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1.
Dispersing La 2O 3 on δ- or γ-Al 2O 3 significantly enhances the rate of NO reduction by CH 4 in 1% O 2, compared to unsupported La 2O 3. 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 La 2O 3 precursor used, the pretreatment, and the La 2O 3 loading. The most active family of catalysts consisted of La 2O 3 on γ-Al 2O 3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m 2) occurred between the addition of one and two theoretical monolayers of La 2O 3 on the γ-Al 2O 3 surface. The best catalyst, 40% La 2O 3/γ-Al 2O 3, 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 La 2O 3/Al 2O 3 catalysts exhibited stable activity under high conversion conditions as well as high CH 4 selectivity (CH 4 + NO vs. CH 4 + O 2). The addition of Sr to a 20% La 2O 3/γ-Al 2O 3 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 La 2O 3/Al 2O 3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La 2O 3. Dispersing La 2O 3 on SiO 2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La 2O 3. This is presumably due to water sensitivity and silicate formation. The La 2O 3/Al 2O 3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 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.
CO_2吸附强化CH_4/H_2O重整制氢是提供低成本高纯氢气和实现CO_2减排的方法之一。其中,催化剂和吸附剂是该工艺的重要组成部分,其活性与选择性制约了反应速率和产率,寿命长短关系到生产成本。综述了CO_2吸附强化CH_4/H_2O重整制氢催化剂和吸附剂的研究现状及存在的问题,机械混合的催化剂与吸附剂在反应过程中存在吸附产物包覆催化活性位点的问题,导致催化剂活性迅速下降。针对该问题,进一步探讨了不同结构双功能复合催化剂的结构特性、研究现状及其在循环-再生过程中存在的问题,核壳型双功能催化剂具有吸附组分与催化剂组分相对独立、催化组分分散分布和比表面积大等优点,在吸附强化制氢中有进一步研究的潜力。利用双功能催化剂的结构特点,实现反复循环再生过程中催化与脱碳反应的匹配,是推动CO_2吸附强化CH_4/H_2O重整制氢技术工业化发展的关键。 相似文献
4.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
5.
Mixed oxides of alumina and zirconia having a relative composition of 50, 80 and 100% Zr 2O were synthesized by means of sol–gel methods. The catalysts were sulfated with H 2SO 4 1N, and were loaded with 0.3% Pt metal using the incipient wetness technique. The characterization of the physicochemical properties was carried out using XRD, N 2-adsorption at 78 K, and SEM. The catalytic properties of the Al 2O 3–ZrO 2 series were studied by means of dehydration of 2-propanol at 180°C and isomerization of n-hexane at 250°C, 1 atm. The sulfated solids presented a high surface acidity and a limited crystallinity, together with high activity for alcohol dehydration (i.e. 2-propanol). On the other hand, the Al 2O 3–ZrO 2 solid solutions (i.e. those having a 20–80% composition) turned out to be the most active ones for the isomerization of n-hexane. 相似文献
6.
Both NO decomposition and NO reduction by CH 4 over 4%Sr/La 2O 3 in the absence and presence of O 2 were examined between 773 and 973 K, and N 2O decomposition was also studied. The presence of CH 4 greatly increased the conversion of NO to N 2 and this activity was further enhanced by co-fed O 2. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH 4 in the absence of O 2, and reduction with 1% O 2 in the feed were 8.3·10 −4, 4.6·10 −3, and 1.3·10 −2 μmol N 2/s m 2, respectively. This oxygen-enhanced activity for NO reduction is attributed to the formation of methyl (and/or methylene) species on the oxide surface. NO decomposition on this catalyst occurred with an activation energy of 28 kcal/mol and the reaction order at 923 K with respect to NO was 1.1. The rate of N 2 formation by decomposition was inhibited by O 2 in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH 4 continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O 2 with equal activation energies of 26 kcal/mol. The addition of O 2 increased the reaction order in CH 4 at 923 K from 0.19 to 0.87, while it decreased the reaction order in NO from 0.73 to 0.55. The reaction order in O 2 was 0.26 up to 0.5% O 2 during which time the CH 4 concentration was not decreased significantly. N 2O decomposition occurs rapidly on this catalyst with a specific activity of 1.6·10 −4 μmol N 2/s m 2 at 623 K and 1220 ppm N 2O and an activation energy of 24 kcal/mol. The addition of CH 4 inhibits this decomposition reaction. Finally, the use of either CO or H 2 as the reductant (no O 2) produced specific activities at 773 K that were almost 5 times greater than that with CH 4 and gave activation energies of 21–26 kcal/mol, thus demonstrating the potential of using CO/H 2 to reduce NO to N 2 over these REO catalysts. 相似文献
7.
In the present study, both t-phase zirconia and m-phase zirconia particles are incorporated into an alumina matrix. Dense Al 2O 3/(t-ZrO 2+m-ZrO 2) composites were prepared by sintering pressurelessly at 1600 °C. The microstructure of the composites are characterized, the elastic modulus, strength and toughness determined. Because the ZrO 2 inclusions are close to each other in the Al 2O 3 matrix, the yttrium ion originally in t-ZrO 2 particles can diffuse to nearby m-ZrO 2 particles during sintering, and the m-phase zirconia is thus stabilized after sintering. The strength of the Al 2O 3/(t-ZrO 2+m-ZrO 2) composites after surface grinding can reach values as high as 940 MPa, which is roughly three times that of Al 2O 3 alone. The strengthening effect is contributed by microstructural refinement together with the surface compressive stresses induced by grinding. The toughness of alumina is also enhanced by adding both t-phase and m-phase zirconia, which can reach values as high as two times that of Al 2O 3 alone. The toughening effect is attributed mainly to the zirconia t–m phase transformation. 相似文献
8.
Stable suspensions based on methylethylketone (MEK), n-butylamine and nitrocellulose were developed for the electrophoretic deposition (EPD) of Al 2O 3 and ZrO 2 powder. Deposits with a high green density, smooth surface and high deposition yield were obtained upon adding 10–15 vol.% n-butylamine in combination with 1 wt.% nitrocellulose. The influence of the reaction between MEK and n-butylamine, forming water and imines, on the electrophoretic deposition behaviour was investigated. Experimental results revealed that the zeta potential is not a straightforward indication of the stability of these suspensions, since the maximum absolute zeta potential did not correspond with a maximum suspension stability, due to the additional electrosteric stabilisation of the adsorbed charged nitrocellulose. 相似文献
9.
CH 4/CO 2 reforming over La 2NiO 4 and 10%NiO/CeO 2–La 2O 3 catalysts under the condition of supersonic jet expansion was studied via direct monitoring of the reactants and products using the sensitive technique of cavity ring-down spectroscopy. Vibration–rotational absorption lines of CH 4, H 2O, CO 2 and CO molecules were recorded in the near infrared spectral region. Our results indicated that La 2NiO 4 is superior to 10%NiO/CeO 2–La 2O 3 in performance. In addition, we observed enhanced reverse-water-gas-shift reaction at augmented reaction temperature. The formation of reaction intermediates was also investigated by means of time-of-flight mass spectrometry and there was the detection of CH x+, OH + and H + species. 相似文献
10.
Attempts had been made to synthesize Al2O3-2SiO2 nanopowders by sol-gel method with tetraethoxysilane(TEOS) and aluminum nitrate(ANN) as the starting materials.DTS,TEM,SEM and BET were employed to study the effects of process parameters on the size,specific surface area and structure(morphology) of powders.The alkali-activation reactivity of the powders was tested for manufacturing geopolymers and their hydrothermal reactions were performed for fabricating zeolites.The results show that the optimum process parameters and drying method for preparing Al2O3-2SiO2 nanopowders are as follows:the molar ratio of water and ethanol to TEOS are 0:1 and 12:1 respectively at synthetic temperature of 50 ℃ and the drying method is azeotropic distillation with microwave drying.The average particle diameters of the powders were about 70 nm and the largest BET specific surface area was up to 669 m2·g·1.The compressive strength of the geopolymer and the calcium exchange capacity(by CaCO3) of NaA zeolite prepared with the powders reached to 29 MPa and 366 mg·g·1 respectively. 相似文献
11.
Ethanol steam reforming was studied over Ni/Al 2O 3 catalysts. The effect of support (- and γ-Al 2O 3), metal loading and a comparison between conventional H 2 reduction with an activation method employing a CH 4/O 2 mixture was investigated. The properties of catalysts were studied by N 2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). After activity tests, the catalysts were analyzed by scanning electron microscopy (SEM) and thermogravimetric analysis (TG/DTA). Ni supported on γ-Al 2O 3 was more active for H 2 production than the catalyst supported on -Al 2O 3. Metal loading did not affect the catalytic performance. The alternative activation method with CH 4/O 2 mixture affected differently the activity and stability of the Ni/γ-Al 2O 3 and the Ni/-Al 2O 3 catalyst. This activation method increased significantly the stability of Ni/-Al 2O 3 compared to H 2 reduction. SEM and TG/DTA analysis indicate the formation of filamentous carbon during the CH 4/O 2 activation step, which is associated with the increasing catalyst activity and stability. The effect of temperature on the type of carbon formed was investigated; indicating that filamentous coke increased activity while encapsulating coke promoted deactivation. A discussion about carbon formation and the influence on the activity is presented. 相似文献
12.
In this work, the microwave-assisted CO 2 reforming of CH 4 over mixtures of carbonaceous materials and an in-lab prepared Ni/Al 2O 3 was studied. Ni/Al 2O 3 is not heated by microwave radiation, and for this reason, microwave receptors, such as carbonaceous materials, must be mixed with this catalyst. In order to evaluate the role of the carbonaceous component of the blend, two different carbonaceous materials were used: an activated carbon, FY5, and a metallurgical coke, CQ. The carbonaceous component acted not only as microwave receptor but also as catalyst and, consequently, it influenced the catalytic activity of the mixture. FY5 + Ni/Al 2O 3 was found to be a better catalyst than CQ + Ni/Al 2O 3, since FY5 on its own showed a better catalytic activity than CQ. Ni/FY5, which consists of Ni impregnated directly onto the microwave receptor, was also evaluated as a catalyst. It was found that the catalytic activity of the mixture FY5 + Ni/Al 2O 3 was better than that of Ni/FY5. Finally, the influence of the heating device on the catalytic activity of FY5 + Ni/Al 2O 3 was studied. Conversions over FY5 + Ni/Al 2O 3 and microwave heating were found to be similar to conversions over Ni/Al 2O 3 and conventional heating. 相似文献
13.
Hydrogen production from ethanol reforming over nickel catalysts supported on lanthanum loaded Al 2O 3 substrates was studied. Activity results revealed the enhancement in the reforming stability of the Ni catalysts with the increase in the lanthanum loading on Al 2O 3 substrates. Catalytic behavior of Ni/La–Al 2O 3 catalysts in the ethanol steam reforming was found to be the contribution of the activity of the La–Al 2O 3 supports for the ethanol dehydration reaction and the activity of the nickel metallic phase that catalyzes both dehydrogenation and CC bond rupture. Physicochemical characterization of catalysts revealed that acidity, nickel dispersion and nickel-support interaction depend on the La-loading on Al 2O 3. The better reforming stability of catalysts with the increase in La content was explained in terms of the ability of nickel surface and/or La–Ni interactions to prevent the formation of carbon filaments. 相似文献
14.
The phase diagram of the Al 2O 3–ZrO 2–Nd 2O 3 system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1675 °C and it corresponds to the ternary eutectic Nd 2O 3·11Al 2O 3 + F-ZrO 2 + NdAlO 3. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al 2O 3–ZrO 2–Nd 2O 3 system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. 相似文献
15.
A series of SAPO-34 molecular sieves with different SiO 2/Al 2O 3 ratios have been synthesized for the methanol-to-olefin (MTO) reaction. Their physico-chemical properties are characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N 2 adsorption-desorption. The results are compared with those of the commercial HZSM-5, which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO 2/Al 2O 3 ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO 2/Al 2O 3 ratio of 0.4 exhibits the highest BET surface area. FT-IR spectra indicate that HZSM-5 has both Br?nsted and Lewis acid sites and Br?nsted acid sites are stronger, whereas SAPO-34 samples are dominated only by Lewis acid sites. When the SiO 2/Al 2O 3 ratio increases, propylene and butylenes become the predominant product of the MTO reaction over HZSM-5. In contrast, the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene. According to the product distribution, the reaction mechanism over HZSM-5 catalysts is proposed. 相似文献
16.
Ni/Al 2O 3 catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons. There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts. The properties of these very complex systems depend on the conditions of successive preparation stages (calcination, reduction) or the process conditions. A series of Ni/Al2O3 catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties. Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al2O3 catalysts. Catalysts were further characterized by BET area, H2 chemisorption and X-ray diffraction measurements. The TPR curves of Ni-Mo/Al2O3 catalysts are very complex. Mo addition leads to the decrease of catalysts reducibility. However, complete reduction of NiO and MoO3 can be achieved at 800 °C. The reduction course depends on the sequence of nickel and molybdenum addition into the support. Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al2O3 and Ni-Mo/Al2O3 samples show the possibility of Ni-Mo solid solution formation. 相似文献
17.
The system Al 2O 3–ZrO 2 was studied by differential thermal analysis in inert atmosphere and in vacuum. The eutectic was located at 1866°C and 40% mass of ZrO 2. Zirconia solid solution at the eutectic temperature is up to 1.1±0.3% mass of Al 2O 3. Enthalpy of melting of this eutectic is 1080±90 J/g. Pure ZrO 2 transforms from monoclinic to tetragonal at 1162±7°C, but the saturated solid solution of ZrO 2, with 0.7±0.2% mass Al 2O 3 at this temperature, transforms at 1085±5°C. Inverse transitions occur with hysteresis correspondingly at 1055±5 and 995±5°C. Enthalpy of transformation of pure ZrO 2 from monoclinic to tetragonal phase is 42±5 J/g (5.2±0.6 J/mol) but only 30±5 J/g for a ZrO 2 saturated solid solution. 相似文献
18.
In this contribution, a commercial spherical SiO 2 was modified with different amounts of La 2O 3, and used as the support of Ni catalysts for autothermal reforming of methane in a fluidized-bed reactor. Nitrogen adsorption, XRD and H 2-TPR analysis indicated that La 2O 3-modified SiO 2 had higher surface area, strengthened interaction between Ni and support, and improved dispersion of Ni. CO 2-TPD found that La 2O 3 increased the alkalescence of SiO 2 and improved the activation of CO 2. Coking reaction (via both temperature-programmed surface reaction of CH 4 (CH 4-TPSR) and pulse decomposition of CH 4) disclosed that La 2O 3 reduced the dehydrogenation ability of Ni. CO 2-TPO, O 2-TPO (followed after CH 4-TPSR) confirmed that only part amount of carbon species derived from methane decomposition could be removed by CO 2, and O 2 in feed played a crucial role for the gasification of the inactive surface carbons. Ni/ xLa 2O 3-SiO 2 ( x = 10, 15, 30) possessed high activity and excellent stability for autothermal reforming of methane in a fluidized-bed reactor. 相似文献
19.
Ni catalysts supported on γ-Al 2O 3, CeO 2 and CeO 2–Al 2O 3 systems were tested for catalytic CO 2 reforming of methane into synthesis gas. Ni/CeO 2–Al 2O 3 catalysts showed much better catalytic performance than either CeO 2- or γ-Al 2O 3-supported Ni catalysts. CeO 2 as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO 2 had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al 2O 3 catalysts for this reaction. A weight loading of 1–5 wt% CeO 2 was found to be the optimum. Ni catalysts with CeO 2 promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO 2-promoted catalysts are attributed to the oxidative properties of CeO 2. 相似文献
20.
以不同温度焙烧的苏州高岭土为原料,采用原位晶化法合成高硅铝比小晶粒NaY分子筛,考察晶种胶添加量、陈化温度、晶化温度和m(高土)∶m(偏土)对晶化过程和产物性质的影响。结果表明,m(高土)∶m(偏土)=1时,在晶种胶添加质量分数15%、陈化温度90℃和晶化温度100℃条件下,以普通高岭土为原料原位合成NaY样品的相对结晶度约为80%,骨架硅铝比(SiO2与Al2O3物质的量比)为6.4,平均粒径约500nm。调整原料中m(高土)∶m(偏土)可以控制原位晶化样品中的分子筛含量。以细化高岭土为原料合成的NaY分子筛(平均约445nm)粒径小于普通高岭土合成的样品。骨架硅铝比高于6.0的原位晶化样品的骨架坍塌温度高于950℃,具有很高的结构稳定性。 相似文献
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