Chlorinated alumina-supported metal

Chlorinated alumina-supported metal catalysts are the typical catalysts used today for catalytic naphtha reforming, which is performed at temperatures of480-550 °C (410). Modem versions of this type of catalyst are mul-timetaUic the catalytic properties of platinum are improved by the addition of another metal, often rhenium. Further elements that may be added are tin, silicon, germanium, lead, gallium, indium, iridium, thorium, lanthanum, cerium, cobalt, and nickel. AH these components are supported on chlorinated y-alumina (with a surface area of 150—300 m g ), which provides the acid function (411). 

For hydrocarbon reactions, metals (particularly platinum and its alloys) are frequently applied to acidic supports to catalyse hydrogen transfers. Thus platinum on a chlorinated alumina support accelerates the acid catalysed isomerization of n-alkanes (at about 150°C). In hydrocracking, the metal catalyses hydrogenation of heavy aromatic and polyaromatic components the resulting cycloparaffins (cycloalkanes) undergo zeolitic cracking, with... 

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,... 

The surface saturation by sulfur has to be compared to the irreversible adsorbed sulfur introduced by Menon and Prasad (22) and Apesteg-uia et al. (23). The study of H2S adsorption on supported catalysts was carried out by Menon and Prasad (22) and Apesteguia et al., Parera et al., and Barbier et al. and Marecot (23-25). For alumina supports, it was shown (23-25) that chlorine inhibits the adsorption of H2S on the support. Yet this adsorption on pure alumina is wholly reversible at 500°C, as is shown in Fig. 2. On Pt/Al203 at 500°C, only a fraction of the adsorbed sulfur is quickly desorbed in a hydrogen atmosphere. This result enabled the preceding authors (22-25) to develop the notion of reversible and irreversible adsorbed sulfur. The irreversible form, which does not exist on pure alumina, would interact with the metal. The quantity of irreversible sulfur, determined after 30 h of desorption under hydrogen flow at 500°C, does not depend on the sulfiding conditions (Table I). 

Chlorinated hydrocarbons (CHCs) are widely used in industry but bring both environmental and health risks 5,120 catalytic oxidation is a low cost method for their destruction. The most active catalysts are the platinum group metals supported on alumina, but high temperature is needed to obtain a satisfactory rate and to overcome chloride poisoning,121 but hydrogen chloride attacks the alumina support, so the use of other supports that... 

The selection of the carrier is relatively simple. It may be imposed by the type of reaction to be promoted. For instance, if the latter requires a bifunctional catalyst (metal + acid functions), acidic supports such as silica-aluminas, zeolites, or chlorinated aluminas, will be used. On the other hand, if the reaction occurs only on the metal, a more inert support such as silica will be used. In certain cases, other requirements (shock resistance, thermal conductivity, crush resistance, and flow characteristics) may dominate and structural supports (monoliths) have to be used. For the purpose of obtaining small metal particles, the use of zeolites has turned out to be an effective means to control their size. However, the problem of accessibility and acidity appearing on reduction may mask the evidence of the effect of metal particle size on the catalytic properties. 

In summary, several investigators have attempted to use TPR to elucidate the structure and the interactions of Re and Pt in supported catalysts. The interaction between the two metals has been found to be influenced by the Re loading, the ratio of the two metals, the chlorine content, the water partial pressure in the H2 used for reduction, and especially, the temperature of drying or calcination preceding reduction. When an alumina supported Re-Pt sample prepared from salt precursors was dried at 200 °C, TPR showed that the co-reduction of the two metals occurred at a temperature intermediate between that characteristic for the two monometallic counterparts. In contrast, when the catalyst was dried or pre-oxidized at 500 °C, two separate reduction peaks were observed (see Figure 40, taken from ref. 

The catalytic oxidation of dichloromethane was investigated by Van den Brink et al. [71], using Y-AI2O3, which is commonly employed as a support of noble metals for catalytic oxidation. Studies used a combination of flow and infrared spectroscopy experiments over a range of reaction temperatures. This paper is interesting as it provides a comparison with many of the studies using alumina supported catalysts, and it demonstrates that alumina is not a passive component in many chlorinated the VOC oxidation reactions. 

Five catalyst types were used in these product distribution studies Pd/C, Pd/alumina, pure Pd metal powder, Pd/Fe, and Pd/Cu/support. The last two catalysts are not traditional materials. The Pd/Cu, which was used in the reduction of nitrate, was a bimetallic catalyst on an alumina, silica, or polymer support. Fe is an atypical support in that it has the intrinsic ability to reductively dehalogenate chlorinated compounds by oxidizing to Fe2+ however, the rapid reaction rates associated with Pd/Fe are indicative of Pd-catalyzed reactions, which are much faster than Fe reactions. 

Applications to monometallic catalysts include the analysis of chlorine (Cl Ka) in alumina (Fig. 4.9), and metals analysis of supported Pt (La) used for reforming (implying the presence of chlorine) and analysis of Pd in an alumina matrix for selective hydrogenation catalysts. 

The process of ethane oxidative chlorination imposes heavy demands on the catalysts. The conventional salt supported catalysts are composed of Cu, K, Ca, Mn, Co, Fe, Mg, and other metal chlorides containing various additives these salts are precipitated on alumina, zeolites, silica gel, and other supports. Catalytic systems that represent solid solutions of iron cations in the lattice of the a-A Oa and a-Ct203 phases doped with cations, such as K, Ba, Ce, and Ag are also known [7]. 

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