CuO/CeO2催化剂的制备及CO氧化性能研究

制备了CuO/Al2 O3和CuO/CeO2催化剂,通过CO氧化反应,结合BET、XRD、SEM、EDS、H2-T PR、Raman和XPS等表征对催化剂的理化性质进行了分析.结果表明,活性组分CuO具有CO氧化活性,CuO/Al2 O3催化剂较不活泼的Al2 O3-550载体氧化活性显著提高;利用金属载体相互作用制备...     

Pt/C催化剂制备方法的选择

研究了以HCl酸洗、H_2O_2、浓H_2SO_4、HNO_3氧化处理后的活性炭为载体,用不同方法制备了Pt担载量为3%的担载型Pt/C催化剂。TEM统计结果表明,HCl酸洗、HNO_3氧化活性炭为载体,甲醛还原法制备的催化剂分散度最高,平均粒径最小为2．2nm。FT-IR结果表明,HNO_3氧化处理活性炭,活性炭表面含氧基团明显增加。     

用Pt/C催化剂通过浸渍-还原法制备疏水催化剂

选择XC-72R炭黑为载体,采用改进的浸渍-还原法制备了2~3 nm高分散度Pt/C催化剂。研究了还原温度、还原剂、pH和甲醛用量等工艺条件对Pt粒径大小及分散度的影响,采用透射电镜和X射线衍射等对催化剂进行表征。结果表明,提高溶液pH和反应温度、增加甲醛用量均有助于得到Pt粒子粒径较小的高分散度Pt/C催化剂,较佳的工艺条件为:用乙二醇与水为炭黑分散溶剂,反应温度80~90℃,pH≈11,甲醛用量80倍于PtCl62-物质的量,可以制备Pt粒子粒径在2 nm左右的高分散度Pt/C催化剂。     

柴油车DOC催化剂Pt/CeZrO2载体的制备及影响

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。     

过渡金属对Pt/SiC催化剂上CO氧化性能的影响

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。     

不同Pt前体制备Pt/CeO_2催化剂对其结构及性能的影响

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/CeO_2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/CeO_2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/CeO_2催化剂,能够将优先合成好的Pt纳米粒子直接以金属态Pt~0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Pt~0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Pt~(2+)的形式与CeO_2之间形成了Pt-O-Ce相互作用,载体表面暴露Pt~0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Pt~(2+)的形式参与到Pt-O-Ce键成键中,表面Pt~0缺失,催化剂表现出明显的失活现象。Pt/CeO_2催化剂中,起主要活性作用的是金属态Pt~0,胶体粒子原位沉积法能够实现Pt~0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。     

MnOx对Pt/CeZrO2催化剂在水汽和CO2环境下CO氧化的影响

以CeZrO₂固溶体为载体,发现MnO_x的添加能促进Pt/CeZrO₂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H₂O和CO₂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CO₂对Pt/CeZrO₂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CO₂的能力。反应动力学结果表明,在Pt/CeZrO₂催化剂上,反应气中引入H₂O和CO₂后,CO的反应级数有明显升高,说明H₂O和CO₂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/CeZrO₂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H₂O和CO₂与CO的竞争吸附,从而改善了催化剂的抗H₂O和CO₂性能。     

固相反应制备Pt/C催化剂

利用固相反应法制得具有较高催化活性的Pt/C催化剂,探讨了制备条件对催化剂性能的影响。结果显示:用水作浸渍介质、n(NaOH)/n(H2PtCl6)=6 4、固相还原剂为聚甲醛时,制得的Pt/C催化剂中Pt粒子的平均粒径为3 8nm。线性扫描伏安结果表明:在30℃、扫速为50mV/s时,制得的Pt/C催化剂在c(CH3OH)=0 5mol/L和c(H2SO4)=0 5mol/L混合溶液中,甲醇氧化的峰电流密度为11 3mA/cm2;而同样条件下,E TEK公司商品化的Pt/C催化剂为9 2mA/cm2。     

Pt/C催化剂制备工艺对硅氢加成催化性能的影响

通过活性炭负载铂制备了一种硅氢加成反应用多相催化剂(Pt/C),考察了活性炭处理、还原pH值、催化剂铂负载量、反应时间对Pt/C催化苯乙烯与三乙氧基硅烷加成反应催化性能的影响.结果表明:用15%硝酸处理活性炭载体,pH值为8.5环境下还原的负载量为5%的Pt/C催化剂具有最好的催化效果,苯乙烯转换率为100%,β-加成产物选择性为94.9%.     

纳米CeO_2载体对Au-Pd催化剂性能的影响

采用十六胺和不同铈前驱体(硝酸铈铵或硝酸亚铈)分别合成了纳米CeO2(H4和H3),考察了纳米CeO2载体的织构性质对Au-Pd催化剂甲醇部分氧化制氢(POM)性能的影响,用HRTEM、N2吸附、XRD和TPR等对样品进行了表征。结果表明,铈前驱体对载体的性能有较大的影响,以硝酸铈铵为前驱体所制H4载体具有较小的粒径(约5 nm)和平均孔径(5.3 nm)、较大的比表面积(243 m2/g),而硝酸亚铈所制H3载体具有较大的平均孔径(7.9 nm)。POM结果表明,纳米CeO2负载的Au-Pd催化剂具有较好的催化性能,300℃时,Au-Pd/H3的活性和H2选择性分别达100%和59.7%。低温时催化剂的活性和H2选择性为:Au-Pd/H3>Au-Pd/H4,而高温时顺序相反,这是由于低温时催化剂的孔径对反应物和产物的扩散影响较大,高温时催化剂的比表面积和活性组分分散度起主要作用。     

Kinetic modeling of CO oxidation on Pt/CeO2 in a gradientless reactor

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.     

Chemical and microstructural investigation of Pt/CeO2 catalysts reduced at temperatures ranging from 473 to 973 K

The combined application of chemical techniques and HREM shows that platinum deactivation in Pt/CeO₂ catalysts steadily increases with the reduction temperature (T_r: 473–1173 K). Though no suppression of the H₂ adsorption was observed, the TPD-H₂ traces indicate the occurrence of significant chemical changes with T_r. As revealed by HREM, the metal decoration starts at T_r: 973 K, a temperature well above those at which the chemical effects can be observed.     

Characterization of the dynamic oxygen migration over Pt/CeO2-ZrO2 catalysts by O/O isotopic exchange reaction

To characterize the oxygen mobility over metal supported catalysts on a dynamic and in situ base, ¹⁸O/¹⁶O isotopic exchange reaction combined with CO oxidation was designed and exemplified on three kinds of three way catalysts of Pt/CeO₂-ZrO₂ (CZ-O, CZ-D and CZ-R). The obtained oxygen diffusion coefficients, oxygen release rate, and oxygen storage capacity were discussed and correlated with XRD spectra and other physical parameters. It was found that the oxygen mobility and oxygen storage capacity were parallel to the structural homogeneity of Zr introduction into the CeO₂ frame work, and decreased as: CZ-R > CZ-D > CZ-O. These results indicated that this combined isotopic exchange technique could be used to quantify the surface and bulk oxygen mobility, the oxygen storage capacity and oxygen release rate over the metal supported catalysts, and could be employed as a meaningful probe into the nature of CeO₂-ZrO₂ oxygen storage material. The oxygen mobility is also another important indicator for the development of oxygen storage materials.     

Optimizing the Pt-FeOx Interaction over Atomic Pt/FeOx/CeO2 Catalysts for Improved CO Oxidation Activity

The metal-supported CeO₂ catalysts (such as Pt/CeO₂) have been considered as the most promising exhaust-treatment catalyst to meet the future emission standard. However, the Pt-O-Ce interface on Pt/CeO₂ system seems to over-stabilize the Pt sites to cause low activity for CO oxidation. In this work, by adding Fe oxides, the enhanced Pt-FeO_x interaction was formed with the disappearance of the Pt-O-Ce interface, facilitating the electron transfer from the support to the atomically dispersed Pt on the Pt-FeO_x interface for the dramatically CO (preferential) oxidation performance. The single-atom Pt/1.5FeO_x/CeO₂ performed the best catalytic activity with a reaction rate of 0.58 s⁻¹ at 144 °C (T₁₀₀). Such strategy in resorting the special metal-support interaction to tune the active sites can be extended to other metal-oxide systems for further optimized catalysis.     

担载型铂基催化剂制备方法的研究

担载型铂基催化剂广泛用于加氢、脱氢及选择氧化反应中,同时它也是重要的直接醇类燃料电池的电催化材料。本文主要介绍了担载型铂基催化剂制备方法的研究概况,并对其优缺点进行了评述。     

The role of the oxidic support on the deactivation of Pt catalysts during the CO2 reforming of methane

Pt supported on γ-Al₂O₃, TiO₂ and ZrO₂ are active catalysts for the CO₂ reforming of methane to synthesis gas. The stability of the catalysts increased in the order Pt/γ-A1₂O₃ < Pt/TiO₂ < Pt/ZrO₂. For all catalysts, the decrease in activity with time on stream is caused by carbon formation, which blocks the active metal sites for reaction. With Pt/TiO₂ and Pt/ZrO₂, deactivation started immediately after the start of the reaction, while the Pt/γ-A1₂O₃ catalyst showed an induction period during which carbon was accumulated without affecting the catalytic activity.     

Pt/MnOx–CeO2 catalysts for the complete oxidation of formaldehyde at ambient temperature

MnO_x–CeO₂ mixed oxides with a Mn/(Mn + Ce) molar ratios of 0–1 were prepared by a modified coprecipitation method and investigated for the complete oxidation of formaldehyde. The MnO_x–CeO₂ with Mn/(Mn + Ce) molar ratio of 0.5 exhibited the highest catalytic activity among the MnO_x–CeO₂ mixed oxides. Structure analysis by X-ray powder diffraction and temperature-programmed reduction of hydrogen revealed that the formation of MnO_x–CeO₂ solid solution greatly improved the low-temperature reducibility, resulting in a higher catalytic activity for the oxidation of formaldehyde. Promoting effect of Pt on the MnO_x–CeO₂ mixed oxide indicated that both the Pt precursors and the reduction temperature greatly affected the catalytic performance. Pt/MnO_x–CeO₂ catalyst prepared from chlorine-free precursor showed extremely high activity and stability after pretreatment with hydrogen at 473 K. 100% conversion of formaldehyde was achieved at ambient temperature and no deactivation was observed for 120 h time-on-stream. The promoting effect of Pt was ascribed to enhance the effective activation of oxygen molecule on the MnO_x–CeO₂ support.     

Kinetics of acetone hydrogenation over Pt/Al2O3 catalysts

The hydrogenation of acetone to isopropanol has been studied in the vapour phase over Pt/Al₂O₃ catalysts. The rate law obtained at a total pressure of 1 atm and temperatures between 303 and 363 K is of the form V=kP⁰_aP^1/2_H exp (-44 kJ mol^?1 RT^?1). The kinetic results are consistent with a Langmuir-Hinshelwood hydrogenation mechanism involving a half hydrogenated species and a non-competitive chemisorption of acetone and hydrogen on the platinum surface. The specific activity (calculated per platinum surface atom) has been found to be scarcely dependent on the platinum particle size. It is suggested that the chemisorption sites are made of a very small ensemble of platinum atoms.     

Support and precursor effects on the preparation of new heterogenized Pt/Sn catalysts for the selective hydroformylation of 1-pentene

New heterogenized Pt/Sn catalysts selective for the hydroformylation of 1-pentene have been synthesized. The complex cis-[PtCl₂(PPh₃)₂] and the SnCl₂.2H₂O or SnC₂O₄ precursors have been anchored on silica-, magnesia- and alumina-carriers. X-ray photoelectron spectroscopy was used to determine the surface composition and the nature of the anchored species. The hydroformylation activity was found to depend on the type of support and tin precursor used. Only the silica supported catalysts were active in the hydroformylation reaction. Samples prepared from SnCl₂-2H₂O were 200-fold more active than those prepared from SnC₂O₄. Selectivity ton-hexanal of the silica-supported catalyst prepared from SnCl₂-2H₂O was as high as 94.4% at 39.2% conversion of 1-pentene.