Promoters alumina

The industrial catalysts for ammonia synthesis consist of far more than the catalyticaHy active iron (74). There are textural promoters, alumina and calcium oxide, that minimise sintering of the iron and a chemical promoter, potassium (about 1 wt % of the catalyst), and possibly present as K2O the potassium is beheved to be present on the iron surface and to donate electrons to the iron, increasing its activity for the dissociative adsorption of N2. The primary iron particles are about 30 nm in size, and the surface area is about 15 m /g. These catalysts last for years. 

Meunier, F.C., Zuzaniuk, V., Breen, J.P. et al. (2000) Mechanistic differences in the selective reduction of NO by propene over cobalt and silver-promoted alumina catalysts A kinetic and in situ DRIFTS study, Catal. Today, 59, 287. 

Ronning, M., Nicholson, D.G., and Holmen, A. 2001. In situ EXAFS study of the bimetallic interaction in a rhenium-promoted alumina-supported cobalt Fischer-Tropsch catalyst. Catal. Lett. 72 141 -6. 

An ex-carbonyl K-promoted alumina-supported catalyst prepared from Ru3(CO),2 and decarbonylated under H2 at 450°C was more dispersed and more active and selective for C2-C5 olefins in the Fischer-Tropsch reaction than conventionally prepared samples [108]. 

Further, a stabilization of the total surface of the main catalyst by added substances may explain some promoter effects, but this explanation holds only for a few multicomponent catalysts. For the iron-alumina catalyst, a beneficial stabilizing effect of the promoter alumina on the fine structure of the iron has to be accepted as a partial explanation. The fact that highly dispersed pure iron sinters at temperatures above 300°C. to a considerable extent, and that sintering practically does not occur with iron of the same high dispersion which contains 1 to 2% of alumina, is a strong qualitative support for this concept. In a quantitative way, the work of P. H. Emmett (47) and his associates has proved this point beyond any doubt it gives similarly valuable... 

Alumina is one of the most widely used catalyst supports in the petroleum industry because it is robust, porous, relatively inexpensive, and—what is especially important—it is capable of contributing acid-catalyzed activity that can be tailored to suit the requirements of a diverse array of catalytic processes. These include reforming (52, 55), hydrotreating (84, 55), and paraffin isomerization (56-55). Since pure alumina is relatively inactive for the skeletal isomerization reactions that are necessary in such processes, its acid activity is promoted through the addition of catalyst components such as fluoride, chloride, phosphate, silica, or boria. After a discussion of pure alumina itself, we will review pertinent studies of surface acidity and catalytic activity of the promoted aluminas. 

Sulfur compounds adsorb onto surface-active metal (or metal oxide) sites, causing deactivation in a large number of petroleum, petrochemical, and chemical catalytic applications. Acidic catalysts such as zeolites and promoted aluminas are poisoned by nitrogen compounds by chemisorption onto active sites also located on the surface. 

Mixed oxides of Ce and other lanthanides (La, Nd) were studied by Kubsch et al. [133], who found segregation of these trivalent ions to the surface in samples calcined at 1253 K a high Eb peak in the 01s feature was observed, being ascribed to carbonates formed in the trivalent ion-rich surface. A tendency to formation of such mixed oxides was detected in (Ce,Tb)Ox supported on lanthana-promoted alumina after calcination the La XP spectrum displayed two components, ascribed to La species on the AI2O3 surface and dissolved into the Ce,Tb oxide respectively [146]. A high Eb Ols peak observed there was ascribed to both alumina 0 ions and carbonate species on La-rich zones while the (Ce,Tb) oxide gave lower Eb values. 

Table 2 shows electrical conductivity data of the catalysts and the support. A is the electrical conductivity of alumina. B is the electrical conductivity of Sn and alkali metals promoted alumina. C is the electrical conductivity of Pt catalyst while D is the electrical conductivity of Pt-Sn catalyst. E is the electrical conductivity of Pt-Sn-Alkali metals catalyst. The data shows that the addition of metal to alumina increases electrical conductivity. The addition of Sn to Pt catalyst augments electrical conductivity approximately three times. Further incorporation of the alkali metals results in an order of magnitude further increases. 

The catalytic behavior of an iron-promoted alumina is clearly different. In the presence of the Claus gases, a catalytic cycle involves the conversion of oxygen impurities via transformation of iron sulfide into iron sulfate, which is easily regenerated in the stream to sulphur by reaction with H2S [14] (Figure 4). In summary, Fe/alumina... 

Figure 5. CS2 conversion at near equilibrium, obtained with aluminas and promoted aluminas under Ri conditions, with 200 ppm O2, and contact times of 2 s and 3 s.

It is well-known that a new generation of hydrotreating catalysts prepared with a silica promoted alumina support has been developed and are in use in a number of commercial hydrotreating units. Improved and more flexible operation should be possible especially in thermally cracked feedstocks with these catalysts having a higher HDS activity and resistance to carbon deposition than conventional CoMo or NiMo catalysts. 

Model 1-6 is a new hydrodearomatization (HDA) catalyst developed by ICERP to be used in aromatics hydrogenation of gas oil blends. The catalyst has been obtained by a highly improved NiO dispersion on the promoted alumina support having a bimodale pore distribution with a total pore volume of minimum 45 cmVg. 1-6 has a good HDA activity under rather moderate hydrotreating conditions i.e. 60 bar total pressure and a remarkable sulphur resistance. 

Successful ammonia conversion required discovery of a catalyst, which would promote a sufficiently rapid reaction at 100-300 atm and 400-500°C to utilize the moderately favorable equilibrium obtained under these conditions. Without this, higher temperatures would be required to obtain sufficiently rapid rates, and the less favorable equilibrium at higher temperatures would necessitate higher pressures as well, in order to obtain an economic conversion to ammonia. The original synthesis experiments were conducted with an osmium catalyst. Haber later discovered that reduced magnetic iron oxide (Fe304) was much more effective, and that its activity could be further enhanced by the presence of the promoters alumina (AI2O3 3%) and potassium oxide (K2O 1%), probably from the introduction of iron lattice defects. Iron with various proprietary variations still forms the basis of all ammonia catalyst systems today. 

Sinfelt, J.H. and Rohrer, J.C. "Cracking of hydrocarbons over a promoted alumina catalyst."/. Phys. Chem. 66 1559-1560 1962. 

Literature on the use of promoters is voluminous, and all claim enhancement of semi-hydrogenation selectivity. One of the more successful commercial catalysts for ethyne conversion to ethene, uses a silver promoted alumina-supported palladium catalyst [23]. Other promoting metals have been used, including rhodium and gold [24,25], copper [26-28], zinc (shown to inhibit oligomerization) [29-... 

The catalyst was prepared on a cordierite monolith having 62 cells per cm2, xhe support was coated with a promoted alumina-ceria (6 % Ce02) wash-coat and impregnated with 1.06 g/1 of platinum plus rhodium, with a Pt/Rli mass ratio of 5. After impregnation, the catalyst was calcined for 2 hours at 500°C. Activity measurement... 

Three of the recently introduced arsenic adsorbents, iron-doped alumina, iron-oxide coated sand, and granular ferric hydroxide, merit a brief discussion here because of their demonstrated effectiveness in removing arsenic. Because ferric hydroxide has a higher capacity for arsenic than does an equivalent surface area of aluminum hydroxide, iron-doped aluminas have been designed for the purpose of improving their arsenic capacity. One such adsorbent is Alcan AAFS-50, a brown-colored promoted alumina that is advertised to have five times the arsenic capacity and less pH sensitivity than conventional activated aluminas (6). Unlike conventional aluminas, AAFS-50 cannot be regenerated, but it reportedly can be landfilled without special treatment. Our recent research (7) showed... 

Results of some studies indicatethat the maximal degree of sulfidation depends strongly on the preparation and pretreatment method, i.e., 52% and 86% for two Co-promoted, alumina supported catalysts of near to equal chemical composition, and 80% and 100% for two nickel promoted... 

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