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1.
In this work, we explored the potential of mesoporous zeolite-supported Co–Mo catalyst for hydrodesulfurization of petroleum resids, atmospheric and vacuum resids at 350–450°C under 6.9 MPa of H 2 pressure. A mesoporous molecular sieve of MCM-41 type was synthesized; which has SiO 2/Al 2O 3 ratio of about 41. MCM-41 supported Co–Mo catalyst was prepared by co-impregnation of Co(NO 3) 2·6H 2O and (NH 4) 6Mo 7O 24 followed by calcination and sulfidation. Commercial Al 2O 3 supported Co–Mo (criterion 344TL) and dispersed ammonium tetrathiomolybdate (ATTM) were also tested for comparison purposes. The results indicated that Co–Mo/MCM-41(H) is active for HDS, but is not as good as commercial Co–Mo/Al 2O 3 for desulfurization of petroleum resids. It appears that the pore size of the synthesized MCM-41 (28 Å) is not large enough to convert large-sized molecules such as asphaltene present in the petroleum resids. Removing asphaltene from the resid prior to HDS has been found to improve the catalytic activity of Co–Mo/MCM-41(H). The use of ATTM is not as effective as that of Co–Mo catalysts, but is better for conversions of >540°C fraction as compared to noncatalytic runs at 400–450°C. 相似文献
2.
Small Co clusters ( d<10 nm) supported over mixed La–Co–Fe perovskites were successfully synthesized. These catalysts were active for Fischer–Tropsch (FT). Depending on the Co to Fe ratios the mixed perovskite exhibited two different forms: the rhombohedral phase of LaCoO 3 is maintained for the mixed perovskite when x>0.5, the orthorhombic phase of LaFeO 3 is found for x<0.5. Interestingly only one of these structures is active for the FT reaction: the orthorhombic structure. This is most likely due to the capacity of this material to maintain its structure even with a high number of cation vacancies. These cations (mostly Co) were on purpose extracted and reduced. Magnetic measurements clearly showed their metallic nature. Rhombohedral Co–Fe mixed perovskites ( x≥0.5) cannot be used as precursors for Fischer–Tropsch catalysts: their partial reduction only consists in a complete reduction of Co 3+ into Co 2+. The partial reduction of orthorhombic perovskites (x<0.5) leads to active Fischer–Tropsch (FT) catalysts by formation of a metal phase well dispersed on a cation-deficient perovskite. The FT activity is related to the stability of the precursor perovskite. When initially calcined at 600 °C, a maximum of 8.6 wt.% of Co0 can be extracted from LaCo0.40Fe0.60O3 (compared to only 2 wt.% after calcination at 750 °C). The catalyst is then composed of Co0 particles of 10 nm on a stable deficient perovskite LaCo0.053+Fe0.603+O2.40. Catalytic tests showed that up to 70% in the molar selectivity for hydrocarbons was obtained at 250 °C, 40% of which was composed of the C2–C4 fraction. 相似文献
3.
In this work the catalytic behaviour of pure zinc manganite, ZnMn 2O 4, and cobalt–zinc manganites for the reduction of NO by propane and propene is reported. The NO and N 2O decomposition as well as the reduction of N 2O by propane and propene were also investigated. The catalysts are prepared starting from carbonate monophasic precursors that are decomposed in air at 973 K for 24 h. In all cases a spinel-like phase is obtained. Pure zinc manganite is an efficient catalyst for the NO reduction with both propane and propene and the selectivity to N 2 and CO 2 was almost one. However the presence of cobalt in the catalyst enhances the catalytic activity, in particular when propene is used as reducing agent of NO. All catalysts are stable up to 873 K upon contacting with the propane containing reactant stream whereas in the case of propene they preserve the original spinel structure up to about 773 K. In fact with propene the catalysts start to lose their stability as the reaction temperature increases above 773 K and disaggregate, by reduction of the spinel framework Mn 3+ cations to Mn 2+, forming a complex mixture of ZnO and MnO oxides. Despite the collapsing of the spinel phase, the disaggregated polyphasic catalysts still show a good activity and selectivity. An hypothesis for explaining this unusual behaviour is formulated. Finally, the reaction mechanisms presented in literature are consequently revisited on the basis of the results found in this work. 相似文献
4.
Supported nickel phosphides were prepared by treating an amorphous Ni–B alloy on silica–alumina support with phosphine (15 vol.% PH 3/H 2) at relatively low temperature. The amorphous Ni–B/SiO 2–Al 2O 3 precursors were synthesized by silver-induced electroless plating. The amorphous precursors and catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, BET surface area and inductively coupled plasma measurements. The transmission electron micrographs of the Ni 2P/SiO 2–Al 2O 3 particles with their size ranging from 60 to 80 nm showed that they were homogeneously dispersed over the SiO 2–Al 2O 3 support. The as-prepared catalysts exhibited an excellent catalytic activity in the hydrodesulfurization (HDS) of dibenzothiophene. 相似文献
5.
This study reports new gallium-promoted copper-based catalysts prepared by co-impregnation of methoxide–acetylacetonate (acac) precursors from methanolic solutions onto silica and zinc oxide supports. Catalyst performance in the CO 2 hydrogenation to methanol was investigated at 2 MPa and temperatures between 523 and 543 K. A high activity and selectivity for ZnO-supported catalysts was found, which also showed a high stability in terms of both activity and selectivity. The maximum value for the activity was 378 g MeOH/kg cat h at 543 K, with a selectivity of 88% towards methanol production. The high performance of these materials in the CO 2 hydrogenation is related to the presence of Ga 2O 3 promoter and highly dispersed Cu + species on the surface, determined by XPS and Auger on used catalysts. 相似文献
6.
Manganese substituted hexaaluminate has been prepared using environmentally benign surfactants such as Triton X-100, under ambient condition with a commercial alumina sol and metal acetate precursors. The surface area of the pure alumina can be controlled to 10–70 m 2 g −1 using cetyltrimethylammonium chloride after heating in oxygen flow at 1200°C for 6 h. The crystal structure of the obtained alumina was high purity θ-Al 2O 3. Incorporation of La and Mn leads to the formation of the high purity manganese substituted hexaaluminate with a surface area of 30–40 m 2 g −1 which is also controllable using organic additives such as urea. The catalytic activity of the manganese substituted hexaaluminate was comparable to the sol–gel derived hexaaluminate catalyst from metal alkoxides. 相似文献
7.
Supported LaCoO 3 perovskites with 2, 5, 10, 15, 20 and 30 wt.% loading were prepared by impregnation of a Ce 0.8Zr 0.2O 2 support (40 m 2 g −1) with: (i) a solution of La and Co nitrates and (ii) a “citrate” solution, namely containing La and Co nitrates, and citric acid. All precursors were decomposed and calcined at 700 °C for 5 h. XRD investigations indicated the formation of a pure perovskite phase only if citrates were used. These materials were tested as catalysts for methane combustion in the temperature range 300–700 °C. All catalysts showed a lower T50 (the temperature at which the conversion level of methane is 50%) than the Ce 0.8Zr 0.2O 2 support or non-supported LaCoO 3. The activity increased continuously with the perovskite loading. The samples prepared from citrates were slightly more active than from nitrates. This is due to a more homogeneous surface, as indicated by XPS measurements. The presence of a well-characterized perovskite phase (as opposed to highly dispersed elements) seems necessary for good activity. A higher reaction rate per perovskite weight is observed for low loadings when compared to bulk LaCoO 3, but the variation with perovskite loading presents a breakpoint, suggesting complex interactions in the catalysts or in the oxidation mechanism. In spite of the experimental impossibility to evaluate the area developed by the supported perovskite, an approximative approach strongly suggests a synergy between the support and supported species. 相似文献
8.
The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO 2 (70, 85 wt.%)–Al 2O 3 (15, 0 wt.%)–WO x (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N 2 physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO 3 bulk phase. The catalysts increased their SBET for about 15% promoted by Al 2O 3 addition. Various oxidation states of WO x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W 6+ and reduced-state WO x species (either W 4+ or W 0). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers. 相似文献
9.
Co–Nb 2O 5–SiO 2 catalysts were prepared using three different sol–gel procedures: (i) the colloidal sol–gel method using NbCl 5 and SiCl 4 as precursors; (ii) the polymeric sol–gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol–gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl 4. In all procedures, the elimination of the solvent carried out between 80 and 110°C was followed by a reduction in hydrogen flow (30 ml min −1) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb 2O 5) were obtained. The characterization of the catalysts was performed using various techniques: N 2 adsorption and desorption curves at 77 K, NH 3- and H 2-chemisorption, TPO, XPS, XRD, and solid state 1H MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support. 相似文献
10.
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
11.
The catalytic activity and coke resistance of La 2O 3 promoted nickel-based catalysts are investigated in a fixed-bed flow reactor. The contents of carbon deposited on catalysts were measured by a carbon combustion method. Catalysts were characterized by CO–TPD, CO 2–TPD, TPR, XPS and XRD techniques, and the results were correlated with the coke resistance of the catalysts. It is found that the catalytic activity, resistance to carbon deposition and the stability of the catalysts can be greatly improved with the addition of a rare earth oxide. It is found that BaTiO 3 is an ideal support. Thus 5.0 wt.% Ni–0.75 wt.% La–BaTiO 3 catalyst shows great resistance to coke formation and higher thermal stability as well as higher catalytic activity, than the catalysts 5.0 wt.% Ni/La–BaTiO 3 (Ba/La = 1/0.002) and 5.0 wt.% Ni–1.5 wt.% La/BaTiO 3. 相似文献
12.
The role of La 2O 3 loading in Pd/Al 2O 3-La 2O 3 prepared by sol–gel on the catalytic properties in the NO reduction with H 2 was studied. The catalysts were characterized by N 2 physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO. The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La2O3 inclusion. The selectivity depends on the NO/H2 molar ratio (GHSV = 72,000 h−1) and the extent of interaction between Pd and La2O3. At NO/H2 = 0.5, the catalysts show high N2 selectivity (60–75%) at temperatures lower than 250 °C. For NO/H2 = 1, the N2 selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H2O vapor. The high N2 selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdOx phase interacting with La2O3. The formation of this phase is favored by the spreading of PdO promoted by La2O3. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al2O3 the O2 uptake is consistent with the oxidation of PdO to PdO2, and when La2O3 is present the O2 uptake exceeds that amount (1.5 times). La2O3 in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N2. 相似文献
13.
The hydrodechlorination of alachlor with hydrogen in aqueous phase was studied in a trickle bed reactor using different activated carbon-supported catalysts. The reactor was continuously fed with a 50 mg/L solution of alachlor in water and a H 2/N 2 gas stream. The variables studied were space-time (44.8–448.3 kg cat h/mol), H 2:N 2 volumetric ratio in the gas phase (1:1–1:4), temperature (308–373 K) and pressure (0.24–0.6 MPa). The results of the hydrodechlorination experiments were evaluated in terms of alachlor conversion and ecotoxicity of the exit stream. High conversion values and important reductions of ecotoxicity were obtained working under mild conditions of temperature (323–348 K) and pressure (0.24 MPa). Palladium catalysts supported on activated carbon were found as the most active in the hydrodechlorination of alachlor, although copper and nickel catalysts led also to high conversions in the 80–93% range. The hydrodechlorination of alachlor was performed successfully with metal loads between 0.5 and 2.5 wt.% on the catalysts. A significant metal leaching was observed from the nickel and copper catalysts, which negatively affected the ecotoxicity of the final effluents. Oxidative treatment of the activated carbon supports with nitric acid previous to the impregnation with the metal precursor improved the anchorage of the active phase and reduced leaching dramatically. Likewise, the activity was not influenced by the oxidation of the supports and reductions of ecotoxicity by more than 90% were observed. 相似文献
14.
Several solid catalysts (Co 3O 4/γ-Al 2O 3, Fe 2O 3/γ-Al 2O 3, Mn 2O 3/γ-Al 2O 3, Zn–Fe–Mn–Al–O, Pt/γ-Al 2O 3, Ru/CeO 2, Ru/C) have been prepared and used to remove N-containing organic contaminants while processing toxic and hazardous industrial waste waters using wet oxidation by air (WAO). The autoclave tests of catalysts were done to reveal the main advantages of catalysts in water presence at high pressures and temperatures. Catalyst activity was determined with regard to oxygen interaction with model mixtures (water–organic contaminant: acetonitrile, carbamide, dimethyl formamide, or multi-component mixture of aliphatic alcohols). Activity tests were done in a static reactor under ideal mixing regime. Reagents and products were monitored using gas chromatograph Cvet-560, Millichrom-1 HPLC, and routine chemical analysis. Optimum process conditions for the best catalyst (Ru/graphite-like carbon) are as follows: partial oxygen pressure – 1.0 MPa, temperature – 473–513 K. At 0.5–5.0 MPa total pressure and 433–523 K catalysts show high water-resistance and high activity level (residual content of toxic compounds is less than 1%, and no NO x and NH 3 are detected). There are no legal restrictions on catalysts operation, since they are harmless to environment. 相似文献
15.
Fischer–Tropsch synthesis was carried out in slurry phase over uniformly dispersed Co–SiO 2 catalysts prepared by the sol–gel method. When 0.01–1 wt.% of noble metals were added to the Co–SiO 2 catalysts, a high and stable catalytic activity was obtained over 60 h of the reaction at 503 K and 1 MPa. The addition of noble metals increased the reducibility of surface Co on the catalysts, without changing the particle size of Co metal significantly. High dispersion of metallic Co species stabilized on SiO 2 was responsible for stable activity. The uniform pore size of the catalysts was enlarged by varying the preparation conditions and by adding organic compounds such as N, N-dimethylformamide and formamide. Increased pore size resulted in decrease in CO conversion and selectivity for CO 2, a byproduct, and an increase in the olefin/paraffin ratio of the products. By modifying the surface of wide pore silica with Co–SiO 2 prepared by the sol–gel method, a bimodal pore structured catalyst was prepared. The bimodal catalyst showed high catalytic performance with reducing the amount of the expensive sol–gel Co–SiO 2. 相似文献
16.
Coprecipitated Fe-Al 2O 3, Fe-Co-Al 2O 3 and Fe-Ni-Al 2O 3 catalysts is shown to be very efficient in carbon deposition during methane decomposition at moderate temperatures (600–650 °C). The carbon capacity of the most efficient bimetallic catalysts containing 50–65 wt.% Fe, 5–10 wt.% Co (or Ni) and 25–40 wt.% Al 2O 3 is found to reach 145 g/g cat. Most likely, their high efficiency is due to specific crystal structures of the metal particles and formation of optimum particle size distribution. According to the TEM data, catalytic filamentous carbon (CFC) is formed on them as multiwall carbon nanotubes (MWNTs). The phase composition of the catalysts during methane decomposition is studied using a complex of physicochemical methods (XRD, REDD, Mössbauer spectroscopy and EXAFS). Possible mechanisms of the catalyst deactivation are discussed. 相似文献
17.
Alumina–titania supports containing 5–50 wt.% of TiO 2 were prepared by coprecipitation method using inorganic precursors (sodium aluminate and titanium chloride). DTA-TGA, XRD, SEM, TPD NH3, and IR spectroscopy were used to characterise these materials. The study shows that the promoting effect of nickel on the HDS activity of molybdenum catalysts supported on Al 2O 3TiO 2 is significantly lower than that for molybdenum catalyst supported on Al 2O 3, and depends on the TiO 2 content. The SEM results show that in the case of rich Al support (20 wt.% of TiO 2) molybdenum was aggregated on the external surface of the catalyst, whereas it was uniformly dispersed on the external surface of alumina. Results also show that molybdenum is preferably supported on aluminum oxide. Application of Al 2O 3TiO 2 oxides enhances the HDN activity of nickel–molybdenum catalysts. The highest HDN efficiency was obtained for the NiMo/Al 2O 3TiO 2 catalyst containing 50 wt.% of TiO 2. HDN activity was found to depend on protonic acidity and anatase content. 相似文献
18.
Supported LaCoO 3 perovskites with 10 wt.% loading were prepared by impregnation of different supports containing ceria with a solution of La and Co nitrates and citric acid. All precursors were calcined at 700 °C for 5 h. XRD investigations indicated the perovskite formation via “citrate” precursor only on ceria support. All catalysts were tested for toluene total oxidation in the temperature range 100–600 °C. In spite of a large surface area, alumina-supported perovskites showed a lower global activity. It appears then the necessity of the presence of a perovskite phase for good oxidative activity. In terms of reaction rates higher reaction rates per perovskite weight were observed for all supported catalysts when compared to bulk LaCoO 3. 相似文献
20.
The NiSO 4 supported on Fe 2O 3-promoted ZrO 2 catalysts were prepared by the impregnation method. Fe 2O 3-promoted ZrO 2 was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe 2O 3–ZrO 2. The addition of nickel sulfate (or Fe 2O 3) to ZrO 2 shifted the phase transition of ZrO 2 (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Fe 2O 3) and ZrO 2. 15-NiSO 4/5-Fe 2O 3–ZrO 2 containing 15 wt.% NiSO 4 and 5 mol% Fe 2O 3, and calcined at 500 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO 4/Fe 2O 3–ZrO 2 catalysts was very effective for ethylene dimerization even at room temperature, but Fe 2O 3–ZrO 2 without NiSO 4 did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe 2O 3 up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Fe 2O 3 and ZrO 2 and due to consequent formation of Fe–O–Zr bond. 相似文献
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