Edge dispersion of supported MoS2 and WS2 catalysts as evaluated by using Co(CO)3NO as a probe molecule

SiO₂- and Al₂O₃-supported MoS₂ and WS₂ catalysts were prepared to exploit the evaluation technique of the edge dispersion of MoS₂ and WS₂ particles. A chemical vapor deposition (CVD) technique using Co(CO)₃NO as a probe molecule was used for the evaluation. Results were compared with those from conventional techniques such as NO adsorption and TEM. A proportional correlation was obtained between the amount of NO adsorption and the amount of Co atoms accommodated by the CVD technique on WS₂/SiO₂ and WS₂/Al₂O₃ catalysts, demonstrating a selective location of the Co atoms on the edges of WS₂ particles, as previously established for MoS₂ catalysts. A comparison of the amounts of NO adsorption and Co accommodation on MoS₂ and WS₂ catalysts suggested a 70% higher density of sulfur vacancy on MoS₂ particles than on WS₂ particles regardless of the support. The Co atoms on the edges of MoS₂ and WS₂ particles showed the identical NO adsorption property. We propose that Co(CO)₃NO can be used as a probe molecule to evaluate and directly compare the edge dispersions of MoS₂ and WS₂ catalysts. The dispersion of MoS₂ particles was about two times higher than that of WS₂ particles with the SiO₂-supported catalysts. With the Al₂O₃-supported catalysts, MoS₂ and WS₂ particles were dispersed to a similar extent but much more highly dispersed than the counterparts in the SiO₂-supported catalysts. The evaluation of the edge dispersion of MoS₂ and WS₂ particles by means of TEM may pose problems when SiO₂- and Al₂O₃-supported catalysts are compared. The edges of unpromoted MoS₂ particles exhibited a significantly higher intrinsic activity for the HDS of thiophene than those of WS₂ particles.     

A novel preparation-characterization technique of hydrodesulfurization catalysts for cleaner fuels

In the present review of our study, it is shown that the CVD technique using Co(CO)₃NO provides a novel characterization technique of hydrodesulfurization (HDS) catalysts combined with the catalyst preparation. The resultant CVD or designed catalysts are very appropriate for the determination of the CoMoS structure and reaction mechanism due to a selective formation of CoMoS. The CVD technique is also very effective to prepare highly active HDS catalysts, since full promotion of MoS₂ particles can be achieved. The CVD technique can be applied to estimate the surface structure of supported Co(Ni)–MoS₂ catalysts. In addition, the designed catalysts can be used to understand the nature of the support and additives in terms of the intrinsic activity of CoMoS. Thus the information from the CVD technique is unique and invaluable for the development of highly active HDS catalysts.     

Mesoporous molecular sieve MCM-41 supported Co–Mo catalyst for hydrodesulfurization of petroleum resids

In this work, we explored the potential of mesoporous zeolite-supported Co–Mo catalyst for hydrodesulfurization of petroleum resids, atmospheric and vacuum resids at 350–450°C under 6.9 MPa of H₂ pressure. A mesoporous molecular sieve of MCM-41 type was synthesized; which has SiO₂/Al₂O₃ ratio of about 41. MCM-41 supported Co–Mo catalyst was prepared by co-impregnation of Co(NO₃)₂·6H₂O and (NH₄)₆Mo₇O₂₄ followed by calcination and sulfidation. Commercial Al₂O₃ supported Co–Mo (criterion 344TL) and dispersed ammonium tetrathiomolybdate (ATTM) were also tested for comparison purposes. The results indicated that Co–Mo/MCM-41(H) is active for HDS, but is not as good as commercial Co–Mo/Al₂O₃ for desulfurization of petroleum resids. It appears that the pore size of the synthesized MCM-41 (28 Å) is not large enough to convert large-sized molecules such as asphaltene present in the petroleum resids. Removing asphaltene from the resid prior to HDS has been found to improve the catalytic activity of Co–Mo/MCM-41(H). The use of ATTM is not as effective as that of Co–Mo catalysts, but is better for conversions of >540°C fraction as compared to noncatalytic runs at 400–450°C.     

Hydrodesulfurization over supported monometallic, bimetallic and promoted carbide and nitride catalysts

The preparation of alumina-supported β-Mo₂C, MoC_1−x (x≈0.5), γ-Mo₂N, Co–Mo₂C, Ni₂Mo₃N, Co₃Mo₃N and Co₃Mo₃C catalysts is described and their hydrodesulfurization (HDS) catalytic properties are compared to conventional sulfide catalysts having similar metal loadings. Alumina-supported β-Mo₂C and γ-Mo₂N catalysts (Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃, respectively) are significantly more active than sulfided MoO₃/Al₂O₃ catalysts, and X-ray diffraction, pulsed chemisorption and flow reactor studies of the Mo₂C/Al₂O₃ catalysts indicate that they exhibit strong resistance to deep sulfidation. A model is presented for the active surface of Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃ catalysts in which a thin layer of sulfided Mo exposing a high density of sites forms at the surface of the alumina-supported β-Mo₂C and γ-Mo₂N particles under HDS conditions. Cobalt promoted catalysts, Co–Mo₂C/Al₂O₃, have been found to be substantially more active than conventional sulfided Co–MoO₃/Al₂O₃ catalysts, while requiring less Co to achieve optimal HDS activity than is observed for the sulfide catalysts. Alumina-supported bimetallic nitride and carbide catalysts (Ni₂Mo₃N/Al₂O₃, Co₃Mo₃N/Al₂O₃, Co₃Mo₃C/Al₂O₃), while significantly more active for thiophene HDS than unpromoted Mo nitride and carbide catalysts, are less active than conventional sulfided Ni–Mo and Co–Mo catalysts prepared from the same oxidic precursors.     

Hydrodesulfurization activity of CoMo and NiMo supported on Al2O3–TiO2 for some model compounds and gas oils

Catalytic activities of Al₂O₃–TiO₂ supporting CoMo and NiMo sulfides (CoMoS and NiMoS) catalysts were examined in the transalkylation of isopropylbenzene and hydrogenation of naphthalene as well as the hydrodesulfurization (HDS) of model sulfur compounds, conventional gas oil (GO), and light cycle oil (LCO). Al₂O₃–TiO₂ supporting catalysts exhibited higher activities for these reactions except for the HDS of the gas oil than a reference Al₂O₃ supporting catalyst, indicating the correlation of these activities. Generally, more content of TiO₂ promoted the activities. Inferior activity of the catalyst for HDS of the gas oil is ascribed to its inferior activity for HDS of dibenzothiophene (DBT) in gas oil as well as in model solvent decane, while the refractory 4,6-dimethyldibenzothiophene (4,6-DMDBT) in gas oil as well as in decane was more desulfurized on the catalyst. Characteristic features of Al₂O₃–TiO₂ catalyst are discussed based on the paper results.     

The effects of fluorine, phosphate and chelating agents on hydrotreating catalysts and catalysis

The effects of fluorine, phosphate and chelating agents on hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) are reviewed. All three additives enhance the activity of NiMo/Al₂O₃ catalysts in HDN but have only a slightly positive or even a negative effect on the HDS activity of CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts. The positive effect on HDN is due to the enhancement of the hydrogenation of aromatic rings. On the other hand, these three additives diminish the rates of C–N bond breaking and alkene hydrogenation reactions.

All three additives are hard basic ligands that may interact strongly with hard acids such as coordinatively unsaturated Al³⁺ cations on the alumina surface. A strong interaction with the alumina support has several effects. First, molybdate and tungstate anions are no longer strongly bonded to the support and are predominantly present as polyanions, which can be easily sulfided to MoS₂ and WS₂ crystallites. The weaker interaction with the smaller support surface also leads to larger MoS₂ and WS₂ crystallites with a lower dispersion. Second, the Ni²⁺ and Co²⁺ cations will also interact more weakly with the alumina, and this makes the formation of Ni and Co promoter atoms in the catalytically active Ni–Mo–S and Co–Mo–S phases more efficient. Third, the weaker interaction of Mo and W with the support leads to a higher stacking of the MoS₂ and WS₂ crystallites and, thus, to the more active type II Ni–Mo–S and Co–Mo–S phases. The increased stacking is beneficial for geometrically demanding reactions such as the hydrogenation of aromatics. For less demanding reactions, such as alkene hydrogenation, aliphatic C–N bond breaking and thiophene HDS, the loss in dispersion is important.     

Hydrodesulfurization of dibenzothiophenes over molybdenum catalyst supported on TiO2–Al2O3

Composite types of TiO₂–Al₂O₃ supports, which are γ-aluminas coated by titania, have been prepared by chemical vapor deposition (CVD), using TiCl₄ as a precursor. Then supported molybdenum catalysts have been prepared by an impregnation method. As supports, we employed γ-alumina, anatase types of titania, and composite types of TiO₂–Al₂O₃ with different loadings of TiO₂. We studied the conversion of Mo from oxidic to sulfidic state through sulfurization by X-ray photoelectron spectroscopy (XPS). The obtained spectra unambiguously revealed the higher reducibility from oxidic to sulfidic molybdenum species on the TiO₂ and TiO₂–Al₂O₃ supports compared to that on the Al₂O₃ support. Higher TiO₂ loadings of the TiO₂–Al₂O₃ composite support led to higher reducibility for molybdenum species. Furthermore, the catalytic behavior of supported molybdenum catalysts has been investigated for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the TiO₂–Al₂O₃ supported Mo catalysts, in particular for the 4,6-dimethyl-DBT, is much higher than that obtained over Al₂O₃ supported Mo catalyst. The ratio of the corresponding cyclohexylbenzene (CHB)/biphenyl (BP) derivatives is increased over the Mo/TiO₂–Al₂O₃. This indicates that the prehydrogenation of an aromatic ring plays an important role in the HDS of DBT derivatives over TiO₂–Al₂O₃ supported catalysts.     

Factors controlling the selectivity of V2O5 supported catalysts in the oxidative dehydrogenation of propane

The surface properties of a series of V₂O₅ catalysts supported on different oxides (Al₂O₃, H–Na/Y zeolite, MgO, SiO₂, TiO₂ and ZrO₂) were investigated by transmission electron microscopy and FTIR spectroscopy augmented by CO and NH₃ adsorption. In the case of the V₂O₅/SiO₂ system TEM images evidenced the presence of V₂O₅ crystallites, whereas such segregated phase was not observed for the other samples. VO_x species resulted widely spread on the surface of Al₂O₃, H–Na/Y zeolite, MgO and SiO₂, whereas on TiO₂ and ZrO₂ they are assembled in a layer covering almost completely the support. Furthermore, evidences for the presence in this layer of V–OH Brønsted acid sites close to the active centres were found. It is proposed that propene molecules primarily produced by oxydehydrogenation of propane can be adsorbed on this acid centres and then undergo an overoxidation by reaction with redox centres in the neighbourhood. This features could account for the low selectivity of V₂O₅/TiO₂ and V₂O₅/ZrO₂ catalysts.     

Development of new catalysts for deep hydrodesulfurization of gas oil

TiO₂–Al₂O₃ composite supports have been prepared by chemical vapor deposition (CVD) over γ-Al₂O₃ substrate, using TiCl₄ as the precursor. High dispersion of TiO₂ overlayer on the surface of Al₂O₃ has been obtained, and no cluster formation has been detected. The catalytic behavior of Mo supported on Al₂O₃, TiO₂ and TiO₂–Al₂O₃ composite has been investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the Mo catalysts supported on TiO₂–Al₂O₃ composite, in particular for the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) is much higher than that of conversion obtained over Mo catalyst supported on Al₂O₃. The ratio of the corresponding cyclohexylbenzenes/biphenyls is increased over Mo catalyst supported on TiO₂–Al₂O₃ composite support. This means that the reaction rate of prehydrogenation of an aromatic ring rather than the rate of hydrogenolysis of C–S bond cleavage is accelerated for the HDS of DBT derivatives. The Mo/TiO₂–Al₂O₃ catalyst leads to higher catalytic performance for deep HDS of gas oil.     

Maya crude hydrodemetallization and hydrodesulfurization catalysts: An effect of TiO2 incorporation in Al2O3

Hydrotreating of Maya heavy crude oil over high specific surface area CoMo/TiO₂–Al₂O₃ oxide supported catalysts was studied in an integral reactor close to industrial practice. Activity studies were carried out with Maya crude hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and hydrodeasphaltenization (HDAs) reactions. The effect of support composition, the method of TiO₂ incorporation, and the catalyst deactivation are examined. Supported catalysts are characterized by BET specific surface area (SSA), pore volume (PV), pore size distribution (PSD), and atomic absorption. It has been found that sulfided catalysts showed a wide range of activity variation with TiO₂ incorporation into the alumina, which confirmed that molybdenum sulfided active phases strongly depend on the nature of support. The pore diameter and nature of the active site for HDS, HDM, HDN, and HDAs account for the influence of the large reactant molecules restricted diffusion into the pore, and/or the decrease in the number of active sites due to the MoS₂ phases buried with time-on-stream. The textural properties and hysteresis loop area of supported and spent catalysts indicated that catalysts were deactivated at the pore mouth due to the metal and carbon depositions. The atomic absorption results agreed well regarding the textural properties of spent catalysts. Thus, incorporation of TiO₂ with γ-Al₂O₃ alters the nature of active metal interaction with support, which may facilitate the dispersion of active phases on the support surface. Therefore, the TiO₂ counterpart plays a promoting role to HDS activity due to the favorable morphology of MoS₂ phases and metal support interaction.     

Ti-modified alumina supports prepared by sol–gel method used for deep HDS catalysts

The typical physico-chemical properties and their hydrodesulfurization activities of NiMo/TiO₂-Al₂O₃ series catalysts with different TiO₂ loadings were studied. The catalysts were evaluated with a blend of two kinds of commercially available diesels in a micro-reactor unit. Many techniques including N₂-adsorption, UV–vis DRS, XRD, FT-Raman, TPR, pyridine FT-IR and DRIFT were used to characterize the surface and structural properties of TiO₂-Al₂O₃ binary oxide supports and the NiMo/TiO₂-Al₂O₃ catalysts. The samples prepared by sol–gel method possessed large specific surface areas, pore volumes and large average pore sizes that were suitable for the high dispersion of nickel and molybdenum active components. UV–vis DRS, XRD and FT-Raman results indicated that the presence of anatase TiO₂ species facilitated the formation of coordinatively unsaturated sites (CUS) or sulfur vacancies, and also promoted high dispersion of Mo active phase on the catalyst surfaces. DRIFT spectra of NO adsorbed on the pure MoS₂ and the catalysts with TiO₂ loadings of 15 and 30% showed that NiMo/TiO₂-Al₂O₃ catalysts possessed more CUS than that of pure MoS₂. HDS efficiencies and the above characterization results confirmed that the incorporation of TiO₂ into Al₂O₃ could adjust the interaction between support and active metals, enhanced the reducibility of molybdenum and thus resulted in the high activity of HDS reaction.     

Support effects on structure and activity of molybdenum oxide catalysts for the oxidative dehydrogenation of ethane

The structural and catalytic properties of MoO₃ catalysts supported on ZrO₂, Al₂O₃, TiO₂ and SiO₂ with Mo surface densities, n_s, in the range of 0.5–18.5 Mo/nm² were studied for the oxidative dehydrogenation (ODH) of ethane by in situ Raman spectroscopy and catalytic activity measurements at temperatures of 400–540 °C. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO₄ and MoO₅, depending on the support) at low loadings to associated MoO_x units in polymolybdate chains at high loadings and ultimately to bulk crystalline phases for loadings exceeding the monolayer coverage of the supports used. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behaviour of the molybdena catalysts with monolayer coverage. The dependence of reactivity on the support follows the order ZrO₂ > Al₂O₃ > TiO₂ > SiO₂. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity.     

TiO2-coated on Al2O3 support prepared by the CVD method for HDS catalysts

Mo---Co or Mo---Ni catalysts supported on alumina (Al₂O₃) have been widely used for hydrodesulfurization (HDS) of heavy petroleum fractions. In order to enhance the catalytic activities for HDS, a composite type support (TiO₂-Al₂O₃) prepared by the chemical vapor deposition (CVD) method has been studied. We found that Mo catalyst supported on TiO₂-Al₂O₃ showed much higher catalytic activity for HDS of dibenzothiophene derivatives than the catalysts supported on Al₂O₃.     

Mixed oxide supported hydrodesulfurization catalysts—a review

Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al₂O₃ containing mixed oxide supports, TiO₂ containing mixed oxide supports, ZrO₂ containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO₂ containing mixed oxides received maximum attention, especially TiO₂–Al₂O₃ supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication.     

MgO-supported Mo, CoMo and NiMo sulfide hydrotreating catalysts

The most common preparation of high surface area MgO (100–500 m² g⁻¹) is calcination of Mg(OH)₂ obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO₃/MgO catalyst is complicated by the high reactivity of MgO to H₂O and MoO₃. During conventional aqueous impregnation, MgO is transformed to Mg(OH)₂, and well soluble MgMoO₄ is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO₃. Mo species of MoO₃/MgO catalyst are dissolved as MgMoO₄ during deposition of Co(Ni) by conventional aqueous impregnation. This can be avoided by using non-aqueous impregnation. Co(Ni)Mo/MgO catalysts must be calcined only at low temperature because Co(Ni)O and MgO easily form a solid solution. Literature data on hydrodesulfurization (HDS) activity of MgO-supported catalysts are often contradictory and do not reproduced well. However, some results suggest that very highly active HDS sites can be obtained using this support. Co(Ni)Mo/MgO catalysts prepared by non-aqueous impregnation and calcined at low temperature exhibited strong synergism in HDS activity. Co(Ni)Mo/MgO catalysts are much less deactivated by coking than their Al₂O₃-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al₂O₃. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al₂O₃.     

In situ XAFS analysis of catalytically active cobalt species in porous clays for deep hydrodesulfurization

Mesoporous smectite-type clays containing cobalt species in lattice (MST(Co)) were prepared by a hydrothermal method and examined for hydrodesulfurization (HDS). The MST(Co) catalysts showed higher HDS activities than a commercial alumina-supported cobalt–molybdenum catalyst (Co–Mo/Al₂O₃). The active structure of MST(Co) was studied by in situ X-ray absorption fine structure and nitrogen adsorption techniques.     

Catalytic activities of Co(Ni)Mo/TiO2–Al2O3 catalysts in gasoil and thiophene HDS and pyridine HDN: effect of the TiO2–Al2O3 composition

The effect of the TiO₂–Al₂O₃ mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO₂ into the support, and particularly over rich- and pure-TiO₂-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO₂. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO₂ content and large differences are observed between the catalysts supported on pure Al₂O₃ and pure TiO₂. In contrast, in the case of the thiophene test, the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al₂O₃- and pure TiO₂-based catalysts is relatively small and dependent on the H₂ pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H₂ partial pressure on the thiophene HDS, and on the effect of H₂S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking.     

乙二胺四乙酸对NiMo/Al_2O_3催化剂加氢脱氮性能的影响

以氧化铝为载体,Ni和Mo为金属活性组分,添加不同含量乙二胺四乙酸,采用等体积浸渍法制备系列Ni Mo(x)/Al_2O_3(x为乙二胺四乙酸与Ni物质的量比)重质油加氢处理催化剂,考察乙二胺四乙酸加入量对催化剂加氢脱氮性能的影响,并采用N_2物理吸附-脱附、XRD和HRTEM等对催化剂进行表征。结果表明,乙二胺四乙酸的加入增强了金属组分与氧化铝载体间的相互作用,降低了MoS_2活性相的堆垛层数和片层长度,促进了活性相的分散。乙二胺四乙酸与Ni物质的量比为0.5时,MoS_2活性相堆垛层数和片层长度达到良好的结合,对应的催化剂Ni Mo(0.5)/Al_2O_3具有最优的加氢脱氮性能。     

DRIFT study of temperature programmed desorption of NO adsorbed on Co–Mo/Al2O3 sulfided at high pressure

In order to make clear the coordinatively unsaturated sites (CUS) of Co–Mo/Al₂O₃ sulfided at high pressure, the temperature programmed desorption of NO adsorbed on Co–Mo/Al₂O₃ sulfided at high pressure was studied by DRIFT method. The intensity of two IR bands (1835 and 1785 cm⁻¹) of adsorbed NO on Co–Mo/Al₂O₃decreased simultaneously up to 393 K. The higher frequency band disappeared at 393 K, while the lower frequency band remained even at 403 K. In the case of Mo/Al₂O₃, the intensities of two bands appeared at 298 K decreased monotonously with increasing temperature, and disappeared simultaneously over 433 K. In the case of Co/Al₂O₃, two bands disappeared simultaneously over 393 K. These results suggest that two kinds of nitrosyl species are formed on Co–Mo/Al₂O₃. One is dinitrosyl species adsorbed on CUS of Co, and the other is unidentified nitrosyl species. Comparing DRIFT spectra of Co–Mo/Al₂O₃ with those of a physical mixture of Mo/Al₂O₃ and Co/Al₂O₃, it is also suggested that the formation of the latter one correlates with the interaction between Co and Mo in Co–Mo/Al₂O₃. The unidentified nitrosyl species might be the key to explain the dependency of DRIFT spectrum of adsorbed NO on the pressure of sulfiding.     

ZrO2添加对MoO3/Al2O3催化剂耐硫甲烷化性能的影响

采用共沉淀法制备了ZrO₂-Al₂O₃复合载体,并进一步制备了MoO₃/ZrO₂-Al₂O₃催化剂,考察了不同ZrO₂质量分数对催化剂结构及其耐硫甲烷化性能的影响。利用N₂物理吸附、X射线衍射、H₂程序升温还原和透射电子显微镜等手段对催化剂的结构进行了表征。结果表明,MoO₃/ZrO₂-Al₂O₃中ZrO₂的添加可以明显削弱MoO₃与载体间的相互作用,促进Mo物种的还原,适量ZrO₂的存在还有助于提高催化剂的比表面积,改善Mo活性相的分散性,使催化剂表现出优异的耐硫甲烷化活性。