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1.
Fong-Chang Sheu Cheng-Tsung Hong Wen-Long Hwang Cheng-Jec Shih Jung-Chung Wu Chuin-Tih Yeh 《Catalysis Letters》1992,14(3-4):297-304
A series of alumina aluminum borate (AAB) with various Al/B molar ratios were prepared by the coprecipitation method. The supported rhenium oxide catalysts with various contents of Re2O7 were also prepared by the impregnation method with perrhenic acid. The catalytic activity and stability of Re2O7/AAB catalysts for the reaction of propylene metathesis were tested in a fixed-bed microreactor. It was found that Re2O7/AAB is more active, stable and regenerable than Re2O7/Al2O3 for propylene metathesis. The optimum Al/B molar ratio was found to be in the range of 4–10. 相似文献
2.
New catalysts for olefin metathesis are obtained upon interaction between rhenium trisacetylacetonate and -Al2O3 surface. After high temperature treatment in flows of O2 and N2 and addition of organometallic compound as a cocatalyst the activity of the resulting catalyst exceeds that of known Re/Al2O3 catalysts prepared by impregnation. The catalysts exhibit maximal activity at a cocatalyst surface concentration of 3 × 10–7 mol/m2. Further increase of the cocatalyst concentration leads to deactivation. 相似文献
3.
J. C. Mol 《Catalysis Letters》1994,23(1-2):113-118
Photoreduction of MoO3/SiO2 and MoO3/SiO2·Al2O3 catalysts in CO with a laser beam at 308 nm resulted, after addition of cyclopropane to form the active sites, in a high activity for alkene metathesis. Both catalyst systems are active for normal alkenes, e.g. propene, and for functionalized alkenes, e.g. methyl oleate, already at room temperature. 相似文献
4.
《Journal of Industrial and Engineering Chemistry》2014,20(1):145-152
The metathesis of ethylene and 2-pentene for propylene production was investigated over Re2O7/SiO2-Al2O3 catalysts. The SiO2-Al2O3 (50 wt% Al2O3) were obtained by co-precipitation, physical mixing, and sol–gel coating. The presence of isolated layers/grains γ-Al2O3 either in bulk (physical mixing) or on the surface (sol–gel coating) resulted in isomerization-free metathesis. On the contrary, the Re2O7 catalysts supported on co-precipitated SiO2-Al2O3 or the direct synthesis showed both metathesis and double-bond shift isomerization activities and as a consequence, higher propylene yield was obtained via the secondary metathesis reaction. The catalytic properties were also correlated with the Al-atom rearrangements and the acidic characters/strengths. 相似文献
5.
Influence of feed components on the activity and stability of cobalt molybdenum alumina metathesis catalyst 总被引:1,自引:0,他引:1
Alkene metathesis plays a vital role industrially in the upgrading of low value alkenes to higher value alkenes such as linear internal alkenes in the C10–C18 range. These in turn find application as feedstock for manufacturing of surfactants and detergents. Industrial alkene cuts contain component(s) that might be detrimental to the catalyst active sites during the metathesis reaction leading to catalyst deactivation. The focus of this study was to investigate the effect of some of the components present in typical low value feed streams on the activity and stability of a CoO/MoO3/Al2O3 catalyst. The results indicated that the feed composition does have a major influence on the metathesis reactivity of the catalyst. Pure 1-octene (98%), which was used as a reference feed was spiked with various components that had a concentration of 100 ppm. Results revealed a trend in terms of the severity of the component that deactivated the catalyst to be water > methylcyclopentadiene dimer > methylcyclopentane > toluene > 2-pentanone > 2-methyl-1,5-hexadiene > 2-methyl-1-hexene > butanol.
A study was also undertaken to examine whether the component (methylcyclopentadiene dimer as an example) that deactivates the catalyst is a temporary or permanent poison. Results showed that methylcyclopentadiene dimer is a temporary poison. The carbonaceous deposits (oligomers) formed during the reaction seem to be the primary cause of catalyst deactivation. However, the catalyst deactivation mechanism in the presence of water in 1-octene feed is mostly linked to the molecular structural change of the catalyst rather than accumulation of carbonaceous deposits on the surface of the catalyst. 相似文献
6.
A set of Co promoted 10% Mo/Al2O3 samples have been characterized by means of Raman spectroscopy under ambient as well as in situ dehydrated conditions. Under ambient conditions, the degree of the polymerization of surface molybdenum oxide species decreases with increasing Co loading. Under dehydrated conditions, the polymeric molybdenum oxide species is absent with the addition of only 0.2% Co. At low Co loadings (2%), before the formation of CoMoO4 compound, the spectral features are very similar under ambient conditions. Dehydration causes the upward shift of the Mo=O symmetric stretching mode. A broad band around 920–930 cm–1 was thus observed. This band has been suggested to be associated with the Co-Mo interaction species. In contrast to crystalline CoMoO4, this species shows a reversibility on H2 reduction-O2 reoxidation treatments. From the results obtained, it is proposed that cobalt oxide interacts with the most polymerized molybdenum oxide species to form Co-Mo interaction species and/or crystalline CoMoO4; therefore, the amount of the surface molybdenum oxide species decreases with a change in the molecular structure as a function of the Co concentration. 相似文献
7.
Dalmo Mandelli Marcelo J. D. M. Jannini Regina Buffon Ulf Schuchardt 《Journal of the American Oil Chemists' Society》1996,73(2):229-232
Impregnation of SiO2.Al2O3 (24.3% Al2O3 with 6% B2O3 increases the activity of supported Re2O7 in the ethenolysis of methyl oleate, but reduces the activity of CH3ReO3 on the same support. Re2O7/SiO2.Al2O3/B2O3-SnBu4 is shown to be an effective catalyst for the ethenolysis of methyl linoleate and of the methyl esters of olive oil, and can
be recycled after calcination at least five times without loss of activity. 相似文献
8.
Laser Raman spectroscopy was used to characterize alumina-supported molybdenum and tungsten oxides at loadings ranging from 0.5 to 15 wt% Mo and 0.5 to 30 wt% W. The structure of calcined Mo6+/Al2O3 and W6+/A12O3 was governed by the point of zero surface charge of each system, with the point of zero surface charge being dependent on metal loading. The structures formed by the molybdenum and tungsten overlayers at the sample point of zero surface charge were found to be analogous to the structures formed by molybdenum and tungsten oxyanions in aqueous solution at a solution pH equal to the sample point of zero surface charge. 相似文献
9.
Two catalysts, alumina and manganese oxide supported on alumina, have been prepared by calcination and precipitation-impregnation methods, respectively. The catalysts are characterised by the following techniques: Brunner-Emmett-Teller-N2 adsorption-desorption for surface area, temperature programmed desorption of NH3 and n -butyl amine back titration methods for surface acidity, powder X-ray diffraction for textural properties, and Fourier transform infrared spectroscopy for the anionic radicals. The catalytic activity has been determined under heterogeneous conditions in the condensation reaction between o -phenylenediamine and benzil. The product purity is checked by thin-layer chromatography and melting point. The products are also analysed by LC-MS and 1H-NMR techniques. The yields of the products have been found to be good and catalysts exhibited excellent recyclability. The effect of changing the reaction parameters such as temperature, reaction time, amount of the catalyst, nature of solvent and molar ratio of reactants on the yield of the product has been studied. The surface acidity of the catalysts plays an important role in activating the reaction. 相似文献
10.
11.
Gaigneaux Eric M. Liu Haichao Imoto Hideo Shido Takafumi Iwasawa Yasuhiro 《Topics in Catalysis》2000,11(1-4):185-193
The catalytic performance of a novel SbRe2O6 compound has been investigated in the selective oxidation of isobutylene to methacrolein at 673 K. The initial reactivity
of the catalyst strongly depended on catalyst pretreatment conditions. The catalyst was more active after pretreatments under
more oxidative atmospheres. However, the activity of the catalyst always reached an identical level at the steady state, independent
of the pretreatment conditions. Scanning electron microscopy and in situ confocal Raman microscopy revealed that the reactivity
of SbRe2O6 was attributable to the presence at its surface of Re2O7 which benefitted from a cooperation with Sb4Re2O13. The two phases resulted from a partial decomposition of SbRe2O6 in the presence of oxygen. When deposited on Sb4Re2O13, Re2O7 was stabilized and did not volatilize under the reaction conditions. The phenomenon is likely the origin of the cooperation
between Sb4Re2O13 and Re2O7.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
13.
规整填料型加氢脱硫催化剂的制备及性能评价 总被引:3,自引:0,他引:3
用电化学方法制备多孔氧化铝膜,并负载Mo-Co活性组分制得了金属支撑-多孔层规整填料型加氢催化剂。采用BET和SEM技术表征了多孔性氧化铝膜的物理结构,并考察了电解及后处理条件的影响。结果表明,电解液浓度、氧化时间、水封时间、水封温度等对多孔氧化铝膜的比表面积影响显著。采用二次氧化的方法,在质量分数为4%的草酸电解液、氧化时间1 h、80℃水封3 h条件下,所制备的多孔氧化铝膜具有相对较大的比表面积。汽油重馏分加氢反应结果表明该类催化剂具有较高的催化活性和选择性。 相似文献
14.
M. Zdražil 《Catalysis Letters》1994,27(3-4):337-344
A new slurry impregnation method (SIM) of the preparation of a catalyst or catalyst precursor MoO3/Al2O3 is described. Aqueous slurry of powdered MoO3 is mixed with alumina extradátes and the mixture is refluxed. A low solubility of MoO3 is sufficient for transport of MoO3 from powder form via solution to the surface of the support. The catalysts were tested by hydrodesulfurization of thiophene at 1.6 MPa and 280–400°C. Their activity was similar to the activity of industrial and laboratory MoO3/Al2O3 samples prepared by conventional impregnation with solution of ammonium heptamolybdate. The advantage of the SIM method is that calcination, producing nitrogeneous waste gases, is not required and that all deposited molybdenum species are adsorbed and not precipitated. 相似文献
15.
For a series of catalysts containing 1 wt. % Pt and SnPt ratios ranging from ca. 1 to 8, the only crystalline alloy phase detected by XRD was SnPt (11). The XRD intensity of lines for the SnPt (11) alloy phase increase with increasing SnPt ratios, indicating the presence of unalloyed Pt in the samples containing low tin loadings. 相似文献
16.
Øyvind Borg Edd A. Blekkan Sigrid Eri Duncan Akporiaye Bente Vigerust Erling Rytter Anders Holmen 《Topics in Catalysis》2007,45(1-4):39-43
The effect of calcination temperature and atmosphere on the properties of γ-Al2O3 supported cobalt Fischer-Tropsch catalysts has been investigated. One common precursor for all the catalysts was prepared
by incipient wetness impregnation of γ-Al2O3 with an aqueous solution of cobalt nitrate hexahydrate. It was subjected to four different calcination atmospheres (air/50%
steam: 30 mL/min, air: 30 mL/min, air: 50 mL/min, N2: 30 mL/min) and eight different calcination temperatures (range: 473–723 K), making the total number of samples 32. Both
the post calcination nitrogen content and the cobalt dispersion were measured. The results demonstrated that in order to maximise
the cobalt dispersion, it is necessary to use low calcination temperatures and remove the precursor decomposition products
(NO, NO2, H2O) efficiently. The Fischer-Tropsch synthesis performance of two catalysts calcined at the same temperature, but at different
air flow rates was evaluated. No significant effect of the air flow rate was found on the turnover frequency or C5+ selectivity, but a high flow rate resulted in 30% higher activity per gram catalyst. 相似文献
17.
For several decades olefin metathesis reactions over supported Mo, W, and Re oxides catalysts have attracted remarkable interest owning to their growing industrial applications. Therefore, particular attention was devoted to improve the catalytic activity of these catalysts. In the way of exploration of the catalytic performances of these heterogeneous Mo, W, and Re oxides systems, it was found that high dispersion of metal oxide on the support surface and the oxidation state of the metal oxide on the surface of catalyst play crucial factors on the catalysts efficiency. Importantly, these factors have an origin in the preparation methods and the properties of the used supports. In this regard, we have tried to address the various preparation methods of immobilized Mo, W, and Re oxide catalysts as well as properties of supporting material to better understand their impacts on the catalytic performances of these catalysts. 相似文献
18.
Samuel D. Jones Luke M. Neal Helena E. Hagelin-Weaver 《Applied catalysis. B, Environmental》2008,84(3-4):631-642
Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N2O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH2O formation. The lower catalytic activity may be due to strong Cu-Al2O3 interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH2O formation, which at low Cu concentrations is not reformed to CO2 and H2. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu2O is present on the spent nanoparticle catalysts and it is likely that the Cu+/Cu0 ratio is of importance both for the catalytic activity and the CO selectivity. 相似文献
19.
The application of in situ Raman, IR, and UV-Vis DRS spectroscopies during steady-state methanol oxidation has demonstrated
that the molecular structures of surface vanadium oxide species supported on metal oxides are very sensitive to the coordination
and H-bonding effects of adsorbed methoxy surface species. Specifically, a decrease in the intensity of spectral bands associated
with the fully oxidized surface (V5+) vanadia active phase occurred in all three studied spectroscopies during methanol oxidation. The terminal V = O (∼1030 cm−1) and bridging V–O–V (∼900–940 cm−1) vibrational bands also shifted toward lower frequency, while the in situ UV-Vis DRS spectra exhibited shifts in the surface
V5+ LMCT band (>25,000 cm−1) to higher edge energies. The magnitude of these distortions correlates with the concentration of adsorbed methoxy intermediates
and is most severe at lower temperatures and higher methanol partial pressures, where the surface methoxy concentrations are
greatest. Conversely, spectral changes caused by actual reductions in surface vanadia (V5+) species to reduced phases (V3+/V4+) would have been more severe at higher temperatures. Moreover, the catalyst (vanadia/silica) exhibiting the greatest shift
in UV-Vis DRS edge energy did not exhibit any bands from reduced V3+/V4+ phases in the d–d transition region (10,000–30,000 cm−1), even though d–d transitions were detected in vanadia/alumina and vanadia/zirconia catalysts. Therefore, V5+ spectral signals are generally not representative of the percent vanadia reduction during the methanol oxidation redox cycle,
although estimates made from the high temperature, low methoxy surface coverage IR spectra suggest that the catalyst surfaces
remain mostly oxidized during steady-state methanol oxidation (15–25% vanadia reduction). Finally, adsorbed surface methoxy
intermediate species were easily detected with in situ IR spectroscopy during methanol oxidation in the C–H stretching region
(2800–3000 cm−1) for all studied catalysts, the vibrations occurring at different frequencies depending on the specific metal oxide upon
which they chemisorb. However, methoxy bands were only found in a few cases using in situ Raman spectroscopy due to the sensitivity
of the Raman scattering cross-sections to the specific substrate onto which the surface methoxy species are adsorbed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The latest developments in the immobilization of well-defined transition metal-based catalysts relevant for CC and CSi coupling reactions are summarized. In this context, both ruthenium- and molybdenum-based metathesis as well as hydrosylation catalysts are covered. Particular attention will be attributed to synthetic aspects of the novel immobilization techniques as well as comparisons between the catalytic activities of the immobilized catalysts and their parent homogeneous systems. Finally, the influence of the chemical nature of both the support and linker on catalysts characteristics will be discussed. 相似文献