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1.
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
2.
A series of nano-sized Ni/Al 2O 3 and Ni/La–Al 2O 3 catalysts that possess high activities for NH 3 decomposition have been successfully synthesized by a coprecipitation method. The catalytic performance was investigated under the atmospheric conditions and a significant enhancement in the activity after the introduction of La was observed. Aiming to study the influence of La promoter on the physicochemical properties, we characterized the catalysts by N 2 adsorption/desorption, XRD, H 2-TPR, chemisorption and TEM techniques. Physisorption results suggested a high specific surface area and XRD spectra showed that nickel particles are in a highly dispersed state. A combination of XRD, TEM and chemisorption showed that Ni 0 particles with the average size lower than 5.0 nm are always obtained even though the Ni loading ranged widely from 4 to 63%. Compared with the Ni/Al 2O 3 catalysts, the Ni/La–Al 2O 3 ones with an appropriate amount of promoter enjoy a more open mesoporous structure and higher dispersion of Ni. Reduction kinetic studies of prepared catalysts were investigated by temperature-programmed reduction (TPR) method and the fact that La additive partially destroyed the metastable Ni–Al mixed oxide phase was detailed. 相似文献
3.
Reforming of methane with carbon dioxide into syngas over Ni/γ-Al 2O 3 catalysts modified by potassium, MnO and CeO 2 was studied. The catalysts were prepared by impregnation technique and were characterized by N 2 adsorption/desorption isotherm, BET surface area, pore volume, and BJH pore size distribution measurements, and by X-ray diffraction and scanning electron microscopy. The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed bed reactor. The coke content of the catalysts was determined by oxidation conducted in a thermo-gravimetric analyzer. Incorporation of potassium and CeO 2 (or MnO) onto the catalyst significantly reduced the coke formation without significantly affecting the methane conversion and hydrogen yield. The stability and the lower amount of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters and to their increased CO 2 adsorption, forming a surface reactive carbonate species. Addition of CeO 2 or MnO reduced the particle size of nickel, thus increasing Ni dispersion. For Ni–K/CeO 2–Al 2O 3 catalysts, the improved stability was further attributed to the oxidative properties of CeO 2. Results of the investigation suggest that stable Ni/Al 2O 3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and CeO 2 (or MnO) as promoters. 相似文献
4.
The reformation of biomass-derived ethanol to a hydrogen-rich gas stream suitable for feeding fuel cells is investigated as an efficient and environmentally friendly process for the production of electricity for mobile and stationary applications. Steam reforming of ethanol is investigated over Ni catalysts supported on La 2O 3, Al 2O 3, YSZ and MgO. The influence of several parameters on the catalytic activity and selectivity is examined including reaction temperature, water-to-ethanol ratio and space velocity. Results reveal that the Ni/La 2O 3 catalyst exhibits high activity and selectivity toward hydrogen production and, most important, long term stability for steam reforming of ethanol. The enhanced stability of this catalyst may be due to scavenging of coke deposition on the Ni surface by lanthanum oxycarbonate species which exist on top of the Ni particles under reaction conditions. 相似文献
5.
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
6.
The importance of the hydrodearomatisation (HDA) is increasing together with tightening legislation of fuel quality and exhaust emissions. The present study focuses on hydrogenation (HYD) kinetics of the model aromatic compound naphthalene, found in typical diesel fraction, in n-hexadecane over a NiMo (nickel molybdenum), Ni (nickel) and Ru (ruthenium) supported on trilobe alumina (Al 2O 3) catalysts. Kinetic reaction expressions based on the mechanistic Langmuir–Hinshelwood (L–H) model were derived and tested by regressing the experimental data that translated the effect of both naphthalene and hydrogen concentration at a constant temperature (523.15 and 573.15 K over the NiMo catalyst and at 373.15 K over the Ni and Ru/Al 2O 3 catalysts) on the initial reaction rate. The L–H equation, giving an adequate fit to the experimental data with physically meaningful parameters, suggested a competitive adsorption between hydrogen and naphthalene over the presulphided NiMo catalyst and a non-competitive adsorption between these two reactants over the prereduced Ni and Ru/Al 2O 3 catalysts. In addition, the adsorption constant values indicated that the prereduced Ru catalyst was a much more active catalyst towards naphthalene HYD than the prereduced Ni/Al 2O 3 or the presulphided NiMo/Al 2O 3 catalyst. 相似文献
7.
A series of LaAl 11O 18- and Al 2O 3-supported LaCrO 3 and Cr 2O 3 combustion catalysts was prepared. Different active phase–support combinations were prepared and applied to cordierite monoliths. The washcoat materials were aged in flowing humid air at temperatures between 1100°C and 1400°C, after which they were characterized by BET, XRD, TPR, and EDS. The monolith catalysts were evaluated in methane combustion. The presence of an active phase retarded sintering of the Al 2O 3 support, whereas the active phase slightly decreased the thermal stability of LaAl 11O 18. X-ray measurements revealed extensive interaction between support and active phase in the washcoat materials. A substituted perovskite, LaCr 1−xAl xO 3, is proposed to be formed in nearly all samples containing both lanthanum and chromium. The accessibility of chromium decreased rapidly after aging. The activities of the Al 2O 3-supported catalysts were higher than of those supported on LaAl 11O 18, which was related to the higher surface area of the former. 相似文献
8.
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
9.
考察过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧活性的影响以及过渡金属负载量及循环条件对甲烷降解性能的影响,采用扫描电镜、N_2吸附-脱附以及H_2程序升温还原技术对催化剂进行表征。结果表明,过渡金属Ni的添加对催化剂在(375~475)℃下的甲烷催化燃烧活性产生影响。催化剂经多次重复使用后,催化燃烧活性提高。分析原因为经过渡金属Ni改性后,可与载体形成NiAl_2O_4尖晶石,促进活性组分形成较小晶粒,并改善活性组分分散度,提高催化剂催化活性。 相似文献
10.
Surface-phase ZrO 2 on SiO 2 (SZrOs) and surface-phase La 2O 3 on Al 2O 3 (SLaOs) were prepared with various loadings of ZrO 2 and La 2O 3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH 4/CO 2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al 2O 3 and Pt/SiO 2 catalysts. CO 2 or CH 4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides. The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
11.
Combustion of CO, ethyl acetate and ethanol was studied over CuO x/Al 2O 3, CuO x–CeO 2/Al 2O 3, CuMn 2O 4/Al 2O 3 and Mn 2O 3/Al 2O 3 catalysts. It was found that modification of the alumina with ceria before subsequent copper oxide deposition increases the activity for combustion of CO substantially, but the effect of ceria was small on the combustion of ethyl acetate and ethanol. The activity increases with the CuO x loading until crystalline CuO particles are formed, which contribute little to the total active surface. The CuO x–CeO 2/Al 2O 3 catalyst is more active than the CuMn 2O 4/Al 2O 3 catalyst for the oxidation of CO but the CuMn 2O 4/Al 2O 3 catalyst is more active for the combustion of ethyl acetate and ethanol. Thermal ageing and water vapour in the feed caused a modest decrease in activity and did not affect the CuOx–CeO2/Al2O3 and CuMn2O4/Al2O3 catalysts differently. In addition, no difference in intermediates formed over the two catalysts was observed. Characterisation with XRD, FT-Raman and TPR indicates that the copper oxide is present as a copper aluminate surface phase on alumina at low loading. At high loading, bulk CuO crystallites are present as well. Modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk CuO crystallites associated to the ceria, in addition to the two copper oxide species on the bare alumina. The distribution of copper species depends on the ceria and copper oxide loading. The alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of crystalline CuMn2O4 and Mn2O3, respectively, on Al2O3. 相似文献
12.
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
13.
Factors controlling the product ratio of CO 2/(CO+CO 2) and methods for inhibiting deactivation of catalyst for steam reforming of gasoline were studied. Syngas (H 2+CO) as major product was produced on Ni-Mo/Al 2O 3 and the major product on Ni-Re/Al 2O 3 was H 2 and CO 2 at the same reaction conditions. Hydrogen with a high CO 2/(CO+CO 2) ratio of about 92% was produced by coupling reaction of steam reforming and water gas shift on Ni-Re/Al 2O 3 catalyst at 805 K. The multifunctional activity of the bimetallic catalyst of Ni-Re/Al 2O 3 and the suitable reaction temperature were of crucial significance for the coupling reaction. Although no deactivation could be observed on both Ni-Mo/Al 2O 3 and Ni-Re/Al 2O 3 catalysts for steam reforming of sulfur-free fuels in about 200 h of time on stream, the activity and sulfur-tolerance of Ni-Re/Al 2O 3 was much better than the values of Ni-Mo/Al 2O 3 for steam reforming of sulfur-containing fuels because of the unique role of rhenium in the Ni-Re catalyst. The unique role of rhenium in Ni-Re catalyst was mainly because of alloying of rhenium with nickel to form bimetallic Ni-Re sites and interaction of rhenium with sulfur to form S-Re binds. The sulfur-tolerance of Ni-Re/Al 2O 3 for steam reforming of sulfur-containing gasoline was improved further by addition of a small amount of ZSM-5. The activity and sulfur-tolerance of Ni-Mo/Al 2O 3 was also enhanced by the addition of ZSM-5. 相似文献
14.
MgO-promoted Ni/Al 2O 3 catalysts have been investigated with respect to catalytic activity and coke formation in combined steam and carbon dioxide reforming of methane (CSCRM) to develop a highly active and stable catalyst for gas to liquid (GTL) processes. Ni/Al 2O 3 catalysts were promoted through varying the MgO content by the incipient wetness method. X-ray diffraction (XRD), BET surface area, H 2-temperature programmed reduction (TPR), H 2-chemisorption and CO 2-temperature programmed desorption (TPD) were used to observe the characteristics of the prepared catalysts. The coke formation and amount in used catalysts were examined by SEM and TGA, respectively. H 2/CO ratio of 2 was achieved in CSCRM by controlling the feed H 2O/CO 2 ratio. The catalysts prepared with 20 wt.% MgO exhibit the highest catalytic performance and have high coke resistance in CSCRM. MgO promotion forms MgAl 2O 4 spinel phase, which is stable at high temperatures and effectively prevents coke formation by increasing the CO 2 adsorption due to the increase in base strength on the surface of catalyst. 相似文献
15.
Ce- or Sr-doped LaCoO 3 bulk perovskites were prepared by citric acid method as well as 10 wt.% of LaCoO 3 was deposited on alumina carrier stabilized with lanthanum. Properties of prepared materials were characterized by determination of surface area, acid-basic properties and XRD, XPS, TPDO 2, H 2-TPR measurements as well as catalytic activity and selectivity for ethanol combustion was tested. It was found that substitution of La in LaCoO 3 with either Sr or Ce has only small effect on its activity in ethanol combustion. Strontium inserted into LaCoO 3 structure increases basic character of the perovskite surface as well as selectivity to acetaldehyde (ACA). Substitution of La with cerium has no effect on the concentration of basic sites and does not affect the selectivity to ACA. Activity of LaCoO 3-based catalysts in ethanol combustion and their selectivity to ACA formation can be explained on the basis of the presence of both -oxygen species and sites with basic character on the material surface. Acid-basic properties of supported LaCoO3 are dominated by acidic character of the carrier. Results of XPS and H2-TPR measurements of LaCoO3 supported on La–Al2O3 suggest that perovskite remains in strong interaction with carrier and probably is partially decomposed. Deposition of perovskite on stabilized carrier significantly increases the rate of ethanol combustion. 相似文献
16.
Noble metal (Rh, Pt, Pd, Ir, Ru, and Ag) and Ni catalysts supported on CeO 2–Al 2O 3 were investigated for water gas shift reaction at ultrahigh temperatures. Pt/CeO 2–Al 2O 3 and Ru/CeO 2–Al 2O 3 demonstrated as the best catalysts in terms of activity, hydrogen yield and hydrogen selectivity. At 700 °C and steam to CO ratio of 5.2:1, Pt/CeO 2–Al 2O 3 converted 76.3% of CO with 94.7% of hydrogen selectivity. At the same conditions, the activity and hydrogen selectivity for Ru/CeO 2–Al 2O 3 were 63.9% and 85.6%, respectively. Both catalysts showed a good stability over 9 h of continuous operation. However, both catalysts showed slight deactivation during the test period. The study revealed that Pt/CeO 2–Al 2O 3 and Ru/CeO 2–Al 2O 3 were excellent ultrahigh temperature water gas shift catalysts, which can be coupled with biomass gasification in a downstream reactor. 相似文献
17.
The NO x storage-reduction catalysis under oxidizing conditions in the presence of SO 2 has been investigated on Pt/Ba/Fe/Al 2O 3, Pt/Ba/Co/Al 2O 3, Pt/Ba/Ni/Al 2O 3, and Pt/Ba/Cu/Al 2O 3 catalysts compared with Pt/Ba/Al 2O 3, Pt/Fe/Al 2O 3, Pt/Co/Al 2O 3, Pt/Ni/Al 2O 3, Pt/Cu/Al 2O 3 and Pt/Al 2O 3 catalysts. The NO x purification activity of Pt/Ba/Fe/Al 2O 3 catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/Co/Al 2O 3 and Pt/Ba/Ni/Al 2O 3 catalysts was essentially the same as that of the aged Pt/Ba/Al 2O 3 catalyst, while that of the aged Pt/Ba/Cu/Al 2O 3 and Pt/Cu/Al 2O 3 catalysts was substantially lower than the others. The Fe-compound on the aged Pt/Ba/Fe/Al2O3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al2O3 catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO4 particles formed on the Pt/Ba/Fe/Al2O3 catalyst under oxidizing conditions in the presence of SO2 and promotes the decomposition of BaSO4 and desorption of the sulfur compound under reducing conditions. 相似文献
18.
Methane combustion over Pd/Al 2O 3 catalysts with and without added Pt and CeO 2 in both oxygen-rich and methane-rich mixtures at temperatures in the range 250–520°C has been investigated using a temperature-programmed reaction procedure with on-line gas analysis (FTIR). During the temperature loop under oxygen-rich conditions, there was an appreciable hysteresis in the activity of unmodified Pd/Al 2O 3, which was greatly enhanced over Pd–Pt/Al 2O 3. Over both catalysts the hysteresis was reversed under slightly methane-rich atmospheres, and as temperature was reduced, a sudden collapse or fluctuations in activity were shown respectively over Pd–Pt/Al 2O 3 and Pd/Al 2O 3. Such non-steady behaviour was almost eliminated over Pd/Al 2O 3–CeO 2. Under a very narrow range of conditions and over a Pd/Al 2O 3 packed bed, oscillation of methane combustion was observed. 相似文献
19.
Composite types of TiO 2–Al 2O 3 supports, which are γ-aluminas coated by titania, have been prepared by chemical vapor deposition (CVD), using TiCl 4 as a precursor. Then supported molybdenum catalysts have been prepared by an impregnation method. As supports, we employed γ-alumina, anatase types of titania, and composite types of TiO 2–Al 2O 3 with different loadings of TiO 2. We studied the conversion of Mo from oxidic to sulfidic state through sulfurization by X-ray photoelectron spectroscopy (XPS). The obtained spectra unambiguously revealed the higher reducibility from oxidic to sulfidic molybdenum species on the TiO 2 and TiO 2–Al 2O 3 supports compared to that on the Al 2O 3 support. Higher TiO 2 loadings of the TiO 2–Al 2O 3 composite support led to higher reducibility for molybdenum species. Furthermore, the catalytic behavior of supported molybdenum catalysts has been investigated for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the TiO 2–Al 2O 3 supported Mo catalysts, in particular for the 4,6-dimethyl-DBT, is much higher than that obtained over Al 2O 3 supported Mo catalyst. The ratio of the corresponding cyclohexylbenzene (CHB)/biphenyl (BP) derivatives is increased over the Mo/TiO 2–Al 2O 3. This indicates that the prehydrogenation of an aromatic ring plays an important role in the HDS of DBT derivatives over TiO 2–Al 2O 3 supported catalysts. 相似文献
20.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
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