共查询到20条相似文献,搜索用时 31 毫秒
1.
采用分步浸渍法制备了碱/碱土金属修饰Ni基催化剂Ni-M/Al 2O 3 (M=K 2CO 3, Na 2CO 3, MgO, CaO)。探究了碱/碱土金属的添加对改性Ni基催化剂CO 2吸附和甲烷化性能的影响。研究发现,碱/碱土金属的添加提高了Ni/Al 2O 3催化剂表面的碱性活性位点密度,强化了其CO 2吸附性能。碱/碱土金属类型影响Ni-M/Al 2O 3催化剂碱性活性位点的分布、NiO物相的转化及Ni的分散度,进而影响其甲烷化性能。MgO添加使NiO物相转化为与载体呈强相互作用的β型和γ型NiO,降低了催化剂表面的强碱性活性位点比例,有利于CO 2吸附活化。Ni-MgO/Al 2O 3的CO 2吸附容量最高为0.68mmolCO 2/g,其CO 2转化率和CH 4选择性分别高达58.4%和95.4%,其在烟气CO 2捕集与原位甲烷化中极具应用前景。 相似文献
2.
利用热重分析仪、扫描电镜和氮吸附仪对不同粒径的K 2CO 3颗粒和负载型K 2CO 3/Al 2O 3二氧化碳吸收剂的碳酸化特性进行研究。负载后的吸收剂比表面积和孔隙结构得到较大改善,使得碳酸化反应速率和转化率均提高,吸收剂碳酸化特性得到改善。纯K 2CO 3颗粒吸收剂的反应速率和转化率随着粒径的增加而减小,负载型吸收剂的反应速率和转化率随着粒径的增加略增大。研究了不同粒径和反应时间对K 2CO 3/Al 2O 3颗粒微观结构的影响,结果表明K 2CO 3/Al 2O 3颗粒具有较稳定的微观结构。采用负载型粒子模型对K 2CO 3/Al 2O 3吸收剂吸收CO 2碳酸化过程进行研究,所建立的粒子模型计算结果与试验值吻合较好。利用建立的模型对不同CO 2浓度下K 2CO 3/Al 2O 3吸收剂碳酸化反应特性进行模拟计算,模拟结果具备一定的合理性和准确性,为开展进一步研究提供了基础。 相似文献
3.
The storage and release of NO 2 on alumina-supported barium oxide has been studied with particular attention to the stoichiometry of the two processes. At 400 °C the storage process is characterised by a short period of complete uptake, possibly as nitrito or nitro species, followed by a slower partial uptake in which approximately one NO is released for every three NO 2 lost. The latter reaction appears to supply the oxygen necessary to store NO 2 as nitrate ions. Molecular O 2 has little direct involvement even if in large excess. The second storage reaction also occurs, but to a much lesser extent, with Al 2O 3 alone. During temperature programmed desorption, release of NO x from Al 2O 3 peaks at 430 °C with evolution of NO 2 and some O 2. Release from BaO/Al 2O 3 exhibits an additional peak near 520 °C corresponding to formation of NO and a higher O 2 concentration. The NO may arise from NO 2 since BaO/Al 2O 3 has activity for NO 2 decomposition by 500 °C. Although CO 2 at low concentration is rapidly taken up by BaO/Al 2O 3 at 400 °C it is displaced by NO 2 and does not interfere with storage. Thermodynamic calculations show that the formation of Ba(NO 3) 2 by the reaction of NO 2 with bulk BaCO 3 under the conditions used here is more favourable above 380 °C if NO is evolved than if O 2 is consumed. 相似文献
4.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
5.
A glass of composition: SiO 2 = 59·84%; Al 2O 3 = 11·45%; MgO = 15·34%; TiO 2 = 4·23%; K 2O = 3·80%; Na 2O = 2·48%; CaO = 1·08%; Fe 2O 3 = 1·78%; was prepared from porphyric sands by addition of MgO and TiO 2. The quenched glass is demixed on a very fine scale. The non-isothermal devitrification has been studied. Three-dimensional crystal growth has been observed. The experimental data suggest a mechanism controlled by the crystal-glass interface reaction. The crystal growth activation energy E c = 467 ± 20 kJ/mole has been evaluated. The temperature of most efficient nucleation is approximately T N = 720°C. 相似文献
6.
采用挤压-滚圆法制备Na 2CO 3基CO 2吸附剂微球颗粒,在自行设计的CO 2吸收系统中对制备的样品进行脱碳性能测试。结合相关表征测试,探明不同载体、不同负载量的Na 2CO 3基吸附剂的微观结构、脱碳性能以及机械性能的变化规律和内在原因。研究表明:不同载体的Na 2CO 3基吸附剂颗粒脱碳性能存在明显差异,其中氧化铝负载的吸附剂(Na 2CO 3/Al 2O 3)的脱碳性能最好,可达1.14mmol/g。铝酸钙水泥负载的吸附剂(Na 2CO 3/CA)机械性能较好,但其脱碳性能最差。结合吸附剂脱碳和机械性能的综合考量,Na 2CO 3/Al 2O 3是最为合适的CO 2吸附剂,并进一步研究不同Na 2CO 3负载量的影响。研究发现随着Na 2CO 3负载量的变化,吸附剂的微观结构、脱碳性能以及机械性能都存在明显的差异。虽然60%负载量的Na 2CO 3/Al 2O 3吸附剂颗粒的机械性能和脱碳效果较好,但其成球度较差,影响其实际应用。质量分数40%负载量的Na 2CO 3/Al 2O 3吸附剂颗粒具有良好的脱碳性能、机械性能以及成球度,CO 2脱除量为1.36mmol/g。总体而言,利用挤压-滚圆法制备的Na 2CO 3基吸附剂颗粒具有良好的流动特性、脱碳性能和机械性能,适用于电厂烟气中的CO 2脱除。 相似文献
7.
The formation and stability of BaAl 2O 4 and BaCeO 3 in Pt-Ba/Al 2O 3 and Pt-Ba/CeO 2 based NO x storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO 3. The formation of BaAl 2O 4 started above 850 °C, whereas the formation of BaCeO 3 was already observed at 800 °C and was faster than that of BaAl 2O 4. The stability of BaAl 2O 4 and BaCeO 3 in various liquid and gaseous atmospheres was different. BaAl 2O 4 was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO 3) 2 and γ-alumina in the presence of HNO 3, whereas BaCeO 3 was decomposed to much lower extent under these conditions. Interestingly, BaCeO 3 was transformed to Ba(NO 3) 2/CeO 2 in the presence of NO 2/H 2O at 300–500 °C. Also, the presence of CO 2 led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NO x-storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts. 相似文献
8.
Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2. 相似文献
9.
The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO 2, SiO 2–Al 2O 3, activated carbon, mordenite type zeolites, MgO, TiO 2 and Al 2O 3. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO 2 and Al 2O 3 containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO x catalysts supported on TiO 2 and Al 2O 3 also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO x/TiO 2 revealed stronger water tolerance than CrO x/Al 2O 3 due to the surface hydrophobicity. 相似文献
10.
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO x adsorber catalyst, Pt/K/Al 2O 3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al 2O 3 phase with associated hydroxyl groups at the surface, and an alkalized-Al 2O 3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al 2O 3 and 65% for the alkalized-Al 2O 3. NO 2 and CO 2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al 2O 3 adsorbs 0.087 μmol CO 2/m 2and 2.0 μmol NO 2/m 2, and Pt/K/Al 2O 3 adsorbs 2.0 μmol CO 2/m 2and 6.4 μmol NO 2/m 2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al 2O 3 during both lean and rich periods of the NO x adsorber catalyst cycle. 相似文献
11.
A novel process concept called tri-reforming of methane has been proposed in our laboratory using CO 2 in the flue gases from fossil fuel-based power plants without CO 2 separation [C. Song, Chemical Innovation 31 (2001) 21–26]. The proposed tri-reforming process is a synergetic combination of CO 2 reforming, steam reforming, and partial oxidation of methane in a single reactor for effective production of industrially useful synthesis gas (syngas). Both experimental testing and computational analysis show that tri-reforming can not only produce synthesis gas (CO + H 2) with desired H 2/CO ratios (1.5–2.0), but also could eliminate carbon formation which is usually a serious problem in the CO 2 reforming of methane. These two advantages have been demonstrated by tri-reforming of CH 4 in a fixed-bed flow reactor at 850 °C with supported nickel catalysts. Over 95% CH 4 conversion and about 80% CO 2 conversion can be achieved in tri-reforming over Ni catalysts supported on an oxide substrate. The type and nature of catalysts have a significant impact on CO 2 conversion in the presence of H 2O and O 2 in tri-reforming in the temperature range of 700–850 °C. Among all the catalysts tested for tri-reforming, their ability to enhance the conversion of CO 2 follows the order of Ni/MgO > Ni/MgO/CeZrO > Ni/CeO 2 ≈ Ni/ZrO 2 ≈ Ni/Al 2O 3 > Ni/CeZrO. The higher CO 2 conversion over Ni/MgO and Ni/MgO/CeZrO in tri-reforming may be related to the interaction of CO 2 with MgO and more interface between Ni and MgO resulting from the formation of NiO/MgO solid solution. Results of catalytic performance tests over Ni/MgO/CeZrO catalysts at 850 °C and 1 atm with different feed compositions confirm the predicted equilibrium conversions based on the thermodynamic analysis for tri-reforming of methane. Kinetics of tri-reforming were also examined. The reaction orders with respect to partial pressures of CO 2 and H 2O are different over Ni/MgO, Ni/MgO/CeZrO, and Ni/Al 2O 3 catalysts for tri-reforming. 相似文献
12.
Nanosized particles dispersed uniformly on Al 2O 3 particles were prepared from the decomposition of precursor Cr(CO) 6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr 2O 3, CrC 1−x, and C. A solid solution of Al 2O 3–Cr 2O 3 and an Al 2O 3–Cr 2O 3/Cr 3C 2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al 2O 3–Cr 2O 3/Cr-carbide (Cr 3C 2 and Cr 7C 3) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr 3C 2 and Al 2O 3 is non-coherent, while the interface between Cr 7C 3 and Al 2O 3 is semi-coherent. 相似文献
13.
2,4,6-Trimethylphenol was selectively oxidized to 3,5-dimethyl-4-hydroxybenzaldehyde in very good yields using catalytic or equivalent amounts of CuCl 2 in the presence of K 2CO 3 and H 2O 2 in i-PrOH at 65 °C. The effect of the molar ratios of CuCl 2, K 2CO 3 and H 2O 2 on the yields and product distribution was examined. The oxidation reaction was found to proceed smoothly without the use of additives or ligands which were reported to be necessary. 相似文献
14.
Chromium oxide catalysts supported on TiO 2 and Al 2O 3 were examined in a fixed-bed flow reactor system for the removal of PCE (perchloroethylene), a simulant of 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo- p-dioxin), and in a pilot plant employing actual flue gas from a sintering plant for the removal of PCDDs/PCDFs (poly-chlorinated dibenzo-dioxin/poly-chlorinated dibenzo-furan). The 12.5 wt.% chromium oxides supported on TiO 2 and Al 2O 3 revealed excellent stability and performance of PCE removal in the feed gas stream containing water vapor. In a pilot plant study, the catalysts washcoated on the honeycomb reactor revealed 93–95% of PCDDs/PCDFs removal activity over CrO x/Al 2O 3-HC20 (CrO x/Al 2O 3 catalyst washcoated on 20 cell-honeycomb), and more than 99% of the decomposition activity over CrO x/TiO 2-HC20 (CrO x/TiO 2 catalyst washcoated on 20 cell-honeycomb) at 325 °C and 5000 h −1 of reactor space velocity without the de novo synthesis of PCDDs/PCDFs. In particular, CrO x/TiO 2-HC20 showed 94% of PCDDs/PCDFs decomposition activity even at 280 °C reaction temperature. The catalyst also exhibited significant NO removal activity. The chromium oxide seems to be a promising catalyst for the removal of PCDDs/PCDFs and NO x contained in the flue gas. 相似文献
15.
利用等体积浸渍法制备K 2CO 3/γ-A1 2O 3负载型固体碱催化剂,应用于棉籽油和甲醇酯交换反应制备生物柴油。对催化剂使用前的保存条件、水分、重复使用性能、游离脂肪酸影响以及失活和再生进行了分析。结果表明,固体催化剂K 2CO 3/γ-Al 2O 3具有较好的抗水性,酸度对催化剂影响明显,重复使用4次未经活化的催化剂,催化活性明显降低,催化剂应密封保存。K 2CO 3/γ-A1 2O 3负载型固体碱催化剂经济实惠且催化效果良好。 相似文献
16.
The durability of plasma-sprayed metals bonded with a polyimide adhesive has been studied. Metal adherend surfaces were prepared for adhesive bonding by plasma-spraying inorganic powders on aluminum and titanium. The plasma-sprayed materials included Al 2O 3, AlPO 4. MgO, and SiO 2 on aluminum, and TiO 2, TiSi 2, MgO, and SiO 2 on titanium. The coatings were sprayed at two different thicknesses. Durability studies of samples prepared in a wedge-type geometry were carried out. Bonded specimens were maintained in an environmental cycle that included exposure to the conditions; low temperature, - 20°C; relative humidity at elevated temperature, 70% RH at 66°C; elevated temperature (160°C) in air, high temperature (160°C) in vacuum (130 torr, 0.2 atm.), and room temperature. Crack growth rate and mode of failure were determined. The results of the durability tests indicate that thin coatings (25 μm) of plasma-sprayed materials perform better than thicker (150 μm) coatings. The crack growth rate for thin coatings (25 μm) of Al 2O 3, AlPO 4, SiO 2, and MgO plasma-sprayed on aluminum was equivalent to that for phosphoric acid anodized aluminum. Similarly, the durability performance for titanium samples prepared with a 25 μm-thick TiO 2, TiSi 2, and SiO 2 plasma-sprayed coatings was equivalent to that for a Turco®-prepared titanium surface. Although the evaluation of durability as a function of surface chemistry was an objective of the study, it was not possible to evaluate the effect, since most failures occurred within the adhesive (cohesive failure) during the environmental tests. That failure occurred in the adhesive indicates that the coating-adherend and the coating-adhesive interactions are sufficiently robust to prevent interfacial failure under the experimental conditions investigated. 相似文献
17.
The influence of different promoters (CeO 2, MnO x, K 2CO 3) on various properties of a standard coprecipitated Cu/ZnO/Al 2O 3 catalyst has been examined. The catalysts prepared were characterized by Cu surface area, PTIR and TPR measurements. It was found that addition of K 2CO 3 reduced the Cu surface area by about 30%, whereas the Cu surface area did not decrease with addition of the other promoters. The reduction behaviour was affected by the addition of K 2CO 3 as well as by MnO x, but not by CeO 2. The cause of these effects is possibly an electronic interaction between the promoter and Cu ions.The effect of the different promoters on the activity and selectivity has also been studied. The K 2CO 3 promoted catalyst has an optimum selectivity to higher alcohols at 280 °C; addition of Mn made the catalyst more selective towards methanol. At 300 °C, the Ce promoted catalyst had a high selectivity to methanol and iso-butanol. The promoting effect of the additives may be caused by stabilization of the surface intermediates leading to alcohols. Infrared measurements of adsorbed CO or adsorbed methanol on materials with and without K did not, however, provide any evidence for a difference in reaction mechanism. 相似文献
18.
The effects of a large number of sintering aids for the densification of magnesia were examined. Al 2O 3, BaO, Fe 2O 3, P 2O 5, SiO 2, TiO 2, Y 2O 3 and ZrO 2 are effective for the sintering of CVD-MgO powders at low doping levels. The effects of TiO 2 and ZrO 2 are significant. Heavy doping is harmful for densification. The eight oxides above are also effective for the sintering of seawater MgO, but the degree of effectiveness is smaller than for CVD-MgO. In the doping of BaO, P 2O 5, SiO 2 and TiO 2, which form eutectic liquids with MgO below 1600°C, there is an optimum firing temperature for densification. Vickers hardness of doped MgO is proportional to the relative density and is unaffected by doping. Corrosion resistance of MgO ceramics for liquid PbO is also unaffected by dopants, except for P2O5. 相似文献
19.
Reforming of methane with carbon dioxide to synthesis gas (CO/H 2) has been investigated over rhodium supported on SiO 2, TiO 2, γ-Al 2O 3, MgO, CeO 2, and YSZ (ZrO 2 (8 mol% Y 2O 3)) catalysts in the temperature range of 650–750°C at 1 bar total pressure. A strong carrier effect on the initial specific activity, deactivation rate, and carbon accumulation was found to exist. A strong dependence of the specific activity of the methane reforming reaction on rhodium particle size was observed over certain catalysts. Tracing experiments (using 13CH 4) coupled with temperature-programmed oxidation (TPO) revealed that the carbon species accumulated on the surface of the Rh/Al 2O 3 catalyst during reforming reaction at 750°C are primarily derived from the CO 2 molecular route. The amount of carbon present on the working catalyst surface which is derived from the CH 4 molecular route is found to be very small. 相似文献
20.
The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al 2O 3, TiO 2, ZrO 2 and MgO. The promotion of V 2O 5/Al 2O 3 catalyst with alkali metals (Li, Na, K) was also attempted. Evaluation of temperature programmed reduction patterns showed that the reducibility of V species is affected by the support acid–base character. The catalytic activity is favored by the V reducibility of the catalyst as it was confirmed from runs conducted at 450–550°C. V 2O 5/TiO 2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support’s nature also affects the selectivity to propene; V 2O 5 supported on Al 2O 3 catalyst exhibits the highest selectivity. Reaction studies showed that addition of alkali metals decreases the catalytic activity in the order non-doped>Li>Na>K. Propene selectivity significantly increases in the presence of doped catalysts. 相似文献
|