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1.
The texture of Fe 2O 3 support and Ru/Fe 2O 3 catalysts supported on iron oxides obtained from β-FeOOH (B) or δ-FeOOH (D) and their catalytic activity in WGSR were studied. Also their susceptibilities to reduction and reoxidation, were studied by TPR, using H 2 or CO and TPO methods. In the case of TPR CO the composition of the reducing mixture containing traces of H 2O enabled investigation of water gas shift reaction (WGSR). The catalysts from series D were found more readily reducible and oxidised than those from series B. The supported ruthenium enhanced the redox effects and caused the appearance of additional effects related directly to its presence. Depending on the kind of support and on ruthenium presence considerable differences in temperatures of WGSR onset were found. It is suggested that the susceptibility of the catalysts to reduction and oxidation is responsible for their activity in the WGSR. 相似文献
2.
The effect of pretreatment on the dispersion of supported noble metal Catalyst prepared from amine precursors in basic solution have been studied. The following metal precursors were used: Pt(NH 3) 4(NO 3) 2, Pd(NH 3) 4(NO 3) 2, Ru(NH 3) 6Cl 3 and [Rh(NH 3) 5Cl]Cl 2 Pretreatment in oxygen, prior to reduction in H 2 at 400C, resulted in poor dispersions for Ru and Rh, moderate dispersions for Pd and high dispersions for Pt. Pretreatment in H 2 resulted in poor dispersions for Pd and Pt and high dispersions for Ru and Rh. Decomposition of the adsorbed Pt and Pd precursors in argon resulted in very high dispersions. 相似文献
3.
The catalytic activity of supported noble metal catalysts (Pt, Rh, Ru, and Pd) for the WGS reaction is investigated with respect to the physichochemical properties of the metallic phase and the support. It has been found that, for all metal-support combinations investigated, Pt is much more active than Pd, while Rh and Ru exhibit intermediate activity. The turnover frequency (TOF) of CO conversion does not depend on metal loading, dispersion or crystallite size, but depends strongly on the nature of the metal oxide carrier. In particular, catalytic activity of Pt and Ru catalysts, is 1-2 orders of magnitude higher when supported on “reducible” (TiO 2, CeO 2, La 2O 3, and YSZ) rather than on “irreducible” (Al 2O 3, MgO, and SiO 2) metal oxides. In contrast to what has been found in our previous study over Pt/TiO 2 catalysts, catalytic activity of dispersed Pt does not depend on the structural and morphological characteristics of CeO 2, such as specific surface area or primary crystallite size. 相似文献
4.
The novelty of using pyrolysis oil in the steam-iron process to produce pure hydrogen is introduced. In this process, products of pyrolysis oil gasification are used to reduce iron oxides which are subsequently oxidized with steam, resulting in pure hydrogen. Two process alternatives are considered: (i) a once-through concept in which cheap iron oxide (in our case sintered pellets of natural iron ore, Fe 2O 3) is used in one cycle, before further processing in a blast furnace, and (ii) a continuous system, in which specially developed iron oxides (in our case an ammonia catalyst) are cycled between a reduction and oxidation reactor. By injecting pyrolysis oil in a fluidized bed filled with Fe 3O 4 at 800 °C, it has been shown that CO and H 2 as well as coke by the gasification reactions contribute to the reduction. Experiments including a complete redox cycle with the ammonia catalyst have shown that a hydrogen production in the oxidation of 0.84 N m 3/kg dry pyrolysis oil (LHV H 2/LHV oil = 0.4) can be obtained when the conversion of iron oxides are low (1.0%). The gas produced in the reduction step under these conditions contains 38% of the heating value of the input and has an LHV of 7.8 MJ/N m 3 gas product. Deactivation of the iron oxides has been observed by a decreasing reduction rate in subsequent redox cycles. BET and SEM analysis showed a decrease in surface area, which could partly explain the observed deactivation. 相似文献
5.
The water-gas shift (WGS) activity of platinum catalysts dispersed on a variety of single metal oxides as well as on composite MO x/Al 2O 3 and MO x/TiO 2 supports (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, La, Ce, Nd, Sm, Eu, Gd, Ho, Er, Tm) has been investigated in the temperature range of 150–500 °C, using a feed composition consisting of 3% CO an 10% H 2O. For Pt catalysts supported on single metal oxides, it has been found that both the apparent activation energy of the reaction and the intrinsic rate depend strongly on the nature of the support. In particular, specific activity of Pt at 250 °C is 1–2 orders of magnitude higher when supported on “reducible” compared to “irreducible” metal oxides. For composite Pt/MO x/Al 2O 3 and Pt/MO x/TiO 2 catalysts, it is shown that the presence of MO x results in a shift of the CO conversion curve toward lower reaction temperatures, compared to that obtained for Pt/Al 2O 3 or Pt/TiO 2, respectively. The specific reaction rate is in most cases higher for composite catalysts and varies in a manner which depends on the nature, loading, and primary crystallite size of dispersed MO x. Results are explained by considering that reducibility of small oxide particles increases with decreasing crystallite size, thereby resulting in enhanced WGS activity. Therefore, evidence is provided that the metal oxide support is directly involved in the WGS reaction mechanism and determines to a significant extent the catalytic performance of supported noble metal catalysts. Results of catalytic performance tests obtained under realistic feed composition, consisting of 3% CO, 10% H 2O, 20% H 2 and 6% CO 2, showed that certain composite Pt/MO x/Al 2O 3 and Pt/MO x/TiO 2 catalysts are promising candidates for the development of active WGS catalysts suitable for fuel cell applications. 相似文献
6.
Different γ-Al 2O 3 supported Ir, Pd, Ru, Rh and Pt catalysts were tested in enantioselective 1-phenylpropane-1,2-dione hydrogenation using cinchona alkaloid modifiers. Activity and enantioselectivity over Ir and Ru catalysts were low. Pd catalyst was active in the hydrogenation of 1-phenylpropane-1,2-dione, however, the enantioselectivity over this catalyst was almost negligible. Over Pd hydrogenation proceeded mainly via hydrogenation of the C 1O 1 carbonyl group, which is attached to the phenyl ring. Hydrogenation over Pd did not proceed in the second hydrogenation step via an enol form as found for ethyl pyruvate hydrogenation over Pd. The structure-selectivity relationship and solvent effects are similar over Pt and Rh in the first hydrogenation step. However, in the second hydrogenation step of hydroxyketones to diols large mechanistical differences between Pt and Rh were observed. Although the activity over Rh catalysts was lower than over Pt after optimization the best result obtained with Rh/γ-Al 2O 3 (5754 Lancaster) was 60% ee in toluene at maximum yield of 28%, which makes Rh a promising metal for enantioselective hydrogenation. 相似文献
7.
在液相还原法制备的纯Cu2O样品中,采用浸渍法分别引入Mg、Al、Fe助剂制备Cu2O-MgO、Cu2O-Al2O3、Cu2O-Fe2O3催化剂。采用XRD、FT-IR、TEM和H2-TPR等对催化剂进行表征,研究不同助剂的加入对甲醛乙炔化反应的影响。结果表明,不同助剂对催化剂的结晶度和可还原性能有较大影响,进而使甲醛乙炔化表现出不同的催化活性。相比MgO与Al2O3,Fe2O3的引入,使Cu2O结晶度明显下降,主要是由于Fe2O3与Cu2O之间产生强的相互作用,有利于乙炔亚铜活性物种的形成,从而表现出最优的催化性能。 相似文献
8.
The catalytic multifunctional system based on H 3PW 12O 40·6H 2O (HPW), Pt and support (Zr–Ce or Zr–Ti mixed oxides) has been investigated for lean NO x storage and reduction. It was applied in the NO x storage and reduction (NSR) concept by including a cyclic operation of short NO x storage (oxygen rich phase) and reduction (hydrocarbon rich phase: hexane). For NO x reduction, the assistance of hydrogen is one of the key parameters possibly as a result of the regeneration of metallic sites active for mild oxidation of the hydrocarbon (by forming C xH yO z). The difference in oxygen mobility of supports (higher in the case of Zr–Ce than for Zr–Ti) became another strategic parameter for catalyst selection since the possibility of total hydrocarbon oxidation. The influence of temperature was also considered for optimizing NO x storage and reduction. 相似文献
9.
The effect of different reducing agents (H 2, CO, C 3H 6 and C 3H 8) on the reduction of stored NO x over PM/BaO/Al 2O 3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO 2-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 H 2 and CO have a relatively high NO x reduction efficiency compared to C 3H 6 and especially C 3H 8 that does not show any NO x reduction ability except at 350 °C over Pd/BaO/Al 2O 3. The type of precious metals affects the NO x storage-reduction properties, where the Pd/BaO/Al 2O 3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al 2O 3 catalyst shows a high reduction ability but a relatively low NO x storage capacity. 相似文献
10.
Ce xTi 1−xO 2 oxides have been synthesised by sol–gel method with x varying from 0 to 0.3 and characterised by XRD and TPR. The structure of oxides changes with the Ce/Ti molar ratio. The presence of ceria in Ce-Ti oxides inhibits the phase transition from anatase to rutile. When x = 0.3 (Ce 0.3Ti 0.7O 2 sample), the solid presents an amorphous state. The TPR results indicate that the presence of Ti enhances the reducibility of cerium oxide species. Catalytic oxidation of propene is investigated on Ce-Ti oxides and the better conversion is obtained with Ce 0.3Ti 0.7O 2 but the CO 2 selectivity reaches 63% at 400 °C. Gold is then deposited on theses oxides to improve the catalytic activity. On the basis of characterisation data (H 2 TPR), it has been suggested that gold influences the reduction of the Ce-Ti oxide support and the catalytic activity to the propene oxidation. Thus, Au/Ce-Ti-O system catalysts are promising catalysts for propene oxidation. 相似文献
11.
A total of 10 noble metal (Rh, Pt, Pd, Ru and Ir) catalysts, either supported on CeO 2 or Ce 0.63Zr 0.37O 2, were prepared. Catalysts were fully characterized using XRD, N 2 adsorption at −196 °C, TEM and H 2 chemisorption. Oxygen storage processes were carefully investigated. The influence of temperature was checked and a key role of oxygen diffusion was further demonstrated. A review of the reactions involved in the CO transient oxidation reaction is finally proposed. 相似文献
12.
利用小型固定床实验台实验研究了铁氧化物在典型流化床温度和CO还原性气氛下的形态迁移及其生成物对NO的催化还原作用,采用分级还原结合X射线衍射(XRD)表征分析,确定铁氧化物与CO和NO反应后生成物的价态及各种铁氧化物对NO的还原机制。结果表明,Fe 2O 3在实验条件下可依次被CO还原为Fe 3O 4、FeO和单质铁,反应过程中随着还原度的增加,还原速率逐级下降,从Fe 2O 3还原到Fe 3O 4的速率最高,FeO还原到Fe速率最低,在实验温度范围内,床温升高有利于提高Fe 2O 3到Fe 3O 4的还原速率和还原度。不同形态的铁氧化物对NO的催化还原特性不同,Fe 2O 3及其部分还原后生成的Fe 3O 4都不能直接与NO反应,Fe 2O 3对CO催化还原NO的效果很弱,而Fe 3O 4对CO还原NO的反应却有很强的催化作用,而进一步还原生成FeO与单质铁还可直接与NO反应。 相似文献
13.
The electrochemical behaviours of several iron(II) mixed oxides, Fe(II) M2O 4 [where M = Fe(III), Al(III) and Cr(III)], and Fe(II) Ti(IV)O 3 were investigated using a carbon paste electrode with 1 M HCl binder. Solids containing Fe(III), Al(III) and Ti(IV) are not oxidized when the potential varies from +0.2 to + 1.1 V/ sce whereas FeCr 2O 4 exhibits two oxidation peaks. The first one at about +0.4 V/ sce, is due to iron(II) ions because the finest particles (< 100 nm) are immediately chemically solubilized. The second peak occurring at more positive potential is larger and corresponds to the oxidation of the biggest particles. This behaviour is similar to that of the reduction of Fe 2O 3 described elsewhere. So the oxidation phenomenon is the addition of two consecutive steps: a chemical solubilization followed by an oxidation and the shape of the second peak is influenced by the morphology of the oxide under study. Influences of the nature of the binder, of the synthesis procedure and of the grinding are reviewed. 相似文献
14.
氯化氢催化氧化制氯气具有高效率、低能耗、环境友好等优点,一直是研究的热点。首先采用浸渍法制备RuO_2/TiO_2催化剂,并通过催化活性评价和H_2-TPR表征优化Ru的负载量。然后制备Ce、Mn、La、Zr、Co等氧化物修饰的MO_x-TiO_2(M=Ce、Mn、La、Zr、Co)载体及RuO_2/MOxTiO_2催化剂,考察不同修饰物对催化剂氯化氢氧化性能的影响。结果表明,采用该型号TiO_2载体时最佳负载质量分数为2%~3%;MO_x-TiO_2载体中MOx修饰物均呈高分散状态,La、Zr、Ce等氧化物修饰后,TiO_2晶粒尺寸增大,其中Zr、Mn、Co等氧化物掺杂进入TiO_2晶格。Ce和Zr氧化物修饰可以提高RuO_2/TiO_2催化剂催化活性,Mn、Co、La等氧化物修饰对活性有不利影响。Mn、Co氧化物修饰可以降低反应活化能,所以这两种氧化物修饰的催化剂催化活性较低是由指前因子减小导致的,这意味着进一步提高RuO_2/MO_x-TiO_2(M=Mn、Co)催化剂活性组分分散性才能开发出活性更好的催化剂。 相似文献
15.
The selective catalytic reduction of NO x by methane on noble metal-loaded sulfated zirconia (SZ) catalysts was studied. Ru, Rh, Pd, Ag, Ir, Pt, and Au-loaded sulfated zirconia catalysts were compared with the intact sulfated zirconia. For the NO–CH 4–O 2 reaction, Ru, Rh, Pd, Ir, and Pt showed promotion effect on NO x reduction, while for the NO 2–CH 4–O 2 reaction, only Rh and Pd showed promotion effect. Over intact and Rh, Pd, Ag, and Au-loaded sulfated zirconia, NO x conversion in NO 2–CH 4–O 2 reaction was significantly higher than that in NO–CH 4–O 2 reaction, while clear difference was not observed over Ru, Ir, and Pt-loaded sulfated zirconia. Comparison of [NO 2]/([NO]+[NO 2]) in the effluent gases in NO–O 2 and NO 2–O 2 reactions showed that Ru, Ir, and Pt has high activity for NO oxidation under the reaction conditions. These facts suggest that effects of these metals toward NO x reduction by methane can be categorized into the following three groups: (i) low activity for NO oxidation to NO 2, and high activity for NO 2 reduction to N 2 (Pd, Rh); (ii) high activity for NO oxidation to NO 2, and low activity for NO 2 reduction to N 2 (Ru, Ir, Pt); (iii) low activity for both reactions (Ag, Au). To confirm these suggestions, combination of these metals were investigated on binary or physically-mixed catalysts. The combination of Pd or Rh with Pt or Ru gave high activity for the selective reduction of NO x by methane. 相似文献
16.
Defective structures, surface textures, oxygen mobility, oxygen storage capacity (OSC), and redox properties of RE 0.6Zr 0.4O 2 and of RE 0.6Zr 0.4−xY xO 2 (RE=Ce, Pr; x=0, 0.05) solid solutions have been investigated using X-ray diffraction (XRD), temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), O 2−H 2 and O 2−CO titration, 18O/ 16O isotope exchange, CO pulsing reaction, and X-ray photoelectron spectroscopy (XPS) techniques. The effects of doping noble metal onto RE 0.6Zr 0.4−xY xO 2 on oxygen mobility and surface oxygen activities have also been studied. Based on the experimental outcomes, we conclude that: (i) a Pr-based solid solution has better redox behavior than a Ce-based one; (ii) incorporation of yttrium ions in the lattices of CZ and PZ solid solutions could result in an enhancement in oxygen vacancy concentration, Ce 4+/Ce 3+ and Pr 4+/Pr 3+ redox properties, lattice oxygen mobility, and oxygen storage capacity; and (iii) doping the noble metal (Rh, Pt, and Pd) onto RE-based solid solution has positive effect on the properties concerned in this work. 相似文献
17.
The reduction of NO x by hydrogen under lean burn conditions over Pt/Al 2O 3 is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al 2O 3. In this case, although pure H 2 and pure CO are ineffective for NO x reduction under lean burn conditions, H 2/CO mixtures are very effective. With a realistic (1:3) H 2:CO ratio, typical of actual exhaust gas, Pd/Al 2O 3 is significantly more active than Pt/Al 2O 3, delivering 45% NO x conversion at 160 °C, compared to >15% for Pt/Al 2O 3 under identical conditions. The nature of the support is also critically important, with Pd/Al 2O 3 being much more active than Pd/SiO 2. Possible mechanisms for the improved performance of Pd/Al 2O 3 in the presence of H 2+CO are discussed. 相似文献
18.
利用固相法合成了3种钙钛矿型复合氧化物Fe 2O 3-CaTi xM 1-xO 3,研究了其结构、晶型和氧化还原活性。在固定床反应器中考察了该氧化物对两步法甲烷催化氧化制合成气及水分解制氢的活性及选择性。X射线衍射结果表明3种钙钛型复合氧化物均由正交晶系钙钛矿相和赤铁矿相组成。3种钙钛矿复合氧化物对甲烷的氧化活性顺序为Fe 2O 3-CaTi 0.85Ni 0.15O 3 >Fe 2O 3-CaTi 0.85Co 0.15O 3 >Fe 2O 3-CaTi 0.85Fe 0.15O 3。固定床反应结果表明,以Fe 2O 3-CaTi 0.85Ni 0.15O 3为氧载体催化剂,CH 4转化率可达96%,CO和H 2产率达71%,同时水分解反应的转化率为40%。利用Aspen Plus ®对Fe 2O 3-CaTi 0.85Ni 0.15O 3在混合太阳能氧化还原过程的效率及合成油和H 2产率进行了模拟。模拟计算结果证明基于复合氧化物的混合太阳能氧化还原过程可以有效提高CH 4利用率。 相似文献
19.
In the steam gasification of biomass, the additive effect of noble metals such as Pt, Pd, Rh and Ru to the Ni/CeO 2/Al 2O 3 catalyst was investigated. Among these noble metals, the addition of Pt was most effective even when the loading amount of added Pt was as small as 0.01 wt.%. In addition, the catalyst characterization suggests the formation of the Pt–Ni alloy over the Pt/Ni/CeO 2/Al 2O 3. 相似文献
20.
The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO3/Al2O3 catalyst than on the Pd/CeO2/Al2O3 and Pd/Nb2O5/Al2O3 catalysts. The explanation for the very high N2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Meδ+ stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N2 selectivity. 相似文献
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