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1.
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
2.
MoO 3/TiO 2 catalysts of varying molybdenum content were prepared at various pHs and concentrations of the impregnating solution using the equilibrium deposition filtration (EDF) method. Moreover, a catalyst corresponding to the EDF one with the maximum Mo loading was prepared using the conventional non-dry impregnation (NDI) method. The above catalysts were characterized using X-ray powder analysis, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy, and tested for the selective catalytic reduction of NO by NH 3 in the temperature range 250–450 °C. It was found that the application of EDF results in an improved MoO 3/TiO 2 catalyst exhibiting higher activity than the corresponding sample prepared by the conventional NDI method. The catalytic activity correlates well with the concentration of the Mo species strongly interacting with the anatase surface. The concentration of the above species is maximized when the EDF method is employed to prepare the catalysts. This is especially, so when low pH and Mo concentration of impregnating solution are used. 相似文献
3.
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
4.
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
5.
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
6.
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
7.
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
8.
Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH 3. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH 3 is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH 3/N 2 mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V 2O 5/TiO 2 catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures. 相似文献
9.
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
10.
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
11.
An automated robotic method using a solution at pH=2 containing four precursor salts dissolved has been developed and validated for high-throughput preparation of Mo, Nb, Sb and V mixed metal oxide solids, which are known to be selective for propane oxidation to acrylic (AA) and acetic (AcA) acids. Spherical shaped silica beads of exceptionally narrow size distribution were synthesised using oil drop technique from a Brace™ instrument. Automated impregnation of the beads by the previous solution has been developed and validated. Catalytic studies were performed using a conventional micro-reactor system with an Ultra-Fast™ GC analysis (<2 min against >30 min). After calcination of the samples under either N 2 or air at 873 K, a mixture of phases was obtained, such as VSbO 4, Mo xM 1−xO 2.8 (M=V and/or Nb), Sb 4(2)Mo 10O 31, and other minor phases, such as MoO 3 if activated in air. Mixed oxide samples calcined under N 2 gave better catalytic activity and selectivity to AA/AcA compared to those calcined under air. Measures of catalytic performance of 16 supposedly identical materials fell within a ±5% range of the median values, showing that our experimental set-up is relevant to combinatorial studies. By preparing 15 samples of different chemical composition, optimum catalytic performance was found to correspond to Mo 0.55 Nb 0.09 Sb 0.18V 0.18 mixed oxide calcined at 773 K under N 2, containing a mixture of phases, in particular Mo xM 1−xO 2.8 and Sb 2Mo 10O 31, similarly to the M1 and M2 phases observed for MoNbTeV mixed oxide catalysts. 相似文献
12.
NO reduction to N 2 by C 3H 6 was investigated and compared over Cu-Al 2O 3 catalysts prepared by four different methods, namely, the conventional impregnation, co-precipitation, evaporation of a mixed aqueous solution, and xerogel methods. It was found that the catalyst preparation method as well as the Cu content exerts a significant influence on catalyst activity. For the catalysts prepared by the first three preparation methods, with the increase of Cu content from 5 to 15 wt%, the maximum NO reduction conversion decreased slightly, but the temperature for the maximum NO reduction also decreased. For the xerogel Cu-Al 2O 3, there was a significant decrease in NO reduction conversion with the increase of Cu content from 5 to 10 wt%. In the absence of water vapour, the Cu-Al 2O 3 catalyst prepared by the impregnation method exhibited the highest activity toward NO reduction. The purity of alumina support was found to be a crucial factor to the activity of the Cu-Al 2O 3 catalyst prepared by impregnation. In the presence of water vapour, a substantial decrease in NO conversion was observed for the Cu-Al 2O 3 catalysts prepared by the first three methods, especially for the impregnated Cu-Al 2O 3 catalyst. In contrast, the presence of water vapour showed only a minor influence on the xerogel 5 wt% Cu-Al 2O 3 and it showed the highest activity for NO reduction in the presence of 20% water vapour. The xerogel 5 wt% Cu-Al 2O 3 catalyst was also found to be less affected by a 5 wt% sulfate deposition than the Cu-Al 2O 3 catalysts prepared by other methods. 相似文献
13.
Drastic activity increases were observed by the treatments of the magnesium-rich MgMo 0.99O y catalysts, which are poorly active for the oxidative dehydrogenation of propane, with inorganic or organic acid to remove excess magnesium on the surface. MoO 3 loading on magnesium-rich MgMo 0.99O y catalysts also resulted in drastic activity increases. The activity increases followed non-effective loadings of MoO 3 in the range 0–2 wt%, because it is necessary to neutralize the surface magnesium with MoO 3 before the formation of molybdenum-rich surface. The pH of the aqueous (NH 4) 6Mo 7O 24 solution for the MoO 3 loading apparently influenced the activity. Under the acidic conditions the MoO 3 loading resulted in the drastic activity increase but under the basic conditions the effect of the MoO 3 loading was poor, suggesting that a cluster-type MoO 3 on MgMoO 4 surface is responsible for the activity of propane oxidative dehydrogenation. 相似文献
14.
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
15.
A detailed study on the influence of the addition of molybdenum ions on the catalytic behaviour of a selective vanadium–magnesium mixed oxide catalyst in the oxidation of n-butane has been performed. The catalysts have been prepared by impregnation of a calcined V–Mg–O mixed oxides (23.8 wt% of V 2O 5) with an aqueous solution of ammonium heptamolybdate, and then calcined, and further characterised by several physico-chemical techniques, i.e. SBET, XRD, FTIR, FT-Raman, XPS, H 2-TPR. MgMoO 4, in addition to Mg 3V 2O 8 and MgO, have been detected in all the Mo-doped samples. The incorporation of molybdenum modifies not only the number of V 5+-species on the catalyst surface and the reducibility of selective sites but also the catalytic performance of V–Mg–O catalysts. The incorporation of MoO 3 favours a selectivity and a yield to oxydehydrogenation products (especially butadiene) higher than undoped sample. In this way, the best catalyst was obtained with a Mo-loading of 17.3 wt% of MoO 3 and a bulk Mo/V atomic ratio of 0.6. From the comparison between the catalytic properties and the catalyst characterisation of undoped and Mo-doped V–Mg–O catalysts, the nature of selective sites in the oxidative dehydrogenation of n-butane is also discussed. 相似文献
16.
采用液相原位还原法制备Pd/α-Al2O3催化剂,并应用于CO氧化偶联合成草酸二甲酯反应。对比实验发现,甲醛液相原位还原法制得的Pd基催化剂具有优异的催化活性,当Pd负载质量分数低至0.1%时,催化剂仍表现出较高的活性和稳定性。采用XRD和BET等对催化剂及载体进行表征,结果表明,催化剂活性与载体的比表面积、孔容和孔径没有必然联系。通过TEM发现,0.1%-Pd/α-Al2O3催化剂中的主要活性组分Pd具有较小的颗粒和较高的分散性,通过HRTEM发现,液相原位还原法制备的催化剂能够有效暴露出Pd(111)晶面。 相似文献
17.
Two series of catalysts, V 2O 5/TiO 2 and modified V 2O 5/TiO 2, were prepared with a conventional impregnation method. They were tested in the selective oxidation of toluene to benzoic acid under microwave irradiation. The reaction conditions were optimized over V 2O 5/TiO 2. It was found that in the microwave catalytic process the optimum reactor bed temperature of the titled reaction decreases to 500 K (600 K in the conventional process). The modification of V 2O 5/TiO 2 with MoO 3, WO 3, Nb 2O 5 or Ta 2O 5, which has no negative influence on the reaction in the conventional catalytic process, can greatly promote the catalytic activities in the microwave process, leading to a high yield of benzoic acid (41%). The effects of microwave electromagnetic field on the catalysts are discussed. 相似文献
18.
The surface structure analysis of a model catalyst MoO x/TiO 2(110) was for the first time performed by polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) in three different directions of the crystal surface. Two samples of MoO x/TiO 2(110) were prepared by an impregnation of (NH 4) 6Mo 7O 24·4H 2O using ultra high purity water and normal distilled water. The PTRF-XAFS analysis revealed that anisotropic Mo dimer species was preferentially formed on the TiO 2(110) surface, with Mo–Mo bond (0.335 nm) parallel to the
direction when the ultra high purity water was used as the solvent. On the other hand, the Mo oxide on the surface prepared using normal distilled water had a symmetric tetrahedral structure (MoO 4) with Mo–O of 0.176 nm, which was due to the coexistence of alkaline metals at the surface. 相似文献
19.
The WO 3–TiO 2 catalysts with different WO 3 loadings prepared by the coprecipitation method were investigated in comparison with those prepared by the conventional impregnation method for the activity and durability in the high temperature SCR of NO by NH 3 and the structural and physico-chemical properties which were characterized by BET and XRD measurements, IR, Raman and XPS spectroscopies. The catalyst prepared by coprecipitation, as compared with that prepared by impregnation, was found to exhibit a higher SCR activity at high temperatures and also to possess a larger surface area, higher Brønsted acidity and larger monolayer capacity of the support with WO 3. Increasing the WO 3 loading of the catalysts enhances the SCR activity and simultaneously increases the Brønsted acidity. The observed improvement of SCR activity for the catalyst prepared by coprecipitation is mainly attributed to the higher Brønsted acidity and the presence of the more highly dispersed WO 3 species which is suggested by the larger monolayer capacity of ca. 13 μmol(W)/m 2 and no crystalline WO 3 on TiO 2 detected with XRD at the high WO 3 loading up to 40 wt.%. The catalyst with 20 wt.% WO 3, as compared with that prepared by impregnation, was found to exhibit a better thermal durability at high temperatures from 550 to 600 °C. The better durability is attributed to that the reduction of the surface area and the formation and subsequent growth of crystalline WO 3 upon aging are more remarkably inhibited. 相似文献
20.
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
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