Catalyst supports chlorinated alumina

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,... 

Upon heating in air the TGA-DTA measurement showed that the spent catalyst sample lost 5% weight and two exothermal peaks (at 300°C and 400°C) were observed. Similar measurements with spent alumina (without CuO) showed only one peak in the DTA diagram (405°C). A fresh and spent Cu0/A1203 sample were characterized with EDAX. The analysis showed that chlorine was present on the spent catalyst, whereas it was totally absent in the fresh sample. The origin of chlorine was from a chlorine containing impurity in the hydroxy ketone I which irreversibly adsorbed on the catalyst. Adsorbed chlorine is known to increase the acidity of the alumina support and thereby may enhance cracking or polymerisation processes which finally lead to catalyst deactivation. The dark-yellow colour of the initially white supports after use in the reaction indicated that residues were retained on the catalyst. The yellow colour disappeared after calcination in air at 500°C,... 

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. 

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 choice of a catalyst support depends on the physical and chemical characteristics of the catalyst and the supportT on desired or undesired interactions with components of the system to be catalysed and on the necessity of controlling mass and heat transfer in the process (Figure 1) [1A]. Often it is necessary to compromise between various demands or to dope the support to enhance or reduce given properties. Chlorine doping of alumina used in reforming catalysts is a case in point [37]. 

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. 

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... 

The behavior of modified Rli/Ce02-Al203 catalyst is shown in Fig.5. Contrarily to what was found on AI2O3, for modified catalysts supported on ceria-alumina, chlorine has only a sliglit effect on the OSC values. This difference would be result of the presence of ceria that could promote a better distribution of chlorine at the carrier surface. Sulfates would increase the oxygen storage capacity of the modified catalyst. This effect would only be apparent and would be due partly to the sulflir reduction by CO which masks the inliibitor effect of sulfur on OSC. This can be observed by comparison with the oxygen mobilities. 

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). 

Earlier reference has been made to sulphonic acid resins and supported mineral acids as heterogeneous catalysts. The chlorination of alumina provides a strongly acidic surface, while the performance of a number of solid superacid catalysts (— Ho values up to 16) has recently been reported. However a number of mixed oxides of metals and metalloids also show useful acidic properties. 

Thus, the kinetic and EXAFS results can only be explained if the Cl coming from HCl or evolved during reduction is reabsorbed on the support and subsequently released and readsorbed on the Pt surface during calcination. During reduction, Hj adsorbs dissociatively on the Pt surface and reacts with the adsorbed complex to likely yield HCl, which desorbs as a gas and is transported onto the support. Recent results on chlorinated Pt catalysts supported on model flat alumina substrates" " indicate that no Cl is observed after reduction at 300°C. Therefore, the surface-Cl interaction during reduction is affected by the porous structure of the supported catalysts. 

Jensen and coworkers studied phosgene synthesis using a micropacked-bed reactor [7]. A silicon reactor consisting of a 20 mm long, 625 (im wide and 300 pm deep reaction channel (volume 3.75 mL) was employed (Figure 11.2). In order to avoid corrosion by chlorine, the microchannels were coated with a thin sflicon dioidde film (5000.. A fixed bed of activated carbon catalyst (1.3 mg, 53-73 pm) supported on alumina particles ( 3mg, 53-71 pm) was placed inside the microchannel. Chlorine and CO were mixed and fed into the microchannel network. The exit stream could be analyzed on-line using a mass spectrometer. 

The most active catalysts are derived from supported platinum group metals, or copper chromite when the VOC contains chlorine. The catalyst supports are produced as high surface area gamma-alumina spheres, extmdates or cylindrical pellets that can be used in dust free conditions. Alternatively, when treating large volumes of effluent gas, honeycomb monohths made from cordierite or metal sheets are coated with a surface washcoat of the same alumina are particularly usefiil. The supports are selected to be stable at the operating temperature of the reaction. 

Erivanskaya and co-workers also studied the dehydrocyclization of 2-n-butylnaphthalene over supported palladium, rhodium, and iridium catalysts (56-55). Palladium-alumina showed the lowest C6-dehydrocyclization activity, but was the most active for the C5-dehydrocyclization of 2-n-butyl-naphthalene. A later study showed, however, that this enhanced activity was due to the high chlorine content of the palladium-alumina catalyst and not to some mysterious inherent catalytic activity of palladium (56). 

With PCE transformation, the product (ethane) was the same for all supports but yields (measured by both ethane and Q production) varied 50-55% ethane yield was obtained on C, 68% yield on Pd/PEI/silica, and 80-85% yield on alumina. The possibility that lower yields resulted from PCE sorbed to the support was considered the C catalyst was therefore heated to 180°C in an attempt to desorb any species. However, only a few nanomoles of PCE (tenths of a percent of the original mass) and traces of lesser chlorinated ethylenes were detected. This suggests that the low ethane... 

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