共查询到20条相似文献,搜索用时 375 毫秒
1.
A perovskite material of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF), with both electronic and ionic conductivity, was synthesized by a combined citrate–EDTA complexing method. The dense membrane tube made of BSCF was fabricated using the plastic extrusion method. The partial oxidation of methane (POM) to syngas was performed in the tubular BSCF membrane reactor packed with a LiLaNiO/γ–Al 2O 3 catalyst. The reaction performance of the membrane reactor was investigated as functions of temperature, air flow rate in the shell side and methane concentration in the tube side. The mechanism of POM in the membrane reactor was discussed in detail. It was found that in the tubular membrane reactor, combustion reaction of methane with permeated oxygen took place in the reaction zone close to the surface of the membrane, then followed by steam and CO 2 reforming of methane in the middle zone of the tube side. The membrane tube can be operated steadily for 500 h in pure methane with 94% methane conversion and higher than 95% CO selectivity, and higher than 8.0 ml/cm 2 min oxygen permeation flux. 相似文献
2.
Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/γ-Al 2O 3 catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3 which has an oxygen permeation flux around 11.5 ml/cm 2 min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/γ-Al 2O 3 in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91–93% and a H 2 selectivity of 95–97% have been achieved. 相似文献
3.
A disk-type Sm 0.4Ba 0.6Co 0.2Fe 0.8O 3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H 2). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH 4 diluted with Ar. While CH 4 conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH 4 conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH 4 compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH 4 was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H 2 was fed. It is implied that the oxidation of CO and H 2 with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO 2 and H 2O react with CH 4 by reforming reactions to form syngas. 相似文献
4.
Partial conductivities in the SrCe(Y)O 3−δ system have been studied in oxidising conditions in the temperature range 923–1273 K. Compositions with variable Y content (5 and 10 at.%), Sr deficiency (3 at.%), and with the addition of Fe 2O 3 as sintering aid (2 mol%) were analysed. A modified Faradaic efficiency method and oxygen permeation measurements were employed to appraise the oxide-ionic transport. Oxide-ion transference numbers in air lie in the range 0.19–0.80 and decrease with increasing temperature in the range 973–1223 K. Modelling of total conductivity as a function of oxygen partial pressure ( p(O 2)) confirmed that protonic transport is minor under the studied conditions. SrCe 0.95Y 0.05O 3−δ exhibits greater oxide-ion conductivity than SrCe 0.9Y 0.1O 3−δ, indicative of dopant–vacancy association at high dopant contents. Conversely, oxygen permeability is slightly higher for SrCe 0.9Y 0.1O 3−δ as a result of faster surface-exchange kinetics. The oxygen flux through Fe-free membranes is dominated by the bulk in low p(O 2) gradients, when the permeate-side p(O 2) is higher than 0.03 atm, but surface exchange plays an increasing role with increasing p(O 2) gradient. Addition of Fe 2O 3 to SrCe(Y)O 3−δ lowers the sintering temperature by 100 K but results in the formation of intergranular second phases which block oxide-ionic and electronic transport, and thus oxygen permeation. The average thermal expansion coefficients (TECs) are (10.8–11.6) × 10 −6 K −1 in the temperature range 373–1373 K for all studied compositions. 相似文献
5.
La 2NiO 4 tubular membranes of relative density over 92% were used to separate oxygen from air and facilitate the partial oxidation of methane to H 2 and CO at 900 °C. When methane was fed into a tube of inner surface area 5.11 cm 2 at a rate of 10.5 ml/min, methane throughput conversion was 89%, CO selectivity 96%, H 2/CO ratio 1.5, and the equivalent oxygen flux was 6.8 ml/min. The surface of the La 2NiO 4 membrane exposed to CH 4 decomposed into La 2O 3 and Ni, while the surface in contact with air remained almost unchanged. It is suggested that the conversion of methane in the membrane reactor involves the reforming of methane by the H 2O and CO 2 catalyzed by nickel. 相似文献
6.
Dependence of microwave dielectric properties on the crystal structure of (Zn 1/3B 2/35+) xTi 1 − xO 2 (B 5+ = Nb, Ta) ceramics was investigated as a function of Zn 1/3B 2/35+O 2 (B 5+ = Nb, Ta) content (0.4 ≤ x ≤ 0.7). Dielectric constant ( K) and the temperature coefficient of resonant frequency ( TCF) of sintered specimens were strongly dependent on the structural characteristics of oxygen octahedra in rutile structure. Cation rattling and the distortion of oxygen octahedra were dependent on the bond length ratio of apical ( dapical)/equatorial ( dequatorial) of oxygen octahedra. The quality factor ( Qf) was dependent on the reduction of Ti ion as well as the microstructure of the sintered specimens. 相似文献
7.
Performances of BaTi 1 − xNi xO 3 perovskites, prepared using sol–gel method, as catalysts for partial oxidation of methane to syngas have been studied. The catalysts were characterized by XRD, BET and TEM. The experimental studies showed the calcination temperature and Ni content exhibited a significant influence on catalytic activity. Among catalysts tested, the catalyst BaTi 0.8Ni 0.2O 3 exhibited the best activity and excellent stability. 相似文献
8.
Catalytic combustion of methane has been investigated over AMnO 3 (A = La, Nd, Sm) and Sm 1−xSr xMnO 3 ( x = 0.1, 0.3, 0.5) perovskites prepared by citrate method. The catalysts were characterized by chemical analysis, XRD and TPR techniques. Catalytic activity measurements were carried out with a fixed bed reactor at T = 623–1023 K, space velocity = 40 000 N cm 3 g −1 h −1, CH 4 concentration = 0.4% v/v, O 2 concentration = 10% v/v. Specific surface areas of perovskites were in the range 13–20 m2 g−1. XRD analysis showed that LaMnO3, NdMnO3, SmMnO3 and Sm1−xSrxMnO3 (x = 0.1) are single phase perovskite type oxides. Traces of Sm2O3 besides the perovskite phase were detected in the Sm1−xSrxMnO3 catalysts for x = 0.3, 0.5. Chemical analysis gave evidence of the presence of a significant fraction of Mn(IV) in AMnO3. The fraction of Mn(IV) in the Sm1−xSrxMnO3 samples increased with x. TPR measurements on AMnO3 showed that the perovskites were reduced in two steps at low and high temperature, related to Mn(IV) → Mn(III) and Mn(III) → Mn(II) reductions, respectively. The onset temperatures were in the order LaMnO3 > NdMnO3 > SmMnO3. In Sm1−xSrxMnO3 the Sr substitution for Sm caused the formation of Mn(IV) easily reducible to Mn(II) even at low temperature. Catalytic activity tests showed that all samples gave methane complete conversion with 100% selectivity to CO2 below 1023 K. The activation energies of the AMnO3 perovskites varied in the same order as the onset temperatures in TPR experiments suggesting that the catalytic activity is affected by the reducibility of manganese. Sr substitution for Sm in SmMnO3 perovskites resulted in a reduction of activity with respect to the unsubstituted perovskite. This behaviour was related to the reduction of Mn(IV) to Mn(II), occurring under reaction conditions, hindering the redox mechanism. 相似文献
9.
The first oxygen permeation data of a dense hollow fiber perovskite membrane based on BaCo xFe yZr zO 3 − δ are reported. The hollow fiber was prepared by a phase inversion process. Dense fibers were obtained with the following typical geometries: outer diameter, 800–900 μm; inner diameter, 500–600 μm; length, 30 cm. The O 2-permeation through the hollow fiber perovskite membrane was studied in a high-temperature gas permeation cell under different operation conditions. The increase of the helium gas flow rate reduces the oxygen partial pressure ( pO2) on the core side and a higher oxygen permeation flux is observed. High oxygen flux of 0.73 m 3 (O 2)/(m 2 (membrane) h) was achieved at 850 °C under the operation parameters Fair (shell side) = 150 ml/min and FHe (core side) = 30 ml/min. The oxygen partial pressure dependence of the O 2 permeation flux indicated an interplay of both surface reaction and bulk diffusion as rate limiting steps. During 5 days of permeation a high and stable oxygen flux was observed. X-ray diffraction patterns of fresh and spent membranes after the permeation measurements revealed that no degradation after oxygen permeation appears. 相似文献
10.
Catalytic methane combustion and CO oxidation were investigated over AFeO 3 (A=La, Nd, Sm) and LaFe 1−xMg xO 3 ( x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterized by X-ray diffraction (XRD). Redox properties and the content of Fe 4+ were derived from temperature programmed reduction (TPR). Specific surface areas (SA) of perovskites were in 2.3–9.7 m 2 g −1 range. XRD analysis showed that LaFeO 3, NdFeO 3, SmFeO 3 and LaFe 1−xMg xO 3 ( x·0.3) are single phase perovskite-type oxides. Traces of La 2O 3, in addition to the perovskite phase, were detected in the LaFe 1−xMg xO 3 catalysts with x=0.4 and 0.5. TPR gave evidence of the presence in AFeO 3 of a very small fraction of Fe 4+ which reduces to Fe 3+. The fraction of Fe 4+ in the LaFe 1−xMg xO 3 samples increased with increasing magnesium content up to x=0.2, then it remained nearly constant. Catalytic activity tests showed that all samples gave methane and CO complete conversion with 100% selectivity to CO 2 below 973 and 773 K, respectively. For the AFeO 3 materials the order of activity towards methane combustion is La>Nd>Sm, whereas the activity, per unit SA, of the LaFe 1−xMg xO 3 catalysts decreases with the amount of Mg at least for the catalysts showing a single perovskite phase ( x=0.3). Concerning the CO oxidation, the order of activity for the AFeO 3 materials is Nd>La>Sm, while the activity (per unit SA) of the LaFe 1−xMg xO 3 catalysts decreases at high magnesium content. 相似文献
11.
With an aim to improve the 5 V capacity and cyclability of the LiMn 1.5Ni 0.5O 4 spinel oxide, three series of Cr substitutions have been pursued with y ≤ 0.2: LiMn 1.5Ni 0.5−yCr yO 4, LiMn 1.5−0.5yNi 0.5−0.5yCr yO 4, and LiMn 1.5−0.33yLi 0.33yNi 0.5−yCr yO 4. While the first series involves an increase in the Mn 3+ content, the second and third series are designed to maintain charge neutrality (Mn 4+, Ni 2+, Cr 3+, and Li +) without introducing Mn 3+ ions. The LiMn 1.5Ni 0.5−yCr yO 4 series experiences a widening of the 4 V plateau and a decrease in the 5 V capacity compared to LiMn 1.5Ni 0.5O 4 due to an increase in the Mn 3+ content. On the other hand, the LiMn 1.5−0.5yNi 0.5−0.5yCr yO 4 series shows a suppression of the 4 V plateau and an increase in the 5 V capacity due to the elimination of the Mn 3+ions. The LiMn 1.5−0.33yLi 0.33yNi 0.5−yCr yO 4 series shows a suppression of the 4 V plateau at low Cr contents, but an increase in the 4 V plateau as the Cr content increases above 0.1. Among the various compositions investigated, LiMn 1.45Ni 0.45Cr 0.1O 4 exhibits the best combination of high 5 V capacity (128 mAh/g at 5–4.2 V) and excellent capacity retention (98% in 50 cycles) compared to 118 mAh/g and 92% for LiMn 1.5Ni 0.5O 4. 相似文献
12.
The impact of oxygen permeability using an ionic oxygen conducting membrane reactor with surface catalyst was investigated for the oxidative coupling of methane to higher hydrocarbons. Dense Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCFO), Ba 0.5Sr 0.5Mn 0.8Fe 0.2O 3−δ (BSMFO) and BaBi 0.4Fe 0.6O 3 (BBFO) membrane disks with Pt/MgO catalysts were prepared by sol–gel deposition or wash-coating. It is demonstrated that the oxygen supply by permeation needs to fit to the consumption during the coupling reaction. In case of insufficient oxygen supply comparably poor conversions are observed while higher oxygen fluxes lead to increased methane conversions, especially in the presence of an efficient catalyst. Generally, increasing catalytic activity leads to lower C 2 selectivity, especially for low oxygen permeation fluxes. The concept of a reactor employing dense catalytic membranes is viable, but the present study identifies further potential when the activity of the catalyst for the oxidative coupling is improved, leading to an overall enhanced performance of the membrane reactor. 相似文献
13.
Pt-Rh/Ce xZr 1−xO 2-Al 2O 3 with 0.6 and 1.0 wt.% noble metal loadings were prepared and characterized for their metal dispersion with respect to Ce xZr 1−xO 2-free Pt-Rh/Al 2O 3 in fresh, thermally aged and oxychlorinated states. Thermal ageing at 973 K led to loss of metal dispersion in all cases but to negligible effect on the dispersion of the Ce xZr 1−xO 2 component where present. Oxychlorination was able to fully recover metal dispersion in all cases but led to different effects on the redox properties of Ce xZr 1−xO 2 which appeared to be related to the metal loadings. Despite showing improved dispersion following regeneration, higher loaded catalyst showed no improvement in light-off performance for either NO reduction or CO oxidation and showed poorer oxygen storage (OSC) ability, particularly at higher temperatures. Lower loaded catalyst showed improved dispersion, improved OSC and reduced light-off temperatures for NO reduction and CO oxidation after oxychlorination compared to that in the thermally aged state. 相似文献
14.
A series of the Ce 1−xCu xO 2−x/Al 2O 3/FeCrAl catalysts ( x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H 2-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce 1−xCu xO 2−x/Al 2O 3/FeCrAl catalysts the surface phase structure were the Ce 1−xCu xO 2−x solid solution, -Al 2O 3 and γ-Al 2O 3. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce 1−xCu xO 2−x solid solution. The Cu component of the Ce 1−xCu xO 2−x/Al 2O 3/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce 1−xCu xO 2−x solid solution and the Al 2O 3 washcoats and the FeCrAl support. 相似文献
15.
The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi 2(Zn 1/3Nb 2/3) 2O 7 (BZN) and Bi 2(Zn 1/3Nb 2/3−xV x) 2O 7 (BZNV, x = 0.001) sintered under air and N 2 atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V 2O 5 and N 2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N 2 atmosphere with r = 76.1, Q = 850 and Qf = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with r = 76.7, Q = 890 and Qf = 3580 GHz. The temperature coefficient of resonant frequency τf was not obviously influenced by the different atmospheres. For BZN ceramics the τf was −79.8 ppm/°C while τf is −87.5 ppm/°C for BZNV ceramics. 相似文献
16.
A novel process called Liquid Source Misted Chemical Deposition (LSMCD) was used to synthesize Al-doped LiMn 2O 4 cathode films for Lithium microbatteries. The cathode films were characterized by XRD, SEM, cyclic volatmmetry, and charge/discharge test. LiMn 1.8Al 0.2O 4 film crystallized at 800 °C in rapid thermal annealing (RTA) for 5 min under oxygen atmosphere exhibited more improved electrochemical rechargeability than spinel LiMn 2O 4 film because the substitution of Al 3+ for Mn 3+ increased Mn---O bonding strength in the spinel framework and suppressed the two-phase behavior of the unsubstituted spinel during the intercalation/deintercalation that is the origin of the failure mechanism in the 4 V region. As a result, LiMn 1.8Al 0.2O 4 film showed an initial discharge capacity of 52 μAh/cm 2 μm and no capacity fade over 100 cycles. 相似文献
17.
We have used a complex sol–gel process to synthesize a family of compounds LiNi xCo 1−xO 2 ( x = 0, 0.25, 0.5, 0.75, 1). These compounds are candidates for electrode materials in high-energy-density batteries. Starting sols were prepared from xNi 2+ + (1 − x) Co 2+ acetates/ascorbic acid aqueous solutions by alkalizing with LiOH and NH 3. With thermal treatment in air, nickel carbonates formed in quantities roughly proportional to Ni concentration. The carbonate impurities could not be fully removed by heating in air to high temperatures. Because formation of pure layered oxides was inhibited by the presence of the carbonates, we developed a new way to remove them from just-formed precursors by treating the intermediate phases (those formed after calcination at 750 °C) with concentrated HNO 3 and H 2O 2. All resulting powders were phase pure by X-ray diffraction and were easily friable. Various electrochemical properties of compacts prepared from these powders were measured. 相似文献
18.
Ceramics with a composition close to BaZn 2Ti 4O 11 were synthesized according to various substitutional mechanisms in order to verify an existence of a homogeneity range in the vicinity of this composition. Structural and microstructural investigations showed that the crystal structure of BaZn 2Ti 4O 11 was formed in the homogeneity range corresponding to the formula BaZn 2 − xTi 4O 11 − x (0 < x < 0.1). Densely sintered BaZn 2 − xTi 4O 11 − x (0 < x < 0.1) ceramics exhibited a dielectric constant around 30, τf = −30 ppm/K and high Q × f values, which increased from 68,000 GHz at x = 0 to 83,000 GHz at x = 0.05. Structurally, the deficiency of Zn in BaZn 2 − xTi 4O 11 − x (0 < x < 0.1) resulted in a slight decrease in the unit-cell volume. The influence of secondary phases in the BaZn 2Ti 4O 11-based materials on the microwave dielectric properties was also investigated. A presence of small amounts of ZnO, BaTiO 3, hollandite-type solid solutions (Ba xZn xTi 8 − xO 16) and BaTi 4O 9 caused a decrease in Q × f values. 相似文献
19.
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
20.
Nanoparticles of Ce xZr 1−xO 2 ( x = 0.75, 0.62) were prepared by the oxidation-coprecipitation method using H 2O 2 as an oxidant, and characterized by N 2 adsorption, XRD and H 2-TPR. Ce xZr 1−xO 2 prepared had single fluorite cubic structure, good thermal stability and reduction property. With the increasing of Ce/Zr ratio, the surface area of Ce xZr 1−xO 2 increased, but thermal stability of Ce xZr 1−xO 2 decreased. The surface area of Ce 0.62Zr 0.38O 2 was 41.2 m 2/g after calcination in air at 900 °C for 6 h. TPR results showed the formation of solid solution promoted the reduction of CeO 2, and the reduction properties of Ce xZr 1−xO 2 were enhanced by the cycle of TPR-reoxidation. The Pd-only three-way catalysts (TWC) were prepared by the impregnation method, in which Ce 0.75Zr 0.25O 2 was used as the active washcoat and Pd loading was 0.7 g/L. In the test of Air/Fuel, the conversion of C 3H 8 was close to 100% and NO was completely converted at λ < 1.025. The high conversion of C 3H 8 was induced by the steam reform and dissociation adsorption reaction of C 3H 8. Pd-only catalyst using Ce 0.75Zr 0.25O 2 as active washcoat showed high light off activity, the reaction temperatures ( T50) of 50% conversion of CO, C 3H 8 and NO were 180, 200 and 205 °C, respectively. However, the conversions of C 3H 8 and NO showed oscillation with continuously increasing the reaction temperature. The presence of La 2O 3 in washcoat decreased the light off activity and suppressed the oscillation of C 3H 8 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 La 2O 3 in active washcoat can enhance the thermal stability of catalyst significantly. 相似文献
|