Noble metals, alumina-supported

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]. 

C and 4 h for Raney catalysts. Due to lower reducibility and stronger interaction of Co- and Ni-oxides with alumina, 10 wt % metal was used. Despite the higher metal content of these catalysts they were less active than the alumina supported noble metals and their selectivity to RNH2 was lower than that of Ru. The selectivity pattern on noble metals was in good agreement with literature data [1,4],... 

Toluene disproportionation and transalkylation are important industrial processes in the manufacture of p-xylene. Toluene disproportionation [Eq. (5.73)] transforms toluene into benzene and an equilibrium mixture of isomeric xylenes. The theoretical conversion of toluene is 55%. Commercial operations are usually run to attain 42 18% conversions. In conventional processes308 309 324 325 alumina-supported noble metal or rare-earth catalysts are used in the presence of hydrogen (350-... 

One of the characteristic features of the metal-catalysed reaction of acetylene with hydrogen is that, in addition to ethylene and ethane, hydrocarbons containing more than two carbon atoms are frequently observed in appreciable yields. The hydropolymerisation of acetylene over nickel—pumice catalysts was investigated in some detail by Sheridan [169] who found that, between 200 and 250°C, extensive polymerisation to yield predominantly C4 - and C6 -polymers occurred, although small amounts of all polymers up to Cn, where n > 31, were also observed. It was also shown that the polymeric products were aliphatic hydrocarbons, although subsequent studies with nickel—alumina [176] revealed that, whilst the main products were aliphatic hydrocarbons, small amounts of cyclohexene, cyclohexane and aromatic hydrocarbons were also formed. The extent of polymerisation appears to be greater with the first row metals, iron, cobalt, nickel and copper, where up to 60% of the acetylene may polymerise, than with the second and third row noble Group VIII metals. With alumina-supported noble metals, the polymerisation prod-... 

Hannemann S, Grunwaldt J-D, Gunther D, Krumeich F, Lienemann P, Baiker A. Combination of flame synthesis and high throughput experimentation preparation of alumina supported noble metal particles and their application in the catalytic partial oxidation of methane. Appl Catal A. 2007 316 226. 

G. G. Olympiou, C. M. Kalamaras, C. D. Z. Yazdi, A. M. Efstathiou, Mechanistic aspects of the water-gas shift reaction on alumina-supported noble metal catalysts in situ DRIFTS and SSITKA - mass spectrometry studies, Catal. Today 127 (2007) 304-318. 

Solymosi, F. and Erdohelyi, A. (1980) Hydrogenation of CO2 to CH4 over alumina-supported noble metals. Journal of Molecular Catalysis, 8,471-474. 

Figure 10.1. X-ray diffraction patterns of fresh and used catalysts (a) fresh catalysts (b) Rh/Al203 (c) Pt/Al203 (d) Pd/Al203. (1) fresh (2) the used catalyst at the catalyst bed inlet (3) the used catalyst at the catalyst bed outlet. Fresh reduced in hydrogen flow at 1123 K. Used reaction conditions of 1123 K, CHVHzO/Oz/Ar = 40/30/20/10, W/F = 0.40 gh mol, 4 h [3]. (Reproduced from Applied Catalysis A - General, 275(1-2), Li BT, Maniyama K, Nunmnabi M, Kunimori K, Tomishige K, Temperature profiles of alumina-supported noble metal catalysts in autothermal reforming of methane, 157-72, 2004, with permission from Elsevier.)...

Li BT, Maruyama K, Nurunnabi M, Knnimori K, Tomishige K. Temperature profiles of alumina-supported noble metal catalysts in autothermal reforming of methane. Appl Catal A General 2004 275 157-72. 

Oh, S., Mitchell, P. and Siewert, R. (1991). Methane Oxidation over Alumina-supported Noble Metal Catalysts with and without Cerium Additives, J. Catal, 146, pp. 287-301. 

Previous kinetic investigations dealing with the NO + H2 reaction over supported noble metal-based catalysts showed different kinetic features according to the nature of the support [29,53-58], Initially, this reaction has been described in the absence of oxygen on Rh deposited on silica and alumina by the following mechanism [29],... 

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,... 

Supported noble metal catalysts (Pt, Pd, Ag, Rh, Ni, etc.) are an important class of catalysts. Depositing noble metals on high-area oxide supports (alumina, silica, zeolites) disperses the metal over the surface so that nearly every metal atom is on the surface. A critical property of supported catalysts is that they have high dispersion (fraction of atoms on the surface), and this is a strong function of support, method of preparation, and treatment conditions. Since noble metals are very expensive, this reduces the cost of catalyst. It is fairly common to have situations where the noble metals in a catalyst cost more than 100,000 in a typical reactor. Fortunately, these metals can usually be recovered and recycled when the catalyst has become deactivated and needs to be replaced. 

Among the early systemmatic studies of the metal-catalysed hydrogenation of acetylene were those of Sheridan et al. [158,168—170] who investigated the kinetics and product distributions over pumice-supported metals. Subsequently, the reaction has been extensively studied by Bond et al. [9,165,171—175] over pumice- and alumina-supported metals and metal powders. The reaction of acetylene with deuterium over nickel [91, 163] and alumina-supported noble Group VIII metals [164,165] has also been investigated. 

The reaction of acetylene with deuterium has been studied over alumina-supported noble Group VIII metals [164,165], whilst over nickel-pumice catalysts the reaction of perdeuteroacetylene with hydrogen has been investigated [163]. In both of these studies, the deuteroethylene distributions have been interpreted in terms of the steady state analysis discussed in Sect. 4.4. Typical deuteroethylene distributions together with the values of p, q and s are shown in Table 16. 

Gasolines contain a small amount of sulfur which is emitted with the exhaust gas mainly as sulfur dioxide. On passing through the catalyst, the sulfur dioxide in exhaust gas is partially converted to sulfur trioxide which may react with the water vapor to form sulfuric acid (1,2) or with the support oxide to form aluminum sulfate and cerium sulfate (3-6). However, sulfur storage can also occur by the direct interaction of SO2 with both alumina and ceria (4,7). Studies of the oxidation of SO2 over supported noble metal catalysts indicate that Pt catalytically oxidizes more SO2 to SO3 than Rh (8,9) and that this reaction diminishes with increasing Rh content for Pt-Rh catalysts (10). Moreover, it was shown that heating platinum and rhodium catalysts in a SO2 and O2 mixture produces sulfate on the metals (11). 

The PROX reaction has been extensively investigated on Pt catalysts supported on AI2O3 [341-343] and zeolites [344], Oh and Sinkevitch [341] compared the efEciency of several noble metals over alumina the CO conversion was found to decrease in the following order Ru > Rh > Pt > Pd (metal loading 0,5 wt% for all catalysts). Other systems, which have been investigated for the PROX reaction include metal oxides [345], oxide-supported noble metal catalysts [346] and bimetallic [347] catalysts. 

Fio. 21. The dependence of selectivity upon hydrogen pressure for the reaction CjHj + Hj catalyzed by alumina-supported noble Group VIII metals initial Pc.H, = 50... 

It was observed that, when supported R catalysts reach temperatures as high as -1273 K, the phase transition occurring in the major support component (y- -> 8,0-Al2Oj) has lethal effects on the adsorptive properties of the supported noble metal. It was also observed that, when a supported R catalyst reaches temperatures higher than those at which the catalyst was first fired and/or reduced, but still lower than those needed for the y—> 8,0-Al2O3 phase transition, the R° adsorptive capacity of pure-alumina-supported catalysts is somewhat increased, whereas the capacity of ceria-containing catalysts is appreciably decreased. This effect was ascribed to an increased strong interaction between R particles and the ceria component of the support. 

Noble metals are placed on oxide supports at least partly for reasons of economy and stability, and sometimes to make catalytic use of the acidity of the support. Noble metals commonly used include Pt, Rh, Ir, and Re supports include alumina, silica, and zeolites. The catalysts are often chlorided or sulfided to enhance their selectivity for a specific reaction. Chlorination and... 

Catalysts for total hydrocarbon and volatile organic compounds (VOC) combustion in waste gases contain noble metals supported on alumina. The noble metals are platinum, palladium, combinations of platinum and palladium, or rhodium and the typical content is 0.3-0.5 wt%. The BASF RO-25 catalyst, specified for VOC combustion, is reported to contain 0.5% palladium on 0-AI2O3 characterized by a surface area of 109 w g (428). 

Unlike the supported noble metals discussed so far, where it is customary, although not always justifiably so, to assume that all of the metal is present in its reduced state following pre-treatment in hydrogen, for base metal catalysts such as supported Ni, it is quite common to find a fraction present in an unreduced state. This is not confined to alumina and the consequence of Ni aluminate formation," but is also common for silica" and silicate supported... 

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