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1.
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
2.
This is the first report of a group study on the preparation of a MoO 3/Al 2O 3 catalyst to find predominant preparation parameters for better and reproducible catalyst preparations. Variously prepared MoO 3/Al 2O 3 catalysts possessing 13 wt% MoO 3 were subjected to multiprong characterizations and catalytic tests. It was found that the surface area of the support was the most predominant preparation parameter for the dispersion of Mo oxide species; the dispersion increased as the surface area of the support increased. The formation of crystalline MoO 3 was observed at a surface Mo concentration higher than 3.2 Mo nm −2. With sulfided MoO 3/Al 2O 3, it was established that the dispersion of Mo sulfide species increased with increasing surface area of the support and was in proportion to that of Mo oxide precursor species. The hydrodesulfurization activity of sulfided MoO 3/Al 2O 3 was proportional to the NO adsorption capacity. It is suggested that a homogeneous distribution of Mo oxide species is attained by an equilibrium adsorption technique. However, it was revealed that the surface area of the catalyst and Mo distribution were considerably modified by preparation parameters, such as drying processes, other than the surface area. 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.
A new preparation method for supported MoO 3 catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO 3/water is used instead of the solution ammonium heptamolybdate, AHM [(NH 4) 6Mo 7O 24]. The MoO 3/γ-alumina, MoO 3/active carbon, and MoO 3/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO 3 was sufficient to transport molybdenum species from solid MoO 3 to the adsorbed phase. The equilibrium was achieved after several hours at 95 °C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250 °C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180 °C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO 3/γ-Al 2O 3 catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO 3/SiO 2 catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH 4) 6Mo 7O 24. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction. 相似文献
5.
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
6.
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
7.
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
8.
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
9.
The effect of deposition and order of potassium introduction on the texture and activity of Mo/γ-Al 2O 3 catalysts in water gas shift (WGS) reaction was investigated. The samples were synthesised by incipient wetness impregnation of the carrier with aqueous solutions of the corresponding salts followed by drying and calcination after each deposition step. The prepared catalyst precursors were sulphided at 400°C for 2 h with 6% H 2S in H 2 before testing in WGS reaction in a glass flow apparatus at 400°C under atmospheric pressure. The results show that potassium deposition alone on the bare γ-Al2O3 (sample K/Al2O3) decreases the specific surface after calcination by blocking the constrictions between the pores in the primary porous texture. In the WGS reaction conditions part of the pores are deblocked and a redistribution in the pore volumes occurs. The deposition of the Mo (sample Mo/Al2O3) also results in a decrease in both specific surface and total pore volume with respect to the bare support. However after catalytic activity test no substantial changes in its texture were observed. The addition of K to the Mo (sample KMo/Al2O3) leads to nonuniformity in distribution of molybdenum–oxygen entities due to partial migration of the MoOx species to the external surface. The specific surface is not changed during the reaction test. The deposition of Mo on K/Al2O3 contributes to the uniform distribution of oxomolybdenum species in the porous texture of the support. This uniformity is preserved to a high extent in the catalytic reaction as well. The activity in the synthesised samples in the WGS reaction decreases in the order MoK/Al2O3 > Mo/Al2O3 > KMo/Al2O3. 相似文献
10.
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
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.
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
13.
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
14.
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
15.
The selective catalytic hydrogenation of naphthalene to high-value tetralin was systematically investigated. A series of Al 2O 3 catalysts containing different active metals (Co, Mo, Ni, W) were prepared by incipient wetness impregnation. The effects of different active metals forms (oxidation, reduction, sulfuration) and reaction conditions on naphthalene hydrogenation were investigated and the catalysts were characterized by XRD, XPS, BET, NH 3- TPD and SEM. Especially, Ni-Mo/Al 2O 3 was first used in this reactive system. The results show that the oxidative 4%NiO-20%MoO 3/Al 2O 3 is the best catalyst for the preparation of tetralin. The conversion of naphthalene and the selectivity of tetralin can reach 95.62% and 99.75% respectively at 200 ℃, 8 h and 6 MPa. Compared with reduced and sulfureted 4%NiO-20%MoO 3/Al 2O 3 catalysts, oxidative 4%NiO-20%MoO 3/Al 2O 3 has a well dispersed and uniform monolayer of the active metals, larger pore volume and size, and larger total acidity. NiO-MoO 3/Al 2O 3 has a synergistic effect between NiO activity and MoO 3 selectivity. 相似文献
16.
The binding of vanadium and nickel porphyrins to γ-Al 2O 3, SiO 2-Al 2O 3 MoO 3/Al 2O 3, NiO/Al 2O 3, and to Co- and Ni-Mo/Al 2O 3 catalysts in their oxide and sulfide forms, and their subsequent decomposition reactions when heated in nitrogen or exposed to hydrogen and thiophene in catalytic hydrodesulfurisation, have been studied by electron spin resonance. We wished to discover which part of the porphyrin molecule became bound to the catalyst and to which surface sites. Our main conclusions are that the porphyrins are bound to the catalyst by a donor-acceptor interaction,, the delocalised π-system of the porphyrin ring being the electron donor, and the Bronsted and/or Lewis acid function of the catalyst being the acceptor. Depending on the conditions, oxidation or hydrogenation of the porphyrin ring at the meso carbons is the initial stage in the decomposition of the bound porphyrins. 相似文献
17.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
18.
以不同孔道结构Al_2O_3作载体,甲醇、乙醇和柠檬酸作分散剂,通过等体积浸渍法制备系列Co/Al_2O_3费托合成催化剂。采用XRD、TG-DSC和H2-TPR等考察制备方法对催化剂结构的影响,并在固定床反应器中对催化剂进行性能评价。结果表明,采用具有适宜孔道结构Al_2O_3作载体才能获得综合性能较好的催化剂,3种分散剂的加入,促进了钴物种在载体上的分散,增强了钴与载体间的相互作用,改善了催化剂费托合成反应活性,显著提高了重质烃时空收率。 相似文献
19.
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
20.
采用浸渍法制备了一系列具有不同CuO含量的Pd-CuO/Al 2O 3催化剂,并将其用于乙醇氧化反应,其结构与性质通过XRD、H 2-TPR和NH 3-TPD等手段进行分析。结果发现,催化剂的活性并不是随着CuO含量的增加而增强,Pd-1.0%CuO/Al 2O 3催化剂表现出最佳的活性,其点火温度和完全转化温度比Pd/Al 2O 3催化剂至少降低了50℃。与Pd/Al 2O 3催化剂相比,含CuO催化剂增强的衍射峰强度以及氢化钯分解峰的消失,说明Pd-Cu合金结构的形成有利于Pd、Cu物种之间的协同作用。对于Pd-1.0%CuO/Al 2O 3催化剂来说,还原峰向低温的移动以及还原峰面积的增大说明该催化剂上氧化性物质更易被还原且数量在增加,这对于氧化反应是十分有利的,新出现的还原峰表示Pd、Cu的相互作用生成了新物种。NH 3-TPD结果中更高含量的低温酸有利于高活性,而且新出现的脱附峰说明形成了新的酸性位点。 相似文献
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