–97% selectivity). The most active catalysts (CoMo-12 and CoMo-4) showed evidence of the presence of non-stoichiometric titanium oxides. The synthesized materials were characterized in depth to evaluate their crystallinity, textural and morphological properties, elemental composition and acidity. Their characterization showed that: (i), the Al 2 O 3 –TiO x interaction increased with decreasing TiO x content; (ii) the strong interaction between TiO x particles and alumina led to the formation of more defined TiO x structures; (iii), an increase in titania content led to the growth of TiO x crystals along the [101] direction (relative to the [001] direction), which in turn, led to the different TiO x morphologies: nanorods → nanotubes → U-shaped nanotubes. The TiCoMoS phase can be formed if the process is performed on Ti 3 O 5 instead of TiO 2 . • Titania loading influenced on the metal–support interaction and the type of titania phases. • Ti–promoted species are related to increase of the direct desulfurization route. • Non–stoichiometric titanium oxides are necessary to formation of TiCoMoS active phase.

Role of the solvent evaporating temperature on the NiMo/TiO2-Al2O3 catalyst and the hydrodesulfurization performance for 4,6-dimenthyldibenzothiophehe

Binary TiO2-Al2O3 serial composites(TA-x) and the NiMo supported catalysts(NiMo/TA-x) were successfully synthesized at different solvent evaporation temperatures,. The materials were characterized by several advanced characterization techniques, and the catalytic hydrodesulfurization (HDS) performances were evaluated. The results revealed that the synthesized TA-x serial composites are amorphous mixtures of TiO2 and Al2O3 with highly ordered two-dimensional hexagonal mesopores. Both the mesostructures and the acidities of the synthesized TA-x composites changed at different evaporation temperature of the solvent. The metal-support interaction(MSI), the existence states and the coordination states of the Mo precursors can be modulated by the changes in the physicochemical property of the TA-x composites caused by the solvent evaporating temperature. A moderate solvent evaporation temperature is favorable for the doping of Ni species into the MoS2 slab and Mo sulfidation degree, thus enhancing the proportion of the NiMoS active phases. Catalyst NiMo/TA-60 exhibits superior activity and the highest direct desulfurization(DDS) pathway selectivity due to the excellent acidity and pore structure property, the highest dispersion and the highest Mo sulfidation degree, a moderate MSI, the highest efficiency in the formation of NiMoS phase and the highest proportion of corner Mo atoms. Moreover, the rate constants of the specific HDS pathways can be correlated with the specific types of active sites: the DDS pathway (kDDS) is closely related to the proportion of corner active sites and the hydrogenation desulfurization pathway (kHYDS) is closely related to the proportion of brim sites. The activity of a single corner active site is found to be approximately 100 times that of a single edge active site. These findings are promising in the design of HDS catalysts for inferior distillates.

Hydrothermal synthesis of bulk Ni impregnated WO3 2D layered structures as catalysts for the desulfurization of 3-methyl thiophene

Unsupported Ni/W catalysts were synthesized using a hydrothermal method to form WO3. The WH-x and WN-x (x is the hydrothermal time) samples were impregnated with Ni and calcined at 450 ºC. The X-Ray diffraction, Raman spectroscopy, and UV–vis results showed that the monoclinic tungsten oxide phase forms the WOx phase in tetrahedral and octahedral coordination. Only in the Ni/WN-x series was detected the octahedral Ni species responsible for promoting the active phase. The XPS analysis revealed that 70% of the Ni promotes the WS2 active phase, forming the NiWS phase and 90% of W formed the WS2 phase. The catalysts tested in the 3-methylthiophene hidrodesulfurization reaction showed good activity under low pressure conditions. The largest activity of the Ni/WN-24 catalyst correlates well with the shorter WS2 slab lengths and the Ni-promoting the active phase. Interestingly, isoprene was obtained as the main product, indicating that the reaction mechanism followed the direct desulfurization (DDS) pathway.

Environmentally benign methane-regulated catalytic desulfurization

Hydrodesulfurization is well established in the industry while costly and environmentally unfriendly due to CO2 emissions and H2S production. An alternative, cost-effective desulfurization process remains unreported. Here, we demonstrate a desulfurization process for dibenzothiophene, one of the most well-known and recalcitrant sulfur-containing model compounds against catalytic desulfurization, under the regulation of methane instead of hydrogen over a combination of two catalysts, generating a new sulfur-containing product, CS2, as an important intermediate in organic chemistry and non-polar solvent with lower environmental impact than H2S. A catalytic mechanism is proposed and supported by extensive experimental and computational evidence. It is discovered that methane acts as a critical initiator and intensifies the direct desulfurization pathway, where two catalysts must work cooperatively and a surface sulfur transfer process is indispensable. This study explores an alternative desulfurization route with unique reaction pathways towards CS2 formation, whose practical potential is also supported by the desulfurization performance over a series of real-world crude samples.

Insights into the intrinsic kinetics for efficient hydrodesulfurization of 4,6-dimethyldibenzothiophene over mesoporous CoMoS2/ZSM-5

The intrinsic kinetics of hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) over mesoporous CoMoS2/ZSM-5 (CoMoS2/MZSM-5) was investigated by comparing the commercial CoMoS2/γ-Al2O3. A pseudo-first-order kinetic model considering the direct desulfurization (DDS) and two detailed partial and full hydrogenation pathways was formulated with simple power law rate equations. The apparent rate constants of five lumped reactions on CoMoS2/MZSM-5 are 2–4 times larger than those of CoMoS2/γ-Al2O3. With both catalyst system, the pre-exponential factor plays a dominant role in the reaction rate of DDS pathway showing equally high activation energies. The apparent activation energies show a critical effect on the reaction rate of two hydrogenation and subsequent desulfurization reactions. Furthermore, the Delplot analysis was applied to identify the reaction sequence of product formation and verify the reaction network. The HDS performance and reaction rates of individual reaction steps can be rationally linked to the morphology and available content of CoMoS phase as identified by HRTEM and XPS characterization. Thus, multi-stacked MoS2 nanocrystallites on CoMoS2/MZSM-5 provide more available sulfur vacancies to facilitate the DDS pathway, and catalyze efficiently the hydrogenation and subsequent desulfurization with the synergy of brim sites and sulfur vacancies.

Insight into metal-support interactions from the hydrodesulfurization of dibenzothiophene over Pd catalysts supported on UiO-66 and its amino-functionalized analogues

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) was studied over a series of Pd catalysts supported on Zr-based metal-organic frameworks, UiO-66 and its amino-functionalized analogues (UiO-66-xNH2, where x represents the molar ratio of 2-amino-1,4-benzenedicarboxylic acid/1,4-benzenedicarboxylic acid) to gain an insight into metal-support interactions. Pd/UiO-66 behaved better than a Pd/γ-Al2O3 catalyst and a Pd/MCM-41 catalyst. The presence of amino groups showed minor negative influence on the conversion of DBT but significantly affected the activities and selectivities of different reaction pathways. With the increase in the content of amino groups, the direct desulfurization (DDS) pathway activity of the Pd/UiO-66-xNH2 catalysts increased, while their hydrogenation pathway activity decreased. This provides an approach for the regulation of the pathway selectivities of Pd HDS catalysts. Based on kinetic analysis and characterization results, we propose that the amino groups affect the HDS performance of Pd/UiO-66 mainly by affecting the adsorption of reacting molecules on metal particles.

Controllable Synthesis of Defect-Rich CoMoS Catalysts with Different Morphologies for the Ultradeep Hydrodesulfurization of 4,6-Dimethydibenzothiophene.

CoMoS catalysts with controllable morphology are prepared by a single-source precursor hydrothermal method using sodium diethyldithiocarbamate trihydrate (DDTC) as the ligand and the sulfur source. The effects of the single-source precursor, the pH of the hydrothermal solution, and the surfactant with respect to the morphology, nanostructure, and hydrodesulfurization (HDS) activity of the CoMoS catalyst are investigated. It is revealed that the coordination between the metal atom and DDTC can effectively control the in-plane and out-of-plane crystal growth of MoS2 and promote the formation of the CoMoS active phase. The lower pH value of the hydrothermal solution facilitates the synthesis of CoMoS catalysts with improved purity, lower crystallinity, and smaller nanocrystallites, and the different surfactants would significantly change the morphologies. For HDS activity, the conversion efficiency of 4,6-DMDBT is increased from 71 to 99% by the CoMoS catalysts that have fewer stacking layers of MoS2 slabs. While the high HDS activity is maintained, a notable improvement in selectivity for the direct desulfurization (DDS) pathway is observed for the CoMoS-CTAB catalyst, where the average slab length of MoS2 is the longest.

Self-sulfidation adsorbent for reactive adsorption desulfurization

The Ni/ZnO-Al2O3-SiO2 adsorbent is a widely used industrial adsorbent for reactive adsorption desulfurization (RADS) process. Metallic Ni and NiO are assumed as the main RADS active sites, and NiSx is the intermediate phase to transfer sulfur to ZnO. However, NiSx could also be the active center for RADS process. In this work, to conduct the desulfurization activity of NiSx, a novel NiSO4/ZnO-Al2O3-SiO2 adsorbent was prepared and examined through a serious experimental and theoretical study over the conventional adsorbents. Results showed that NiSO4 based adsorbents could first self-sulfide to NiSx phases, and then NiSx plays as main active sites for RADS. The NiSO4 phases improved the direct desulfurization selectivity of dibenzothiophene (DBT). By adjusting the content of nickel, the sulfur removal rate of adsorbent with 3 wt% Ni from NiSO4 could achieve the same level of adsorbent prepared with 18 wt% Ni from NiO. Moreover, NiSO4 based adsorbent performs excellent desulfurization activity, and its breakthrough sulfur capacity achieves 122.0 mgS/g. The evolution of Ni species on NiSO4 adsorbent has been studied, and a desulfurization mechanism that takes both NiO and NiSx as active phases has been carried out. NiO phase mainly promotes the hydrodesulfurization pathway, while NiSx phase prefers the direct desulfurization pathway. Finally, the mechanism of RADS on NiSx and the reaction pathways of DBT are also presented.

Modification of ZSM-5 mesoporosity and application as catalyst support in hydrodesulfurization of dibenzothiophene: Experimental and DFT studies

The hydrodesulfurization (HDS) efficiency of NiMoS supported on modified H-ZSM-5 was investigated. The support modification was achieved via desilication (DS) in 3 – 5 M NaOH solution for 0.5 – 1 h, at 65 °C. The desilication of H-ZSM-5 increased both its mesoporosity and external surface area. The catalysts acidity and active phase formation and dispersion were influenced by the desilication of the zeolite supports. The NM/B-Z1/2 catalyst shows better HDS performance with dibenzothiophene (DBT) conversion of 87% after 4 h of reaction, while the catalyst formed from pristine ZSM-5 support (NM/Z) recorded the least DBT conversion of 38%. The DFT simulation energetics revealed that the hydrodesulfurization (HDS) process proceeded via the direct desulfurization (DDS) pathway in good correlation with the experimental findings. Extensive characterization techniques were adopted to gain insight into the physico-chemical properties of the support and the catalysts. Surface area and porosity analyzer was used for textural properties information of both the support and the catalyst. The information about surface and type of acidity, the metal-support interaction, morphology, metal charge content and dispersion of active species NiMo-S was explored by FESEM, FETEM, TPD, Pyr-FTIR, FTIR, XRD and XPS

Conditions for increasing the hydrodesulfurization of dibenzothiophene when co-feeding naphthalene, quinoline, and indole

In this work, we report a statistically significant increase in the rates of direct C–S bond scission of dibenzothiophene when co-reactants such as naphthalene, quinoline, and indole are present during its hydrodesulfurization over a Ni–MoS2/γ-Al2O3 catalyst. The competitive adsorption of these compounds on the same active sites has usually been associated with inhibitory effects of sulfur elimination. However, we carried out statistically designed experiments at temperatures between 260 and 300 °C, concentrations of dibenzothiophene between 1.0 and 3.7 wt%, and concentrations of the co-reactants between 0.13 and 0.52 wt%, and observed that the kinetic constant of the direct desulfurization pathway can increase up to 200% when either naphthalene, indole, or quinoline is co-fed to the reaction system at 260 °C and 3.7 wt% of dibenzothiophene. Therefore, the classical paradigm that aromatics and nitrogen heterocycles always inhibit hydrodesulfurization needs reexamination.

A DFT investigation on the hydrodesulfurization mechanism of 4,6-dimethyldibenzothiophene over different Ni-Mo-S active sites via different direct desulfurization pathways

The computational method based on the first principle of numerical atomic functions of density functional theory (DFT) was established to investigate the effects of ferromagnetism for the auxiliary Ni species on the direct desulfurization (DDS) mechanism of 4,6-dimethydibenzothiophene (4,6-DMDBT) hydrodesulfurization via two different reaction paths on both the corner active site and the edge active site. It is less likely for 4,6-DMDBT undergoing the DDS reaction via both paths on the Ni-Mo-S edge active sites without considering the ferromagnetism due to the relative activation energy needed either for the cleavage of the first C–S bond or for the cleavage of the second C–S bond. However, 4,6-DMDBT can undergo the DDS reaction via the Path 2 DDS mechanism in which the cleavage of the first C–S bond is the reaction rate control step. On the corner site, 4,6-DMDBT inclines to undergo DDS via both the promoted paths and the cleavage of the first C–S bond is the reaction rate control step, the ferromagnetism of the Ni species lowered the activation energy for the reaction rate control step by approximately 4.8 kJ·mol−1. The activation energy for the cleavage of the second C–S bond in the Path 1 DDS mechanism reduced from about 217.92 kJ·mol−1 to 112.32 kJ·mol−1 after taking the ferromagnetism of Ni species into account. Thus, the ferromagnetism of Ni species has a crucial effect on the DDS of 4,6-DMDBT over both the corner active site and the Ni-Mo-S edge active site and should not be neglected.

Electronic states and metallic character of carbide Co/MoS2 catalytic interface

We report computer assisted density functional theory computations of electronic states in carbide Co9S8/MoS2 interface model. The interface model was previously proposed using crystallographic information from experimental high-resolution TEM observations; and directly observed by in-situ heating to confirm carbon deposit occurs at the sulfur edge of Co9S8/MoS2 which creates a thin carbide layer. In here, the total energy for carbon adsorption results eight times more favorable to occur at sulfur edge in comparison to molybdenum or cobalt replacement by permutation of carbon atoms as contained in C, CH, CH2 species by exothermic energies. Amorphous carbon excites 2 pz orbitals as observed on density of states near Fermi level (F E ), and 13% decreased in terms of charge carriers available, causing to decrease its chemical catalytic reactivity and bending of MoS2 slabs as carbon starts to accumulate at the sulfur edge mainly, which is attributed to charge distribution around the adsorption site caused by the foreign atoms, confirmed by electron density plots, that acts as ‘electron traps’. This helps us concluding that carbon replacement can induce change of selectivity in direct desulfurization pathway.

Impact of γ-alumina pore structure on structure and performance of Ni–Mo/γ-Al2O3 catalyst for 4,6-dimethyldibenzothiophene desulfurization

The pore structure plays a vital role in material properties. Therefore, in this study, we prepared γ-Al2O3 with various mesopore diameters to explore the impact of pore structure on the property of Ni–Mo/γ-Al2O3 catalyst and hydrodesulfurization of 4,6-dimethyldibenzothiophene. It reveals that the pore size adjusts the reducibility of Mo species via affecting ammonium heptamolybdate adsorption. The Ni benefits the dispersion and reduction of Mo species. The larger pore imparts weaker polarization of Al3+, which less weakens the interactions between the MoS2 layers. The different polarization of Al3+ results in the diverse Ni–Mo–S structures over the catalysts with various pore sizes, and different active sites in edges and corners are obtained. The optimum pore size of Ni–Mo/γ-Al2O3 catalyst for the desulfurization of 4,6-dimethyldibenzothiophene is 7.0 nm, rather than 5.9 nm for the MoO3/γ-Al2O3 catalyst. The reaction pathway is regulated by the pore size and Ni–Mo–S structure. 4,6-dimethyldibenzothiophene reacts mainly via the hydrogenation pathway over 4.5 nm pore sized catalyst and high edge to corner ratio of the Ni–Mo–S slab (e.g. 2.63). Whereas, the sulfur in 4,6-dimethyldibenzothiophene is preferably eliminated by the direct desulfurization pathway in the pore size of 8.7 nm and low edge to corner ratio of the Ni–Mo–S slab (e.g. 2.04). All these can also be used to design deep desulfurization catalyst for environmental protection.

Noble metal silicides catalysts with high stability for hydrodesulfurization of dibenzothiophenes

Development of highly efficient and long stable hydrodesulfurization (HDS) catalysts still is a great challenge for the refining industry. In this work, a series of intermetallic noble metal silicides supported by carbon nanotubes catalysts (Pt2Si/CNTs, RhxSi/CNTs, and RuSi/CNTs) have been developed by chemical vapor deposition successfully, using dichlorodimethylsilane as Si source. These materials were used as efficient catalysts for the deep HDS of dibenzothiophenes (4,6-DMDBT and DBT) and performed high selectivity to the direct desulfurization pathway. The sequence of HDS activity over noble metal silicides catalysts is in keeping with the sequence of HDS activity of the corresponding metal catalysts, which is Pt2Si/CNTs > RhxSi/CNTs >> RuSi/CNTs. In addition, the Pt2Si/CNTs performed an excellent stability in 100 h stability testing for HDS of 4,6-DMDBT. Therefore, this sulfur-tolerant noble metal silicides could be as promising catalysts for the ultra-deep HDS of fossil-fuel.

Unsupported CoNixMo sulfide hydrodesulfurization catalysts prepared by the thermal decomposition of trimetallic tetrabutylammonium thiomolybdate: effect of nickel on sulfur removal

Herein we report the synthesis of unsupported bimetallic CoMo and trimetallic CoNiMo sulfide catalysts prepared by thermal decomposition (ex situ activation) of carbon-containing precursors and varying the nickel concentration for the hydrodesulfurization (HDS) of dibenzothiophene. The catalysts prepared were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma mass spectrometry and BET surface area measurements. The results from the characterization showed that the addition of an alkyl chained precursor results in non-porous catalysts with low surface area and high carbon content, which negatively affects the formation of crystalline phases such as molybdenum sulfide and their performance in the HDS reaction. Furthermore, the addition of nickel has a negative effect on the catalysts since it was observed that when it was added, the reaction rate values decreased and the catalyst with the highest catalytic activity turned out to be the CoMo catalyst. Although nickel catalysts generally have more affinity for hydrogenation reactions, unsupported trimetallic catalysts showed a preference for the direct desulfurization pathway.

Preparation of Ni2P Supported on Al2O3 and B2O3 Mixed Oxides by Temperature-Programmed Reduction of Phosphate Precursors with Low P/Ni Ratios

Two types of mixed oxides of B2O3 and Al2O3 were prepared. Aluminum borates (ABx, x represents the B/(B + Al) ratio) were prepared by low-temperature thermal decomposition of aluminum nitrate and H3BO3 sustained by the simultaneous oxidation of an organic agent (glycerol), while B2O3-Al2O3 with B/(B + Al) ratio of 0.3 was obtained by incipient wetness impregnation of H3BO3 on a commercial γ-Al2O3 support. Tetrahedrally, pentahedrally, and octahedrally coordinated Al3+ cations were all present in AB0.3 with ratios of 10.9/21.3/67.8, while no pentahedrally coordinated Al3+ was observed in B2O3-Al2O3. B2O3 was enriched in the surface of AB0.3. The Ni2P phase was obtained by temperature-programmed reduction of a phosphate precursor with a P/Ni ratio as low as 1.2 supported over both AB0.3 (Ni-P(1.2)/AB0.3) and B2O3-Al2O3 (Ni-P(1.2)/B2O3-Al2O3). This suggests that the surface B2O3 inhibits the reaction between nickel phosphates and Al2O3, and thus facilitates the formation of Ni2P. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) over the supported Ni2P catalysts occurred mainly by the direct desulfurization pathway, and Ni-P(1.2)/B2O3-Al2O3 was much more active than Ni-P(1.2)/AB0.3. These features make B2O3-Al2O3 a promising support for Ni2P catalysts. The HDS of DBT followed a pseudo-first-order kinetics over Ni-P(1.2)/B2O3-Al2O3, whereas over Ni-P(1.2)/AB0.3 it can be described by pseudo-zero-order kinetics. The pseudo-zero-order kinetics suggests a strong adsorption of DBT on Ni-P(1.2)/AB0.3, which could be responsible for its lower activity.