单晶Au表面和Au/TiO2（110）模型催化剂表面CO氧化反应机理和活性位

在分子尺度上介绍了Au/TiO2(110)模型催化剂表面和单晶Au表面CO氧化反应机理和活性位、以及H2O的作用.在低温(<320 K), H2O起着促进CO氧化的作用, CO氧化的活性位位于金纳米颗粒与TiO2载体界面(Auδ+–Oδ––Ti)的周边. O2和H2O在金纳米颗粒与TiO2载体界面边缘处反应形成OOH,而形成的OOH使O–O键活化,随后OOH与CO反应生成CO2.300 K时CO2的形成速率受限于O2压力与该反应机理相印证.相反,在高温(>320 K)下,因暴露于CO中而导致催化剂表面重组,在表面形成低配位金原子.低配位的金原子吸附O2,随后O2解离,并在金属金表面氧化CO.     

Increasing the number of oxygen vacancies on TiO2 by doping with iron increases the activity of supported gold for CO oxidation

The addition of iron to high-area TiO2 (Degussa P25, a mixture of anatase and rutile) increases the number of oxygen defect sites that react with O2 to form peroxide and superoxide species. In the presence of gold nanoclusters on the TiO2 surface, the superoxide species become highly reactive, and the activity of the supported gold catalyst for CO oxidation is approximately twice that of the most active comparable catalysts described in the literature. Images of the catalyst obtained by scanning transmission electron microscopy combined with spectra of the catalyst measured in the working state (Raman, extended X-ray absorption fine structure, and X-ray absorption near-edge structure) indicate strong interactions of gold with the support and the presence of iron near the interfaces between the gold clusters and the TiO2 support. The high activity of the catalysts is attributed to the presence of defects in these sites that activate oxygen.     

Au/TiO2催化剂上非催化CO氧化反应中活性氧物种的生成和消除

在定量的瞬时产物分析(TAP)反应器中,于80 oC下采用CO脉冲和O2脉冲补充等方法,研究了高温(400 oC)焙烧的Au/TiO2催化剂上活性氧物种的移除反应活性,特别是活性氧物种的性质。以往的研究大多关注的是CO催化氧化反应中活性氧物种及其性质,在典型的反应条件下该物种的形成和消除是可逆的;而本研究表明,催化剂直接焙烧后就存在额外的氧物种;该物种对CO氧化反应也具有活性,但其在典型的反应条件下不生成或生成很少。基于此,讨论了Au/TiO2催化剂上CO氧化反应的机理,特别是不同活性氧物种的作用。     

KOH改性对TiO2结构及其负载金催化剂CO氧化反应活性的影响

以不同浓度KOH处理钛酸丁酯水解产物得到KOH改性TiO2载体.使用N2吸附、热重-差热分析-示差扫描量热、X射线粉末衍射、紫外可见漫反射光谱、透射电镜及X射线光电子能谱研究了KOH对TiO2结构、形貌的影响.结果表明,较低浓度的KOH对TiO2有较显著的改性效果,改变了TiO2的电子结构.对KOH-TiO2负载的金催...     

CO Oxidation on Planar Au/TiO2 Model Catalysts under Realistic Conditions: A Combined Kinetic and IR Study

The oxidation of CO on planar Au/TiO₂ model catalysts was investigated under pressure and temperature conditions similar to those for experiments with more realistic Au/TiO₂ powder catalysts. The effects of a change of temperature, pressure, and gold coverage on the CO oxidation activity were studied. Additionally, the reasons for the deactivation of the catalysts were examined in long-term experiments. From kinetic measurements, the activation energy and the reaction order for the CO oxidation reaction were derived and a close correspondence with results of powder catalysts was found, although the overall turnover frequency (TOF) measured in our experiments was around one order of magnitude lower compared to results of powder catalysts under similar conditions. Furthermore, long-term experiments at 80 °C showed a decrease of the activity of the model catalysts after some hours. Simultaneous in-situ IR experiments revealed a decrease of the signal intensity of the CO vibration band, while the tendency for the build-up of side products (e. g. carbonates, carboxylates) of the CO oxidation reaction on the surface of the planar model catalysts was rather low.     

Intrinsic catalytic structure of gold nanoparticles supported on TiO2

Despite the fragility of TiO(2) under electron irradiation, the intrinsic structure of Au/TiO(2) catalysts can be observed by environmental transmission electron microscopy. Under reaction conditions (CO/air 100?Pa), the major {111} and {100} facets of the gold nanoparticles are exposed and the particles display a polygonal interface with the TiO(2) support bounded by sharp edges parallel to the 〈110〉 directions.     

Catalyst parameters determining activity and selectivity of supported gold nanoparticles for the aerobic oxidation of alcohols: the molecular reaction mechanism

As previously reported for for solventless reactions, gold nanoparticles supported on ceria are also excellent general heterogeneous catalysts for the aerobic oxidations of alcohols in organic solvents. Among organic solvents it was found that toluene is a convenient one. A systematic study on the influence of the particle size and gold content on the support has established that the activity correlates linearly with the total number of external gold atoms, and with the surface coverage of the support. Amongst catalysts with different supports, but similar gold particle size and content, gold on ceria exhibits the highest activity. By means of a kinetic study (influence of sigma+ parameter, kinetic isotopic effect, temperature, alcohol concentration and oxygen pressure) a mechanistic proposal consisting of the formation of metal-alcoholate, beta-hydride shift from carbon to metal and M--H oxidation has been proposed that explains all experimental results.     

纳米结构Au/Fe2O3的制备、表征及催化氧化性能

分别以纳米和块状氧化铁为载体,通过沉积沉淀法制备了Au/Nano-Fe₂O₃和Au/Bulk-Fe₂O₃,并对其进行了表征和催化氧化性能测试。结果表明：对于Au/Nano-Fe₂O₃,5nmAu颗粒被尺寸相当的Nano-Fe₂O₃所包覆,形成新颖的类似核壳结构;对于Au/Bulk-Fe₂O₃,3nmAu颗粒高度分散于Bulk-Fe₂O₃的表面。在1-苯乙醇的氧化反应中,Au/Nano-Fe₂O₃显示出比Au/Bulk-Fe₂O₃更好的催化活性。活性的增强主要与小尺寸的Nano-Fe₂O₃以及Au和Nano-Fe₂O₃更大的接触界面有关。相比于广泛受到重视的Au的尺寸效应来说,对于Au/Nano-Fe₂O₃而言,Fe₂O₃尺寸的影响更大。     

纳米结构Au/Fe_2O_3的制备、表征及催化氧化性能

分别以纳米和块状氧化铁为载体,通过沉积沉淀法制备了Au/Nano-Fe2O3和Au/Bulk-Fe2O3,并对其进行了表征和催化氧化性能测试。结果表明:对于Au/Nano-Fe2O3,5 nm Au颗粒被尺寸相当的Nano-Fe2O3所包覆,形成新颖的类似核壳结构;对于Au/Bulk-Fe2O3,3 nm Au颗粒高度分散于Bulk-Fe2O3的表面。在1-苯乙醇的氧化反应中,Au/Nano-Fe2O3显示出比Au/Bulk-Fe2O3更好的催化活性。活性的增强主要与小尺寸的Nano-Fe2O3以及Au和Nano-Fe2O3更大的接触界面有关。相比于广泛受到重视的Au的尺寸效应来说,对于Au/Nano-Fe2O3而言,Fe2O3尺寸的影响更大。     

常温常湿条件下Au/MeO~x催化剂上CO氧化性能

利用共沉淀法制备了Au/MeO~x催化剂(Me=Al,Co,Cr,Cu,Fe,Mn,Ni,Zn)。在常温常湿条件下,考察了不同氧化物负载的金基催化剂的CO氧化性能。结果表明,氧化物种类对催化剂的活性和稳定性均有较大的影响。Cu,Mn,Cr等氧化物负载的金基催化剂的活性较差,而Zn,Fe,Co,Ni,Al等金属氧化物负载的金基催化剂可将CO完全氧化,又具有一定的稳定性,在相同反应条件下,CO完全转化时的稳定性顺序为Au/ZnO>Au/α-Fe~2O~3>Au/Co~3O~4>Au/γ-Al~2O~3≈Au/NiO。还发现水对Au/MnO~x催化剂的活性和稳定性有负作用,而对180℃焙烧制备的Au/ZnO-180催化剂的活性和稳定性均有明显的湿度增强作用。