Preparation of nanosized Pt-Au alloy catalyst and its activity in methanol oxidation

The alloy catalyst has been widely used because it will be able to improve the activity and selectivity of the single metal catalyst in a given chemical reaction. In this study, the preparation and characteristics of nanosized Pt and Au particles on alumina and their catalytic activity were described. Nanosized Pt-Au catalysts were prepared by impregnation (IMP) method and deposition (DP) method using alumina or ZnO/Al2O3 as support. The size of Pt and Au particles were observed by transmission electron microscopy (TEM), energy dispersive spectroscope (EDS), and X-ray diffraction (XRD). Catalytic activity for oxidation of methanol was measured using a flow reactor. It could be seen that the Pt particle size and dispersion in the alloy catalysts was rarely influenced by preparation methods and Au particles coated by deposition method were well dispersed. TEM images showed that Au particles were well dispersed in the Pt/Au/ZnO/Al2O3 catalyst of which Au particles was supported by deposition method. The catalytic activity for methanol are given in the order of Pt-Au[IMP]/ZnO/Al2O3 > Pt[IMP]/Au[DP]/ZnO/Al2O3 > Au[DP]/Pt[IMP]/ZnO/Al2O3 > Pt-Au[DP]/ZnO/Al2O3. Therefore, Au particle size was doing not play an important role in increasing the oxidation activity, but the Au particles may promote the methanol oxidation.     

Catalytic performance of nanosized Pt-Au alloy catalyst in oxidation of methanol and toluene

The alloy formed between a group-VII metal such as platinum and a group-IB metal such as gold changes the catalytic behavior compared to the monometallic phase, increasing the selectivity toward certain products and also decreasing the deactivation rate. Pt-Au alloy nanoparticles coated on alumina support were found to be catalytically very active for complete oxidation of methanol and toluene. Furthermore, the nanosized Pt-Au particles were added to ZnO/Al2O3 on monolith catalyst. Also, effect of various parameters such as concentration of methanol and toluene and feed flow rate was investigated. Au particles were sized in 20 approximately 30 nm and Pt particles were well dispersed. In case of alumina supported powder catalyst, complete oxidation of methanol occurred at a temperature lower than that of toluene. From oxidation activity of monolithic honeycomb with Pt and Au particles, the conversion of methanol was increased with increasing the concentration of methanol, but conversion of toluene showed a decreasing tendency as the concentration of toluene increased. Also, conversion of methanol over honeycomb catalyst was not largely affected by feed flow rate, while conversion in toluene oxidation was decreased rapidly as feed flow rate was increased. As a result, the Pt-Au/ZnO/Al2O3/M catalyst used is likely to efficiently treat a large volume of exhaust gas containing VOCs.     

Effect of pretreatment conditions on particle size of bimetallic pt-au catalysts supported on ZnO/Al2O3 and its activity for toluene oxidation

Bimetallic Pt-Au catalysts supported on ZnO/Al2O3 were prepared by incipient wetness impregnation (IW-IMP) method with different pretreatment conditions such as flow velocity, calcination temperature, and heating rate under H2 during the calcination procedure, and characterized by X-ray diffraction (XRD), CO chemisorption, and scanning transmission electron microscopy (STEM) equipped energy dispersive spectroscopy (EDS). Furthermore, catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. Finally, relationship between the particle sizes with pretreatment conditions and catalytic activity for toluene on the bimetallic Pt-Au catalysts was discussed. In these results, nanosized bimetallic Pt-Au particles on ZnO/Al2O3 could be prepared by IW-IMP method. Relationship between the Pt and Au particle size and activity for toluene oxidation was clearly observed.     

Complete oxidation of ethylene over supported gold nanoparticle catalysts

Complete oxidation of ethylene was performed over supported noble metals or transition metals oxide catalysts and on monoliths under atmospheric pressure. Gold nanoparticles on Al2O3 or MxOy(M = Mo, Fe, Mn) were prepared by impregnation, coprecipitation, deposition, and dispersion methods. Nanoparticles prepared by impregnation method were irregular and very large above 25 nm, but those by coprecipitation and deposition method were uniformly nanosized at 4-5 nm. The gold nanoparticle were outstandingly active in catalyzing oxidation of ethylene. The activity order of these catalysts with preparation methods was deposition > coprecipitation > impregnation, and Au/Co3O4 prepared by deposition method showed the best performance in ethylene oxidation. The addition of gold particles to MxOy/Al2O3 catalyst enhanced the ethylene oxidation activity significantly. The main role of the gold nanoparticles apparently was to promote dissociative adsorption of oxygen and to enhance the reoxidation of the catalyst.     

金属表面活性剂相转移制表面覆盖式纳米催化剂──影响粒子大小因素的研究

制备了具有不同组成及结构的表面覆盖式催化剂，研究了制备条件、载体物质的溶解度、灼烧升温速度及表面活性剂用量对粒子大小的影响，研究结果表明：表面活性剂对胶体粒子的保护能力因其金属元素的种类而变．制备表面覆盖式纳米粒子的特殊条件对产物粒子的大小并无不利影响，载体粒子的溶解度越大，产物粒子也越大，最佳时灼烧升温速度为2℃／min，金属表面活性剂的最佳用量是其在总的金属元素中的摩尔分数为0．25。     

Preparation and application of granular ZnO/Al2O3 catalyst for the removal of hazardous trichloroethylene

Trichloroethylene (TCE) is a volatile and nerve-toxic liquid, which is widely used in many industries as an organic solvent. Without proper treatment, it will be volatilized into the atmosphere easily and hazardous to the human health and the environment. This study tries to prepare granular ZnO/Al(2)O(3) catalyst by a modified oil-drop sol-gel process incorporated the incipient wetness impregnation method and estimates its performance on the catalytic decomposition of TCE. The effects of different preparation and operation conditions are also investigated. Experimental results show that the granular ZnO/Al(2)O(3) catalyst has good catalytic performance on TCE decomposition and the conversion of TCE is 98%. ZnO/Al(2)O(3)(N) catalyst has better performance than ZnO/Al(2)O(3)(O) at high temperature. Five percent of active metal concentration and 550 degrees C calcination temperature are the better and economic preparation conditions, and the optimum operation temperature and space velocity are 450 degrees C and 18,000 h(-1), respectively. The conversions of TCE are similar and all higher than 90% as the oxygen concentration in feed gas is higher than 5%. By Fourier transform infrared spectrography (FT-IR) analyses, the major reaction products in the catalytic decomposition of TCE are HCl and CO(2). The Brunauer-Emmett-Teller (BET) surface areas of catalysts are significantly decreased as the calcination temperature is higher than 550 degrees C due to the sintering of catalyst materials, as well as the reaction temperature is higher than 150 degrees C due to the accumulations of reaction residues on the surfaces of catalysts. These results are also demonstrated by the results of scanning electron micrography (SEM) and energy disperse spectrography (EDS).     

ZnO/Al_2O_3复合纳米颗粒的制备与表征

为研究ZnO/Al2O3复合纳米颗粒在涂料、化妆品等领域的应用,采用直接沉淀法制备了纳米ZnO,用硫酸铝水解生成的Al2O3对纳米ZnO进行了表面改性。采用IR、TEM、SEM、XRD等手段对改性前后的粉体进行表征。分析结果表明,改性后粉体颗粒的团聚现象减轻。粉体的光催化降解甲基橙的实验研究表明,改性后ZnO粉体的光催化活性明显下降,进一步证明纳米ZnO颗粒表面存在Al2O3的包覆层。     

Mn、Fe和Cu氧化物在低温等离子体催化氧化甲苯体系中的活性比较

采用等体积浸渍法制备了MnOx/γ-Al2O3、FeOx/γ-Al2O3和CuOx/γ-Al2O3催化剂,测定了不同催化剂在低温等离子体场内分解甲苯的活性,用X射线衍射(XRD)、氢气程序升温还原(H2-TPR)技术对催化剂进行表征。结果表明催化剂分解甲苯的活性的顺序是MnOx/γ-Al2O3>FeOx/γ-Al2O3>CuOx/γ-Al2O3。催化剂分解臭氧的实验表明,不同催化活性组分对臭氧的催化分解性能顺序与对甲苯的分解性能顺序是一致的。MnOx/γ-Al2O3催化剂的Mn负载量对其催化活性有明显影响,Mn的含量为1%(质量分数)时,催化剂的活性最高,当能量密度为19J/L时,其对甲苯催化氧化的转化率接近100%。催化剂表征结果表明当Mn含量为1%(质量分数)时,氧化锰在载体γ-Al2O3上最接近单层分散量,此时活性组分与载体表面的相互结合力最强,在载体上有很好的分散性,从而表现出对甲苯分解的最好性能。     

非水溶胶凝胶法制备ZnO/Al2O3复合纳米颗粒

以无水ZnCl2和无水AlCl3为前躯体,丙酮为溶剂,油酸为氧供体,采用非水溶胶凝胶法制备ZnO/Al2O3复合纳米颗粒,通过X-ray衍射（XRD）、红外光谱（IR）、透射电镜（TEM）和紫外可见分光光度计对制备的颗粒进行表征,结果表明,颗粒为无定形态的ZnO/Al2O3复合纳米颗粒,平均粒径为61nm,呈球形单分散状态,具有良好的油溶性,能均匀稳定地分散在20#机械油中。     

Partial oxidation of dimethyl ether using the structured catalyst Rh/Al2O3/Al prepared through the anodic oxidation of aluminum

The partial oxidation of dimethyl ether (DME) was investigated using the structured catalyst Rh/Al2O3/Al. The porous Al2O3 layer was synthesized on the aluminum plate through anodic oxidation in an oxalic-acid solution. It was observed that about 20 nm nanopores were well developed in the Al2O3 layer. The thickness of Al2O3 layer can be adjusted by controlling the anodizing time and current density. After pore-widening and hot-water treatment, the Al2O3/Al plate was calcined at 500 degrees C for 3 h. The obtained delta-Al2O3 had a specific surface area of 160 m2/g, making it fit to be used as a catalyst support. A microchannel reactor was designed and fabricated to evaluate the catalytic activity of Rh/Al2O3/Al in the partial oxidation of DME. The structured catalyst showed an 86% maximum hydrogen yield at 450 degrees C. On the other hand, the maximum syngas yield by a pack-bed-type catalyst could be attained by using a more than fivefold Rh amount compared to that used in the structured Rh/Al2O3/Al catalyst.     

Preparation and characterization of nanosized gold catalysts supported on Co3O4 and their activities for CO oxidation

Gold catalysts supported on Co3O4 were prepared by co-precipitation (CP), deposition-precipitation (DP), and impregnation (IMP) methods. The Au/Co3O4 catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) to understand the different activities for CO oxidation with different preparation methods. Gold particles below 5 nm supported on Co3O4 by DP method were found to be more exposed to the surface than those by CP and IMP methods, and this catalyst was highly active and stable in CO oxidation. Finally, catalytic activity of Au/Co3O4 catalyst for CO oxidation was strongly dependent on the gold particle size.     

浅析加料方式对CuO／ZnO／Al2O3／MgO催化剂性能的影响

本文采用沉淀法制备CuO／ZnO／Al2O3／MgO催化荆,研究加料方式对催化剂性能的影响。结果表明：采用两步法制备的催化剂的Cu、Zn、Al含量最高,CuO和ZnO相互分散程度最好,比表面积最大。本研究结果为沉淀法制备CuO／ZnO／Al2O3／MgO催化剂提供了实用的参考价值。     

Autothermal reforming of propane over Ni catalysts supported on a variety of perovskites

Autothermal reforming of propane for hydrogen over Ni catalysts supported on a variety of perovskites was performed in an atmospheric flow reactor. Perovskite is known for its higher thermal stability and oxygen storage capacity, but catalytic activity of itself is low. A sites of the ABO3 structured perovskites were occupied by La while B sites by one of Fe, Co, Ni, and Al by citrate method. The composition of the reactant mixture was H2O/C/O2 = 8.96/1.0/1.1. The changes in the states of the catalysts after reaction were analyzed by XRD, TPD, and TGA. Ni/LaAlO3 catalyst maintained the perovskite structure after reaction. It showed higher hydrogen yield and thermal stability compared to those of the catalysts with Fe, Co, or Ni in B sites. Catalysts prepared by deposition-precipitation (DP) method showed higher activity than those prepared by impregnation method, presumably due to the smaller sizes of the NiO crystal particles.     

不同载体Mn-Ce催化剂的制备及其脱硝性能

以TiO_2、SiO_2及Al_2O_3为载体,采用分步共混法制备了三种均质整体式Mn-Ce负载型催化剂,探究了不同载体对催化剂脱硝活性、N2选择性及机械强度的影响。结果表明,以TiO_2和SiO_2为载体的催化剂80℃的脱硝率接近90%,而以Al2O3为载体的催化剂仅达46%。催化剂的表征发现这与Mn-Ce/TiO2和Mn-Ce/SiO2催化剂的比表面积和表面酸量较Mn-Ce/Al2O3更大、更多有关。而三种催化剂的N2选择性在80~200℃之间均接近100%,然而Mn-Ce/SiO2催化剂200℃以上N2选择性比其余两种催化剂差。三种催化剂的机械强度为Mn-Ce/TiO2Mn-Ce/SiO2Mn-Ce/Al2O3,其微观形貌显示这与催化剂体相结构的密实状况有关,各催化剂的活性组分氧化物均以无定形态存在。     

Effect of water addition on catalytic activity of nanosized gold catalysts for CO oxidation

The effect of water in the reactant gas on the catalytic activity for CO oxidation over Au/Co3O4 catalysts has been investigated. Water in the reactant gas had a negative effect on the catalytic activity for CO oxidation in Au/Co3O4 catalyst. Furthermore, it was observed that the average particle size of gold on Au/Co3O4 catalysts increased after stability testing both in dry and wet conditions.     

Catalytic activity of CuOn-La2O3/gamma-Al2O3 for microwave assisted ClO2 catalytic oxidation of phenol wastewater

In order to develop a catalyst with high activity and stability for microwave assisted ClO2 catalytic oxidation, we prepared CuOn-La2O3/gamma-Al2O3 by impregnation-deposition method, and determined its properties using BET, XRF, XPS and chemical analysis techniques. The test results show that, better thermal ability of gamma-Al2O3 and high loading of Cu in the catalyst can be achieved by adding La2O3. The microwave assisted ClO2 catalytic oxidation process with CuOn-La2O3/gamma-Al2O3 used as catalyst was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 100 mg/L phenol, and 91.66% of phenol and 50.35% of total organic carbon (TOC) can be removed under the optimum process conditions. Compared with no catalyst process, CuOn-La2O3/gamma-Al2O3 can effectively degrade contaminants in short reaction time and with low oxidant dosage, extensive pH range. The comparison of phenol removal efficiency in the different process indicates that microwave irradiation and catalyst work together to oxidize phenol effectively. It can therefore be concluded from results and discussion that CuOn-La2O3/gamma-Al2O3 is a suitable catalyst in microwave assisted ClO2 catalytic oxidation process.     

粉末增塑挤压制备Al_2O_3/Fe复合型蜂窝材料的组织与性能

为制备性能优良的Al_2O_3/Fe复合型蜂窝材料,首先以316L合金粉末、Al_2O_3粉末和黏结剂为原料,通过粉末增塑挤压及在1 200℃氩气气氛中烧结2h获得了Al_2O_3/Fe复合型蜂窝材料;然后,借助SEM、XRD及万能试验机研究了添加Al_2O_3对Al_2O_3/Fe复合型蜂窝材料组织与性能的影响。结果表明:金属粉末颗粒在烧结过程中结合形成γ-Fe基体网状组织,表面有呈多边形几何状形态的Cr_2O_3形成;添加少量的Al_2O_3可以抑制Cr从基体中析出,降低表面Cr_2O_3的含量,使金属颗粒烧结结合更为紧密,组织表面更加光滑;随着Al_2O_3含量的增加,蜂窝材料表面与催化活性涂层的结合能力增强,复合型蜂窝材料的抗压强度先升高后降低;在Al_2O_3含量为5.0wt%时,抗压强度达26 MPa。所得结论表明5.0wt%Al_2O_3/Fe复合型蜂窝材料力学性能最佳,表面涂覆性能优良。     

Electrical Characteristics of Hybrid Nanoparticle–Nanowire Devices

Gold nanoparticles synthesized by a colloidal method were deposited in an Al₂O₃ dielectric layer of an omega-gated single ZnO nanowire FET. These gold nanoparticles were utilized as localized trap sites. The adsorption of the gold nanoparticles on an Al₂O₃-coated ZnO nanowire was confirmed by high-resolution transmission electron microscopy. In this study, a hybrid nanoparticle-nanowire device was fabricated by conventional Si processing. Its electrical characteristics indicated that electrons in the conduction band of the ZnO nanowire can be transported to the localized trap sites by gold nanoparticles for gate voltages greater than 1 V, through the 10-nm-thick Al ₂O₃ tunneling oxide layer.     

超临界干燥法制备催化剂合成单壁纳米碳管及表征

采用超临界干燥法制备了活性高、比表面大的Fe/Mo/Al₂O₃催化剂.通过超临界干燥,催化剂的比表面由294m²/g提高到401m²/g.在1000℃下用该催化剂催化裂解甲烷, 合成了大产量、高质量的单壁纳米碳管(SWNTs).利用SEM、TEM、HRTEM、TGA 和Raman等手段对所制备的SWNTs进行了表征.结果表明:超临界法制备催化剂合成的粗产品中SWNTs含量在30%以上,大大高于同一配方催化剂采用常规干燥法的产率(约2%); SWNTs的管径分布在0.8-1.0nm之间,其形态以束状为主.     

Bactericidal properties of ZnO–Al2O3 composites formed from layered double hydroxide precursors

ZnO-Al(2)O(3) composites with different Zn/Al molar ratios (R) have been prepared using zinc-aluminium layered double hydroxides (LDHs) Zn( R )Al-CO(3) as precursor. The samples were characterized by XRD, ICP, EDX, EPR and FT-IR. The results show that ZnO is highly dispersed in all of the ZnO-Al(2)O(3) composites. Bactericidal experiments against Staphylococcus aureus ATCC 6538 and Bacillus subtilis var. niger ATCC 9372 were carried out by contacting the bacteria and spores with the ZnO-Al(2)O(3) composites. The composites all showed high bactericidal activity against Staphylococcus aureus ATCC 6538, and the bactericidal efficiency against Bacillus subtilis var. niger ATCC 9372 increased with increasing content of ZnO. The mechanism of bactericidal activity of ZnO-Al(2)O(3) has also been investigated. It is suggested that highly active O(2) (-) and *OH species generated on the surface of ZnO-Al(2)O(3) particles react with the peptide linkages in the cell walls of bacteria or spores resulting in their destruction.