Noble metals, supported, preparation

Cu-, Ni-, and noble metal-supported catalysts Fixed-bed reactor, 100-600°C H20/EtOH = 6-10 LHSV = 1.6-2.0 h"1 Catalysts were prepared by impregnation and coprecipitation techniques. Among the catalysts tested in the SRE reaction, the Cu0/Zn0/Al203 exhibited better performance. Sheng et al.266... 

One of the goals of this work was to prepare directly noble metals supported on BN powder in a single operation. The molecular precursor of the noble metal must react with the support... 

Liquid-phase reductive deposition as a novel nanoparticle synthesis method and its application to supported noble metal catalyst preparation, Y. Sunagawa, K. Yamamoto, H. Takahashi, and A. Muramatsu, Catal Today, 2008,132, 81. 

Base metals frequently are used in nonsupported form, but noble metals rarely are, except in laboratory preparations. Supporting the noble metals makes a more efficient catalyst on a weight of metal basis and aids in recovery of the metal. Neither of these factors is of much importance in experimental work, but in industrial processing both have significant impact on economics. 

Usually noble metal NPs highly dispersed on metal oxide supports are prepared by impregnation method. Metal oxide supports are suspended in the aqueous solution of nitrates or chlorides of the corresponding noble metals. After immersion for several hours to one day, water solvent is evaporated and dried overnight to obtain precursor (nitrates or chlorides) crystals fixed on the metal oxide support surfaces. Subsequently, the dried precursors are calcined in air to transform into noble metal oxides on the support surfaces. Finally, noble metal oxides are reduced in a stream containing hydrogen. This method is simple and reproducible in preparing supported noble metal catalysts. 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

When a supported metal on an oxide is prepared from an adsorbed precursor incorporating a noble metal bonded to an oxophilic metal, the result may be small noble metal clusters, each more-or-less nested in a cluster of atoms of the oxophilic metal, which is cationic and anchored to the support through metal-oxygen bonds [44,45]. The simplest such structure is modeled on the basis of EXAFS data as Re4Pt2, made from Re2Pt(CO)i2 (Fig. 6) [45]. 

Attwood PA, McNicol BD, Short RT. 1980. Electrocatalytic oxidation of methanol in acid electrolyte—Preparation and characterization of noble-metal electrocatalysts supported on pretreated carbon-fiber papers. J Appl Electrochem 10 213-222. 

Simonov PA, Likholobov VA. 2003. Physicochemical aspects of preparation of carbon-supported noble metal catalysts. In Wieckowski A, Savinova ER, Vayenas CG. editors. Catalysis and Electrocatalysis at Nanoparticle Surfaces. New York Marcel Decker. 

There can be no doubt that even with a noble metal such as platinum, the surface can be heavily contaminated with carbon when the latter is used as a supporting material (51). This may be ameliorated by cautious treatment with oxygen which oxidizes this carbon impurity to carbon dioxide. Nevertheless, it is extremely doubtful if any platinum surface in platinum/carbon can be prepared without an appreciable, and perhaps substantial, amount of impurity. 

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

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