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1.
The effects of the volume and pH of the impregnation solution and of the calcination conditions were examined on the physicochemical and catalytic properties of a 13 wt% MoO 3/Al 2O 3 extrudate catalyst. The Al 2O 3 support and drying procedures (static conditions without flowing air) were fixed in the preparations. In the present series of catalysts, the amount of crystalline MoO 3 was marginally small. It was found that the dispersion of Mo oxide species increased as the volume of the impregnation solution increased, gradually approaching a maximum value. The increase in pH (2–8) of the impregnation solution was found to reduce the dispersion of Mo oxide species. The Mo dispersion increased slightly for the impregnation catalysts as the calcination temperature increased (673–873 K), whereas it decreased for the equilibrium adsorption catalysts. The effects of the calcination atmosphere (with or without flowing air, or with flowing humid air) were very small on the dispersion of Mo oxide species under the present preparation conditions. On the other hand, the methanol oxidation activity of MoO 3/Al 2O 3 was sensitive to the preparation parameters examined here. It was demonstrated by means of EPMA and XPS that a considerable migration of Mo took place during the calcination. In the present study on the preparation of a 13 wt% MoO3/Al2O3 catalyst, an impact index is proposed to measure the magnitude of the effects of the respective parameter(s) on the physicochemical and catalytic properties. With the Mo dispersion, the effects of the preparation parameter decreased in the order, surface area of the support >> drying process > volume of the impregnation solution > pH, calcination temperature and atmosphere. The size of the impact index for the dispersion of Mo sulfide species is 70–75% of that for the Mo oxide species. The HDS activity of the catalyst was less affected by the preparation parameters than the Mo sulfide dispersion. The preparation parameters affected the segregation of Mo on the outer surface of extrudates in a decreasing order: drying process > volume of the impregnation solution > pH, calcination conditions. It was found that the oxidation of methanol was affected most intensely by the drying procedures. The volume of the impregnation solution, calcination conditions and pH of the impregnation solution also strongly affected the oxidation activity. The impact index suggests that the sensitivity to the preparation variables of the physicochemical and catalytic properties of MoO3/Al2O3 decreases in the order, methanol oxidation activity > surface Mo segregation > Mo oxide dispersion > Mo sulfide dispersion > HDS activity. 相似文献
2.
Ten types of 13 wt% MoO 3/Al 2O 3 catalysts were prepared by a conventional impregnation or equilibrium adsorption method using a common extrudate support. These catalysts were subjected to a comprehensive characterization and catalytic reactions to find important preparation parameters in practical preparations. It was demonstrated in the present group study that the formation of crystalline MoO 3 was strongly correlated with the Mo segregation on the outer surface of the extrudate. When the amount of the impregnation solution was large (ca. 10 cm 3 g-Al 2O 3−1), a considerably homogeneous distribution and high dispersion of Mo oxide species were attained irrespective of the other preparation parameters. It is suggested that when a pore volume impregnation or incipient wetness technique is employed, drying processes strongly affect the dispersion and distribution of Mo oxide species. Drying at a reduced pressure is suggested to result in a segregation of Mo oxides on the outer surface of the extrudate, and accordingly a formation of crystalline MoO 3. 相似文献
3.
In the present part of the group study on the preparation of 13 wt% MoO 3/Al 2O 3, the effects of drying processes were investigated on the physicochemical and catalytic properties. Two series of catalysts were prepared by a conventional impregnation technique and by an equilibrium adsorption method using a common extrudate support. XPS and EPMA results demonstrated that the distribution of Mo oxide species in extrudates was strongly affected by drying processes. A rapid drying, in particular at a reduced pressure, was found to induce a strong segregation of Mo oxides on the outer surface of the extrudates, forming a sharp egg shell type distribution of Mo. On the other hand, drying under static conditions produced a moderate egg shell type distribution, suggesting that a slow drying rate is favorable for a homogeneous distribution of Mo. The equilibrium adsorption technique was found to provide considerably flat Mo profiles inside the extrudates except for the utmost surfaces where Mo concentrations increased steeply. 相似文献
4.
Al 2O 3–SiO 2 mixed oxide has been investigated as a support for hydrotreating catalyst with variation of its composition [Si/(Si + Al) = 0.06, 0.12, 0.31, 0.56, 0.78] and its interaction with the surface active metals (NiMo). The composition of support and surface species (NiMo) of catalysts were characterized by specific surface area, atomic absorption, SEM-EDX, XRD, temperature programmed reduction (TPR), Raman analysis, scanning electron microscopy (STEM) and transmission electron microscopy (TEM). Incorporation of SiO 2 in Al 2O 3 promotes a weak interaction between the active phases and particularly catalyst that predominated with SiO 2 content. The oxide and sulfided catalysts characterization indicated that the effect of support is responsible to form different catalytic sites. Crystallization of MoO 3 phases and a relatively longer crystal of MoS 2 in the sulfided catalyst were attributed to an increasing SiO 2 content in the support. The catalytic behavior of the NiMo supported catalysts is explained in terms of structural changes on the surface due to the support and active metal interactions. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalyst having lower SiO 2 content in the support. 相似文献
5.
One series of oxidized K–MoO 3/γ-Al 2O 3 samples with different Mo loadings (MoO 3/Al 2O 3 (wt ratio)=0.05–0.45) was prepared by impregnating K and Mo compounds and successive calcination in air at 800°C. The oxidized samples were sulfided and then utilized for mixed alcohols synthesis from syngas. The structural information from laser Raman spectroscopy (LRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ammonia saturation, temperature programmed desorption (TPD) and ethanol decomposition were studied to elucidate the reaction properties. The results indicated that with Mo loading increased from MoO3/Al2O3=0.05 to 0.25, the total yields of mixed alcohols and hydrocarbons decreased, but the selectivity to mixed alcohols was enhanced sharply from 3% to 50%. With Mo loading increased from MoO3/Al2O3=0.25 to 0.45, the CO conversion was enhanced, but the selectivity to mixed alcohols leveled off. On these catalysts, Fischer–Tropsch (FT) synthesis to linear alcohols and the condensation reaction of low alcohols to form branched i-C4OH occurred at the same time. With increased Mo loading, activity of the alcohols condensation became high. Structural studies demonstrated that on oxidized samples with increased Mo loading the same K–Mo–O species was formed, but the dispersion of these K–Mo species decreased. The catalyst's acidity decreased remarkably with Mo loading up to MoO3/Al2O3=0.25, and stayed unchanged as Mo loading was further increased to MoO3/Al2O3=0.45. With increased Mo loading, the activity for ethanol dehydration changed parallel to the acidity. Results of the activity experiments for mixed alcohols' synthesis and the structural measurements indicated that the dispersion state of Mo species and the content of unreduced Mo species influenced the total CO conversion, and that the acidity of the catalyst controlled the selectivity to mixed alcohols. 相似文献
6.
The relationship between the activity and surface molybdenum species of nitrided 12.5% MoO 3/Al 2O 3 was studied in the hydrodenitrogenation (HDN) of carbazole at 573 K and 10.1 MPa total pressure. The surface molybdenum species were determined by the desorption of nitrogen gas during TPD. The surface area of NH 3-cooled Mo/Al 2O 3 nitrided at 773 and 1173 K was decreased by 8% and 61% from 245 m 2 g −1 of the fresh MoO 3/Al 2O 3, respectively. The NH 3-cooled Mo/Al 2O 3 catalysts had slightly higher surface area than the He-cooled catalysts. The HDN rate increased with increasing nitriding temperature in the HDN of carbazole on the nitride catalysts. The NH 3-cooled Mo/Al 2O 3 catalysts nitrided at 1173 K were the most active in carbazole HDN and the He-cooled catalyst nitrided at 773 K was the least. 相似文献
7.
The most common preparation of high surface area MgO (100–500 m 2 g −1) is calcination of Mg(OH) 2 obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO 3/MgO catalyst is complicated by the high reactivity of MgO to H 2O and MoO 3. During conventional aqueous impregnation, MgO is transformed to Mg(OH) 2, and well soluble MgMoO 4 is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO 3. Mo species of MoO 3/MgO catalyst are dissolved as MgMoO 4 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 Al 2O 3-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al 2O 3. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al 2O 3. 相似文献
8.
The preparation of alumina-supported β-Mo 2C, MoC 1−x ( x≈0.5), γ-Mo 2N, Co–Mo 2C, Ni 2Mo 3N, Co 3Mo 3N and Co 3Mo 3C catalysts is described and their hydrodesulfurization (HDS) catalytic properties are compared to conventional sulfide catalysts having similar metal loadings. Alumina-supported β-Mo 2C and γ-Mo 2N catalysts (Mo 2C/Al 2O 3 and Mo 2N/Al 2O 3, respectively) are significantly more active than sulfided MoO 3/Al 2O 3 catalysts, and X-ray diffraction, pulsed chemisorption and flow reactor studies of the Mo 2C/Al 2O 3 catalysts indicate that they exhibit strong resistance to deep sulfidation. A model is presented for the active surface of Mo 2C/Al 2O 3 and Mo 2N/Al 2O 3 catalysts in which a thin layer of sulfided Mo exposing a high density of sites forms at the surface of the alumina-supported β-Mo 2C and γ-Mo 2N particles under HDS conditions. Cobalt promoted catalysts, Co–Mo 2C/Al 2O 3, have been found to be substantially more active than conventional sulfided Co–MoO 3/Al 2O 3 catalysts, while requiring less Co to achieve optimal HDS activity than is observed for the sulfide catalysts. Alumina-supported bimetallic nitride and carbide catalysts (Ni 2Mo 3N/Al 2O 3, Co 3Mo 3N/Al 2O 3, Co 3Mo 3C/Al 2O 3), 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. 相似文献
9.
Ni/Al 2O 3 catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons. There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts. The properties of these very complex systems depend on the conditions of successive preparation stages (calcination, reduction) or the process conditions. A series of Ni/Al2O3 catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties. Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al2O3 catalysts. Catalysts were further characterized by BET area, H2 chemisorption and X-ray diffraction measurements. The TPR curves of Ni-Mo/Al2O3 catalysts are very complex. Mo addition leads to the decrease of catalysts reducibility. However, complete reduction of NiO and MoO3 can be achieved at 800 °C. The reduction course depends on the sequence of nickel and molybdenum addition into the support. Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al2O3 and Ni-Mo/Al2O3 samples show the possibility of Ni-Mo solid solution formation. 相似文献
10.
采用共沉淀法制备了ZrO 2-Al 2O 3复合载体,并进一步制备了MoO 3/ZrO 2-Al 2O 3催化剂,考察了不同ZrO 2质量分数对催化剂结构及其耐硫甲烷化性能的影响。利用N 2物理吸附、X射线衍射、H 2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,MoO 3/ZrO 2-Al 2O 3中ZrO 2的添加可以明显削弱MoO 3与载体间的相互作用,促进Mo物种的还原,适量ZrO 2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。 相似文献
11.
In reverse water gas shift (RWGS) reaction CO 2 is converted to CO which in turn can be used to produce beneficial chemicals such as methanol. In the present study, Mo/Al 2O 3, Fe/Al 2O 3 and Fe-Mo/Al 2O 3 catalysts were synthesised using impregnation method. The structures of catalysts were studied using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, inductively coupled plasma atomic emission spectrometer (ICP-AES), temperature programmed reduction (H 2-TPR), CO chemisorption, energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) techniques. Kinetic properties of all catalysts were investigated in a batch reactor for RWGS reaction. The results indicated that Mo existence in structure of Fe-Mo/Al 2O 3 catalyst enhances its activity as compared to Fe/Al 2O 3. This enhancement is probably due to better Fe dispersion and smaller particle size of Fe species. Stability test of Fe-Mo/Al 2O 3 catalyst was carried out in a fixed bed reactor and a high CO yield for 60 h of time on stream was demonstrated. Fe 2(MoO 4) 3 phase was found in the structures of fresh and used catalysts. TPR results also indicate that Fe 2(MoO 4) 3 phase has low reducibility, therefore the Fe 2(MoO 4) 3 phase signifificantly inhibits the reduction of the remaining Fe oxides in the catalyst, resulted in high stability of Fe-Mo/Al 2O 3 catalyst. Overall, this study introduces Fe-Mo/Al 2O 3 as a novel catalyst with high CO yield, almost no by-products and fairly stable for RWGS reaction. 相似文献
12.
A new preparation of supported MoO 3 is described. Slurry MoO 3/water is used instead of the solution (NH 4) 6Mo 7O 24. Preparation and HDS activity are illustrated for MoO 3 supported over Al 2O 3, active carbon and ZrO 2. Another application of the new principle is the preparation of high surface area MoO 3/MgO by the reaction of MgO with slurry (NH 4) 6Mo 7O 24/methanol. Texture of MgO that is deteriorated in aqueous solution of (NH 4) 6Mo 7O 24 is stable in that slurry. “Slurry impregnation” is a special case of equilibrium adsorption impregnation. It is simple and it provides monolayer dispersion of molybdena. 相似文献
13.
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
14.
Catalytic reactions of n-pentane and 1-pentene were performed as a function of reaction temperature, on different molybdenum oxides and metal surfaces. These oxides such as Mo 2O 5 and MoO 2 were obtained following the exposure of MoO 3/TiO 2 to hydrogen at different temperatures up to 673 K. Metallic Mo(0) state is obtained at reduction temperatures beyond 723 K. Identification of the Mo chemical species was performed using in situ XPS-UPS surface techniques. The combination of both techniques provides valuable information on the chemical composition of the upper 10 atomic monolayers. X-ray diffraction and HRTEM techniques were also employed. The reduction procedure of MoO 3 does not follow the same pathway when it is deposited on an Al 2O 3 support. A strong electronic interaction between the two species promotes the formation of an Al 2(MoO 4) 3 complex as revealed by XRD measurements. Catalytic active functions present on the different Mo species surfaces are of the acidic type (Lewis and Brönsted) on Mo 2O 5, metal-acid (bifunctional) on MoO 2 and metal function on metallic Mo(0). Consequently, a specific catalytic reaction of n-pentane, such as hydroisomerization to iso-pentane, which is rationalized in terms of a bifunctional mechanism, is expected to occur on MoO 2. Different isomerization reactions of 1-pentene were obtained in the case of MoO 3/TiO 2 and MoO 3/Al 2O 3 at reduction temperatures below 573 K. However, in the case of Mo on the alumina support, the conversion of 1-pentene to iso-pentane is low and irreproducible, contrary to what has been observed for Mo on titania. 相似文献
15.
A novel TiO 2/Al 2O 3/cordierite honeycomb-supported V 2O 5–MoO 3–WO 3 monolithic catalyst was studied for the selective reduction of NO with NH 3. The effects of reaction temperature, space velocity, NH 3/NO ratio and oxygen content on SCR activity were evaluated. Two other V 2O 5–MoO 3–WO 3 monolithic catalysts supported on Al 2O 3/cordierite honeycomb or TiO 2/cordierite honeycomb support, two types of pellet catalysts supported on TiO 2/Al 2O 3 or Al 2O 3, as well as three types of pellet catalysts V 2O 5–MoO 3–WO 3–Al 2O 3 and V 2O 5–MoO 3–WO 3–TiO 2 were tested for comparison. The experiment results show that this catalyst has a higher catalytic activity for SCR with comparison to others. The results of characterization show, the preparation method of this catalyst can give rise to a higher BET surface area and pore volume, which is strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO 2/Al 2O 3 cannot be excluded. 相似文献
16.
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
17.
The typical physico-chemical properties and their hydrodesulfurization activities of NiMo/TiO 2-Al 2O 3 series catalysts with different TiO 2 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 N 2-adsorption, UV–vis DRS, XRD, FT-Raman, TPR, pyridine FT-IR and DRIFT were used to characterize the surface and structural properties of TiO 2-Al 2O 3 binary oxide supports and the NiMo/TiO 2-Al 2O 3 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 TiO 2 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 MoS 2 and the catalysts with TiO 2 loadings of 15 and 30% showed that NiMo/TiO 2-Al 2O 3 catalysts possessed more CUS than that of pure MoS 2. HDS efficiencies and the above characterization results confirmed that the incorporation of TiO 2 into Al 2O 3 could adjust the interaction between support and active metals, enhanced the reducibility of molybdenum and thus resulted in the high activity of HDS reaction. 相似文献
18.
High surface area (>300 m 2 g −1) nano-structured TiO 2 oxides (ns-T) were used as CoMo hydrodesulfurization catalyst support. Cylindrical extrudates were impregnated by incipient wetness with Mo (2.8 Mo at. nm −2) and Co (atomic ratio Co/(Co + Mo) = 0.3). Characterization of impregnated precursors was carried out by N 2 physisorption, XRD and atomic absorption and laser-Raman spectroscopies. Sulfided catalysts (400 °C, H 2S/H 2) were studied by X-ray photoelectronic spectroscopy. As indicated by XRD and after various preparation steps (extrusion, Mo and Co impregnation and sulfiding) the nano-structured material was well preserved. XPS analyses showed that Co and Mo dispersion over the ns-T support was much higher than that on alumina. Very high surface S concentration suggested that even ns-T was partially sulfided during catalyst activation. Dibenzothiophene hydrodesulfurization activity (5.73 MPa, 320 °C, n-hexadecane as solvent) of CoMo/ns-T was two-fold to that of an alumina-supported commercial CoMo catalyst. The improvement was even more remarkable in intrinsic pseudo kinetic constant basis. No important differences in selectivity over the catalysts supported on either Al 2O 3 or ns-T were observed, where direct desulfurization to biphenyl was favored. Both Mo dispersion and sulfidability were enhanced on the ns-T support where Mo 4+ fraction was notably increased (100%) as to that found on CoMo/Al 2O 3. 相似文献
19.
The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO3/Al2O3 catalyst than on the Pd/CeO2/Al2O3 and Pd/Nb2O5/Al2O3 catalysts. The explanation for the very high N2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Meδ+ stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N2 selectivity. 相似文献
20.
In the present work, with the aim of searching for new, highly effective catalysts for deep HDS, a series of NiMo catalysts with different MoO 3 loadings (6–30 wt.%) was prepared using SBA-15 material covered with ZrO 2-monolayer as a support. Prepared catalysts were characterized by N 2 physisorption, small- and wide-angle XRD, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, SEM-EDX and HRTEM, and their catalytic activity was evaluated in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS). It was observed that ZrO 2 incorporation on the SBA-15 surface improves the dispersion of the Ni-promoted oxidic and sulfided Mo species, which were found to be highly dispersed, up to 18 wt.% of MoO 3 loading. Further increase in metal charge resulted in the formation of MoO 3 crystalline phase and an increase in the stacking degree of the MoS 2 particles. All NiMo catalysts supported on ZrO 2-modified SBA-15 material showed high activity in HDS of 4,6-DMDBT. The best catalyst having 18 wt.% MoO 3 and 4.5 wt.% NiO was almost twice more active than the reference NiMo/γ-Al 2O 3 catalyst. High activity of NiMo/Zr-SBA-15 catalysts and its evolution with metal loading was related to the morphological characteristics of the MoS 2 active phase determined by HRTEM. 相似文献
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