Silica-magnesia

For many years the most common catalyst was an amorphous or noncrystalline type called 3A. Initially, all 3A catalyst contained 13% alumina and 87% silica. To improve activity maintenance, the alumina content was increased to 25%. Both 13 and 25% alumina grades continue to be used the choice at a given refinery is based on the specific situation. Another amorphous type catalyst, containing silica-magnesia and called 3E, is also used. 

The NO spectrum has now been studied for the molecule adsorbed on ZnO, ZnS (18), 7-AI2O3, silica-alumina, silica-magnesia (20), an A-type zeolite (97), H-mordenite (98), and a variety of Y-type zeolites including NaY (19), MgY, CaY, BaY, SrY (81), decationated-Y (19), ScY, LaY, and A1HY (99). The nitric oxide molecule has mainly been used as a... 

A variety of material could be used as the basis for cracking catalyst, including synthetic silica-alumina, natural clay, or silica-magnesia. If these materials did not contain significant amounts of metals such as chromium or platinum that catalyzed the burning of carbon, the burning rate of the coke is independent of the base as shown in Fig. 7. 

Fio. 7. Comparison of intrinsic combustion rate constant on various noncatalyzing oxide bases (0) Filtrol 110 ( ) silica-magnesia (O) Fuller s earth. The dashed line denotes standard noncatalyzed kinetics. 

Silica-magnesia matrices have not yet been properly evaluated as an RCC catalyst matrix. However, such a matrix in conjunction with stabilized zeolite might provide an attractive matrix with a Kaolin-enhanced dual pore structure. Silica-magnesia matrices are notorious for their poor regeneration characteristics. When prepared by the dual pore Kaolin-enhanced method, they might be easier to regenerate and, thereby, open up a new family of residuum catalysts. Such catalysts have not yet been explored. 

J. Walker and S. A. Kay showed that the brown product of the action of iodine in aq. or chloroform soln. on magnesia is a case of adsorption analogous to the adsorption of acids by silk, and of iodine by starch. P. Guichard studied the adsorption products with iodine vapour and alumina, silica, magnesia, and beryllia. 

Natural clay catalysts were replaced by amorphous synthetic silica-alumina catalysts5,11 prepared by coprecipitation of orthosilicic acid and aluminum hydroxide. After calcining, the final active catalyst contained 10-15% alumina and 85-90% silica. Alumina content was later increased to 25%. Active catalysts are obtained only from the partially dehydrated mixtures of the hydroxides. Silica-magnesia was applied in industry, too. 

Dehydration and dehydrogenation combined utilizes dehydration agents combined with mild dehydrogenation agents. Included in this class of catalysts are phosphoric add, silica-magnesia, silica-alumina, alumina derived from aluminum chloride, and various metal oxides. 

The purpose of the present work is to study the precursor (metallic chlorides or carbonyl compounds), particle size and support (silica, magnesia and titania) effects in the selective hydrogenation of carvone employing rhodium as active metal. 

The acid function of the catalyst is supplied by the support. Among the supports mentioned in the literature are silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, silica-titania, acid-treated clays, acidic metal phosphates, alumina, and other such solid acids. The acidic properties of these amorphous catalysts can be further activated by the addition of small proportions of acidic halides such as HF, BF3, SiFit, and the like (3.). Zeolites such as the faujasites and mordenites are also important supports for hydrocracking catalysts (2). 

Passage of a mixture of cyclohexanone and ammonia over a variety of catalysts, e.g., thoria-alumina197 or silica-magnesia,198 at 200°-420° provides 6-pentyl-l,2,3,4,7,8,9,10-octahydrophenanthridine, which has also been obtained in a similar way from 2-( 1-cyclohexenyl)-cyclohexanone, %-hexaldehyde, and ammonia at 350°.199... 

Figure 9.6 represents the differential heats of NH3 and SOj adsorption as a function of coverage for silica, magnesia and y-alumina samples [15]. 

P. Carniti et al. [50] PP Thermogravimetric analysis Si02, silica-magnesia, sihca-titanate, mordenite, SALA, SAHA... 

The cracking of petroleum products is probably the most common dealkylation reaction. Silica-almnina, silica-magnesia, and a clay (montmorillonite) are common dealkylation catalysts.. ... 

Magnesia has strong basic sites but no acid sites (Table XVII) (e.g., 147, 179,180,189,203). However, acidity is generated when magnesia is added to silica (Table XVIII) (74,104). This acidity is exclusively of the Lewis type (59). Its acid sites are more widely distributed as compared with silica-alumina. The acid strength distribution of amorphous silica-alumina and silica-magnesia is more heterogeneous than that observed for any of the pure zeolites (H Y, ZSM-5, mordenite, etc.). This may in part be due to the presence of surface Al and Mg cations located in different environments. 

Commercial production of synthetic silica-alumina catalysts for use in fluid cracking was initiated in 1942. The synthetic catalysts were first manufactured in ground form, but means were later developed for production in MS (micro-spheroidal) form. First shipments of the MS catalyst were made in 1946. The synthetic catalysts contain 10 to 25% alumina. Synthetic silica-magnesia catalyst has also been used commercially in fluid-catalyst units (19,100). Magnesia content is 25 to 35% as MgO (276). 

The fundamental relationship between cracking activity and acidity is indicated by the fact that a single correlation line is obtained with catalysts of different chemical composition and made in different ways (222). Silica-alumina, silica-magnesia, silica-zirconia, and activated-clay catalysts were included in the comparison. Acidity in this case was meas-... 

Silica- magnesia Catalyst Activated clay Silica- alumina... 

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