Metal Oxide Supports

Supports are often prepared first and the catalyst and promoter components added later (60). Metal oxide supports are usually prepared by precipitation from aqueous solutions. Nitrates are commonly used anions alkaUes and ammonium are commonly used cations. Metal oxide supports, eg, sihca and alumina, are prepared in the form of hydrogels. Mixed oxides such as siUca—alumina are made by cogelation. Carefiil control of conditions such as pH is important to give uniform products. 

An Application NMR of V oxide films on metal oxide supports... 

A number of olefins may be polymerised using certain metal oxides supported on the surface of an inert solid particle. The mechanism of these polymerisation reactions is little understood but is believed to be ionic in nature. 

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. 

Metal oxide support in the form of powder, bead, honeycomb, or cloth is dispersed or immersed in an aqueous solution of HAuCU, the pH of which is adjusted... 

Olefin metathesis has been discovered on heterogeneous catalysts, which are typically transition-metal oxides supported on oxide supports, for example... 

In spite of the low affinity for binding to oxygen, gold(III) alkoxo, hydroxo and even 0X0 complexes have been obtained [6, 7]. These are valuable models for Au-O(H) species which are likely to be involved in oxidation reactions catalyzed by metal-oxide-supported gold [8]. All these complexes have displayed interesting chemical reactivity and, in some cases, remarkable catalytic activity. 

Utilization of Specific Surface Interaction of Gold Compounds with the Metal Oxide Supports... 

The approach comprises deposition-precipitation (DP) of Au(OH)3 onto the hydroxide surfaces of metal oxide supports from an alkaline solution of HAUCI4 [26] and grafting of organo gold complexes such as dimethyl gold (Ill)acetylacetonate (hereafter denoted as Au acac complex) [27] and Au(PPh3)(N03) [28] either in gas and liquid phase are advantageous in that a variety of metal oxides commercially available in the forms of powder, sphere, honeycomb can be used as supports. 

Active gold catalysts are advantageous in that water usually enhances the catalytic activity [39]. Reducible or semiconductive metal oxide supports do not need moisture for room temperature catalytic activity, while non-reducible metal oxides such as AI2O3 and Si02 do [39] (Figure 10). 

Figure 31 shows that among metal oxide supports, TOF markedly changes depending on not only the kind of metal oxides but also on their size [98]. Especially, fine particles of Ce02 with mean diameter of 5 nm present the highest catalytic activity. On the other hand, Prati and her coworkers [31] reported that gold NPs supported on activated carbons are very active and selective in the liquid phase oxidation of various alcohols. 

Figure 31. Effect of metal oxide supports in glucose oxidation over gold catalysts [98].

The present model deals with a supported transition metal cation which is highly dispersed, at the molecular scale, on an oxide, or exchanged in a zeolite. In the case of zeolite-supported cations, the formation of different metal species in metal/zeolite catalysts (metal oxides, metal oxocations, besides cationic species) has been considered by different authors who have suggested these species to play key roles in SCR catalysis [14,15], This supported cation can also be considered as located at a metal oxide/support interface. 

Metal oxide sensors (MOS), smart, 22 717 Metal oxide supported catalysts, 5 336-337 coke formation on, 5 267—270 Metal passivation, in industrial water treatment, 26 137 Metal peroxides, 18 410 Metal phosphates, tertiary, 18 840 Metal-phosphorus alloys, 19 59 Metal phthalocyanines, electrochromic materials, 6 572t, 576-577 Metal prefinishing, detersive systems for, 8 413t... 

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