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 nanosized gold particle addition to supported metal oxide catalyst in methanol oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nano-sized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.     

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.     

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.     

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.     

Pt-au alloying at the nanoscale

The formation of nanosized alloys between a pair of elements, which are largely immiscible in bulk, is examined in the archetypical case of Pt and Au. Element specific resonant high-energy X-ray diffraction experiments coupled to atomic pair distribution functions analysis and computer simulations prove the formation of Pt-Au alloys in particles less than 10 nm in size. In the alloys, Au-Au and Pt-Pt bond lengths differing in 0.1 ? are present leading to extra structural distortions as compared to pure Pt and Au particles. The alloys are found to be stable over a wide range of Pt-Au compositions and temperatures contrary to what current theory predicts. The alloy-type structure of Pt-Au nanoparticles comes along with a high catalytic activity for electrooxidation of methanol making an excellent example of the synergistic effect of alloying at the nanoscale on functional properties.     

Structural characterization and catalytic activity of Pt dendrimer encapsulated nanoparticles supported over Al2O3 for SCR of NOx

Pt/Al2O3 and Pt-Mg/Al2O3 nano composites were successfully prepared by dendrimer templated synthesis route. The obtained dendritic nanoparticles were dispersed in alumina support and they were evaluated for SCR of NOx using methane as reductant. Thermal analysis results of uncalcined samples revealed that the oxygen can accelerate the rate of dendrimer shell decomposition. X-ray diffractograms of 500 degrees C calcined samples disclosed the amorphous nature of materials, whereas 1000 degrees C air calcined samples showed enhanced crystallinity as well as diffraction pattern corresponding to Pt and PtO. HRTEM images of Pt40-G4OH dendritic nanoparticles showed uniform particulate distribution with average particle size of 2.4 nm. The STEM results of 0.5 Pt/Al2O3 sample calcined at 500 degrees C exhibited a wide range of particles between 2 and 20 nm. This indicates the huge segregation of platinum metal particles during impregnation and subsequent calcination. Among the synthesized materials 0.5 wt% Pt/Al2O3 sample showed excellent conversion and selectivity for SCR of NOx.     

{H3[PMo12O40]/Pt/PAMAM}复合膜的制备及对甲醇的电催化氧化

采用循环伏安法在玻碳电极上制备了{H3[PMo12O40]/Pt/PAMAM}复合膜,用X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、电子能谱技术(EDS)、原子力显微镜(AFM)和循环伏安法(CV)研究了膜的组成、形貌及其对甲醇的电催化氧化活性。结果表明,Pt纳米粒子在PAMAM基底上分散均匀;最外层沉积H3[PMo12O40]后,与相同条件下制备的Pt/PAMAM膜相比,{H3[PMo12O40]/Pt/PAMAM}复合膜修饰电极对甲醇的氧化有更强的电催化活性。     

Synthesis and physicochemical characterizations of nanostructured Pt/Al2O3-CeO2 catalysts for total oxidation of VOCs

Pt/Al(2)O(3)-CeO(2) nanocatalysts with Pt loading of 1% and ceria loading of 10, 20 and 30% were successfully prepared via wet impregnation method to be utilized in catalytic oxidation of BTX. The nanocatalysts were characterized using XRD, FESEM, TEM, N(2) adsorption, FTIR and TPR-H(2) techniques. The XRD patterns confirmed the formation of cerium oxide as the crystalline phase on alumina with the average crystallite size of 8.1-8.7 nm, derived by Scherrer equation. FESEM images confirmed that these nanocatalysts had ceria particles in nano-ranges. TEM analysis showed that platinum particles were fairly well dispersed on Al(2)O(3)-CeO(2) with an average size of 5-20 nm. BET surface area presented large surface area for nanocatalysts. TPR patterns showed that by adding 1% platinum to support, the reducibility is highly increased. These patterns also revealed the promoting effect of ceria on reducibility of Pt and Al(2)O(3). The results of toluene oxidation indicated that the synthesized nanocatalysts were highly active and able to remove nearly 100% of toluene and xylene and about 85% of benzene as representative VOCs. The presence of nanoparticles along with good characteristics of the synthesized nanocatalysts presented them as highly efficient materials for catalytic oxidation of VOCs.     

介孔碳化钨负载铂催化剂对甲醇氧化的电催化性能

采用硬模板法制备了介孔碳化钨(m-WC), 进一步还原铂的前驱体(H2PtCl6)得到Pt/m-WC催化剂。采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等测试手段对样品的物相、结构和形貌进行了表征。结果表明, 所制得的m-WC载体为单一的碳化钨相, 孔径为10~20 nm, Pt/m-WC催化剂中Pt的粒径约为3.4 nm, 主要以金属态形式存在, 相对比较均一的Pt纳米粒子均匀地分散在载体的表面和孔道中。电化学测试结果表明, 与普通WC载Pt催化剂(Pt/c-WC)相比, Pt/m-WC催化剂具有较大的电化学活性表面积, 对甲醇呈现出更高的电催化氧化活性和更好的稳定性。     

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。     

Electrocatalysts for methanol oxidation based on platinum/carbon nanofibers nanocomposite

New carbon nanomaterials, i.e., carbon nanotubes and nanofibers, with special physico-chemical properties, are recently studied as support for methanol oxidation reaction electrocatalysts replacing the most widely used carbon black. Particularly, carbon fibrous structures with high surface area and available open edges are thought to be promising. Platelet type carbon nanofibers, which have the graphene layers oriented perpendicularly to the fiber axis, exhibit a high ratio of edge to basal atoms. Different types of carbon nanofibers (tubular and platelet) were grown by plasma enhanced chemical vapour deposition on carbon paper substrates. The process was controlled and optimised in term of growth pressure and temperature. Carbon nanofibers were characterised by high resolution scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties. Then carbon nanofibers of both morphologies were used as substrates for Pt electrodeposition. High resolution scanning electron microscopy images showed that the Pt nanoparticles distribution was well controlled and the particles size went down to few nanometers. Pt/carbon nanofibers nanocomposites were tested as electrocatalysts for methanol oxidation reaction. Cyclic voltammetry in H2SO4 revealed a catalyst with a high surface area. Cyclic voltammetry in presence of methanol indicated a high electrochemical activity for methanol oxidation reaction and a good long time stability compared to a carbon black supported Pt catalyst.     

Structural and electronic studies of supported Pt and Au epitaxial clusters on tungsten oxide surface

In the present paper we investigated the growth and electronic properties of Pt or Au clusters and formation of Pt-Au bimetallic clusters prepared “in-situ” on tungsten oxide surface by physical deposition under vacuum. The epitaxial tungsten oxide thin films were prepared by oxidation of W(110) single-crystal surface using a RF oxygen plasma source followed by thermal annealing. The chemical state of the system, the interaction between deposit and substrate and formation of Pt-Al alloy were investigated by photoelectron spectroscopy excited by synchrotron radiation (SRPES) and K;α X-ray source (XPS). We found that in contrary to Au clusters the Pt ones strongly interacts with the substrate. Deposition of both Pt and Au on the surface at the substrate temperature of 300 °C gave rise to the formation of bimetallic core-shell clusters. The detail structure of the bimetallic system depends on the order of deposited metals. These findings can explain some properties of Pt/WOx and Au/WOx as well as Pt-Au/WOx bimetallic catalysts and gas sensors.     

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。     

Microwave polyol synthesis of Pt/C catalysts with size-controlled Pt particles for methanol electrocatalytic oxidation

Pt/C catalysts with different mean size of Pt particles were prepared by a microwave-assisted polyol process and characterized by TEM and XRD. The effects of the synthesis solution pH on Pt particles size and distribution, and their activity for methanol electrooxidation were investigated. Pt nanoparticles were small and uniform with mean size of 2.7 nm under the pH of 9.5. Pt/C catalyst showed high activity for methanol electrooxidation.     

Electro-oxidation of methanol on TiO2 nanotube supported platinum electrodes

TiO2 nanotubes have been synthesized using anodic alumina membrane as template. Highly dispersed platinum nanoparticles have been supported on the TiO2 nanotube. The supported system has been characterized by electron microscopy and electrochemical analysis. SEM image shows that the nanotubes are well aligned and the TEM image shows that the Pt particles are uniformly distributed over the TiO2 nanotube support. A homogeneous structure in the composite nanomaterials is indicated by XRD analysis. The electrocatalytic activity of the platinum catalyst supported on TiO2 nanotubes for methanol oxidation is found to be better than that of the standard commercial E-TEK catalyst.     

Microwave-assisted synthesis of high-loading, highly dispersed Pt/carbon aerogel catalyst for direct methanol fuel cell

A Pt supported on carbon aerogel catalyst has been synthesized by the microwave-assisted polyol process. The Pt supported on carbon aerogel catalyst was characterized by high resolution transmission electron microscopy and X-ray diffraction. The results show a uniform dispersion of spherical Pt nanoparticles 2·5–3·0 nm in diameter. Cyclic voltammetry and chronoamperometry were used to evaluate the electrocatalytic activity of the Pt/carbon aerogel catalyst for methanol oxidation at room temperature. The Pt/carbon aerogel catalyst shows higher electrochemical catalytic activity and stability for methanol oxidation than a commercial Pt/C catalyst of the same Pt loading.     

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.     

Hydrothermal synthesis of PtRu nanoparticles supported on graphene sheets for methanol oxidation in direct methanol fuel cell

Platinum–ruthenium (PtRu) nanoparticles are dispersed on graphene nanosheets and multi-walled carbon nanotubes (MWCNTs) via a hydrothermal method. Transmission electron microsocopy (TEM) observation shows the uniformly dispersed nanoparticles and the average nanoparticle size has been calculated. The electrochemical measurements demonstrate that the Pt–Ru/graphene catalyst exhibits about two times higher mass activity and better tolerance to poisoning species in methanol electro-oxidation than the Pt–Ru/MWCNTs catalyst. This study indicates that the PtRu anodic catalyst synthesized by hydrothermal method can be applied for direct methanol fuel cells (DMFC).     

Au/LaVO4 Nanocomposite: Preparation, characterization, and catalytic activity for CO oxidation

The size of the gold particles is a very important parameter to get active catalysts. This paper reports a novel colloidal deposition method to prepare Au/LaVO₄ nanocomposite catalyst with monodispersed Au colloids and uniform LaVO₄ nanoplates in nonpolar solvent. Monodispersed Au colloids with tunable size (such as 2, 5, 7, 11, 13, and 16 nm) and LaVO₄ nanocrystals with well-defi ned shapes were pre-synthesized assisted with oleic acid/amine. During the following immobilization process, the particle size and shape of Au and LaVO₄ were nearly preserved. As-prepared Au/LaVO₄ nanocomposite showed high catalytic activity for CO oxidation at room temperature. Since sizes of gold particles were well-defi ned before the immobilization process, size effect of gold particles was easy to be investigated and the results show that 5-nm Au/LaVO₄ nanocomposite has the highest activity for CO oxidation. This synthetic method can be extended further for the preparation of other composite nanomaterials.