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1.
This paper presents a study on the influence of support (Al 2O 3, MgO, SiO 2-Al 2O 3, SiO 2-MgO, β-zeolite, and CeO 2) of Cu-ZnO catalysts for the low-temperature water–gas shift reaction. Supported Cu-ZnO catalysts were prepared by the conventional impregnation method, followed by the H 2 reduction. The activity of Cu-ZnO catalysts for the water–gas shift (WGS) reaction was largely influenced by the kind of support; Cu-ZnO catalysts supported on Al 2O 3, MgO, and CeO 2 showed high activity, while those on SiO 2-Al 2O 3, SiO 2-MgO and β-zeolite showed less activity in the temperature range 423–523 K. XRD analysis demonstrated that the copper species were highly dispersed on the supports used in the present study, except for a MgO support. TPR results of a series of supported CuO-ZnO catalysts suggest that the reducibility of CuO is one of the important factors controlling the activity of the WGS reaction over the supported catalysts. 相似文献
2.
Mesostructured MnO x–Cs 2O–Al 2O 3 nanocomposites have been synthesized by reverse microemulsion method combined with hydrothermal treatment and then applied to the catalytic combustion of methane. Compared to impregnation-derived conventional MnO x/Cs 2O/Com-Al 2O 3 catalyst, the microemulsion-derived catalyst showed higher activity and stability for methane combustion. The T10% of the fresh and of the 72 h aged Mn xO–Cs 2O–Al 2O 3 were 475 and 490 °C, respectively, recommending it as a potential candidate catalyst for application in hybrid gas turbines. The homogeneous composition of the microemulsion-derived nanocomposite catalyst can hinder the loss of Cs + and accelerate the formation of Cs–β-alumina phase, ensuring thus higher activity and stability for methane combustion. 相似文献
3.
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
4.
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
5.
The effect of TiO 2 on the grain growth of the ZnO–Bi 2O 3–CoO–MnO ceramic system prepared by chemical coprecipitation, was studied between 1150 and 1300 °C in air. Bi 2O 3 melts during firing, and then TiO 2 dissolves into Bi 2O 3-rich liquid. TiO 2 initially reacts with Bi 2O 3 to form Bi 4Ti 3O 12. Above ≈1050 °C, Bi 4Ti 3O 12 reacts with ZnO to form Zn 2TiO 4 spinel phase. The kinetic study of grain growth carried out using the expression Gn– Gon= Ko· t·exp(− Q/ RT) gave grain exponent ( n) value as 6 and the apparent activation energy ( Q) as 226.46 kJ/mol. 1.00 mol% TiO 2 addition increased the grain growth exponent value from 6 to 7 and apparent activation energy with 1.00 mol% TiO 2 addition was found to be 197.10 kJ/mol. The ZnO grain size gradually increases with increasing TiO 2 content. Addition of TiO 2 may increase the reactivity of the Bi 2O 3-rich liquid towards the ZnO grain, thus affecting the ZnO grain growth. 相似文献
6.
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
7.
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
8.
Pd-only three-way catalysts prepared by the sol–gel method were investigated by the three-way catalytic performance test with a simulated exhaust gas in a continuous U-tube quartz reactor at a gas hourly space velocity of 72 000 h −1. The catalysts were characterized with XRD, XPS, BET surface area and pore volume. The activity and thermal stability of the Pd–Al 2O 3 catalyst prepared at pH 10 were superior to those at pH 4 during hydrolysis and condensation, which could be explained by the anchoring effect. Zr and V were found to be good promoters for the enhancement of the thermal stability and SO 2 resistance, respectively. Optimally formulated catalyst, Pd(1)–V(2)–Zr(10)–Al 2O 3, was thermally stable up to 900 oC and showed a much more improved low-temperature activity and excellent SO 2 resistance. 相似文献
9.
Mixed oxides of general formulae Ta yNb 1−yO 5 (0< y<1) have been synthesized by a modified sol–gel method. Characterization of the samples has been carried out by x-ray diffraction, SEM/EDX, FTIR spectroscopy and thermal analysis. The electrochemical properties have been studied in a lithium cell. The first discharge capacity decrease from 206 ( y=0.25) to 136 mA h g −1 ( y=0.75). Ta yNb 1−yO 5 samples undergo an irreversible structural changes induced by electrochemical Li +-insertion. For all compositions, the new compounds formed after the first discharge has a very high cyclability, as shown the low capacity loss <1% per cycle. 相似文献
10.
Perovskites of different La 1−xSr xAl 1−y−y′Fe yMg y′O 3−δ compositions ( x=0, 0.1, 0.15, 0.2 and y=0.1, 0.3, 0.5, 0.8) were prepared from a reactive precursor slurry of hydrated oxides. Each sample was aged between 16 and 26 h up to 1473 K. Activity in methane combustion (1%/air) was determined in a plug-flow reactor, with 1 g catalyst and 24 l/h flowrate. Gradual decrease in activity due to thermal aging was observed, the degree of activity loss being composition dependent. Nevertheless, activity of samples aged at 1370 K was nearly independent of composition. The best thermal stability showed LaAl 0.65Fe 0.15Mg 0.2O 3 perovskite. None of the magnesium substituted perovskites performed better than a La 0.85Sr 0.15Al 0.87Fe 0.13O 3 reference sample. 相似文献
11.
A series of CuO–ZnO/Al 2O 3 solids were prepared by wet impregnation using Al(OH) 3 solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O 2 at temperatures ranged between 125°C and 200°C. The results showed that CuO interacts with Al2O3 to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl2O4 at 600°C while stimulates its production at 800°C. The treatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol−1 in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature. 相似文献
12.
The effect of the Pd addition method into the fresh Pd/(OSC + Al 2O 3) and (Pd + OSC)/Al 2O 3 catalysts (OSC material = Ce xZr 1−xO 2 mixed oxides) was investigated in this study. The CO + NO and CO + NO + O 2 model reactions were studied over fresh and aged catalysts. The differences in the fresh catalysts were insignificant compared to the aged catalysts. During the CO + NO reaction, only small differences were observed in the behaviour of the fresh catalysts. The light-off temperature of CO was about 20 °C lower for the fresh Pd/(OSC + Al 2O 3) catalyst than for the fresh (Pd + OSC)/Al 2O 3 catalyst during the CO + NO + O 2 reaction. For the aged catalysts lower NO reduction and CO oxidation activities were observed, as expected. Pd on OSC-containing alumina was more active than Pd on OSC material after the agings. The activity decline is due to a decrease in the number of active sites on the surface, which was observed as a larger Pd particle size for aged catalysts than for fresh catalysts. In addition, the oxygen storage capacity of the aged Pd/(OSC + Al 2O 3) catalyst was higher than that of the (Pd + OSC)/Al 2O 3 catalyst. 相似文献
13.
The current work is devoted to study of CO interaction with PdO/Al 2O 3–(Ce x–Zr 1−x)O 2 catalysts. Ceria–zirconia–alumina supports with different Ce/Zr ratio were prepared by sol–gel technique. The FT-IR characterization of CO adsorbed at −120 and 25 °C on oxidized and reduced samples revealed that Ce/Zr ratio modifies the surface properties of support and oxidation state of palladium. The catalyst with Ce/Zr molar ratio 0.5/0.5 was characterized with the highest ability to stabilize palladium in oxide state and the highest activity to oxidize CO. Redox treatment of catalysts improves their catalytic activity. 相似文献
14.
A novel catalyst based on copper-silver was developed to solve the contradiction between the high conversion temperature of Cu-based catalyst and low N 2 selectivity of Ag-based catalyst during selective oxidation of ammonium gas. The Cu-Ag-based catalyst (Cu 5 wt.%-Ag 5 wt.%/Al 2O 3) displayed a relatively low complete conversion temperature (<320 °C) with a high N 2 selectivity (>95%). Increasing loading of Cu and Ag decreases N 2 selectivity. The low N 2 selectivity of Ag-based catalyst is possibly related to the formation of Ag 2O crystals. Improvement of N 2 selectivity of Ag-based catalyst was obtained by doping Cu to decrease crystallized Ag 2O phase. The temperature programmed reaction (TPR) data show that N 2O is the main byproduct of oxidation of ammonia at temperature lower than 200 °C. Two bands of nitrate species at 1541 and 1302 cm −1 were observed on Ag 10 wt.%/Al 2O 3 at the temperature higher than 250 °C, which indicates the formation of NO x during the selective catalytic oxidation of ammonia. No nitrate species was observed on Cu 10 wt.%/Al 2O 3 and Cu 5 wt.%-Ag 5 wt.%/Al 2O 3, while only one nitrate species (1543 cm −1) existed on Cu 10 wt.%-Ag 10 wt.%/Al 2O 3. We proposed that mixing Ag with Cu inhibited the formation of NO x during the selective catalytic oxidation of ammonia over Cu-Ag/Al 2O 3. 相似文献
15.
La xSr 2−xMnO 4 (0 ≤ x ≤ 0.8) oxides were synthesized and single-phase K 2NiF 4-type oxides were obtained in the range of 0.1 ≤ x < 0.5. The catalytic activity of La xSr 2−xMnO 4 for NO–CO reaction increased with increasing x in the range of solubility limit of La. La 0.5Sr 1.5MnO 4 showed the highest activity among La xSr 2−xMnO 4 prepared in this study, but its activity was inferior to perovskite-type La 0.5Sr 0.5MnO 3. Among the Pd-loaded catalysts, however, Pd/La 0.8Sr 1.2MnO 4 showed the higher activity and the selectivity to N 2 than Pd/La 0.5Sr 0.5MnO 3 and Pd/γ-Al 2O 3. The excellent catalytic performance of Pd/La 0.2Sr 1.2MnO 4 could be ascribable to the formation of SrPd 3O 4 which was detected by XRD in the catalyst but not in the other two catalysts. 相似文献
16.
Mixed oxides of the general formula La 0.5Sr xCe yFeO z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO 3 and SrFeO 3−x and oxides -Fe 2O 3 and CeO 2 depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH 4+O 2 (“lean-NO x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La 3+ cation at A-site with divalent Sr +2 and tetravalent Ce +4 cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La 0.5Sr xCe yFeO z materials to reduce NO by CO or by CH 4 under “lean-NO x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s −1) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al 2O 3 catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La 0.5Sr xCe yFeO z solids and their catalytic activity. O 2 TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O 2 TPD studies was observed for the La 0.5Sr 0.2Ce 0.3FeO z and La 0.5Sr 0.5FeO z solids. 相似文献
17.
A series of CoO x/Al 2O 3 catalysts was prepared, characterized, and applied for the selective catalytic reduction (SCR) of NO by C 3H 8. The results of XRD, UV–vis, IR, Far-IR and ESR characterizations of the catalysts suggest that the predominant oxidation state of cobalt species is +2 for the catalysts with low cobalt loading (≤2 mol%) and for the catalysts with 4 mol% cobalt loading prepared by sol–gel and co-precipitation. Co 3O 4 crystallites or agglomerates are the predominant species in the catalysts with high cobalt loading prepared by incipient wetness impregnation and solid dispersion. An optimized CoO x/Al 2O 3 catalyst shows high activity in SCR of NO by C 3H 8 (100% conversion of NO at 723 K, GHSV: 10,000 h −1). The activity of the selective catalytic reduction of NO by C 3H 8 increases with the increase of cobalt–alumina interactions in the catalysts. The influences of cobalt loading and catalyst preparation method on the catalytic performance suggest that tiny CoAl 2O 4 crystallites highly dispersed on alumina are responsible for the efficient catalytic reduction of NO, whereas Co 3O 4 crystallites catalyze the combustion of C 3H 8 only. 相似文献
18.
The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La 1−xCa xAl 11−y−zMg yTi zO 18 ( x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl 11O 18 and second phases LaAlO 3 and -Al 2O 3 are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste. 相似文献
19.
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
20.
In order to improve a “Three Function Catalysts Model”, the present paper deals with alumina based catalysts containing cobalt and palladium for the NO reduction by methane. The deNOx temperature window was estimated by adsorption and subsequent desorption of NO in lean conditions. Two NOx desorption peaks were detected for both catalysts. For Pd(0.63)Co(0.58)/Al2O3, the two desorption peaks appeared at 205 and 423 °C, whereas for Pd(0.14)Co(0.57)/Al2O3, the maxima desorption temperature peaks were at 205 and 487 °C. In addition, NO oxidation was also studied to evaluate the catalyst first function. It was found that, the oxidation begins on Co–Pd/Al2O3 around 250 °C. On Pd(0.63)Co(0.58)/Al2O3, 8% of deNOx were found in the range of the second NOx desorption peak temperature (410 °C). During TPSR, CxHyOz species such as formaldehyde were detected. These oxygenate species are the reactive intermediate for deNOx by methane. 相似文献
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