共查询到18条相似文献,搜索用时 109 毫秒
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以SiC为载体、Pt为活性组分、过渡金属Fe、Co和Ni为助剂,采用浸渍法制备CO氧化催化剂。考察浸渍方法、助剂及其负载量、空速和催化剂焙烧温度等对Pt/SiC催化剂性能的影响。结果表明,助剂的加入提高了活性组分Pt在载体表面的分散度,并产生一定的相互作用,从而提高了催化剂活性,其中,铁助剂的助催化效果较好。共浸渍法制备的催化剂的催化活性优于分步浸渍法,Pt-Fe/SiC催化剂制备中焙烧温度500 ℃时,催化剂活性较佳,适量Fe助剂的添加能够显著提高Pt/SiC催化剂的活性。 相似文献
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分别用氢氧化钠(NaOH)、草酸(H2C2O4)和碳酸钠(Na2CO3)为沉淀剂制备CeZrO2固溶体,并以此为载体制备了Pt/CeZrO2柴油车DOC催化剂,通过XRD、BET、H2-TPR和催化氧化反应等手段对催化剂物理化学特性进行研究。结果发现,以NaOH作为沉淀剂制备的CeZrO2固溶体比表面积大(68.8 m2·g-1)、氧活动性强[表面氧耗氢量达1143 μmol·(g cat(-1],同时贵金属Pt在其表面高度分散,因此制得的Pt/CeZrO2柴油车DOC催化剂催化效果好,特别是催化氧化碳氢化合物(C3H6),T90比H2C2O4和Na2CO3为沉淀剂制备的Pt/CeZrO2催化剂降低了将近40℃。另外载体制备方式对催化剂抗硫性影响也十分显著。故选择一种合适的载体沉淀剂可使制得的DOC催化剂具备良好的活性及抗硫性。 相似文献
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Pt与载体间的相互作用会影响到本征Pt纳米粒子的催化活性,不同Pt前体制备Pt/CeO2催化剂会使其表现出完全不同的催化性能。分别采用金属胶体粒子原位沉积法、浸渍法以及浸渍还原的方式制备了Pt/CeO2催化剂,通过X 射线衍射、程序升温还原、X射线光电子能谱以及高分辨透射电镜对催化剂进行表征,在CO氧化以及甲苯燃烧反应中评价催化剂活性。结果表明,胶体粒子原位沉积法制备Pt/CeO2催化剂,能够将优先合成好的Pt纳米粒子直接以金属态Pt0的形式负载到载体表面,且保证其高度均匀分散,丰富的表面Pt0很好地充当了CO、甲苯反应时的活化位点,催化剂表现出优异的性能;浸渍还原法中,Pt纳米粒子之间会发生团聚现象,同时部分Pt又以Pt2+的形式与CeO2之间形成了Pt-O-Ce相互作用,载体表面暴露Pt0含量的下降是催化剂表现出较弱活性的主要原因;浸渍法中,以Pt离子对Pt进行负载,Pt完全以Pt2+的形式参与到Pt-O-Ce键成键中,表面Pt0缺失,催化剂表现出明显的失活现象。Pt/CeO2催化剂中,起主要活性作用的是金属态Pt0,胶体粒子原位沉积法能够实现Pt0的直接负载,对于提高Pt基催化剂中Pt的利用率,降低Pt资源消耗都具有重要意义。 相似文献
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较宽的范围内研究了富氢气中CO氧化的动力学,其中CO浓度为0.4%-1.8%,O2浓度为0.26%。1.14%,催化剂为Pt/发光沸石(Pt/MD)或Pt/Al2O3。 相似文献
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以CeZrO_2固溶体为载体,发现MnO_x的添加能促进Pt/CeZrO_2催化剂的CO氧化性能,并研究了MnO_x含量对催化剂CO氧化活性及抗H_2O和CO_2性能的影响。结果表明,随着MnO_x含量增加,催化剂活性呈现先升高后降低的趋势,在MnO_x含量为0.5%(质量分数)时活性最佳。MnO_x的添加降低了Pt颗粒尺寸并影响催化剂还原性能从而促进反应活性。水汽和CO_2对Pt/CeZrO_2催化剂的CO氧化活性有抑制作用,而MnO_x的加入能显著提高催化剂的抗水汽和CO_2的能力。反应动力学结果表明,在Pt/CeZrO_2催化剂上,反应气中引入H_2O和CO_2后,CO的反应级数有明显升高,说明H_2O和CO_2在催化剂表面与CO竞争吸附,导致CO反应活性下降;而在Pt/MnO_x/CeZrO_2催化剂上,CO的反应级数略有升高,说明MnO_x的添加能有效抑制H_2O和CO_2与CO的竞争吸附,从而改善了催化剂的抗H_2O和CO_2性能。 相似文献
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文章简要阐述了微波电介质加热原理,解释了Pt/C催化剂制备时分散体系的选择依据,考察了脉冲微波加热与连续微波加热两种模式对微波辅助乙二醇法合成Pt/C催化剂甲醇电催化氧化性能的影响。研究发现:脉冲微波加热模式制备的催化剂的性能显著好于连续微波加热模式,当微波输出功率为620 W,采用10 s ON/10 s OFF的脉冲模式加热5次时,制得的Pt/C催化剂的甲醇电氧化性能最好。 相似文献
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在200℃,有H2存在的情况下,将掺杂氧化镓的Pt/WOx/ZrO2(Pt/WZG)与Pt/WOx/ZrO2(Pt/WZ)在正庚烷上进行异构化反应,并作比较。这两类催化剂都能得到较高的异构化选择性。催化剂的活性完全取决于表面负载的WOx的量以及WOx/Ga2O3-ZrO2(WZG)和WOx/ZrO2(WZ)载体的煅烧温度。Pt/WZA和Pt/WZ催化剂的最大催化活性都是WOx中W含量是10wt%,这比800℃煅烧温度下理论分子层的WZG和WZ载体含量稍微高点。Pt/WZG催化剂比Pt/WZ有较高的最大催化活性。 相似文献
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J.L. Ayastuy M.P. Gonzlez-Marcos J.R. Gonzlez-Velasco M.A. Gutirrez-Ortiz 《Applied catalysis. B, Environmental》2007,70(1-4):532-541
The catalytic activity of Pt on alumina catalysts, with and without MnOx incorporated to the catalyst formulation, for CO oxidation in H2-free as well as in H2-rich stream (PROX) has been studied in the temperature range of 25–250 °C. The effect of catalyst preparation (by successive impregnation or by co-impregnation of Mn and Pt) and Mn content in the catalyst performance has been studied. A low Mn content (2 wt.%) has been found not to improve the catalyst activity compared to the base catalyst. However, catalysts prepared by successive impregnation with 8 and 15 wt.% Mn have shown a lower operation temperature for maximum CO conversion than the base catalyst with an enhanced catalyst activity at low temperatures with respect to Pt/Al2O3. A maximum CO conversion of 89.8%, with selectivity of 44.9% and CO yield of 40.3% could be reached over a catalyst with 15 wt.% Mn operating at 139 °C and λ = 2. The effect of the presence of 5 vol.% CO2 and 5 vol.% H2O in the feedstream on catalysts performance has also been studied and discussed. The presence of CO2 in the feedstream enhances the catalytic performance of all the studied catalysts at high temperature, whereas the presence of steam inhibits catalysts with higher MnOx content. 相似文献
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Mazen A. Shalabi Bashir H. Harji Christopher N. Kenney 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1996,65(4):317-324
Cerium oxide is a major additive in three-way catalysts used in emission control of automobile exhaust. Pt/CeO2 was studied in order to better understand the role of ceria in promoting CO oxidation reaction. The kinetics of carbon monoxide oxidation on Pt/cerium oxide catalyst, was studied over the temperature range 100–170°C. Steady state kinetic measurements of CO oxidation were obtained in a computer controlled micro-CSTR reactor. Activation energies were reported to vary between 39·5 and 51·2 kJ mol−1. At low concentrations of either reactant (CO, O2) and total conversion, the catalyst exhibited multiple steady states, similar to the multiplicity behavior of Pt/Al2O3. The total conversion was reached at 120°C. In comparison, the total conversion at low reactant concentrations was reached at a temperature of 148°C for the alumina-supported catalyst. Langmuir–Hinshelwood mechanisms gave a good fit to the data. However, no single rate expression could effectively describe the CO oxidation data over the whole concentration in the product of the CSTR reactor. The facts gathered indicate that oxygen adsorbed on interfacial Pt/Ce sites and ceria lattice oxygen provides oxygen for CO oxidation. Cerium oxide has been found to lower CO oxidation activation energy, enhance reaction activity and tends to suppress the usual CO inhibition effect. 相似文献
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A comparison of CO oxidation on ceria-supported Pt,Pd, and Rh 总被引:2,自引:0,他引:2
Steady-state, CO-oxidation kinetics have been studied at differential conversions on model, ceria-supported, Pt, Pd, and Rh catalysts, from 467 to 573 K, and the results compared to the alumina-supported metals. On each of the ceria-supported metals, there is a second mechanism for CO oxidation under reducing conditions which involves oxygen from ceria reacting with CO on the metals. The rates of this second process are independent of which metal is used. The process has a significantly lower activation energy (14±1 kJ/mol compared to 26±2 kJ/mol on alumina-supported catalysts) and different reaction orders for both CO (zeroth-order compared to –1) and 02 (0.40 to 0.46 compared to first-order). This second process leads to significant rate enhancements over alumina-supported catalysts at low temperatures, especially for Pt. The implications of these results for automotive catalysis are discussed. 相似文献
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In situ X-ray diffraction experiments have been conducted during rate oscillations of catalytic CO oxidation on a supported Pt catalyst, EuroPt-1. The measurements which were carried out at atmospheric pressure with flow rates of 200 ml/min showed that the non-isothermal oscillations in the reaction rate were accompanied by periodic intensity variations of a Bragg peak. A Debye function analysis of beam profiles recorded at the two extrema of the oscillations revealed that the Pt catalyst undergoes a periodic oxidation and reduction during rate oscillations. The diffraction experiments are therefore considered to be the first experimental proof that the oxide model proposed originally by Sales, Turner and Maple to explain rate oscillations in the CO + O2 reaction at atmospheric pressure is in fact correct. 相似文献
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Mitsutaka Okumura Shyunichi Nakamura Susumu Tsubota Toshiko Nakamura Masashi Azuma Masatake Haruta 《Catalysis Letters》1998,51(1-2):53-58
In order to clarify the effect of metal oxide support on the catalytic activity of gold for CO oxidation, gold has been deposited
on SiO2 with high dispersion by chemical vapor deposition (CVD) of an organo-gold complex. Comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both CVD and liquid phase methods, showed that there were no appreciable differences in their catalytic
activities as far as gold is deposited as nanoparticles with strong interaction. The perimeter interface around gold particles
in contact with the metal oxide supports appears to be essential for the genesis of high catalytic activities at low temperatures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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MnOx promotional effects on olefins synthesis directly from syngas over bimetallic Fe‐MnOx/SiO2 catalysts
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Zhengpai Zhang Weiwei Dai Xin‐Chao Xu Jun Zhang Bianfang Shi Jing Xu Weifeng Tu Yi‐Fan Han 《American Institute of Chemical Engineers》2017,63(10):4451-4464
The direct synthesis of lower olefins via the Fischer‐Tropsch reaction (FTO) has been performed over a series of Fe‐MnOx/SiO2 catalysts. The addition of MnOx could improve the dispersion of iron species, and promote the reduction of iron oxide during the activation and subsequent carburization. Moreover, the results of characterization demonstrated that MnOx could enhance the surface basicity of the catalysts due to electronic effects and promote the formation of iron carbides. For the first time, the intrinsic power‐law kinetics for FTO was obtained for both Fe20/SiO2 and Fe20‐Mn1/SiO2 catalysts. Kinetic parameters and structure characterizations indicated that MnOx could facilitate the CO dissociation on the catalyst surface, thus enhancing the adsorption strength and capacity of surface carbonaceous intermediates. The weak hydrogenation of carbonaceous species would boost the selectivities toward lower olefins. Finally, a plausible mechanism for FTO, involving the promotional effects of MnOx on Fe, has been proposed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4451–4464, 2017 相似文献
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After a high-temperature reduction (HTR) at 773 K, TiO2-supported Au became very active for CO oxidation at 313 K and was an order of magnitude more active than SiO2-supported Au, whereas a low-temperature reduction (LTR) at 473 K produced a Au/TiO2 catalyst with very low activity. A HTR step followed by calcination at 673 K and a LTR step gave the most active Au/TiO2 catalyst of all, which was 100-fold more active at 313 K than a typical 2% Pd/Al2O3 catalyst and was stable above 400 K whereas a sharp decrease in activity occurred with the other Au/TiO2 (HTR) sample. With a feed of 5% CO, 5% O2 in He, almost 40% of the CO was converted at 313 K and essentially all the CO was oxidized at 413 K over the best Au/TiO2 catalyst at a space velocity of 333 h–1 based on CO + O2. Half the chloride in the Au precursor was retained in the Au/TiO2 (LTR) sample whereas only 16% was retained in the other three catalysts; this may be one reason for the low activity of the Au/TiO2 (LTR) sample. The reaction order on O2 was approximately 0.4 between 310 and 360 K, while that on CO varied from 0.2 to 0.6. The chemistry associated with this high activity is not yet known but is presently attributed to a synergistic interaction between gold and titania. 相似文献
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Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) measurements were conducted to analyze the electrochemical oxidation of CO dissolved in bulk electrolyte solution on a polycrystalline Pt electrode during linear sweep (cyclic) voltammetry (CV) in 1% and 100% CO-saturated 0.1 M HClO4. A CO adlayer was first formed on Pt at 0.05 V vs. the reversible hydrogen electrode (RHE) during CO bubbling in each electrolyte, followed by the CV measurement. In 1% CO-saturated 0.1 M HClO4, a well-developed prepeak was found, showing an onset and a peak at around 0.25–0.3 V and 0.42 V, respectively. A major contribution of bridge-bonded CO, CO(B), to the prepeak is concluded based on a decrease in the corresponding band intensity. In 100% CO-saturated 0.1 M HClO4, the onset of bulk CO oxidation takes place around 0.25–0.3 V, which is closely associated with a band intensity decrease of CO(B), whereas atop (linear) CO, CO(L), did not exhibit intensity change in this potential region. This suggests that vacant sites made available upon oxidation of CO(B) serve as active sites for bulk CO oxidation. The oxidation of CO(B) at such low potentials is interpreted in terms of an adsorption energy on Pt that is lower than that for CO(L) and also of the specific structure of an adlayer that consists of intermixed CO(L) and CO(B). The bulk CO oxidation becomes diffusion-limited by dissolved CO above ca. 0.72 V, where we observed hardly any infrared spectral features ascribed to reaction intermediates. During a negative-going scan back to 0.05 V from 1.2 V, a steep decrease of the bulk CO oxidation current takes place around 0.66 V, at which preferential adsorption of CO(L) is observed. A rigid CO(L) island formation is strongly suggested from its high CO stretching frequency vs. its very small initial coverage and from its subsequent dependence on potential, with a linear Stark shift characterized by a slope of −29 cm−1/V. Such an island formation is in marked contrast to the adlayer structure with intermixed CO(L) and CO(B) initially formed at 0.05 V during CO bubbling. It is concluded that the Pt surface saturated with the CO adlayer formed initially at 0.05 V exhibits a low overpotential for bulk CO oxidation owing to its adlayer structure with intermixed atop and bridge-bonded CO. 相似文献