Alumina-supported Systems

Past efforts in developing coal liquefaction catalysts have focused on alumina-supported systems and, except for exploratory studies, little attention has been given to systematic development of novel formulations. A particularly promising approach to the development of new catalysts specifically designed lor coal liquefaction processes lies in the formulation of multicomponent systems that, in comparison to work on single or bimetallic systems, are essentially unexplored. Use of multimetallic systems offers the possibility of multifunctional catalysts that are needed to perform the many different reactions encountered in coal processing. Because of its versatility for the preparation of multimetallic catalysts, the HTO system is an excellent candidate for further development. 

A second approach makes use of oxides, such as AI2O3, Ti02, ZrOg (and others), as supports, promoted with base metal cations. Among such cations, Co, Ni, Cu, Fe, Sn, Ga, Au, In, and Ag have all been tested, and their activity in the SCR of NO by hydrocarbons (HCs) has been reviewed. These studies have mainly focused on alumina supported systems, which ensure hydrothermal stability up to high operating temperatures (1073 K), promoted with gii2,i42,i43 jj i44-i46 active components, as they appear as the... 

A more detailed scenario can be found for alumina supported systems. Figure 10.7 illustrates the typical catalytic behavior for the SCR of NOx displayed by alumina supported systems, promoted with increasing loadings of a base metal. In this case, the catalytic activity... 

In both runs, a variation of temperature and partial pressures was performed to determine the effective kinetic parameters, which is summarized in Table 16.5. The rather low activation energies might indicate a possible influence of mass transfer due to pore diffusion. Interestingly, the boehmite-supported catalyst showed almost no dependence on the CO partial pressure, whereas the y-alumina-supported system showed a partial reaction order of 0.17. Water partial reaction order was found to be almost of first order in both cases (Figure 16.9). 

A great many materials have been used as catalyst supports in hydrogena-tion, but most of these catalyst have been in a quest for an improved system. The majority of catalyst supports are some form of carbon, alumina, or silica-alumina. Supports such as calcium carbonate or barium sulfate may give better yields of B in reactions of the type A- B- C, exemplified by acetylenes- cjs-olefins, apparently owing to a weaker adsorption of the intermediate B. Large-pore supports that allow ready escape of B may give better selectivities than smaller-pore supports, but other factors may influence selectivity as well. 

In this study butyl acetate (AcOBu) was hydrogenolysed to butanol over alumina supported Pt, Re, RePt and Re modified SnPt naphtha reforming catalysts both in a conventional autoclave and a high throughput (HT) slurry phase reactor system (AMTEC SPR 16). The oxide precursors of catalysts were characterized by Temperature-Programmed Reduction (TPR). The aim of this work was to study the role and efficiency of Sn and Re in the activation of the carbonyl group of esters. 

NASA conducted studies on the development of the catalysts for methane decomposition process for space life-support systems [94], A special catalytic reactor with a rotating magnetic field to support Co catalyst at 850°C was designed. In the 1970s, a U.S. Army researcher M. Callahan [95] developed a fuel processor to catalytically convert different hydrocarbon fuels to hydrogen, which was used to feed a 1.5 kW FC. He screened a number of metals for the catalytic activity in the methane decomposition reaction including Ni, Co, Fe, Pt, and Cr. Alumina-supported Ni catalyst was selected as the most suitable for the process. The following rate equation for methane decomposition was reported ... 

In addition to other polystyrene [138] and silica supports [139, 140, 141, 142, 143,144], iron and cobalt precatalysts have been immobilised on calcosilicate [145], magnesium dichloride [146,147,148,149], MCM-41 zeolite [150,151], clay [152] and fluorotetrasilicic mica [153], Supported systems have also been examined using alternative activators [154, 155, 156, 157, 158, 159]. For example, silica- and alumina-supported samples 5 have been activated with AK/ -Bu), to afford highly active, thermally robust catalysts [154], IR spectroscopy in DRIFT mode... 

Impregnating a basic colloidal suspension (pH = 12) on alumina does not induce proton liberation, thus the pH is constant (Fig. 13.25b). The system keeps its initial properties, i.e. negative charges for alumina support and PdO particles. Repulsive interactions are created between the alumina surface and the PdO particles so that the particles deposited on the support are redispersed, and finally isolated from each other. 

There exist a maximum allowable thickness of the supported gel layers above which it is not possible to obtain crack-free membranes after calcination. For Y-alumina membranes this thickness depends on a number of (partly unknown) parameters and has a value between 5 and 10 /im. One of the important parameters is certainly the roughness and porosity of the support system, because unsupported membranes (cast on teflon) are obtained crack-free up to 100 )xm. The xerogel obtained after drying was calcined over a wide range of temperatures. At 390°C the transition of boehmite to y-AljOj takes place in accordance with the overall reaction... 

These catalysts require temperatures above 100° and usually 150-200° for reasonable rates. Alkylsodium compounds at their decomposition temperatures (50-90°) have also been used by Pines and Haag (9). Lithium reacted with ethylene diamine has also been reported by Reggel et al. (4) as a catalyst for this reaction. The homogeneous system thus formed seems to lower the temperature requirement to 100° (4), whereas the use of potassium amide in liquid ammonia requires 120° (S). Sodium reacted with ethylene diamine has been reported to be an ineffective catalyst (4)- The most active catalyst systems reported so far are high-surface alkali metals and activated-alumina supports. They are very effective at or near room temperature (10-12). 

Dioxins, 1,4-oxathiins, and 1,4-dithiins have often been prepared by elimination reactions from saturated analogs as described in CHEC-II(1996) <1996CHEC-II(6)447>. Since then, a synthesis of tetramethyl l,4-dithiin-2,3,5,6-tetracarboxylate 241 has been reported in low yield (12%) by thermal decomposition of the 1,4,2,5-dithiadiazine system 240 in refluxing o-dichlorobenzene in the presence of DMAD <1997J(P1)1157>. Recently, 2,6-divinyl-l,4-dithiin 68 has been isolated from the reaction of l,4-bis(4-bromobut-2-ynyloxy)benzene with an excess of alumina-supported sodium sulfide. The formation of 68 has been presumed to take place via cyclic sulfide 242 <2003S849>. 

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