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1.
The WO3/SiO2 catalyst for propylene production by metathesis of ethylene and 2-butene was preheated at different temperatures to investigate the effect of calcination temperatures on the active species and elucidate the structure-reactivity relationship. The influence of calcination temperatures on the physicochemical properties of the catalyst, relating to the active species, was deduced from an array of characterization results. It has been found that the surface tetrahedral tungsten species with high metal-support interaction were formed on the catalyst calcined at 550°C as confirmed by Raman, UV-Vis and TPR-H2 spectra.  相似文献   

2.
An advanced heterogeneous catalyst for olefin disproportion was prepared by supporting WO3 on titanium-silica sieve (MTS-9). The nature of the surface tungsten oxide species present in these catalysts was determined as a function of tungsten oxide loading by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectra (UV–DRS) and ultraviolet–visible Raman (UV-Raman). The catalyst showed high activity for the metathesis of butene to propene. The active centers are not crystallites of WO3 but rather surface tungsten oxide species. The conversion of butene varies with the degree of catalyst loading.  相似文献   

3.
《Comptes Rendus Chimie》2015,18(6):644-653
Different gases were employed to pretreat WO3/SiO2 for the metathesis of 1-butene and ethene to propene. Air-pretreated WO3/SiO2 was inactive, whereas N2-, N2/H2-, and H2-pretreated WO3/SiO2 exhibited high 1-butene conversion and propene selectivity. Tetragonal WO3 and partially reduced WO2.92 were found to be the active phases/species, whereas monoclinic WO3 was inactive. N2/H2- and H2-pretreated WO3/SiO2 contained both W6+ and W5+ species (i.e., nonstoichiometric WO3−x). Air- and N2-pretreated WO3/SiO2 only contained monoclinic W6+ species (WO3) before the reaction. However, the used N2-pretreated WO3/SiO2 contained both W6+ and W5+ species, suggesting that the N2 pretreatment can facilitate the formation of some W5+ species during the reaction. This in situ partial reduction can activate the N2-pretreated WO3/SiO2 for the metathesis.  相似文献   

4.
A WO3/SiO2 catalyst is used in industry to produce propylene from 2-butene and ethylene metathesis. Catalysts with various WO3 loading (4% to 10%) were prepared by impregnation and tested for the metathesis of ethene and trans-2-butene. Ion exchange of NaOH onto the WO3/SiO2 catalyst was used to mitigate the acidity of the catalysts in a controlled way. At low WO3 loading, the treatment with large amounts of NaOH resulted in a significant decrease in metathesis activity concomitant with significant W leaching and marked structural changes (XRD, Raman). At higher WO3 loading (6% to 10%), the treatment with NaOH mainly resulted in a decrease in acidity. FT-IR experiments after adsorption of pyridine showed that the Lewis acidic sites were poisoned by sodium. Nevertheless, the metathesis activity remained constant after the NaOH treatment. This suggested that the remaining acidity on the catalyst was enough to ensure the efficient formation of the carbene active sites. Interestingly, Na poisoning resulted in some modification of the selectivity. The mitigation of acidity was shown to favor propene selectivity over the formation of isomerization products (cis-2-butene, 1-butene, etc.). Moreover, treatment with NaOH led to a shorter induction period and reduced coke formation on the WO3/SiO2 catalyst.  相似文献   

5.
A new propene production route from 1-butene metathesis has been developed on heterogeneous 10WO3/Al2O3-HY catalysts with different HY contents. It is found that the catalysts play bi-functionally first for the isomerization of 1-butene to 2-butene and then for the cross-metathesis between 1-butene and 2-butene to propene and 2-pentene. The combination of HY zeolite and Al2O3 is prerequisite for the production of propene. The propene yield keeps increasing with the HY content in the range of 10–70 wt%, where 10WO3/Al2O3-70HY exhibits the highest propene yield. The MS-H2-TPR and MS-O2-TPO characterizations indicate that the increase of HY content in the catalysts weakens the interaction between W species and supports, whereas enhance the probability of coking on the metal species and acid sites.  相似文献   

6.
Macro-/mesoporous Al2O3 supports were prepared by using monodisperse polystyrene (PS) microspheres as a template. The pore volume and BET surface area of the Al2O3 supports increased considerably with increasing amounts of the PS microspheres; further investigation showed that PS template only increased the volume of macro-pores but did not change the volume of meso-pores or micro-pores. Macro-/mesoporous Re2O7/Al2O3 metathesis catalysts were prepared through loading Re2O7 onto the as-prepared macro-/mesoporous Al2O3 supports, and their catalytic performance was tested in a fixed-bed tubular reactor using the metathesis of normal butylenes as a probe reaction. The results showed that the prepared macro-/mesoporous Re2O7/Al2O3 catalyst had high activity with consistent selectivity; propylene and pentene accounted for more than 90 wt% of the metathesis products, while the amount of ethylene plus hexane was less than 10 wt%, the majority of which was hexane. These Re2O7/Al2O3 catalysts had not only higher activity, but also longer working life span and higher tolerance to carbon residues than conventional Re2O7/Al2O3 catalysts.  相似文献   

7.
Deactivation by poisoning is studied in the metathesis of 2-butene to propene on mesoporous titanosilicate-supported WO3 (WO3/MTS–9), for which we focus on the effect of polar organic oxygenates on the activity of the catalyst. It is found that deactivation is strongly influenced by these oxygenates in feedstock, and the rate of deactivation increases with the increase of the polarity of the organic oxygenates. The deactivation by poisoning is reversible. The deactivation catalyst can be recovered by treatment in a nitrogen atmosphere at a high temperature.  相似文献   

8.
Summary The distribution of supported species in a series of W/TiO2 catalysts (1.8 – 28 wt% WO3) has been determined by Raman and X-ray photoelectron spectroscopy (XPS, ESCA). The results show that three tungsten species are present on oxidic W/TiO2 catalysts. A tungsten interaction species is formed almost exclusively for catalysts with W loadings lower or equal to 6.7 wt% WO3. WO3 is observed above 6.7 wt% WO3. For W loadings higher than 10 wt%, a disordered W species WDS is also present. The amounts of WDS and WO3 increase with increasing W content above 10 wt% WO3.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday  相似文献   

9.
Surface silanol structures, acid properties, and tungsten dispersion of the sol-gel-derived 7W/SiO2–xAl2O3 (x = 0.2–23 wt%) were investigated by means of 29Si, 27Al, and 1H MAS NMR, NH3-TPD, in-situ NH3-IR spectroscopy, XRD, and Raman spectroscopy. The surface silanol structure changed upon Al and tungsten loadings; however, loading of 1 wt% Al2O3 appeared to be the threshold for preserving the Si(OH)Al with isolated bridge after impregnation of 7 wt% W. The 7W/SiO2–1Al2O3 (1 wt% Al2O3) was also found to exhibit the lowest ratio of Bronsted to Lewis acid with the highest amount of Lewis acid sites and the best catalyst performances in propene self-metathesis at 550 °C in terms of both propene conversion and ethylene/butene selectivity. Despite its low tungsten dispersion, the metathesis activity was correlated well with the higher amount of tungsten carbene species, which were formed on the catalysts containing higher isolated bridge silanol and the presence of higher Lewis acid sites.  相似文献   

10.
The A1, O, AlO, A12O, Al2O2, WO2, and WO3, partial pressures in the vapor over Al2O3 in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1+, O+, AlO+, A12O+, Al2O2+, WO2+, and WO3+, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO3(g) = WO2(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A12O2 were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δat H o(AlO, g, 0) = 510.7 ± 3.3 kJ mol−1, Δat H o(Al2O, g, 0) = 1067.2 ± 6.9 kJ mol−1, and Δat H o(Al2O2, g, 0) = 1556.7 ± 9.9 kJ mol−1.  相似文献   

11.
Oxidative desulfurization (ODS) of organic compounds containing sulfur element from a model oil was performed using tungsten oxide catalysts supported on mesoporous silica with cubic Ia3d mesostructure, well-defined mesopores (7.2 nm), high surface area (719 m2/g), and three-dimensional pore network (WO x /KIT-6). The prepared WO x /KIT-6 catalysts (5–20 wt% WO x ) were characterized by X-ray diffraction analysis, N2 sorption measurements, electron microscopy, H2-temperature programmed reduction, Raman spectroscopy, and thermogravimetric analysis. Among the mesoporous catalysts, 10 wt% WO x /KIT-6 exhibited the best catalytic performance. Sulfur-containing organic compounds, such as dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene, were completely (100 %) removed from the model oil over 10 wt% WO x /KIT-6 catalyst in 2 h. In addition, the catalyst could be reused several times with only slight decrease in catalytic activity.  相似文献   

12.
Although surface of amorphous silica is widely accepted to be neutral or slightly acidic, siliceous mesoporous materials have been found to act as excellent acid catalysts by us and other groups. On the other hand the increment in propene production is one of the significant objectives to be achieved in the present petroleum chemistry. Especially the one-path conversion of ethene to propene (ETP reaction, 3C2H4 → 2C3H6) is the most desired process. In our efforts, the specific acid catalysis of mesoporous silica was combined with the catalysis of nickel ion, which could turn the new type of ETP reaction into reality. The one-path conversion of ethene was 68% and the propene selectivity was 48% with 43% of butenes in a continuous gas-flow system at 673 K and an atmospheric pressure. The reactivity of lower olefins and the dependences of the ETP reaction on the contact time and the partial pressure of ethene followed the reaction mechanism consisting of dimerization of ethene to 1-butene, isomerization of 1-butene to 2-, and metathesis of 2-butene and ETP. The Ni-loaded mesoporous silica catalysts were characterized mainly by EXAFS and TPR techniques. The local structures of the nickel species active for the ETP reaction were very similar to that of layered nickel silicate, while those on the inert catalysts were the same as that of NiO particles.
Masakazu IwamotoEmail:
  相似文献   

13.
Solid solution phases of a formula Fe8V10W16–xMoxO85 where 0≤x≤4, have been obtained, possessing a structure of the compound Fe8V10W16O85. It was found on the base of XRD and DTA investigations that these solution phases melted incongruently, with increasing the value of x, in the temperature range from 1108 (x=0) to 1083 K (x=4) depositing Fe2WO6 and WO3. The increase of the Mo6+ ions content in the crystal lattice of Fe8V10W16O85 causes the lattice parameters a=b contraction with cbeing almost constant. IR spectra of the Fe8V10W16–xMoxO85 solid solution phases have been recorded.  相似文献   

14.
Promoting effects of Mg in heterogeneous Mo/HBeta–Al2O3 catalyst have been carefully studied for cross-metathesis of ethene and butene-2 to propene. The catalyst shows good stability with Mg content in the range of 1–2 wt%. Such effect may be attributed to the elimination of weak acid sites through introduction of Mg which suppresses the side olefin oligomerization reaction, as evidenced from NH3-TPD and 1H MAS NMR results. Addition of more Mg content to 3 wt% may change the state and reducibility of Mo species, as indicated from the UV–vis, UV-Raman and H2-TPR measurements. The increasing difficulty for the reduction of Mo(VI) species is closely related with the poor performance of 3 wt% Mg–4Mo/HBeta–30% Al2O3 catalyst in the metathesis reaction.  相似文献   

15.
Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H2O2). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO3 crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO3 implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance.  相似文献   

16.
A new family of cobalt and rare-earth metal tungstates (CoRE2W2O10 where RE=Y, Dy, Ho and Er) were synthesized by heating in the solid-state equimolar CoWO4/RE2WO6 mixtures. The obtained compounds are isostructural and crystallize in the monoclinic system. They melt incongruently in an inert atmosphere at 1494 K (CoY2W2O10), 1523 K (CoDy2W2O10), 1517 K (CoHo2W2O10) and 1493 K (CoEr2W2O10). For each CoRE2W2O10 compound the solid product of melting is an adequate RE2WO6.  相似文献   

17.
We prepared PTA coating solution by hot plate evaporation, N2 bubbling evaporation, and rotary evaporation. N2 bubbling and rotary evaporation are very efficient way to synthesize PTA which reduces the synthesis process time to 1/5, compared to hot plate evaporation method. Another strong point is that N2 bubbling and rotary evaporation make it possible to control excess hydrogen peroxide and water contents in PTA. The PTA formula were WO3·0.13H2O2·10.0H2O for hot plate method, WO3·0.16H2O2·7.1H2O for N2 bubbling method, and WO3·0.15H2O2·3.00H2O for rotary evaporation method. Thermal analysis and mass spectroscopy analysis show that water is evaporated at around 100 °C and hydrogen peroxide is dissociated at the range of 150 and 250 °C. Amorphous phase of WO3 thin film prepared from rotary evaporated PTA solution has the best electrochromic property, light transmission difference from 91% at its bleached state and 5.5% colored state, and charge density of 22 mC/cm2. It is thought that the control of excess hydrogen peroxide and water contents in PTA is very important to enhance the electrochromic properties of WO3 thin film.  相似文献   

18.
Trimetallic NiMoW/Al2O3 catalyst was prepared using mixed H4SiMo3W9O40 heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al2O3 and NiW/Al2O3 catalysts based on H4SiMo12O40 and H4SiW12O40, respectively, were synthesized as reference samples. The use of mixed H4SiMo3W9O40 heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al2O3 catalyst. The synergistic enhancement of the activity of the NiMo3W9/Al2O3 catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.  相似文献   

19.
Mer-[Mo(CO)3(p-C5H4N-CN)3] was prepared by UV-irradiation of a THF solution of Mo(CO)6 and para-cyanopyridine under heating. The complex was characterized by FT-IR, MS, 1H and 13C NMR and showed catalytic activity for olefin hydroformylation (1-hexene, cyclohexene and 2,3-dimethyl-2-butene as model olefins; 600 psi synthesis gas (pCO/pH2 = 1); 100 °C; 24 h; toluene). An examination of the complex catalyzed hydroformylation of a real naphtha cut (El Palito refinery, Venezuela), under the same conditions, also showed activity in the conversion to oxygenated products.  相似文献   

20.
WO3 films have been prepared onto IrO2-coated Ti substrate by electro-deposition, and as-deposited and annealed films have been characterized by using Raman spectroscopy. It was found that the asdeposited film consists of orthorhombic WO3 · H2O phase, which transforms to amorphous WO3 by annealing at 250°C and to monoclinic phase by annealing at and above 350°C. All electrochemical experiments were carried on Ti/IrO2/WO3 annealed at 450°C. The open-circuit potential could change significantly due to the hydration of the coating film. However this process is fairly slow. Reproducible voltammograms could be obtained quickly, further revealing high electrochemical stability of the Ti/IrO2/WO3 electrode. And the shapes of CV show the approximate rectangular mirror image, showing the typical characteristic of capacitive behavior. The specific capacitance obtained at a scan rate of 50 mV s−1 is 46 F g−1.  相似文献   

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