Catalysts reduced bimetallic

Physicochemical attributes of catalysts were mostly controlled by nitridation temperature although there was a little influence on catalyst reducibility and acidity, better nitride species were formed at 973 K and TGA results revealed that complete nitridation occurs between 750-973 K and the feed gas stream containing H2 NH3=1 1 is preferably better mixture for the nitridation of Co-Mo bimetallic catalysts. 

Valence State of Rhenium in Reduced Bimetallic Catalysts With and Widiout Alkali Metals... 

Although typical catalyst preparation procedures vary slightly from one laboratory to another, the "conventional approach" is to deposit a metal salt on a support, convert this salt to the oxide, and then reduce to the metallic state. When two metals are simultaneously so treated and reduced, bimetallic clusters may form. However, it cannot be assumed that bimetallic clusters are produced since monometallic separate particles may predominate. In fact, it is perhaps the unusual case where bimetallics do form since there are many possible paths, both thermodynamic and kinetic, that can lead to (1) separate monometallic s, (2) one metal not reduced, (3) thermal segregation of bimetallic precursor particle, and/or (4) volatilization or migration of one metal. 

Properties of supported catalysts by bimetallic substrates depend on the changes in geometry of the catalyst material by the strain of the substrate. Using a bimetallic substrate multiphes the possibilities to tune the catalyst to specific requirements. The chemistry of the nanosized overlayer is affected by the different orbital overlaps of atoms from the catalyst cluster and those from the substrate. Additionally, small supported metallic islands show low coordination and reduced near-neighbor distances thus their chemical properties are different with respect to those of flat surfaces. " Reactivity of several bimetallics were also studied by Balbuena et al., including bimetallics systems . Norskov et al. found several relations for the bimetallic systems considering local and nonlocal effects have also been reported. ... 

Reduction temperature seems to have positive influence on metal dispersion for both mono- and bimetallic catalysts. There was no reduction temperature that improved the activity in all catalysts. Cracking or deep hydrogenolysis was directly related to higher ruthenium content and to higher mean cluster size. Catalysts reduced at 773 K are more suitable to produce isoparaffins. 

The ESCA data (Table 3) confirmed the complete reduction of Cu in CU/AI2O3 and Cu/Si02 catalysts B.E.=932.2-932.7 eV, and no reduction of Zn in Zn/Al203 catalyst B.E. = 1021.2 eV corresponding to ZnO [15]. ESCA indicated the influence of Zn on the state of Cu metallic phase since the B.E. of Cu 2p3/2 electrons was decreased by 0.5 eV in reduced bimetallic catalyst compared with reduced C11/AI2O3. ESCA eilso confirmed the partial reduction of ZnO in bimetallic cataljrst since the B.E. of Zn 2p3/2 electrons was decreased by 0.3 eV compared with reduced Zn/Al203 sample (Table 3). 

The complex [(OC)4Fe(//-PPh2)Pd( -Cl)]2 is a selective catalyst for the isomerization of 1-octene to 2-octene and the hydrogenation of 1-hexyne in the presence of 1-hexene. At 448 K, under 100 atm H2, 93% of a sample of 1-hexyne in benzene was reduced to hexene and only 3% to hexane. This is unexpected because palladium is usually an excellent catalyst for the hydrogenation of olefins. It also catalyzes the carbonylation of 1-octene under mild conditions (348 K, 50 atm). The total yield of esters was ten times greater than with [PdCl2(PPh3)2] as a catalyst. This bimetallic complex was also an effective catalyst for the carbonylation of 1,5-cyclooctadiene. ... 

By TPR, it has been shown that at the addition of second metal, the temperature of Co reduction is shifted to lower value by up to 200°C depending on the amount of second metal. The comparison of monometallic and bimetallic catalysts reduced at the same temperature - 300°C demonstrates that the addition of second metal leads to increasing the degree of Co reduction from 42 to 69.0-78.1% depending on content of second metal (Table 4). 

Besides by electron microscopy, the catalyst (precursor) systems were characterized by Mossbauer spectroscopy, XRD, and thermal an ysis. It was demonstrated that the proportion of the metals within the stoichiometric cyanide precursors was retained in the reduced bimetallic catalysts. Heteronuclear cyanide complexes are therefore very well appropriate to produce bimetallic catalysts of a uniform chemic composition of the individual suppmted alloy particles. 

Supported bimetallic Re—Pt catalysts are important in selective reforming of petroleum. It is believed that sulhding the catalyst before use gives ReS units which act as inert diluents to reduce the size of a local ensemble of platinum atoms. Selectivity for desirable dehydrocyclization and isomerization reactions... 

A MgO-supported W—Pt catalyst has been prepared from IWsPttCOIotNCPh) (i -C5H5)2l (Fig. 70), reduced under a Hs stream at 400 C, and characterized by IR, EXAFS, TEM and chemisorption of Hs, CO, and O2. Activity in toluene hydrogenation at 1 atm and 60 C was more than an order of magnitude less for the bimetallic cluster-derived catalyst, than for a catalyst prepared from the two monometallic precursors. 

Sodium or potassium severely poisons Pt-Re catalysts but the manner in Which the alhali metal operates is not apparent. The present study was designed to use ESCA to determine the valence state of Re in Pt-Re bimetallic catalysts. The valence state would be determined in san les that had been reduced and transferred to the instrument without exposure to an oxidizing atmosphere. Catalysts with and without potassium would be examined. 

In order to verify the presence of bimetallic particles having mixed metal surface sites (i.e., true bimetallic clusters), the methanation reaction was used as a surface probe. Because Ru is an excellent methanation catalyst in comparison to Pt, Ir or Rh, the incorporation of mixed metal surface sites into the structure of a supported Ru catalyst should have the effect of drastically reducing the methanation activity. This observation has been attributed to an ensemble effect and has been previously reported for a series of silica-supported Pt-Ru bimetallic clusters ( ). 

Herein we briefly mention historical aspects on preparation of monometallic or bimetallic nanoparticles as science. In 1857, Faraday prepared dispersion solution of Au colloids by chemical reduction of aqueous solution of Au(III) ions with phosphorous [6]. One hundred and thirty-one years later, in 1988, Thomas confirmed that the colloids were composed of Au nanoparticles with 3-30 nm in particle size by means of electron microscope [7]. In 1941, Rampino and Nord prepared colloidal dispersion of Pd by reduction with hydrogen, protected the colloids by addition of synthetic pol5mer like polyvinylalcohol, applied to the catalysts for the first time [8-10]. In 1951, Turkevich et al. [11] reported an important paper on preparation method of Au nanoparticles. They prepared aqueous dispersions of Au nanoparticles by reducing Au(III) with phosphorous or carbon monoxide (CO), and characterized the nanoparticles by electron microscopy. They also prepared Au nanoparticles with quite narrow... 

Noble metal ions can be easily reduced to the corresponding zero-valent metal atoms. Therefore, bimetallic nanoparticles consisting of two different noble metals have been extensively investigated for purpose of novel catalysts and optical materials. A simultaneous reduction of two noble metal ions with alcohol is a simple and useful technique to prepare bimetallic nanoparticles. The alcohol reduction of metal ions M + is followed by Equation (1). 

Ru(bipy)3 formed in this reaction is reduced by the sacrificial electron donor sodium ethylenediaminetetra-acetic acid, EDTA. Cat is the colloidal catalyst. With platinum, the quantum yield of hydrogenation was 9.9 x 10 . The yield for C H hydrogenation was much lower. However, it could substantially be improv l by using a Pt colloid which was covered by palladium This example demonstrates that complex colloidal metal catalysts may have specific actions. Bimetalic alloys of high specific area often can prepared by radiolytic reduction of metal ions 3.44) Reactions of oxidizing radicals with colloidal metals have been investigated less thoroughly. OH radicals react with colloidal platinum to form a thin oxide layer which increases the optical absorbance in the UV and protects the colloid from further radical attack. Complexed halide atoms, such as Cl , Br, and I, also react... 

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

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