Pd-Pt-Ce/Al_2O_3催化剂在VOC净化处理中的催化性能

采用浸渍法制备Pd-Pt-Ce/Al_2O_3催化剂,考察贵金属Pd和Pt负载量、助剂种类及负载量、空速对催化甲苯燃烧活性的影响。结果表明,适宜的贵金属负载量和助剂可极大提高Pd-Pt/Al_2O_3催化剂活性,当Pd和Pt质量分数分别为0.05%和0.005%、助剂Ce质量分数为1%时,Pd-Pt-Ce/Al_2O_3催化剂在低温条件下表现出较好的催化性能。空速对催化剂的催化活性影响较为明显,适宜的空速低于20 000 h-1。     

H-USY负载MnOx催化剂上CH4选择催化还原NOx性能的研究

采用高比表面积、抗硫、抗湿的新型USY分子筛为载体制备MnOx催化剂,考察了以CH4为还原剂,在不同Mn含量MnOx催化剂上,选择性催化还原NOx的性能和有关影响因素.研究表明:5%(wt.)的Mn/H-USY具有最高的NO选择性还原活性,在500℃时NOx达最大转化率20.8%;分段填装Mn/H-USY和Ni/H-USY催化剂可显著拓宽活性温度范围,促进NO转化率(最高转化率可达24.4%),降低N2O生成量.本实验中使用傅立叶红外分析仪进行在线检测反应物与产物浓度.     

贵金属催化剂用于低浓度甲烷的去除

制备不同负载量的Pd基和Pt基催化剂,建立催化剂活性评价装置,考察贵金属Pd和Pt负载量对甲烷转化率的影响,结果表明,甲烷转化率最高的Pd和Pt负载质量分数分别为1.25%和2%,相同负载质量分数0.1%时,Pd基催化剂的甲烷转化率优于Pt基催化剂。催化剂的BET比表面积大小不能反映催化剂的催化活性,二者之间无线性关系。     

过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧性能的影响

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。     

铜、钡对单钯型汽车尾气净化催化剂性能影响研究

制备了Pd/Ni/La-Ce-Al、Pd/cu/Ni La-Ce-Al、Pd/Ba/Ni-La-Ce-A1 3 种类型的汽车尾气净化催化剂,考察了3种催化剂对CO、C3H8和NO氧化还原活性.研究结果表明,铜不适合作为Pd/Ni/La-ce-Al催化剂的助剂;钡是提高Pd/Ni/La-Ce-Al催化剂性能特别是改善其NO还原性能的良好助剂.     

PdNi合金催化剂的制备及其电化学性能研究

用改良的浸渍法合成了不同合金度的碳载PdNi纳米粒子,考察其对氧还原和氢氧化反应的催化行为,研究表明,Pd75Ni25氧还原质量比活性最高,Pd85Ni15的氢氧化催化活性最优,这两种PdNi合金催化剂为燃料电池非Pt阴阳极催化剂提供了一个选择。     

Pt/Pt-Ce/γ-Al_2O_3催化氧化甲苯研究

通过等体积浸渍法制备单贵金属Pt/γ-Al_2O_3和双金属Pt-Ce/γ-Al_2O_3催化剂,考察Ce对催化剂活性的影响,确定催化剂最优配比。结果表明,当Pt的负载量为质量分数0.5%时,Pt/γ-Al_2O_3催化活性最高;当Pt的负载量为质量分数0.2%,Ce的负载量为质量分数1.0%时,Pt-Ce/γ-Al_2O_3催化剂的催化活性最高。Pt-Ce/γ-Al_2O_3催化剂的甲苯转化率高于Pt/γ-Al_2O_3催化剂。随着Pt负载量增大,催化剂孔容、孔径减小。粉体式催化剂性能优于整体式催化剂,但差别不大;Ce的添加有助于催化剂活性的提升。     

低负载贵金属催化剂对二甲醚催化燃烧的催化活性

采用浸渍法以g-Al2O3为载体制备了多种低负载量的Pd和Pt催化剂,在微型固定床反应器装置上进行了二甲醚(DME)催化燃烧实验. 考察了不同贵金属负载量的Pd/g-Al2O3和Pt/g-Al2O3催化剂的活性,及浸渍顺序对Pd-Pt/g-Al2O3双金属负载催化剂活性的影响,并测试了贵金属负载摩尔比不同的双金属负载催化剂的活性. Pt负载量0.025%(w)的催化剂在190℃将DME完全燃烧;Pd和Pt共同负载的催化剂[Pd:Pt=2:1(mol), Pt 0.025%(w), Pd 0.027%(w), Pt先负载]性能更好,在175℃将DME完全燃烧;200 h实验后2种催化剂活性降低均小于5%.     

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。     

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%.     

Catalytic hydrodehalogenation of halon 1211 (CBrClF2) over γ-alumina-supported Ni, Pd and Pt catalysts

The hydrodehalogenation of halon 1211 over Ni, Pd and Pt supported on γ-alumina was studied. The effect of reaction temperature and hydrogen/halon 1211 input ratio was examined. Steady state catalytic activities of Pd and Pt are very similar, and much higher than that of Ni. Hydrodehalogenation over Pd favours the formation of CH₂F₂, while Pt and Ni produce primarily CH₄ and CH₃F, respectively. Product profiles suggest that the hydrodehalogenation of halon 1211 over Pd and Pt follows a reaction mechanism which is similar to hydrodehalogenation of CFC-12. Over Ni catalysts, the primary hydrodehalogenation reactions are those which first remove one halogen (Cl or Br) and then remove two halogens (one F and either Br or Cl). The higher mobility of hydrogen atom on the surface of Pt is consistent with the observation that only trace amounts of C₂₊ hydrocarbons were detected when Pt was used compared with Pd and Ni. Increasing selectivity to CH₂F₂ with time on stream over Pd and Pt is mainly ascribed to the transformation of support alumina to partially fluorinated alumina.     

Bimetallic Pt/Pd diesel oxidation catalysts: Structural characterisation and catalytic behaviour

Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies on supported bimetallic Pt/Pd diesel oxidation catalyst (Pt:Pd weight ratio 2:1) after various treatments were compared with those of monometallic Pd and Pt catalysts prepared under similar conditions. After calcination and thermal ageing, the coexistence of alloyed bimetallic Pt/Pd particles and of tetragonal PdO has been found in the bimetallic Pt/Pd catalyst. PdO is present in form of crystals at the surface of the Pt/Pd particles or as isolated PdO crystals on the support oxide. Bimetallic Pt/Pd nanoparticles were already formed in the Pt/Pd catalyst after calcination. Hydrogen treatment causes the formation of randomly alloyed Pt/Pd nanoparticles. In the thermally aged catalyst, a strong indication for an enrichment of Pt in the interior of the particle and of Pd at its outer shell was found. In the monometallic catalyst, the Pd is found to be completely oxidised already after calcination and to consist of metallic Pd in zero-valent state exclusively after reductive treatment. Ageing under hydrothermal oxidative atmosphere leads to complete oxidation of the Pd species. After calcinations, the catalytic activity of the Pt/Pd catalyst studied is comparable to those of monometallic Pt catalysts. In contrast to monometallic Pt catalysts, the alloyed system show significant stabilisation against sintering and a much higher activity after the thermal ageing step. This stabilisation of dispersion and the presence of Pt atoms on the surface of the Pt/Pd particles are considered to cause the higher catalytic activity of metallic particles for the oxidation of carbon monoxide and propene after ageing.     

Hydrogenation of Sunflower Oil over M/SiO2 and M/Al2O3 (M = Ni,Pd, Pt,Co, Cu) Catalysts

This work is aimed at evaluating the performance of several catalysts in the partial hydrogenation of sunflower oil. The catalysts are composed of noble (Pd and Pt) and base metals (Ni, Co and Cu), supported on both silica and alumina. The following order can be proposed for the effect of the metal on the hydrogenation activity: Pd > Pt > Ni > Co > Cu. At a target iodine value of 70 (a typical value for oleomargarine), the production of trans isomers is minimum for supported nickel catalysts (25.7–32.4 %, depending on the operating conditions). Regarding the effect of the support, Al₂O₃ allows for more active catalysts based on noble metals (Pd and Pt) and Co, the effect being much more pronounced for Pt. Binary mixtures of catalysts have been studied, in order to strike a balance between catalyst activity and product distribution. The results evidence that Pd/Al₂O₃–Co/SiO₂ mixture has a good balance between activity and selectivity, and leads to a very low production of trans isomers (11.8 %) and a moderate amount of saturated stearic acid (13.5 %). Consequently, the utilization of cobalt‐based catalysts (or the addition of cobalt to other metallic catalysts) could be considered a promising alternative for the hydrogenation of edible oil.     

Effect of Metal Type on Partial Hydrogenation of Rapeseed Oil-Derived FAME

Supported SiO₂ catalysts were studied for the partial hydrogenation of rapeseed oil-derived fatty acid methyl esters (FAME) for improving its oxidative stability. The effect of metal type: Pt, Pd, and Ni, on catalytic activity and cis–trans selectivity was investigated. Hydrogenation activity was studied in terms of turn over frequency (TOF) of C18:3, C18:2, C18:1, and C18:0 FAME. The highest TOF of C18:3, C18:2, and C18:1 was found for Pd catalyst. However, C18:0 TOF of Pt is higher than that of the Pd catalyst. The higher in C18:0 TOF can explain the low selectivity towards trans-monounsaturated FAME of the Pt catalyst, which is due to the subsequent hydrogenation of the intermediate trans-monounsaturated to saturated FAME. On the other hand, Ni showed the lowest TOFs when compared with the Pt and Pd catalysts.     

Enhancement of oxygen reduction activity by sequential impregnation of Pt and Pd on carbon support

Two Pd-based PtPd bimetallic catalysts (mole ratio of Pt to Pd=1: 18) were prepared by co-impregnation (Pt-Pd/C) and sequential impregnation of Pt on Pd/C [Pt(Pd/C)] for the application to oxygen reduction reaction (ORR). The prepared bimetallic catalysts had lower ORR activities than Pt/C, while they showed largely enhanced activity compared to Pd/C. In particular, the extent of enhancement was found to be dependent on the surface composition. The observed mass and specific activities of Pt(Pd/C) were more than two times higher than those of Pt-Pd/C. The superior activity of Pt(Pd/C) observed from the performed studies was attributed to its Pt-rich surface.     

二硝基甲苯加氢制甲苯二胺催化剂的研究进展

综述了二硝基甲苯液相加氢合成甲苯二胺催化剂的研究进展,并介绍了(Pd+Pt)/C等贵金属催化剂、雷尼镍催化剂、负载型镍基催化剂、非晶态镍催化剂和漆原镍催化剂的最新研究成果。通过对比上述各催化剂在生产成本、制备工艺及催化二硝基甲苯加氢性能等方面的优缺点,发现非晶态镍催化剂不但价格低廉,而且在1 MPa低压二硝基甲苯液相加氢的反应中表现出与(Pd+Pt)/C工业催化剂相似的活性和选择性,是替代二硝基甲苯液相加氢贵金属和雷尼镍工业催化剂的首要选择;漆原镍催化剂制备工艺简单,价格低廉,且在众多的加氢反应中表现出与骨架镍催化剂相似的催化性能,也具有较大的工业化潜质。     

Hydrodesulfurization of 4,6-dimethyldibenzothiophene over Pt, Pd, and Pt–Pd catalysts supported on amorphous silica–alumina

The activities and selectivities of Pt, Pd, and Pt–Pd supported on amorphous silica–alumina (ASA) in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DM-DBT) were investigated. The ASA-supported catalysts had much higher activities than alumina-supported catalysts, due to the creation of electron-deficient metal particles. Pd had a high hydrogenation activity for 4,6-DM-DBT, but the removal of sulfur from 4,6-DM-DBT and its HDS intermediates occurred faster over Pt than over Pd. Comparison of two Pt/ASA catalysts with different Pt loadings showed that the metal dispersion strongly influenced the product selectivity. Larger metal particles led to relatively faster hydrogenation and slower C–S bond breaking. Bimetallic Pt–Pd catalysts were much more active than the monometallic constituents, indicating that the metal particles were alloyed. Acid-catalyzed cracking and isomerization occurred especially over Pt/ASA.     

Noble metal promoted Ni0.03Mg0.97O solid solution catalysts for the reforming of CH4 with CO2

Reforming of CH₄ with CO₂ to produce syngas was studied over Ni_0.03Mg_0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd or Rh (the atomic ratio M/(Ni + Mg) was about 2 × 10^–4, M = Pt, Pd or Rh). It was found that although the Ni_0.03Mg{0.97}O catalyst showed an excellent stability and activity at the reaction temperature of 1123 K, it lost its activity completely within 51 h when the reaction temperature was as low as 773 K. However, both the activity and the stability at 773 K were improved significantly by adding Rh, Pt, or Pd. This synergistic effect is rationally explained by the promoted reducibility of Ni. On all these catalysts, the amount of deposited carbon during the reaction was very low, suggesting that carbon deposition was not the main cause of the deactivation. Also, the catalytic activity of bimetallic catalysts increased gradually with the noble metal loading, but after passing through a maximum, it decreased with superfluous addition. The maximum was found to be located at around the atomic ratio of M/(Ni + Mg) 0.02% (M = Pt, Pd and Rh). This phenomenon could most probably be attributed to the different composition of Pt-Ni alloy particles formed after the reduction.     

Tungsten–palladium selective hydrogenation catalysts

Steady-state, steam-reforming rates for methane were measured on model and high-surface-area, ceria-supported Pd catalysts and compared to rates on Pd/silica between 600 and 825 K. Specific rates on Pd/ceria were higher than those on Pd/silica by a factor of 10 ⁵ and were higher even than rates reported in the literature for Ni catalysts. Model catalysts prepared with Pt or Rh on ceria also showed very high rates, essentially identical to rates for Pd/ceria. However, catalysts prepared by addition of Pd to ceria which had been calcined to high temperatures (>1175 K) before the addition of Pd were not active. Based on these results, we suggest that steam reforming on ceria-supported catalysts occurs through a bifunctional mechanism in which oxygen from ceria reacts with dissociated methane on the precious metal. High-temperature calcination of ceria significantly changes its reducibility, so that the reaction is not enhanced. This revised version was published online in August 2006 with corrections to the Cover Date.     

Methanol decomposition over supported palladium and platinum

Methanol decomposition over supported Pt and Pd catalysts was investigated in the temperature range from 453 to 573 K with the partial pressure of methanol up to 0.8 arm. The specific activity of Pd was higher than that of Pt, and alumina-supported Pd was more active than silicasupported Pd, although aluminasupported catalysts produced dimethyl ether as a by-product. A silica-supported Pd catalyst prepared from a tetraamine salt solution with a proper pH exhibited higher activity than the other silica-supported Pd catalysts. Dependence of the decomposition rate on the partial pressure of methanol was similar regardless of the metal, the support or the preparation method. The apparent reaction orders were near 0.3 at low pressures below about 0.4 atm and became near zero or slightly negative at higher pressures. The apparent activation energies were about the same for most of the catalysts and were in the range from 66 to 77 kJ/g-mol.