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1.
The influence of the ZrO 2 support modification by Y 2O 3 and the presence of ethylenediamine (“en”) during the preparation of Co/ZrO 2 were studied and compared with a reference catalyst conventionally prepared by impregnation of ZrO 2 with an aqueous solution of Co(NO 3) 2. The effect of the en/Co molar ratio ( x = 1–3) was studied. Activation of cobalt species was followed by differential thermal and thermogravimetric analyses (DTA/TG) analyses and by specific surface area measurements which evidence the complete cobalt precursor decomposition at 450 °C, whatever the support composition and the en/Co molar ratio. The addition of an aqueous solution of ethylenediamine to a cobalt nitrate solution led to a strong increase in the catalytic activity of the activated solids for the toluene deep oxidation as compared to the reference catalyst. The best catalytic results were explained in terms of cobalt oxides dispersion (X-ray diffraction (XRD)) and also in terms of Co-support interaction (H 2-temperature-programmed reduction (TPR)). The generated cobalt species were reducible at much lower temperatures and were more active in the toluene total oxidation. Finally, an efficient catalyst was produced combining the modifications of the support by yttrium oxide and of the precursor (use of ethylenediamine). 相似文献
2.
Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO 2/Al 2O 3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO 3) 2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO 2 is highly dispersed on the surface of Al 2O 3 up to 10 wt.% ZrO 2, beyond this value tetragonal ZrO 2 is formed. The presence of a small amount of ZrO 2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO 2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO 2, but it does not accelerate the activity of 0.2% Pd/ZrO 2/Al 2O 3 for methane combustion. 0.2% Pd/ZrO 2/Al 2O 3 dried at 120 °C shows highest activity for CH 4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH 4 combustion. 相似文献
3.
The influence of different metal oxide supports (i.e. ZrO 2, ThO 2, UO 2, TiO 2 and SiO 2) on the performance of Ni- and/or Co-containing catalysts [Ni and/or Co/MO 2 mole ratio (where M=Zr, Th, U, Ti or Si)=1.0] in the oxidative methane-to-syngas conversion at very low contact time (GHSV=5.2×10 5 cm 3 g −1 h −1 at STP) was investigated. The nickel-containing ZrO 2, ThO 2 and UO 2 catalysts (with or without pre-reduction by hydrogen at 500°C) showed good performance in the process; the order of their performance is NiO–ThO 2>NiO–UO 2>NiO–ZrO 2. The NiO–TiO 2 showed appreciable catalytic activity only after its reduction at 800°C. However, this catalyst and the NiO–SiO 2 catalyst showed poor performance in the process. These two catalysts are also deactivated very fast, mostly because of sintering of Ni and/or formation of catalytically inactive binary metal oxide phases by solid–solid reaction at the high catalyst calcination and/or catalytic reaction temperature. Although the Ni-containing ThO 2, UO 2 and ZrO 2 catalysts showed good performance, carbon deposition on them during the process is fast. However, because of the addition of cobalt to these catalysts (with Co/Ni=1.0), the rate of carbon deposition on them in the process is drastically reduced. This Co addition however resulted in a significant decrease in both the conversion and selectivity; the decrease in the selectivity was small. 相似文献
4.
Ni catalysts supported on various solid solutions of ZrO 2 with alkaline earth oxide and/or rare earth oxide were synthesized. The catalytic activities were compared for partial oxidation of methane and autothermal reforming of methane. For partial oxidation of methane, the Ni catalyst supported on a CaO–ZrO 2 solid solution showed a high activity. Incorporation of CaO in the ZrO 2 matrix was effective for increasing the reduction rate of the NiO particles and for decreasing the coke formation. On the other hand, the Ni particles supported on the CaO–CeO 2–ZrO 2 solid solution had a strong interaction with the support, and the Ni particles showed high activity and stability for autothermal reforming of methane. 相似文献
5.
A new and simple method for obtaining highly dispersed Co/ZrO 2 catalyst is described. The presence of ethylenediamine during the preparation of Co/ZrO 2 was studied and compared with a reference catalyst conventionally prepared. Addition of an aqueous solution of ethylenediamine
to a cobalt nitrate solution had a dramatic effect on the catalytic performance of the catalyst as compared with a reference
catalyst. This promotional effect was explained in terms of higher cobalt dispersion in the catalysts using ethylenediamine.
The reason why ethylenediamine improves dispersion of the cobalt species was explained in terms of the size of the stable
complex ions which could be formed in situ during impregnation. The best catalytic results were also explained in terms of Co-support interaction since new cobalt species
were reducible at lower temperatures. 相似文献
6.
Catalytic activity of ZrO 2 supported PdO catalysts for methane combustion has been investigated in comparison with Al 2O 3 supported PdO catalysts. It was found that the drop of catalytic activity owing to decomposition of PdO at a high temperature region (600–900°C) was suppressed by using ZrO 2 support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al 2O 3 catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO 2 catalyst the consumption of hydrogen was also observed at 200–300°C. This result indicates that the stable PdO species were present in the PdO/ZrO 2 catalyst. In order to confirm the formation of the solid solution of PdO and ZrO 2, X-ray diffraction (XRD) analyses of the mixtures of ZrO 2 and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO 2 in the mixture was larger than that of ZrO 2. Furthermore, the Pd thin film on ZrO 2 substrate was prepared as a model catalyst and the depth profile of the elements in the Pd thin film was measured by Auger electron spectroscopy (AES). It was confirmed that Zr and O as well as Pd were present in the Pd thin film heated at 900°C in air. It was considered that the PdO on ZrO 2 support might be stabilized by the formation of the solid solution of PdO and ZrO 2. 相似文献
7.
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
8.
The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration ( λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co 3O 4/CeO 2 and Co 3O 4/CeO 2–ZrO 2 containing 30 wt.% of Co 3O 4. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples). Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g−1 h−1). The catalytic performance of Co3O4/CeO2 and Co3O4/CeO2–ZrO2 were compared with those of two pure Co3O4 oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co3O4/CeO2 and Co3O4/CeO2–ZrO2 as well as to their reducibility. Particular attention was paid to the thermal stability of the Co3O4 phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co3O4 heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co3O4 decomposition into CoO was observed. Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co3O4 and by promoting the reduction at low temperature. 相似文献
9.
The aim of this work was to identify the optimum synthesis conditions and the most effective technique for noble metal deposition in a perovskite/palladium-based catalyst for natural gas combustion. The solution combustion synthesis (SCS) of perovskite/zirconia-based materials was investigated, by starting from metal nitrates/glycine mixtures. Characterization and catalytic activity tests were performed on as-prepared powders and then repeated after calcination for 2 h at 900 °C in calm air. Calcination appeared to be beneficial in that, despite lowering the specific surface area, it promoted the simultaneous crystallization of both LaMnO 3 and ZrO 2 and the half-conversion temperature ( T50), regarded as an index of catalytic activity, was lowered. Two phases, both active towards methane oxidation – lanthanum manganate and palladium oxide – were combined so as to evaluate their synergism in terms of catalytic activity. Pd was therefore added either via incipient wetness impregnation on LaMnO 3·2ZrO 2 or through a one-step SCS-based route. Characterization and catalytic activity tests followed suit. Optimal composition and preparation routes were found: T50 was lowered from 507 °C – pure LaMnO 3 prepared via SCS – to 432 °C attained with a 2% (w/w) Pd load on pre-calcined LaMnO 3·2ZrO 2. 相似文献
10.
MnO 2-ZrO 2 binary oxide catalytic system was applied for the effective utilization of CO 2 as an oxidant in the ethylbenzene dehydrogenation (EBD) to styrene monomer (SM). MnO 2-ZrO 2 oxides were prepared by co-precipitation method and characterized as solid solution mixture having surface area more than 100 2 g −1. 10% MnO 2-ZrO 2 mixed oxide catalyst exhibited conversion of 73% with the selectivity of 98% at 650 °C. The MnO 2-ZrO 2 binary oxides were X-ray amorphous whereas the individual oxides (MnO 2 and ZrO 2) having much lower surface areas were crystalline in nature. As a result, MnO 2-ZrO 2 binary oxides exhibited greatly elevated catalytic activity for the conversion of ethylbenzene (EB) than those of individual oxides in the presence of CO 2. However, in the absence of CO 2 poor catalytic activity and stabilities were observed. Gradual enhancement of activities were demonstrated in the higher CO 2 to EB ratios. Hence, CO 2 had a profound role as a soft oxidant by improving both activity and stability in the EBD over MnO 2-ZrO 2 mixed oxide catalysts. 相似文献
11.
In general, there are three processes for production of synthesis gas; steam reforming, CO 2 reforming and partial oxidation of methane or natural gas. In the present work, we refer to tri-reforming of methane to synthesize syngas with desirable H 2/CO ratios by simultaneous oxy-CO 2-steam reforming of methane. In this study, we report the results obtained on tri-reforming of methane over the Ni/ZrO 2 based catalyst in order to restrain the carbon deposition and to evaluate the catalytic performance. Results of tri-reforming of CH 4 by three catalysts (Ni/Ce–ZrO 2, Ni/ZrO 2 and Haldor Topsoe R67-7H) are showed that the coke on the reactor wall and the surface of catalyst were reduced dramatically. It was found that the weak acidic site, basic site and redox ability of Ce–ZrO 2 play an important role in tri-reforming of methane conversion. Carbon deposition depends not only on the nature of support, but also on the oxidant as like steam or oxygen. Therefore, the process optimization by reactant ratios is important to manufacture the synthesis gas from natural gas and carbon dioxide. 相似文献
12.
SnO 2–ZrO 2 nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO 2 were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO 2–ZrO 2 nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH 3 and CO 2. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO 2 or ZrO 2). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO 2 was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity. 相似文献
13.
A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H 2) was investigated at 750 °C. Also, the catalysts were characterized by XRD, TEM, TPR and ( in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH 4 conversion of 88%, CO selectivity of 94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of Co 3O 4, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl 2O 4 spinel phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al 2O 3 catalysts. 相似文献
14.
One of the key hindrances on development of solid catalysts containing cobalt species for partial oxidation of organic molecules at mild conditions in conventional liquid phase is the severe metal leaching. The leached soluble Co species with a higher degree of freedom always out-performs those of solid supported Co species in oxidation catalysis. However, the homogeneous Co species concomitantly introduces separation problems. We have recently reported for the first time, a new oxidation catalyst system for the oxidation of organic molecules in supercritical CO 2 using the principle of micellar catalysis. [CF 3(CF 2) 8COO] 2Co· xH 2O (the fluorinated anionic moiety forms aqueous reverse micelles carrying water-soluble Co 2+ cations in scCO 2) was previously shown to be extremely active for the oxidation of toluene in the presence of sodium bromide in water–CO 2 mixture, giving 98% conversion and 99% selectivity to benzoic acid at 120 °C. In this study, we show that the effects of varying the type of surfactant counterions and the length of the surfactant chains on catalysis. It is found that the use of [CF 3(CF 2) 8COO] 2Mg· yH 2O/Co(II) acetate is as effective as the [CF 3(CF 2) 8COO] 2Co· xH 2O and the fluorinated chain length used has a subtle effect on the catalytic rate measured. It is also demonstrated that this new type of micellar catalyst in scCO 2 can be easily separated via CO 2 depressurisation and be reused without noticeable deactivation. 相似文献
15.
In this paper, Co 3O 4/CeO 2 catalysts for steam reforming of ethanol (SRE) were prepared by co-precipitation and impregnation methods. The catalysts prepared by co-precipitation were very active and selective for SRE. Over 10%Co 3O 4/CeO 2 catalyst, ethanol conversion was close to 100% and hydrogen selectivity was about 70% at 450 °C. The catalysts were characterized by X-ray diffraction, temperature-programmed reduction (TPR) and BET surface area measurements. The preparation method influenced the interaction between cobalt and CeO 2 evidently. The incorporation of Co ions into CeO 2 crystal lattice resulted in weaker interaction between cobalt and ceria on catalyst surface. In comparison with catalysts prepared by impregnation, more cobalt ions entered into CeO 2 lattice, and resulted in weaker interaction between active phase and ceria on surface of Co 3O 4/CeO 2 prepared by co-precipitation. Thus, cobalt oxides was easier to be reduced to metal cobalt which was the key active component for SRE. Meanwhile, the incorporation of Co ions into CeO 2 crystal lattice was beneficial for resistance to carbon deposition. 相似文献
16.
采用浸渍负载-还原法制备了钴-硼/二氧化锆催化剂,研究了催化剂在催化硼氢化钠水解制氢中的性能。研究了催化剂的制备条件(钴与二氧化锆物质的量比、钴与硼氢化钠物质的量比)对其催化性能的影响,并考察了催化剂用量、反应温度、搅拌转速对硼氢化钠水解制氢的影响。结果表明,在钴与二氧化锆物质的量比为0.16:1、钴与硼氢化钠物质的量比为1:5条件下制备的钴-硼/二氧化锆催化剂催化硼氢化钠水解制氢的速率最快。硼氢化钠水解制氢速率随催化剂用量的增加和反应温度的升高而增大,随搅拌转速的增加呈现先增大后减小的趋势。反应动力学计算出钴-硼/二氧化锆催化剂催化硼氢化钠水解对硼氢化钠的浓度属于零级反应。钴-硼/二氧化锆催化剂的硼氢化钠水解反应活化能为43.97 kJ/mol。 相似文献
17.
A series of CeO 2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N 2O). Addition of CeO 2 to Co 3O 4 led to an improvement in the catalytic activity for N 2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N 2O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O 2, H 2O or NO. Methods of XRD, FE-SEM, BET, XPS, H 2-TPR and O 2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO 2 could increase the surface area of Co 3O 4, and then improve the reduction of Co 3+ to Co 2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N 2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO 2, are responsible for the enhancement of catalytic activity of Co 3O 4. 相似文献
18.
The catalytic properties of transition metal oxides (Cr, Ce, and Co) supported on ZrO 2 synthesized by various methods, as well as the effect of rhodium on the performance of the M xO y/ZrO 2 oxide systems in NO reduction with hydrocarbons (methane, propane–butane mixture, and propene) were studied. Scanning electron microscopy, ammonia thermoprogrammed desorption (NH 3-TPD), XPS, and IR spectroscopy were used to study the physicochemical indices of rhodium-promoted M xO y/ZrO 2 oxide catalysts. The enhancement of the redox properties of the oxide catalysts upon the introduction of rhodium does not alter their bifunctional nature in SCR activity: these catalysts have both redox and strong acid Brønsted-sites. 相似文献
19.
The mixed oxide catalyst (Mn 2O 3 + SnO 2) prepared by the coprecipitation method has been impregnated with Pd metal and it's catalytic behaviour for CO oxidation reaction has been investigated. In the coprecipitated material, Mn 2O 3 and SnO 2 were found to crystallise at 875 K and 1175 K, respectively, which are significantly higher than the crystallisation temperatures of individual oxides prepared under similar conditions. Results of catalytic oxidation of CO, carried out using the pulse method for the mixed oxide system and the individual oxides, suggest significant synergistic effects between these two oxides. The impregnation of palladium metal facilitated CO oxidation and the catalyst Pd/(Mn 2O 3 + SnO 2) was found to be quite effective for CO oxidation even at room temperature. Further, the CO disproportionation has been observed on palladium sites in the temperature range 350 to 400 K for the individual oxide systems. 相似文献
20.
采用沉积-沉淀法制备CuMnO_x/TiO_2新型甲苯燃烧催化剂,考察焙烧温度、Cu与Mn物质的量比、Cu和Mn总负载量、空速及水蒸汽含量对催化甲苯燃烧性能的影响。研究表明,焙烧温度500℃和Cu与Mn物质的量比为1∶1时,催化剂活性最好,反应温度250℃时,甲苯去除率为100%;水蒸汽的出现明显降低了甲苯转化率。XRD和H2-TPR表征结果表明,CuMnO_x/TiO_2催化剂的主要活性相为铜锰尖晶石(Cu1.5Mn1.5O4),它的存在降低了CuMnO_x/TiO_2催化剂的还原温度,是催化活性优良的主要原因。 相似文献
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