Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).     

Catalytic oxidation of hydrogen over Au/TiO2 catalysts

Selective catalytic oxidation of hydrogen in the presence of hydrocarbons was studied in a fixed bed quartz reactor, over 3 wt%Au/TiO₂ and 5 wt%Au/TiO₂ catalysts. This reaction can be utilised in the production of light alkenes via catalytic dehydrogenation, providing in situ heat to the endothermic dehydrogenation reaction and simultaneously removing a fraction of the produced hydrogen. It is important to avoid the non-selective combustion of the hydrocarbons in the mixture. Both 3 wt%Au/TiO₂ and 5 wt%Au/TiO₂ are active for the combustion of hydrogen, but in a gas mixture with propane and oxygen the selectivity is dependent upon the feed ratio of hydrogen and oxygen. At 550 °C, with propane present, no carbon oxides are formed when the H₂:O₂ ratio is four, but at lower ratios some CO₂ and some CO is formed.     

Catalytic oxidation of NO over Ce-doped Mn/TiO2

Mn-Ce/TiO₂ catalyst was prepared by impregnating Mn-Ce on TiO₂ and was characterized by XRD,BET and PL. The influences of Ce-doping concentration,loading,calcinations temperature,space velocity,inlet concentration of NO and volume fraction of oxygen on the performance of catalytic oxidation were examined. The results showed that the effect of doping Ce not only increased the surface area of MnO_x/TiO₂ but also enhanced the dispersion of active phase over TiO₂. At Ce-doping concentration of [Ce]/[Mn]=1/3,10% loading Mn-Ce/TiO₂ catalyst calcined at 300 ℃ for 3 h had high catalytic oxidation activity. When inlet concentration of NO was 300 μL/L,O₂ 10%,space velocity was 41000 h^－1,oxidation rate of NO over Mn-Ce/TiO₂ reached 58% at 200 ℃.     

Cu掺杂Mn／TiO2催化氧化NO性能研究

采用溶胶凝胶法制备了栽体TiO2,在负栽Mn（Ac）：制备Mn／TiO2时掺杂cu,制备了Mn—Cu／TiO2催化剂。考虑了cu的掺杂量、活性组分负载量、焙烧温度等制备条件对其催化氧化No性能的影响。结果表明,最佳条件下制备的催化剂,在反应温度200℃、空速41000h～、No浓度为300×10-6（书）及O2含量为10％条件下,NO氧化率可迭53．08％,250℃时NO氧化率达到74．76％。在220℃以上时H2O对其影响较小,但其抗硫性能还有待进一步研究提高。     

Steam reforming of kerosene over a metal-monolithic alumina-supported Ru catalyst: Effect of preparation conditions and electrical-heating test

A plate-type anodic alumina support (γ-Al₂O₃/Fe–Cr–Ni alloy/γ-Al₂O₃) was used to prepare a series of Ru catalysts. The performance of these catalysts was investigated in the steam reforming of kerosene (SRK). Ethanol solution impregnation was used to enhance metal dispersion on the catalyst surface. The catalyst prepared by ethanol solution impregnation and dried at 120 °C (Ru/Al₂O₃-ED) gave a higher metal dispersion and more favorable activity and durability than that prepared in aqueous solution. However, owing to shrinking caused by the oxidation of ruthenium species, high temperature calcination in air after impregnation greatly decreased the metal dispersion on the catalyst surface, regardless of the impregnation solution type. In contrast to calcination in air, high temperature N₂ treatment could decompose the reducible ruthenium species on the Ru/Al₂O₃-ED completely. This indicates that H₂ pre-reduction is not an essential procedure for the SRK reactions over this catalyst. The experimental results also confirm this hypothesis. The effect of Ce addition was also investigated and was found to enhance significantly the catalyst tolerance to carbon deposition thereby improving the SRK durability of Ru/Al₂O₃-ED under a high space velocity. In addition, owing to the high electrical resistance of the Fe–Cr–Ni alloy, the anodic alumina catalyst itself can be used as a heater, when an electrical current is applied along the alloy layer. Under an electrical-heating pattern, the SRK reaction system reached stability within 15 min, offering a strong possibility for shortening the start-up time of conventional reformers from 1 to 2 h to a few minutes.     

Cu2O/TiO2催化甲醛乙炔化反应的载体效应

以不同温度焙烧的TiO₂为载体,CuCl₂·2H₂O为铜源,NaOH为沉淀剂,L-抗坏血酸钠为还原剂,采用液相还原-沉积沉淀法制备了Cu₂O/TiO₂,借助X射线粉末衍射（XRD）、H₂程序升温还原（H₂-TPR）、N₂-物理吸附、透射电镜（TEM）、X射线光电子能谱（XPS）等手段,研究了TiO₂载体焙烧温度对Cu₂O/TiO₂甲醛乙炔化反应性能的影响。结果表明,低温焙烧得到的TiO₂载体以锐钛矿相存在,与Cu₂O物种间具有弱的相互作用,使得Cu₂O被过度还原为金属Cu,催化活性较低。随着载体焙烧温度的升高,TiO₂中出现金红石相,Cu₂O与载体间相互作用增强,Cu₂O高效转变为乙炔亚铜活性物种,使催化剂表现出最佳的催化性能。     

Catalytic oxidation of HCN over a 0.5% Pt/Al2O3 catalyst

The adsorption of HCN on, its catalytic oxidation with 6% O₂ over 0.5% Pt/Al₂O₃, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N₂O, NO and NO₂, and some residual adsorbed N-containing species were oxidized to NO and NO₂ during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N₂ and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 °C. Furthermore, the temperature of maximum HCN conversion to N₂O is located between 200 and 250 °C, while raising the reaction temperature increases the proportion of NO_x in the products. The co-feeding of H₂O and C₃H₆ had little, if any effect on the total HCN conversion, but C₃H₆ addition did increase the conversion to NO and decrease the conversion to NO₂, perhaps due to the competing presence of adsorbed fragments of reductive C₃H₆. Evidence is also presented that introduction of NO and NO₂ into the reactant gas mixture resulted in additional reaction pathways between these NO_x species and HCN that provide for lean-NO_x reduction coincident with HCN oxidation.     

Na改性Pt/AlOOH对甲醛催化氧化反应活性的影响

具有晶面取向的阳极氧化AlOOH因其低温甲醛催化性能而被用于催化氧化甲醛体系。为丰富AlOOH表面羟基含量,采用Na₂CO₃为Na前体浸渍法改性载体,制备不同Na含量（0.13%、0.19%、0.30%、0.41%,质量分数）的Pt/Na_x/AlOOH催化剂。通过BET、FTIR、XPS、HRTEM等表征分析,发现加入Na后,Na/AlOOH的表面羟基更加丰富,Pt/Na_x/AlOOH催化剂的比表面积增大,拥有更小的Pt颗粒尺寸,表面Pt颗粒分散度提高,Pt0元素价态含量增加。当Na含量为0.41%时,催化剂Pt/0.41Na/AlOOH的Pt分散度高达56%。实验结果证明,Pt/0.41Na/AlOOH展现出最优的HCHO催化活性,60℃时HCHO转化率达100%。     

MnO_x-CeO_2催化剂在低温下催化氧化低浓度甲醛的性能研究

采用修饰共沉淀法制得铈锰氧化物MnO_x-CeO_2催化剂,采用环境舱法,模拟太阳光在贴近真实夏季车内环境的低温低浓度工况下,考察太阳辐射强度、甲醛初始浓度对MnO_x-CeO_2热催化甲醛的性能影响,并进行催化动力学探究。结果表明,该催化剂孔道结构丰富,光热转化能力优秀,与单独的铈锰氧化物相比氧化能力有明显提升。在太阳辐射强度为450～650 W/m²时,初始浓度为0.5 mg/m2时,初始浓度为0.5 mg/m³的甲醛降解率可达76.2%～82.1%,且E-R模型更贴近该实验数据。在太阳辐射强度为550 W/m3的甲醛降解率可达76.2%～82.1%,且E-R模型更贴近该实验数据。在太阳辐射强度为550 W/m²,初始浓度分别为0.2,0.5,1.0 mg/m2,初始浓度分别为0.2,0.5,1.0 mg/m³时,降解率分别为63%,70.6%,78.3%,降解效果明显。此外,5种催化剂(MnO_x-CeO_2、MnO_x-CeO_2-TiO_2、TiO_2、Bi-V-O、CuO-MnO_2)在相同实验条件下的甲醛催化效果表明,MnO_x-CeO_2降解率最高,为78.3%。该催化剂具备良好的稳定性。表明该催化剂在车内等低温低浓度环境下的甲醛催化氧化有着广泛的应用前景。     

Catalytic ozone oxidation of benzene at low temperature over MnOx/Al-SBA-16 catalyst

The low-temperature catalytic ozone oxidation of benzene was investigated. In this study, Al-SBA-16 (Si/Al = 20) that has a three-dimensional cubic Im3m structure and a high specific surface area was used for catalytic ozone oxidation for the first time. Two different Mn precursors, i.e., Mn acetate and Mn nitrate, were used to synthesize Mn-impregnated Al-SBA-16 catalysts. The characteristics of these two catalysts were investigated by instrumental analyses using the Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction. A higher catalytic activity was exhibited when Mn acetate was used as the Mn precursor, which is attributed to high Mn dispersion and a high degree of reduction of Mn oxides formed by Mn acetate than those formed by Mn nitrate.     

Taking advantage of hysteresis in methane partial oxidation over Pt on honeycomb monolith

A honeycomb monolith with a Pt/γ-Al₂O₃ catalyst has been tested in order to highlight and explain the bifurcation behavior of catalytic methane (partial) oxidation under process conditions, elucidating the light off behavior. With CH₄/O₂=1 (rich mixture) and different heating/cooling policies it has been shown that hysteresis occurs only after complete ignition of the catalyst. The dependence of hysteresis on the feed composition was studied, showing that it disappears with lean mixtures, has its maximum for slightly richer than stoichiometric mixtures and then decreases with much richer composition. At the same time, the ignition temperature lowers with increasing CH₄/O₂ ratio. Finally, we suggest a procedure to decrease the ignition temperature by taking advantage of the hysteretic behavior, gradually tuning the feed composition, with the only limit given by the thermal insulation capabilities.     

乙醇在Pt/ZSM-5上催化氧化动力学

在内径为4 mm的石英管燃烧器中进行了富氧条件下乙醇在Pt/ZSM-5上的催化深度氧化动力学实验,反应温度控制在428 K以下,建立了Power-rate law模型和Langmuir-Hinshelwood模型来表征乙醇的低温深度氧化反应,Power-rate law模型和Langmuir-Hinshelwood模型的活化能分别为95.96和103.72 kJ·mol^-1,乙醇和氧气的反应级数分别为0.38和1.38。Langmuir-Hinshelwood模型中,乙醇的吸附常数比氧气的吸附常数大,说明乙醇在催化剂表面的吸附能力比氧气强,提高氧气的浓度比提高乙醇的浓度更有利于提高反应速率,这一点同样反映在氧气的反应级数比乙醇的反应级数大。     

Prolonging catalyst lifetime in supercritical isomerization of 1-hexene over a platinum/alumina catalyst

A series of experiments were carried out for the isomerization of 1-hexene in the temperature range and pressure range 10-100 bar, representing operating points both above and below the critical point of 1-hexene. At constant temperature of , increasing the pressure from 10 to 100 bar led to a substantial conversion increase up to a maximum of 78%. At each pressure, loss of conversion of 1-hexene was observed over the course of 8 h reaction time, which was attributed to the formation of oligomers and eventually coke upon the catalyst surface. Loss of conversion occurred initially more rapidly at the intermediate pressures of 40 and 70 bar, compared with at 10 and 100 bar, where a sustained but gradual decrease of conversion occurred. With increasing temperature in the range , conversion was highest at the condition , 40 bar, which is closest to the critical point of 1-hexene. Higher concentrations of oligomers, which act as coke precursors, were detected with increasing temperature and pressure of the reaction. The mass fraction of coke deposited upon the catalysts was dependent upon operating conditions and was within the range 0.63-1.36%, whilst the metal dispersion reduced from 26.8% for the fresh catalyst to 2.82-4.61% for the range of coked samples. A detailed examination of the void space structural changes, occurring after coking under both sub-and super-critical conditions, has been made. In particular, the void space structures were characterised in terms of external accessibility using percolation theory. The catalysts which were operated at reaction conditions where rapid initial deactivation occurred displayed a lower apparent connectivity in comparison with catalysts operated at conditions favouring a gradual sustained deactivation. It has also been found that, under certain conditions, the apparent connectivity of the remaining pore network can, unexpectedly, appear to increase following coking. This has been attributed to the initial loss of the most inaccessible pores within the network.     

SO2 oxidation over the V2O5/TiO2 SCR catalyst

The effects of V₂O₅ loading of the V₂O₅/TiO₂ SCR catalyst on SO₂ oxidation activity were examined by infrared spectroscopy (DRIFT) and SO₂ oxidation measurement. Vanadium oxide added to the catalyst was found to be well dispersed over the TiO₂ carrier until covered with monolayer V₂O₅. The rate of SO₂ oxidation increased almost linearly with V₂O₅ loading below the monolayer capacity and attained saturation with further increase. The hydroxyl groups bonded to vanadium atoms, V–OH, might be altered by SO₂ oxidation. Both V=O and V–OH groups are likely involved in the adsorption and desorption of SO₂ and SO₃.     

Electro-catalytic oxidation of CO on Pt catalyst supported on carbon nanotubes pretreated with oxidative acids

Characteristics of nanosized Pt electro-catalyst deposited on carbon nanotubes (CNTs) were studied with CO-stripping voltammogram and chronoamperometry measurements. The CNTs were pretreated by oxidation in HNO₃, mixed HNO₃ + H₂SO₄ and H₂SO₄ + K₂Cr₂O₇ solution, respectively, to enable surface modification. Well-homogenized Pt particles (average size: ≈3 nm) were loaded onto the pretreated CNT samples by a modified colloidal method. TEM, BET, FTIR and XRD techniques were used to characterize the physicochemical properties of the pretreated CNT samples. In the electro-oxidation of CO, all the Pt/CNT samples showed lower on-set as well as peak potentials than the conventional Pt/XC-72 electro-catalyst, indicating that the Pt/CNT samples were more resistant to CO poisoning and could be superior anode electro-catalyst for the proton exchange membrane fuel cells (PEMFCs). Moreover, we found that the pretreatment of CNTs in mixed HNO₃ + H₂SO₄ solution was very beneficial for the performance enhancement of Pt/CNT electro-catalyst; the catalyst obtained as such gave the lowest peak potential and the highest catalytic activity for the electro-oxidation of CO. Larger amount of oxygen-containing functional groups, higher percentage of mesopores, and higher graphitic crystallinity of the pretreated CNTs were considered crucial for the performance enhancement, e.g., by strengthening the interaction between Pt nanoparticles and the CNT support and enhancing the mass diffusion in the electro-chemical reaction.     

Fabrication and characterization of La-added MgFe2O4 as catalyst support for CO oxidation

Fe-containing oxides can serve as excellent supports for precious metal catalysts. Therefore, we investigated the catalytic properties of noble metals supported on Fe-containing mixed oxides. MgFe₂O₄ and La-added MgFe₂O₄ (La-MgFe₂O₄) were prepared via complexation with malic acid and characterized by X-ray diffraction, N₂ adsorption–desorption, and Fe K-edge X-ray fine structure analysis. MgFe₂O₄ calcined at 400–800 °C has a spinel structure and is porous. The addition of La to MgFe₂O₄ increased the local structural disorder around Fe, suppressed grain growth, affected the pore size, and increased the specific surface area. In addition, a Pd-loaded La-MgFe₂O₄ catalyst was prepared and found to exhibit higher activity for CO oxidation than a representative Pd/γ-Al₂O₃ catalyst. Further, temperature-programmed reduction studies revealed that the reactivity of the surface lattice oxygen of La-MgFe₂O₄ was enhanced by the Pd loading. Further, diffuse reflectance Fourier transform infrared spectroscopy studies showed that the surface lattice oxygen reacted with CO to form CO₂.     

Catalytic oxidation of trichloroethylene over TiO2 supported ruthenium catalysts

Different types of TiO₂ (anatase, P25 and rutile) supported ruthenium catalysts were synthesized by wet impregnation and directly reduced in H₂. The distribution characteristics of ruthenium species were thoroughly studied before and after trichloroethylene oxidation. The results show that ruthenium oxide species are very unstable in the anatase phase, but quite stable in the rutile phase of TiO₂. This phenomenon results in different catalytic behaviors for the Ru/TiO₂ catalysts. The Ru/TiO₂ (P25) catalyst has the best catalytic performance among these catalysts. The complete conversion temperature of trichloroethylene is in the temperature range of 260–270 °C.     

Kinetics of the propene oxidation over a Pt/alumina catalyst

This article reports the results obtained during the kinetic study of propene total oxidation on a platinum alumina catalyst in excess of oxygen. Reaction partial orders of propene and oxygen exhibited values of about − 0.5 and + 1, respectively. Propene presented a great inhibitory effect whereas an increase of oxygen concentration promoted the reaction. Based on TPD results, a Langmuir–Hinshelwood LH model considering propene to be adsorbed without dissociation was raised. A good agreement between experimental data and predicted results was observed. The value of the adsorption constants obtained confirmed that oxygen was more weakly adsorbed on the catalyst than propene.     

TiSiW_(12)O_(40)/TiO_2催化合成丙酸异丁酯

以TiSiW12O40/TiO2为催化剂,对以丙酸和异丁醇为原料合成丙酸异丁酯的反应条件进行了研究。实验表明:TiSiW12O40/TiO2是合成丙酸异丁酯的良好催化剂,适宜的反应条件为:醇∶酸(摩尔比)=1.2∶1,催化剂用量为反应物料总质量的2.0%,反应时间1.0h,反应温度106～125℃。上述条件下,丙酸异丁酯的收率可达79.1%。