共查询到20条相似文献,搜索用时 156 毫秒
1.
J. A. Roos S. J. Korf R. H. J. Veehof J. G. van Ommen J. R. H. Ross 《Catalysis Today》1989,4(3-4):441-452
In order to examine the importance of the further oxidation of the desired C2 products in the oxidative coupling of methane, ethylene and ethane have been added to the feed (containing methane and oxygen) to a Li/MgO or Ca/Sm2O3 catalyst. The results of these measurements show that neither of these C2 molecules is stable under these conditions with either of the catalysts. Additionally, the rates of the oxidation of ethane and of ethylene alone have been measured using a gradientless reactor for both catalysts as well as for a quartz bed. It was found that the Ca/Sm2O3 material had higher activities for the oxidation of C2H6 and C2H4 (and also of CH4) than had the Li/MgO material. These higher activities result in a lower optimal reaction temperature for the oxidative coupling of methane and are (at least partially) responsible for the lower selectivity to C2 products observed with the Ca/Sm2O3 catalyst compared to that with the Li/MgO catalyst. 相似文献
2.
S. J. Korf J. A. Roos J. M. Diphoorn R. H. J. Veehof J. G. van Ommen J. R. H. Ross 《Catalysis Today》1989,4(3-4):279-292
A comparison has been made of the behaviour in the oxidative coupling of methane of the oxides of Sm, Dy, Gd, La and Tb with that of a Li/MgO material. All but the Tb4O7 (which gave total oxidation) were found to give higher yields than the Li/MgO material at temperatures up to approaching 750°C but the Li/MgO system gave better results at higher temperatures. The cubic structure of Sm2O3 was found to be responsible for its good performance while the monoclinic structure was relatively inactive and unselective. The addition of Na or Ca to cubic Sm2O3 gives a higher optimum C2 yield than that of unpromoted Sm2O3. Sm2O3 and Ca/Sm2O3 catalysts are more stable than Li/MgO, Li/Sm2O3 or Na/Sm2O3. The addition of Li or Na to Sm2O3 causes the structure to change from cubic to monoclinic; the deactivation of the Na/Sm2O3 catalysts is caused by a loss of Na coupled with the formation of the monoclinic form of Sm2O3. 相似文献
3.
A comparative study of methane oxidation using oxygen and nitrous oxide as oxidants over Sm2O3, 5% Li/Sm2O3, La2O3 and 5% Li/La2O3 is reported. In addition a study of the primary selectivities for the different systems is also reported in detail. Both ethane and ethene are confirmed as primary products under the conditions investigated. The results are discussed in terms of a mechanism for methane oxidation in which O− is the selective oxidant for ethane formation and a dioxygen species is responsible for total oxidation of ethane and ethene. 相似文献
4.
Activation of methane using solid oxide membranes 总被引:4,自引:0,他引:4
Dense membranes of mixed-conducting perovskite-type oxides La0.6Sr0.4,CO0.8Fe0.2O3 and La0.8Ba0.2Co0.8Fe0.2O3 were used for methane coupling by application of pressure-driven O2 permeation. High operating temperatures, typically above 800°C, were needed to obtain reasonable oxygen fluxes. Conversions were small (1–3%). Both compositions showed comparable C2 selectivities at low methane partial pressures. At higher pressures the selectivity to C2 hydrocarbons for La0.6Sr0.4CO0.8Fe0.2O3 increased to 67%, whereas La0.8Ba0.2CO0.8Fe0.2O3 showed small C2 selectivities. Strong surface segregation of Sr and Ba was shown by SEM for both compositions. 相似文献
5.
An evolutionary approach in the combinatorial selection and optimization of catalytic materials 总被引:1,自引:0,他引:1
A methodical basis of the evolutionary method for selection and optimization of heterogeneous catalytic materials was developed. For validation, the oxidative dehydrogenation of propane was used as a model reaction. Various oxides (V2O5, MoO3, MnO2, Fe2O3, GaO, MgO, B2O3, La2O3) were chosen as primary components for the generation of catalytic materials. The first generation consisting of 56 catalytic materials was created by combination of the primary components in a stochastic manner. The materials of each preceding generation were selected based on the catalytic results obtained and subjected to an evolutionary procedure applying mutation and crossover operators to create further generations of catalytic materials of different qualitative and quantitative compositions. For illustration, four generations were created with a total number of tested catalytic materials of 224. As a result of the preliminary optimization procedure an increase in the propene yield was achieved with increasing number of generations; the results can be certainly improved by screening further generations of catalytic materials. Under standard conditions used for testing (T=500°C, C3H8/O2=3, p(C3H8)=30 Pa), the highest C3H6 yield amounted to 9.0% (S=57.4%) in the 3rd generation on V0.22Mg0.47Mo0.11Ga0.20Ox. 相似文献
6.
Yun Guo Guanzhong Lu Zhigang Zhang Shunhai Zhang Yan Qi Yi Liu 《Catalysis Today》2007,126(3-4):296-302
Nanoparticles of CexZr1−xO2 (x = 0.75, 0.62) were prepared by the oxidation-coprecipitation method using H2O2 as an oxidant, and characterized by N2 adsorption, XRD and H2-TPR. CexZr1−xO2 prepared had single fluorite cubic structure, good thermal stability and reduction property. With the increasing of Ce/Zr ratio, the surface area of CexZr1−xO2 increased, but thermal stability of CexZr1−xO2 decreased. The surface area of Ce0.62Zr0.38O2 was 41.2 m2/g after calcination in air at 900 °C for 6 h. TPR results showed the formation of solid solution promoted the reduction of CeO2, and the reduction properties of CexZr1−xO2 were enhanced by the cycle of TPR-reoxidation. The Pd-only three-way catalysts (TWC) were prepared by the impregnation method, in which Ce0.75Zr0.25O2 was used as the active washcoat and Pd loading was 0.7 g/L. In the test of Air/Fuel, the conversion of C3H8 was close to 100% and NO was completely converted at λ < 1.025. The high conversion of C3H8 was induced by the steam reform and dissociation adsorption reaction of C3H8. Pd-only catalyst using Ce0.75Zr0.25O2 as active washcoat showed high light off activity, the reaction temperatures (T50) of 50% conversion of CO, C3H8 and NO were 180, 200 and 205 °C, respectively. However, the conversions of C3H8 and NO showed oscillation with continuously increasing the reaction temperature. The presence of La2O3 in washcoat decreased the light off activity and suppressed the oscillation of C3H8 and NO conversion. After being aged at 900 °C for 4 h, the operation windows of catalysts shifted slightly to rich burn. The presence of La2O3 in active washcoat can enhance the thermal stability of catalyst significantly. 相似文献
7.
The performance of unpromoted and MOx-(M: alkali (earth), transition metal and cerium) promoted Au/Al2O3 catalysts have been studied for combustion of the saturated hydrocarbons methane and propane. As expected, higher temperatures are required to oxidize CH4 (above 400 °C), compared with C3H8 (above 250 °C). The addition of various MOx to Au/Al2O3 improves the catalytic activity in both methane and propane oxidation. For methane oxidation, the most efficient promoters to enhance the catalytic performance of Au/Al2O3 are FeOx and MnOx. For C3H8 oxidation a direct relationship is found between the catalytic performance and the average size of the gold particles in the presence of alkali (earth) metal oxides. The effect of the gold particle size becomes less important for additives of the type of transition metal oxides and ceria. The results suggest that the role of the alkali (earth) metal oxides is related to the stabilization of the gold nanoparticles, whereas transition metal oxide and ceria additives may be involved in oxygen activation. 相似文献
8.
Na-oyoshi Iwasaki Takanori Miyake Eriko Yagasaki Toshimitsu Suzuki 《Catalysis Today》2006,111(3-4):391-397
Attention has been increasingly paid to the partial oxidation of lower alkanes to synthesis gas, due to its intrinsic energy saving process. We studied the partial oxidation of ethane (POE) on Co loaded on various supports. The POE performance varied as follows: Y2O3, CeO2, ZrO2, La2O3 SiO2, Al2O3, TiO2 > MgO. Comparing Y2O3 and CeO2, the carbon deposition during the POE was negligible on CeO2 and therefore CeO2 was the most preferable support. By changing space velocity and O2 partial pressure, reaction mechanism of POE was studied and it was revealed that two-step mechanism was prevailing; combustion of ethane to H2O and CO2 and subsequent reforming of ethane with H2O and CO2 to synthesis gas. Co/CeO2 catalyst exhibited high and stable catalytic activity for 10 h; high ethane conversion of 18% (maximum ethane conversion 20% at O2/C2H6 = 0.2) with H2 and CO selectivities of 93 and 84%, respectively. 相似文献
9.
Chunlei Shi Arden B. Walters M. Albert Vannice 《Applied catalysis. B, Environmental》1997,14(3-4):175-188
Dispersing La2O3 on δ- or γ-Al2O3 significantly enhances the rate of NO reduction by CH4 in 1% O2, compared to unsupported La2O3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La2O3 precursor used, the pretreatment, and the La2O3 loading. The most active family of catalysts consisted of La2O3 on γ-Al2O3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m2) occurred between the addition of one and two theoretical monolayers of La2O3 on the γ-Al2O3 surface. The best catalyst, 40% La2O3/γ-Al2O3, had a turnover frequency at 700°C of 0.05 s−1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La2O3/Al2O3 catalysts exhibited stable activity under high conversion conditions as well as high CH4 selectivity (CH4 + NO vs. CH4 + O2). The addition of Sr to a 20% La2O3/γ-Al2O3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO=4 to the latter Sr-promoted La2O3/Al2O3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La2O3. Dispersing La2O3 on SiO2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La2O3. This is presumably due to water sensitivity and silicate formation. The La2O3/Al2O3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
10.
以硝酸锆、硝酸镧和柠檬酸为原料,原位合成了稀土镧(La)掺杂氧化锆(ZrO2)和锆酸镧/氧化锆(La2Zr2O7/ZrO2)复合材料。采用X射线衍射(XRD)和拉曼光谱(Raman)作为分析和表征手段,研究了稀土La掺杂ZrO2和La2Zr2O7/ZrO2复合材料的物相组成以及La2Zr2O7/ZrO2复合材料的高温热稳定性。研究结果表明:稀土La很难进入ZrO2晶格形成固溶体,当稀土La掺杂量较少时,生成以m-ZrO2为主相的m-ZrO2和La2Zr2O7的复合材料;当稀土La掺杂量较大时,生成以La2Zr2O7为主相的t-ZrO2和La2Zr2O7的复合材料。在1 400 ℃煅烧6 h条件下,LZZ11(按La2Zr2O7与ZrO2物质的量比为1∶[KG-*2]1称取原料制备的样品)中的t-ZrO2转变为m-ZrO2相,此时La2Zr2O7失去了对ZrO2的稳定作用。 相似文献
11.
Ye im Erarslano lu I ik Oka Timur Do u John B. Butt 《Chemical Engineering Communications》1995,135(1):71-79
Oxidative coupling of methane to higher hydrocarbons was investigated using alkali and rare earth cuprates such as YBa2Cu3O7-x, La1.8Ba0.2CuO and La2CuO4. Oxygen and methane in helium were fed to the reactor in a cofeed mode. Approximately, 5 g of catalyst in powder form was placed in a quartz flow reactor in all experiments. Oxygen partial pressure was changed as a parameter (P0 = 0.5 to 9.1 kPa) while keeping methane partial pressure and temperature constant at 18kPa and 1023 K respectively. Investigation of catalytic activity in terms of overall methane conversion and C2 + (C2H4+C2H6) product selectivity indicated that higher conversions and lower selectivities were obtained as O2 partial pressure was increased at a constant methane partial pressure of 8kPa. In comparing the performance of the two catalysts, La1.8Ba0.2CuO and La2CuO4; the selectivity results indicated a positive influence of incorporation of Ba into La2CuO4 structure. Similarly, selectivity values substantially increased teaching 86.3% at a reaction temperature of 1023 K and at PCH4./PO3, = 6 when La was replaced by Y and Ba. 相似文献
12.
Ching-Huei Wang Shiow-Shyung Lin Pei-Chang Sung Hung-Shan Weng 《Applied catalysis. B, Environmental》2003,40(4):331-345
This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO2 with C2H4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C2H4/SO2, and pretreatment are all important factors affecting catalyst activity. Fe2O3/γ-Al2O3 was found to be the most active catalyst among six γ-Al2O3-supported metal oxide catalysts tested. With Fe2O3 as the active species, of the supports tested, CeO2 is the most suitable one. Using this Fe2O3/CeO2 catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C2H4/SO2 is 1:1, and the catalyst presulfidized by H2+H2S exhibits a higher performance than those pretreated with H2 or He. Although the feed concentrations of C2H4:SO2 being 3000:3000 ppm provide a higher conversion of SO2, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C2H4 temperature-programmed desorption (C2H4-TPD) and SO2-TPD desorption patterns illustrate that Fe2O3/CeO2 can adsorb and desorb C2H4 and SO2 more easily than can Fe2O3/γ-Al2O3. Moreover, the SO2-TPD patterns further show that Fe2O3/γ-Al2O3 is more seriously inhibited by SO2. These findings may properly explain why Fe2O3/CeO2 has a higher activity for the reduction of SO2. 相似文献
13.
Palladium-substituted lanthanum cuprates: application to automotive exhaust purification 总被引:4,自引:0,他引:4
Nolven Guilhaume Stefan D. Peter Michel Primet 《Applied catalysis. B, Environmental》1996,10(4):325-344
A series of palladium-substituted La2CuO4, corresponding to the formula La2Cu1 −xPdxO4 (x = 0−0.2) were prepared by metal nitrate decomposition in a polyacrylamide gel. This method allows an easy incorporation of palladium in the mixed-oxides, which are formed at moderate temperature with rather high specific areas (13–17 m2/g). The partial substitution of copper for palladium allows a strong improvement of the three-way catalytic activity, in particular for NO reduction. The light-off temperatures for the conversions of CO, NO and C3H6 decreased markedly when increasing the palladium content, the activity of catalysts La2Cu0.9Pd0.1O4 and La2Cu0.8Pd0.2O4 being comparable to that of a Pt-Rh/CeO2–Al2O3 catalyst for NO reduction, and higher for CO and C3H6 oxidation.
All the La2Cu1 − x PdxO4 catalysts are activated under reacting conditions. This activation corresponds to the destruction of the mixed-oxide structure, with formation of reduced Pd0 ions atomically dispersed, surrounded by Cu+ and Cu2+ species on a lanthanum oxycarbonate matrix. This high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial La2Cu1 −xPdxO4 structure. 相似文献
14.
La1−xSrxMnO3 (x=0, 0.1, 0.3, 0.5, 0.7) perovskite-type oxides (PTOs) were prepared by coprecipitation under various calcination temperature, and their performances for the NO reduction were evaluated under a simulated exhaust gas mixture. The X-ray diffraction (XRD) and thermogravimetric analysis were carried out to find the formation process of the perovskite. The NO reduction rate under different reaction temperature, the concentration of oxygen and the presence of hydrocarbon were observed by the input/output analysis. In the presence of 10% excess oxygen, the catalyst La0.7Sr0.3MnO3 calcined at 900 °C showed a NO reduction rate of 61% at 380 °C. The study of the reaction curves showed that C3H8 could act as the reducer for the NO reduction below 400 °C. The NO reduction is highly affected by increasing the O2 concentration from 0.5 to 10%, especially at high temperatures when oxygen becomes more competitive than NO on the oxidation of C3H8, leading to a decrease of the NO reduction from 100% to zero at 560 °C. 相似文献
15.
Hussam Abdulhamid Erik Fridell Magnus Skoglundh 《Applied catalysis. B, Environmental》2006,62(3-4):319-328
The effect of different reducing agents (H2, CO, C3H6 and C3H8) on the reduction of stored NOx over PM/BaO/Al2O3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H2 and CO have a relatively high NOx reduction efficiency compared to C3H6 and especially C3H8 that does not show any NOx reduction ability except at 350 °C over Pd/BaO/Al2O3. The type of precious metals affects the NOx storage-reduction properties, where the Pd/BaO/Al2O3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al2O3 catalyst shows a high reduction ability but a relatively low NOx storage capacity. 相似文献
16.
Puxu Liu Yong Wang Yang Chen Xiaoqing Wang Jiangfeng Yang Libo Li Jinping Li 《中国化学工程学报》2022,42(2):35-41
Direct separation of high purity ethylene (C2H4) from an ethane (C2H6)/ethylene mixture is a critical and challenging task owing to the very similar molecular size and physical properties of the two components. While some studies have attempted this separation, there is a lack of excellent porous materials with strong binding affinity for C2H6-selective adsorption via an energy-efficient adsorptive separation process. Herein, we report a titanium metal-organic framework with strong binding affinity and excellent stability for the highly efficient removal of C2H6 from C2H6/C2H4 mixtures. Single component adsorption isotherms demonstrated a larger amount of adsorbed ethane (1.16 mmol·g-1 under 1 kPa) and high C2H6/C2H4 selectivity (2.7) for equimolar C2H6/C2H4 mixtures, especially in the low-pressure range, which is further confirmed by the results of grand canonical Monte Carlo simulations for C2H6 adsorption in this framework. The experimental breakthrough curves showed that C2H4 with a high purity was collected directly from both 1:9 and 1:15 C2H6/C2H4 (volume ratio) mixtures at 298 K and 100 kPa. Moreover, the unchanged adsorption and separation performance after cycling experiments confirmed the promising applicability of this material in future. 相似文献
17.
以Sm_2O_3, La_2O_3,ZrO_2和CeO_2等氧化物为原料,采用固相反应法制备双位掺杂(Sm1-xLa_x)_2(Zr1-yCe_y)_2O_7(x=0.5;y=0.1,0.2,0.3,0.4)陶瓷材料,研究了其晶体结构、显微组织、介电性能和热导率。结果表明,随着离子掺杂变化,该系列氧化物的结构发生了从焦绿石向萤石的转变。其显微组织比较致密,晶界清洁,但晶粒大小分布不均匀;且随掺杂离子元素含量的增加制备陶瓷材料的介电常数增大,热导率下降,热导率与介电常数成反比。 相似文献
18.
Ling Yang Wei Zhou Hao Li Ali Alsalme Litao Jia Jiangfeng Yang Jinping Li Libo Li Banglin Chen 《中国化学工程学报》2020,28(2):593-597
Separation of ethane from ethylene is a very important but challenging process in the petrochemical industry. Finding an alternative method would reduce the energy needed to make 170 million tons of ethylene manufactured worldwide each year. Adsorptive separation using C2H6-selective porous materials to directly produce high-purity C2H4 is more energy-efficient. We herein report the “reversed C2H6/C2H4 adsorption” in a metal-organic framework Cr-BTC via the introduction of oxygen on its open metal sites. The oxidized Cr-BTC(O2) can bind C2H6 over C2H4 through the active Cr-superoxo sites, which was elucidated by the gas sorption isotherms and density functional theory calculations. This material thus exhibits a good performance for the separation of 50/50 C2H6/C2H4 mixtures to produce 99.99% pure C2H4 in a single separation operation. 相似文献
19.
The oxidative coupling behaviour of a series of K/Ni/Ca oxide catalysts with low nickel-to-calcium ratios has been examined and the results are compared with those for a magnesium-based catalyst. The effect of gas composition and the stability of ethylene under reaction conditions have also been studied. The catalysts were calcined at 1200°C unless otherwise stated. Potassium was added after the calcination stage. It is found that a high calcination temperature of 1200°C is necessary to give a Ca-based catalyst with high activity and selectivity. The catalysts based on MgO were less selective. Substitution of K for Li in the MgO based catalyst gave a slight improvement in the selectivity. A series of experiments was carried out with the K0.1Ni0.012 Ca material with the aim of optimising the yield. It was found that the selectivity could be improved by increasing the concentration of CH4 or by adding CO2 to the feed. However the addition of CO2 decreased the activity of the catalyst. The activity could be increased by increasing the H2O concentration. An increase of the O2 concentration in the feed from 10.85 to 13% with 31% of CH4 and 21% H2O increased the C2 yield from 15.1% to 17.8%. In a series of experiments in which different concentrations of C2H4 were added to the feed, it was found that the main oxidation product of ethylene was CO2. The formation of ethane was unaffected by the addition of ethylene. It is therefore proposed that two different sites are required for the oxidation of ethylene and the activation of methane to form ethane. 相似文献
20.
Selective catalytic reduction of NOx by C3H6 in the presence of H2 over Ag/Al2O3 was investigated using in situ DRIFTS and GC–MS measurements. The addition of H2 promoted the partial oxidation of C3H6 to enolic species, the formation of –NCO and the reactions of enolic species and –NCO with NOx on Ag/Al2O3 surface at low temperatures. Based on the results, we proposed reaction mechanism to explain the promotional effect of H2 on the SCR of NOx by C3H6 over Ag/Al2O3 catalyst. 相似文献