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1.
A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo 2N catalysts is described. The complex precursor (HMT) 2(NH 4) 4Mo 7O 24·2H 2O (HMT: hexamethylenetetramine) is converted to γ-Mo 2N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH 3 flow forms γ-Mo 2N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH 3 shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo 2N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH 3 flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo 2N/γ-Al 2O 3 prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts. 相似文献
2.
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 H 2 pressure. A mesoporous molecular sieve of MCM-41 type was synthesized; which has SiO 2/Al 2O 3 ratio of about 41. MCM-41 supported Co–Mo catalyst was prepared by co-impregnation of Co(NO 3) 2·6H 2O and (NH 4) 6Mo 7O 24 followed by calcination and sulfidation. Commercial Al 2O 3 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/Al 2O 3 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. 相似文献
3.
Properties of the molybdenum nitrides supported on alumina as well as on active carbon has been investigated in the reactions of thiophene and vacuum gas oil (VGO) hydrodesulfurization (HDS) as well as in the reaction of cyclohexene with hydrogen. Supported molybdenum nitride was more active in thiophene hydrogenolysis than sulfided Mo/Al 2O 3. Also in the reaction of VGO HDS alumina supported molybdenum nitride was more active than sulfided counterpart, however Mo 2N supported on active carbon exhibit low activity. In the products of the cyclohexene reaction over supported Mo 2N methyl-cyclopentanes and benzene has been found. 相似文献
4.
A series of supported and unsupported Mo 2N and W 2N phases were synthesized by means of the treatment under ammonia atmosphere at 700°C of Mo and W oxides. The X-ray diffraction and electron microscopy techniques verified the formation of the Mo 2N and W 2N ceramic phases, while the N 2 adsorption (BET) was used to determine the surface areas, between 46–133 m 2/g for Mo 2N (unsupported) and 81–101 m 2/g for W 2N (unsupported). The supported phases had surface areas between 109–113 and 109–122 m 2/g, for Mo 2N/Al 2O 3 and W 2N/Al 2O 3, respectively. The catalytic hydrotreating of a heavy vacuum gas oil (HVGO) derived from Maya crude (i.e. 2.21 wt.% S, 0.184 wt.% N 2) was performed on both, supported and unsupported Mo nitrides and W nitrides, which promoted the HDN reaction preferentially, up to 26.6% on Mo 2N/Al 2O 3 and up to 22.3% on W 2N/Al 2O 3, against 3.26% on the reference catalyst, i.e. CoMo/Al 2O 3 at 350°C and 80 kg/cm 2. Also, the rates for HDN increased with the crystallite size in the unsupported W 2N series. Also, the pore volume and mean pore diameters of the Mo 2N/Al 2O 3 and W 2N/Al 2O 3 series improve substantially with respect to the pure ceramic phases. 相似文献
5.
Co–Mo model sulfide catalysts, in which CoMoS phases are selectively formed, were prepared by means of a CVD technique using Co(CO) 3NO as a precursor of Co. It is shown by means of XPS, FTIR and NO adsorption that CoMoS phases form selectively when the Mo content exceeds monolayer loading. A single exposure of MoS 2/Al 2O 3 to a vapor of Co(CO) 3NO at room temperature fills the edge sites of the MoS 2 particles. It is suggested that the maximum potential HDS activity of MoS 2/Al 2O 3 and Co–Mo/Al 2O 3 catalysts can be predicted by means of Co(CO) 3NO as a “probe” molecule. An attempt was made to determine the fate of Co(CO) 3NO adsorbed on MoS 2/Al 2O 3. The effects of the support on Co–Mo sulfide catalysts in HDS and HYD were investigated by use of CVD-Co/MoS 2/support catalysts. XPS and NO adsorption showed that model catalysts can also be prepared for SiO 2-, TiO 2- and ZrO 2-supported catalysts by means of the CVD technique. The thiophene HDS activity of CVD-Co/MoS 2/Al 2O 3, CVD-Co/MoS 2/TiO 2 and CVD-Co/MoS 2/Al 2O 3 is proportional to the amount of Co species interacting with the edge sites of MoS 2 particles or CoMoS phases. It is concluded that the support does not influence the HDS reactivity of CoMoS phases supported on TiO 2, ZrO 2 and Al 2O 3. In contrast, CoMoS phases on SiO 2 show catalytic features characteristic of CoMoS Type II. With the hydrogenation of butadiene, on the other hand, the Co species on MoS 2/TiO 2, ZrO 2 and SiO 2 have the same activity, while the Co species on MoS 2/Al 2O 3 have a higher activity. 相似文献
6.
In order to make clear the coordinatively unsaturated sites (CUS) of Co–Mo/Al 2O 3 sulfided at high pressure, the temperature programmed desorption of NO adsorbed on Co–Mo/Al 2O 3 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/Al 2O 3decreased 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/Al 2O 3, 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/Al 2O 3, two bands disappeared simultaneously over 393 K. These results suggest that two kinds of nitrosyl species are formed on Co–Mo/Al 2O 3. One is dinitrosyl species adsorbed on CUS of Co, and the other is unidentified nitrosyl species. Comparing DRIFT spectra of Co–Mo/Al 2O 3 with those of a physical mixture of Mo/Al 2O 3 and Co/Al 2O 3, it is also suggested that the formation of the latter one correlates with the interaction between Co and Mo in Co–Mo/Al 2O 3. The unidentified nitrosyl species might be the key to explain the dependency of DRIFT spectrum of adsorbed NO on the pressure of sulfiding. 相似文献
7.
A series of phosphorus promoted γ-Al 2O 3 supported NiMo carbide catalysts with 0–4.5 wt.% P, 13 wt.% Mo and 2.5 wt.% Ni were synthesized and characterized by elemental analysis, pulsed CO chemisorption, BET surface area measurement, X-ray diffraction, near-edge X-ray absorption fine structure, DRIFT spectroscopy of CO adsorption and H 2 temperature programmed reduction. X-ray diffraction patterns and CO uptake showed the P addition to NiMo/γ-Al 2O 3 carbide, increased the dispersion of β-Mo 2C particles. DRIFT spectra of adsorbed CO revealed that P addition to NiMo/γ-Al 2O 3 carbide catalyst not only increases the dispersion of Ni-Mo carbide phase, but also changes the nature of surface active sites. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities of these P promoted NiMo/γ-Al 2O 3 carbide catalysts were performed in trickle bed reactor using light gas oil (LGO) derived from Athabasca bitumen and model feed containing quinoline and dibenzothiophene at industrial conditions. The P added NiMo/γ-Al 2O 3 carbide catalysts showed enhanced HDN activity compared to the NiMo/γ-Al 2O 3 catalysts with both the feed stocks. The P had almost no influence on the HDS activity of NiMo/γ-Al 2O 3 carbide with LGO and dibenzothiophene. P addition to NiMo/γ-Al 2O 3 carbide accelerated CN bond breaking and thus increased the HDN activity. 相似文献
8.
The effects of fluorine, phosphate and chelating agents on hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) are reviewed. All three additives enhance the activity of NiMo/Al 2O 3 catalysts in HDN but have only a slightly positive or even a negative effect on the HDS activity of CoMo/Al 2O 3 and NiMo/Al 2O 3 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. 相似文献
9.
TiO 2–Al 2O 3 composite supports have been prepared by chemical vapor deposition (CVD) over γ-Al 2O 3 substrate, using TiCl 4 as the precursor. High dispersion of TiO 2 overlayer on the surface of Al 2O 3 has been obtained, and no cluster formation has been detected. The catalytic behavior of Mo supported on Al 2O 3, TiO 2 and TiO 2–Al 2O 3 composite has been investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the Mo catalysts supported on TiO 2–Al 2O 3 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 Al 2O 3. The ratio of the corresponding cyclohexylbenzenes/biphenyls is increased over Mo catalyst supported on TiO 2–Al 2O 3 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/TiO 2–Al 2O 3 catalyst leads to higher catalytic performance for deep HDS of gas oil. 相似文献
10.
Composite types of TiO 2–Al 2O 3 supports, which are γ-aluminas coated by titania, have been prepared by chemical vapor deposition (CVD), using TiCl 4 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 TiO 2–Al 2O 3 with different loadings of TiO 2. 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 TiO 2 and TiO 2–Al 2O 3 supports compared to that on the Al 2O 3 support. Higher TiO 2 loadings of the TiO 2–Al 2O 3 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 TiO 2–Al 2O 3 supported Mo catalysts, in particular for the 4,6-dimethyl-DBT, is much higher than that obtained over Al 2O 3 supported Mo catalyst. The ratio of the corresponding cyclohexylbenzene (CHB)/biphenyl (BP) derivatives is increased over the Mo/TiO 2–Al 2O 3. This indicates that the prehydrogenation of an aromatic ring plays an important role in the HDS of DBT derivatives over TiO 2–Al 2O 3 supported catalysts. 相似文献
11.
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/Al 2O 3). The active structure of MST(Co) was studied by in situ X-ray absorption fine structure and nitrogen adsorption techniques. 相似文献
12.
The nitrided MoO 3 catalysts formed using two kinds of treatment with either NH 3 or He after nitriding were studied by temperature-programmed desorption and X-ray diffraction analyses. The catalysts were cooled to room temperature in either flowing NH 3 or He (NH or HE catalyst) after nitriding at 773, 973 and 1173 K with NH 3. The activities of the catalysts were determined during the hydrodenitrogenation of carbazole at 573 K and 10.1 MPa total pressure. MoO 2, γ-Mo 2N, and Mo metal were mainly formed in the NH catalysts nitrided at 773, 973 and 1173 K, respectively. Mo oxides and metals in the NH catalysts were nitrided to γ-Mo 2N and β-Mo 2N 0.78 with low crystallinity during TPD. The surface area of the NH and HE catalysts nitrided at 773 K increased to 66 and 59 m 2 g −1 maximum from 1.1 m 2 g −1 of fresh MoO 3, respectively, but decreased as the nitriding temperature increased to 973 K and 1173 K. The HE catalysts per surface area were more active than the NH catalysts for both the overall HDN reaction and hydrogenation, and the 1173 K-nitrided catalysts were highest. On the other hand, the NH catalysts were more active than the HE catalysts for C–N hydrogenolysis and the 973 K-nitrided catalyst showed a maximum activity for C–N hydrogenolysis. 相似文献
13.
以碳纳米管(CNTs)为载体,通过控制催化剂合成的还原温度制备了一系列负载型Mo基催化剂。采用XRD、TEM、N 2物理吸附、XPS以及NH 3/H 2-TPD等技术对催化剂进行了表征,并研究了Mo基催化剂对硬脂酸催化加氢脱氧性能的影响。结果表明:随着还原温度的升高,催化剂表面的Mo物种逐渐被还原,还原过程为:MoO 3→MoO 2→Mo→Mo 2C。还原温度为450℃和550℃时,催化剂的活性相为MoO 2;还原温度为600℃时,催化剂的活性相为MoO 2/Mo/β-Mo 2C的混合相;还原温度为650℃和700℃时,催化剂的活性相全部转化为β-Mo 2C。与活性相MoO 2催化剂相比,β-Mo 2C催化剂具有更高的加氢脱氧活性。此外,还原温度为600℃的MoO 2/Mo/β-Mo 2C混合相催化剂因具有较大的比表面积、较多的酸中心数量和较强的H 2吸附能力,使得该催化剂在硬脂酸加氢脱氧反应中表现出最优越的催化活性。 相似文献
14.
A series of unsupported dimolybdenum nitride (γ-Mo 2N) catalysts differing in surface area were prepared by temperature programmed reduction of MoO 3 with a mixture of NH 3:N 2 (90:10). Characterization of catalysts by BET, XRD, TPR and XPS techniques was carried out. The samples were used as catalysts in hydrotreating reactions (simultaneous hydrodesulfurization of thiophene and hydrogenation of cyclohexene). Low surface area γ-Mo 2N materials show much higher specific conversions than those with higher surface area. These results indicate that HDS and HYD reactions over γ-Mo 2N seem to be structure-sensitive. The relative exposure extent of crystalline planes (1 1 1) and (2 0 0) over the different catalysts can be associated with their hydrogen adsorption capacities and with their catalytic performances. The catalytic activities are significantly affected by the catalyst pretreatment conditions. 相似文献
15.
Nickel and potassium promoted β-Mo 2C catalysts were prepared for CO hydrogenation to higher alcohols synthesis. The results revealed that β-Mo 2C produced mainly hydrocarbons, but the addition of potassium resulted in a remarkable selectivity shift from hydrocarbons to alcohols over β-Mo 2C. Moreover, it was found that potassium enhanced the ability of chain propagation of β-Mo 2C catalyst and led to a higher selectivity to C 2+OH. The addition of nickel further enhanced higher alcohols synthesis, which showed the optimum at 1/8–1/6 of Ni/Mo molar ratios. The characterization suggested that there might be a synergistic effect of potassium and nickel on β-Mo 2C, which favored the alcohols synthesis. The production of alcohols appeared to be relevant to the presence of Mo 4+ species, whereas the formation of hydrocarbons was closely associated with Mo 2+ and/or Mo 0 species on the surface of β-Mo 2C-based catalysts. 相似文献
16.
Supported Pd–Pt catalysts are efficient for hydrodesulfurization (HDS) and hydrodearomatization (HDA) reactions of diesel fuel and their activity varied with the kinds of supports. Concerning HDA, alumina supported catalysts showed four times higher TOF (turn over frequency) than silica supported one. In order to elucidate the difference in activity, the structural analysis of the active phase was performed. After reduction pretreatment, relatively uniform and large metallic alloy Pd–Pt particles were formed on SiO 2, whereas, Pd and Pt atoms formed rather segregated particles on Al 2O 3. Subsequent X-ray absorption of fine structure (XAFS) analysis under HDS conditions showed no contribution of sulfur for SiO 2 supported catalyst, whereas, formation of sulfided metal species was observed in XAFS spectra for the Al 2O 3 supported catalyst. It is suggested that on Pd–Pt/SiO 2, thin sulfide layer on the metal cluster surface blocked the active sites and lowered the HDA activity. Presence of partially sulfided phase originated from rather segregated structure like Pd–Pt/Al 2O 3 is thought to be requisite for high HDA activity. 相似文献
17.
The structural and catalytic properties of MoO 3 catalysts supported on ZrO 2, Al 2O 3, TiO 2 and SiO 2 with Mo surface densities, ns, in the range of 0.5–18.5 Mo/nm 2 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 (MoO 4 and MoO 5, 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 ZrO 2 > Al 2O 3 > TiO 2 > SiO 2. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity. 相似文献
18.
The catalytic behaviour of multiphasic catalysts based on -bismuth pyrostannate, Bi 2Sn 2O 7, was investigated in the selective oxidation of isobutene into methacrolein. When -Bi 2Sn 2O 7 is mixed with MoO 3, strong cooperation effects on the yield and selectivity in methacrolein occur. However, XRD analyses performed on samples after test revealed the formation of a low quantity of -bismuth molybdate, -Bi 2Mo 3O 12, when the reaction temperature exceeded 673 K. Additional experiments were therefore carried out on the “Bi–Sn–Mo–O” catalysts in order to shed light on the role of Bi 2Mo 3O 12 in the synergetic effects observed in the Bi 2Sn 2O 7–MoO 3 system. The experimental results are discussed in terms of several hypotheses. First, the intrinsic activity of Bi 2Mo 3 O 12 is probably the simplest explanation for the synergetic effects, although experiments have shown that this phase present in a low quantity is only poorly active. Second, catalytic tests made on Bi 2Sn 2O 7–Bi 2Mo 3O 12 mechanical mixtures have evidenced a cooperation between these two ternary oxides, particularly when Bi 2Sn 2O 7 was the major component of the mixture. Consequently, it is likely that a synergy between Bi 2Sn 2O 7 and the in situ generated Bi 2Mo 3O 12 might play a role in the synergy observed in the Bi 2Sn 2O 7–MoO 3 association. Third, as bismuth pyrostannate was previously shown to behave as an oxygen donor phase with respect to WO 3, a remote control mechanism could therefore occur between Bi 2Sn 2O 7 and MoO 3, independently from the formation of -Bi 2Mo 3O 12. 相似文献
19.
Hydrotreating of Maya heavy crude oil over high specific surface area CoMo/TiO 2–Al 2O 3 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 TiO 2 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 TiO 2 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 MoS 2 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 TiO 2 with γ-Al 2O 3 alters the nature of active metal interaction with support, which may facilitate the dispersion of active phases on the support surface. Therefore, the TiO 2 counterpart plays a promoting role to HDS activity due to the favorable morphology of MoS 2 phases and metal support interaction. 相似文献
20.
A series of Co/Al 2O 3 catalysts were prepared by the incipient wetness impregnation method using γ-Al 2O 3 support and (CH 3COO) 2Co·4H 2O solutions, followed by calcination at 500–800 °C. Characterization of catalysts was accomplished by several techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), physisorption of nitrogen, mercury and helium-based pycnometries, Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and pH of zero charge (PZC). Impregnation of support produced a moderate decrease of its surface area and pore volume and also led to minor changes of its PZC. Depending on preparation conditions (i.e., calcination atmosphere and temperature and metal loading), one or more of the following Co-containing compounds were identified: CoO, Co 3O 4 and CoAl 2O 4. The support and prepared Co/Al 2O 3 catalysts were tested to catalyze the ozonation of aqueous pyruvic acid at pH 2.5. Pyruvic acid was shown refractory towards single ozonation but the use of γ-Al 2O 3 and Co/Al 2O 3 catalysts resulted in 56–96% pyruvic acid conversion and 41–78% decrease in DOC after 2 h of ozonation of phosphate-buffered solutions. In the absence of the buffer, conversion rate was enhanced likely as a result of pH increase during the course of the process thus giving rise to the indirect way of ozonation through hydroxyl radicals. Acetic acid was found as the main by-product of pyruvic acid ozonation. Depending on the catalyst used, yield of acetic acid varied from 32 to 49%, values noticeably lower that that obtained from the control non-catalytic ozonation experiment (73%). Differences in catalytic activity amongst the various Co/Al 2O 3 catalysts investigated were attributed to the different Co active phases deposited on the γ-Al 2O 3 surface. The following sequence of increasing activity can be inferred from experimental results: CoO, CoAl 2O 4 and Co 3O 4. All the Co/Al 2O 3 catalysts prepared showed good stability as the percentage of cobalt leached out was rather low. 相似文献
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