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Trimetallic NiMoW/Al2O3 catalysts based on mixed H4[SiMonWn-12O40] (n = 1, 3, 6, and 9) Keggin-type heteropolyacids (HPAs) were synthesized by incipient wetness impregnation of alumina with aqueous solutions of mixed HPAs. For comparison purposes, trimetallic samples were prepared from a mixture of monometallic H4[SiMo12O40] and H4[SiW12O40 ] HPAs with a Mo/W ratio corresponding to the mixed MoW HPAs. The catalysts were sulfided by a liquid phase method and tested in the model reactions of dibenzothiophene hydrodesulfurization and naphthalene hydrogenation, with subsequent addition of quinoline to study the effect of inhibition of target reactions. Further, the catalysts were tested in the hydrotreating of straight-run gas oil to evaluate the efficiency of catalysts on real feedstocks. In order to link catalytic performances with the preparation method and Mo/W ratio, the catalysts were fully characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, high-angle annular dark-field imaging, and quick X-ray absorption spectroscopy. It was found that the Mo/W atomic ratio of the structure-forming metals in the active phase, deriving from the Mo/W ratio in the HPA precursor, directly affects the ratio of the hydrogenation and hydrodesulfurization performances. For feedstock with a high concentration of N-containing compounds, it is necessary to use mixed NiMoW systems with a high tungsten percentage to reduce the inhibitory effect and ensure the quality of the products. The use of new mixed MoW Keggin HPAs has made it possible to enhance the synergistic effect in trimetallic NiMoW catalysts due to the closer interaction between Mo and W, which increased the sulfidation degree of metals and also contributed to the formation of highly active mixed NiMoWS sites.

Bimetallic catalysts MoW/СОK-12 are synthesized on the basis of mesostructured silicate COK‑12 prepared from sodium silicate aqueous solution using the Keggin structure hetero polyacid H4Si-Mo3W9O40 as an oxide precursor of the sulfide active phase and with the use of the mechanical mixture of two monometallic hetero polyacids (H4SiMo12O40 and H4SiW12O40) at a molar ratio of Mo/W = 3/9. Alumina-based analogs with the same surface metal content are used as reference samples. The test samples are analyzed by low-temperature nitrogen adsorption and high-resolution transmission electron microscopy. The catalytic activity is studied in the combined hydrotreatment of dibenzothiophene and naphthalene and in the hydrodesulfurization of 4,6-dimethyldibenzothiophene in a flow unit. It is shown that the use of mesostructured silicate COK-12 as a support leads to an increase in catalytic activity in target hydrotreating reactions.

A bulk MoWS2 catalyst has been synthesized by acid etching of the carrier from the supported MoWS2/Al2O3 catalyst obtained on the basis of the mixed bimetallic heteropoly acid (HPA) H4[SiMo3W9O40]. As reference samples, monometallic MoS2 and WS2 catalysts have been prepared from the corresponding supported analogues, as well as a Mo + WS2 sample based on a mechanical mixture of monometallic HPA in the atomic ratio of Mo/W = 1/3. The catalytic properties of the synthesized catalysts have been studied in model reactions of hydrodesulfurization (HDS) of dibenzthiophene (DBT) and hydrogenation (HYD) of naphthalene in a flow unit. It has been shown that the catalytic activity of the samples in both the DBT HDS and naphthalene HYD reactions increases in the following order: MoS2 < WS2 < Mo + WS2$$ \ll $$ MoWS2. It has been found that the bulk tungsten-containing catalysts exhibit higher specific catalytic activity than the supported counterparts. Increased values of hydrogen uptake according to the results of hydrogen temperature-programmed reduction for the bulk catalysts indicate an increase in the number of active sites and the formation of a more effective active phase compared to supported catalysts.

Mo(W)/SBA-15 catalysts are prepared using heteropoly acids H4SiMo12O40, H4SiW12O40, and H4SiMo3W9O40. The catalysts in the sulfide form are studied by low-temperature nitrogen adsorption, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalytic properties are tested in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. It is shown that the gas-phase sulfiding of Mo(W)/SBA-15 catalysts leads to increase in the average length of particles and the number of Mo(W)S2 layers in active phase particles compared with liquid-phase sulfiding with the use of dimethyl sulfide. The replacement of a quarter of tungsten atoms with molybdenum ones makes it possible to considerably improve the catalytic activity of the mixed catalyst Mo + W/SBA-15 compared with the monometallic counterparts. This effect can be enhanced due to the use of mixed heteropoly acid H4SiMo3W9O40 as a precursor of the active phase of the MoW/SBA-15 catalyst, which is apparently associated with the formation of MoWS2 active sites.

International audience; A series of unsupported mono- and bimetallic MonW12-nS2 catalysts were synthesized by alumina elimination from supported MonW12-nS2/Al2O3 samples using acid etching. Alumina supported catalysts have been in turn prepared by using monometallic H4SiMo12O40 and H4SiW12O40 heteropolyacids (HPAs), their mixture with Mo/W atomic ratio equal to 1/11 and 3/9, and mixed bimetallic H4SiMo1W11O40 and H4SiMo3W9O40 HPAs. All catalysts were characterized by N2 adsorption, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), extended X-ray absorption fine structure (EXAFS) spectroscopy and powder X-ray diffraction (XRD) and their performance were evaluated in simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of naphthalene. The etching process led to a successful removal of all the support and of the partially sulfided species, with sulfidation degrees of both Mo and W above 90 % on the final bulk solids. The active phase also underwent a rearrangement, as higher average length and stacking were measured on the bulk catalysts than on the original supported ones. Mixed MoWS2 phase was evidenced in all solids, prepared from mixed HPAs (MonW12-nS2) or from the mixture of monometallic HPAs (RefMonW12-nS2), by EXAFS and ToF-SIMS, with however a larger quantity on the MoW solids. It seems that the mixed MoWS2 phase observed on the supported MoW catalysts is maintained through the etching process, while on RefMonW12-nS2 the mixed phase, observed in a much lesser extent in the corresponding supported catalyst, could result from the aggregation of the monometallic slabs. MonW12-nS2 catalysts were found more effective than the monometallic catalysts and than the corresponding RefMonW12-nS2, in both dibenzothiophene hydrodesulfurization and naphthalene hydrogenation, which was related to the presence of the mixed phase maintained through the etching of the support.

A series of alumina supported CoMo catalysts with different molybdenum surface density was prepared using incipient wet impregnation method and applying H6[Co2Mo10O38H4] (Co2Mo10HPA) as a single oxidic precursor. Dried and sulfided catalysts were characterized by a variety of techniques, such as N2 adsorption, micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). Catalytic properties have been examined in co-hydrotreating of dibenzothiophene and naphthalene using a fixed bed high-pressure flow reactor. It was found that using Co2Mo10HPA as a single precursor enables more than the double increase of maximum metal loading compared to conventional compounds. This also contributed to a significant increase in catalytic activity in hydrotreating.

MoW alumina supported hydrotreating (HDT) catalysts were synthesized by using mixed SiMonW12-n heteropolyacids (HPAs) and also from a mixture of SiMo12 and SiW12 HPAs with the same Mo/W ratios for reference. Gas phase sulfidation of the catalysts prepared from mixed MoW HPAs led to the formation of a mixed phase evidenced by high-angle annular dark-field (HAADF) images, where a core of Mo atoms was surrounded by W atoms. Contrariwise, most of MoS2 or WS2 slabs were observed in the solids prepared from a mixture of the HPAs. This mixed phase induced higher hydrodesulfurization (HDS) of DBT, as well as hydrogenation (HYD) of naphthalene, than it was observed in the case of the reference catalysts. Comparison of activation procedures (gas phase versus liquid phase) confirmed that sulfidation in gas phase led to more efficient catalysts, even in the case of the formation of the mixed slabs. Beneficial effect of the mixed MoWS phase was even more pronounced in the case of the HDS of a more refractory molecule, 4,6-dimethyldibenzothiophene (4,6-DMDBT), which was attributed to the more hydrogenating properties of this mixed phase.

The catalytic properties of trimetallic NiMoWS catalysts supported on alumina are studied in the process of straight-run diesel fraction hydrotreating. It is shown that the nature of the oxide precursor of the mixed NiMoWS active phase strongly affects catalyst activity in the hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrogenation (HYD) of polycyclic aromatic hydrocarbons (PAH). The NiMoWS/Al2O3 catalyst synthesized from the mixed H4SiMo3W9O40 heteropoly acid is more efficient than the sample prepared from a mixture of individual H4SiMo12O40 and H4SiW12O40 heteropoly acids in both HDS and HDN transformations at the same metal content. The highest activity in PAH hydrogenation is exhibited by the NiMoWS/Al2O3 catalyst prepared using H4SiMo3W9O40.

The effect of quinoline on the hydrodesulfurization and hydrogenation activities of bi- and trimetallic NiMo(W)/Al2O3 hydrotreating catalysts obtained using Keggin heteropoly acids H4SiMo3W9O40, H4SiMo12O40, and H4SiW12O40 (denoted as SiMo3W9, SiMo12, and SiW12, respectively) and a mixture of two monometallic heteropoly acids (SiMo12 and SiW12) was studied. The catalytic properties were determined in a fixed-bed microreactor in hydrotreating of model feedstock containing dibenzothiophene and naphthalene and of the same feedstock with the addition of quinoline. The trimetallic NiMoW/Al2O3 sample based on the mixed SiMo3W9 heteropoly acid exhibited 1.5 times higher catalytic activity in all the reactions studied compared to its analog prepared from a mixture of SiMo12 and SiW12 heteropoly acids with the same metal ratio. The trimetallic NiMoW/Al2O3 catalyst based on the mixed SiMo3W9 heteropoly acid surpassed in the activity the NiMo/Al2O3 sample and was more resistant to the inhibiting effect of quinoline than its analog prepared from a mixture of the two heteropoly acids. The correlations of the inhibiting effect of quinoline with the morphology of the active phase particles and the content of promoted active sites Ni(Mo)WS in the bi- and trimetallic NiMo(W)/Al2O3 catalysts were found.

On the basis of alumina synthesized via addition of mesostructured aluminum hydroxide gel, which is prepared by the hydrolysis of secondary aluminum butoxide in the presence of triblock copolymer Pluronic P123 to the AlOOH commercial powder, and the commercial reference sample, NiWS/Al2O3 catalysts are prepared using H3PW12O40 heteropolyacid and nickel citrate. The physicochemical properties of the supports and catalysts are studied by low-temperature nitrogen adsorption, temperature-programmed desorption of ammonia, and high-resolution transmission electron microscopy. The catalytic properties are investigated in the process of straight-run diesel fraction hydrotreating in a flow unit. It is shown that the use of the synthesized alumina as a catalyst support leads to an increase in the dispersity of nanosized particles of the NiWS active phase. The catalytic activity in targeted reactions also grows appreciably. The causes of these phenomena are discussed.

Alumina supports were synthesized from aluminum hydroxide produced by the hydrolysis of secondary aluminum butoxide in the presence of the triblock copolymer Pluronic P123 (m-AlOOH) and from the commercial AlOOH pseudoboehmite powder (TH-AlOOH), as well as by mixing of m-AlOOH and TH-AlOOH gel in a ratio of 5:95 (m-TH-AlOOH sample). NiW/Al2O3 catalysts were prepared by impregnation of the synthesized supports with H3PW12O40 heteropolyacid and nickel citrate. Physicochemical properties of the supports and catalysts were investigated by low-temperature nitrogen adsorption, X-ray diffraction, NH3 thermo-programmed desorption, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. Catalytic properties were tested in hydrotreatment of straight-run gas oil and vacuum gasoil on a flow unit. The resulting hybrid support had a non-additively higher average pore radius (75 A) and surface area (307 m2/g) than a conventional alumina support and hence preferred morphology of NiWS active phase (3.8 nm against 6.6 nm with the same stacking number) and an increase in the W sulfidation degree (68% against 54%) and Ni content in NiWS phase (44% against 26%). Therefore, the catalyst on the hybrid support exhibits higher activity in hydrodesulfurization, hydrodenitrogenation and hydrogenation of petroleum feeds, and a lower degree of deactivation and coke formation.

CoMo hydrotreating catalysts with varied metal loading (1–4 Mo at nm− 2) based on Co2Mo10 heteropolyacid (HPA) and different supports (γ-Al2O3, SBA-15, SiO2) were prepared by incipient wetness impregnation. The catalysts were characterized by N2 physisorption, high resolution transmission electron microscopy (HRTEM), Raman and X-ray photoelectron spectroscopy (XPS). Catalytic activity was evaluated in co-hydrotreating (HDT) of the model feed containing dibenzothiophene (DBT) and naphthalene. The catalytic properties of CoMo catalysts were shown to depend on the morphological characteristics of CoMoS species, its promotion degree, and metal loading. The sulfidation degree of the initial precursor and effective cobalt amount in the CoMoS species increased with the Mo loading increase from 1 to 4 at nm− 2 in all studied catalysts. The DBT conversion maximum was achieved over CoMo/Al2O3 and CoMo/SBA-15 with 4 Mo at nm− 2. CoMo/SBA-15 catalysts had higher TOF numbers both in DBT HDS and in naphthalene hydrogenation (HYD) at the surface concentration of Mo same as in the other samples. These results can be attributed to optimal morphology of sulfide particles and the Co/Mo promotion degree due to a more suitable interaction between the active phase and support in mesoporous silica channels.

International audience; H4[SiMonW12−nO40] heteropolyacids (HPAs) are interesting precursors for the preparation of alumina-supported hydrotreatment catalysts to introduce both metals simultaneously while maintaining a Mo–W nanoscale proximity. Two heteropolyacids (n = 1 and 3) have been synthesized and used for the first time to prepare hydrotreatment catalysts. Crystal structure refinement has been performed and evidenced the formation of β-H4[SiMo3W9O40] with three ordered Mo sites forming a face. The purity of the samples in aqueous solution has been determined by Raman spectroscopy and polarographic characterization. These heteropolyacids were then impregnated on alumina to prepare supported MoW-based catalysts. As references, catalysts with the same Mo/W ratios have been prepared using monometallic H4SiMo12O40 and H4SiW12O40 HPAs (mixture of these 2 HPAs in the impregnating solution). EXAFS characterization after drying performed simultaneously at the Mo K and W LIII edges indicates preservation of the mixed heteropolyanion SiMonW12−nO404− at the alumina surface even if partial decomposition to Keggin lacunary species could not be excluded and evidences the mixed MoW–S2 slab formation after sulfidation. Better catalytic hydrogenation properties for dibenzothiophene hydrodesulfurization and naphthalene hydrogenation have been obtained when using β-H4[SiMo3W9O40], which is explained by the formation of the mixed MoW–S2 active phase.

Mono- and bimetallic Mo(W)S2 catalysts supported on γ-Al2O3 and SBA-15 have been prepared using the Keggin heteropoly acids (HPAs) H4SiMo12O40 and H4SiW12O40. The catalyst samples have been analyzed by temperature-programmed reduction with hydrogen, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalytic properties have been examined in the joint hydrotreating of dibenzothiophene and naphthalene on a flow-through unit. It has been shown that the use of mesoporous silica SBA-15 as a support can reduce the average length of Mo(W)S2 particles from 4.9 to 3.7 nm and increase the average number of layers and the particle size of the active phase, changes that lead to an increase in catalytic activity by a factor of ~3 relative to the alumina-supported counterparts. The use of a mixture of SiMo12HPA and SiW12HPA for preparing MoW catalysts leads to a significant enhancement of catalytic activity, which is apparently due to the formation of mixed active sites.

Alumina-based NiW catalysts have been prepared from 12-phosphotungstic heteropoly acid (PW12HPA), ammonium metatungstate (NH4)6H2[W12O40], and nickel hydroxide carbonate or nickel nitrate using citric acid (CA) or ethylenediaminetetraacetic acid (EDTA) as a chelating agent. The obtained samples have been studied by N2 adsorption, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy techniques. The catalysts obtained using the PW12HPA and CA have been characterized by the greatest dispersion of active-phase particles, and the use of EDTA has provided the maximum proportion of NiWS. The hydrodesulfurizing activity of catalysts in the hydrotreating of vacuum gas oil has been found to decrease in the following order: Ni-CAPW/Al2O3 > Ni-CAW/Al2O3 > Ni-EDTA-W/Al2O3 > Ni-W/Al2O3, which in general correlates with the particle size of the active phase and the concentration of promoted active sites.

The bimetallic MoWS2/Al2O3 catalyst was synthesized using the Keggin-type mixed heteropolyacid H4SiMo3W9O40. The monometallic catalysts SiMo12/Al2O3 and SiW12/Al2O3 based on the H4SiMo12O40 and H4SiW12O40 acids are prepared as reference samples. The sulfidized catalysts are analyzed by temperature-programmed reduction with hydrogen, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Their catalytic properties are studied in the cohydrotreatment of dibenzothiophene (DBT) and naphthalene on a flow-type setup. The introduction of three molybdenum atoms into the structure of an oxide precursor is shown to increase the degree of sulfidation of the tungsten particles by 20% in comparison with SiW12/Al2O3. The DBT turnover frequency in the hydrodesulfurization (HDS) on the sites on the edges of the active phase of the SiMo3W9/Al2O3 catalyst is shown to be 5.5 times higher than in the presence of SiW12/Al2O3. The bimetallic sample demonstrated the highest selectivity in the preliminary DBT hydrogenation route and activity in the prehydrogenation of naphthalene. The high level of activity of the SiMo3W9/Al2O3 catalyst was due to the formation of a mixed Mo x W(1–x)S2 active phase with a MoW oxide precursor, whose structure contained both metals bonded at the molecular level.

The purpose of the study was to evaluate carbon effect on Co(Ni)-PMo/C/Al2O3 catalysts in co-hydrotreating (co-HDT) of straight-run gas oil (SRGO) and sunflower oil (SO). The catalysts were prepared using 12-molybdophosphoric heteropolyacid, cobalt tartrate, and Al2O3 or C/Al2O3 (2 wt% of carbon) as a support. The solids were characterized by N2 physisorption, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic properties were investigated using a bench-scale flow reactor in co-HDT of mixed feed containing SRGO and 5, 10, and 15 wt% of SO. It was found that Co-РMo catalysts demonstrated higher hydrodesulfurization (HDS) activity in SRGO HDT than its Ni-РMo/C/Al2O3 counterparts. The use of C/Al2O3 led to more active Co-РMo and Ni-РMo catalysts compared with Al2O3 supported ones. Co-PMo samples more significantly lost activities than Ni-PMo after adding SO in the feed. Addition of SO led to an increase in HDS apparent activation energy by 21 kJ mol−1 on Co-РMo and has not affected it in co-HDT of blended feedstock over Ni-PMo. All obtained results showed the high effectiveness of the prepared Ni-РMo/C/Al2O3 catalyst. They showed high HDS, hydrogenation and hydrodenitrogenation activities in co-HDT of the mixed SRGO/SO feedstock as well as catalyst stability against to accelerated deactivation. The possible reasons of the catalytic behavior of the studied samples are discussed based on the characteristics of the freshly sulfided and spent samples as well as determined kinetic parameters.

Trimetallic NiMoW/Al2O3 catalyst was prepared using mixed H4SiMo3W9O40 heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al2O3 and NiW/Al2O3 catalysts based on H4SiMo12O40 and H4SiW12O40, respectively, were synthesized as reference samples. The use of mixed H4SiMo3W9O40 heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al2O3 catalyst. The synergistic enhancement of the activity of the NiMo3W9/Al2O3 catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.

Ni(Co)-PW/Al2O3 catalysts both unmodified and modified with potassium were synthesized with the use of H3PW12O40, CoCO3 or NiCO3, KOH and citric acid. The catalysts were characterized by the techniques such as low-temperature N2 adsorption, temperature-programmed reduction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The prepared samples were tested in hydrotreating of model FCC gasoline that contained 1000 ppm of sulfur from thiophene and 36 wt.% of n-hexene-1 as a representative olefinic compound. The modification with an alkali metal influenced both the characteristics of the catalyst active phase and catalytic properties of (K)-Ni(Co)-PW/Al2O3 samples. The incorporation of potassium led to some l growth of the linear size of active phase crystallites, to a decrease of reactivity and of the number of active sites, to a strong decrease of CoWS and NiWS particle amounts with a simultaneous rise of separate CoSx and NiSx. The potassium addition also induced a drastic drop of hydrodesulfurization (HDS) and hydrogenation (HYDO) activity with a HDS/HYDO selectivity decrease for Ni- and Co-promoted systems and with a significant increase of the selectivity factor for unpromoted PW/Al2O3. The Ni-promoted catalyst proved to be more sensitive to the potassium modification than the Co-promoted one. So, the modified catalysts can be ranged by activity as follows: KWS

International audience; Trimetallic CoMo3W9/Al2O3 catalyst is prepared using the Keggin structure mixed heteropolyacid H4SiMo3W9O40 and cobalt citrate. CoMo12/Al2O3 and CoW12/Al2O3 catalysts based on H4SiMo12O40 and H4SiW12O40, respectively, are synthesized as reference samples. Sulfided catalysts are analyzed by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic properties are investigated in the co-hydrotreatment of dibenzothiophene (DBT) and naphthalene in a flow unit. It is shown that the catalytic activity in both DBT hydrodesulfurization and naphthalene hydrogenation (HYD) decreases in the following sequence: CoMo12/Al2O3 > CoMo3W9/Al2O3 > CoW12/Al2O3, and it correlates with the degree of promotion of active-phase particles by cobalt atoms. A comparison with the published data available for Ni-promoted catalysts makes it possible to reveal the general regularity for bi- and trimetallic Со(Ni)-Mo(W)S catalysts: the use of mixed Mo-W H4SiMo3W9O40 heteropolyacid instead of monometallic H4SiW12O40 causes an increase in the degree of promotion of MoWS2 crystallite edges for the series of catalysts promoted by both cobalt and nickel. The use of nickel as a promoter leads to a higher degree of promotion of edges of active-phase particles in comparison with cobalt; as a result, the NiMo3W9/Al2O3 catalyst is much more active than the CoMo3W9/Al2O3 counterpart. Possible reasons behind the found features are discussed.

International audience; Alumina supported MoW hydrotreating catalyst was synthesized by using bimetallic H 4 [SiMo 3 W 9 O 40 ] Keggin heteropolyacid (HPA). Catalysts based on monometallic H 4 [SiMo 12 O 40 ] and H 4 [SiW 12 O 40 ] and their mixture were also studied. Genesis of the active phase was studied during atmospheric gas sulfidation by H 2 S/H 2 of the catalysts by in-situ Quick X-ray absorption spectroscopy (XAS) and High-Angle Annular Dark-Field (HAADF) imaging. The combination of different chemometric tools such as Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) allowed to determine the number of intermediate species, their chemical nature and concentration profiles during sulfidation. It was found that tungsten sulfidation using bimetallic HPA precursor started at lower temperature, compared to W sulfidation in the monometallic and in the mixture of monometallic HPA catalysts. Simultaneous sulfidation of Mo and W atoms in case of the bimetallic molecular precursor can govern the formation of mixed MoWS 2 phase, which formation during activation was evidenced by HAADF.

International audience; MoW catalysts supported on Al2O3 with equal surface content of metals (Mo + W = 3.9 at/nm2) were synthesized by using mixed Keggin type heteropolyacids (HPAs) H4[SiMo1W11O40] and H4[SiMo3W9O40] and corresponding mixture of monometallic H4[SiMo12O40] and H4[SiW12O40] HPAs. After liquid phase sulfidation, catalysts were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). For the first time, High Angle Annular Dark Field microscopy (HAADF) was used to evidence the morphology and composition of the active sulfide phase. The catalysts were tested in hydrotreating of model feed that contained dibenzothiophene (DBT) and naphthalene. Using mixed SiMonW12-nHPAs as starting precursors had a beneficial effect on the catalytic activity. Incorporation of molybdenum in the structure of SiW Keggin-type HPA led to a decrease of the size of active phase crystallites, to an increase of the metal sulfidation degree and of the number of active sites. Substitution of a quarter of tungsten atoms by molybdenum allowed to achieve DBT conversion comparable to value obtained on pure SiMo12HPA based catalyst and higher conversion of naphthalene. Both SiMonW12-nHPAs based catalysts had higher rate constants in studied reactions compared to their corresponding references prepared from two separate monometallic HPAs. Moreover, MonW12-n/Al2O3 catalysts had the highest selectivity in respect of hydrogenation (HYD) pathway of DBT hydrodesulfurization (HDS). The presence of mixed MoxW1-xS2 slabs was evidenced by HAADF analysis. On Mo3W9/Al2O3, small randomly distributed islands of Mo were present in the WS2 slabs, while on Mo3 + W9/Al2O3, Mo islands appeared larger and in the core of the WS2 slabs. Moreover, on this last sample, some monometallic slabs were also present. It was concluded that using mixed HPA precursors resulted in the formation of mixed MoxW1-xS2 active phase possessing higher synergetic effect between the two metals and consequently higher catalytic activity.