Silica-magnesia catalysts

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). 

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

The silica-magnesia catalysts, DA-5 and Nalco, in the virgin state, along with Davison silica gel have practically their entire area and pore volume contributed by the very smallest of pores that are encountered in catalyst structures that is, pores in the 10 to 15 A. radius range. It is apparent in Fig. 2 that for these materials there is no appreciable adsorption at the high relative pressures. This indicates the absence of large pores. One and one-half monolayers according to the BET theory effectively fill the pore volume of the DA-5 and the Davison silica gel, and only two monolayers are required for Nalco. Very little hysteresis is observed for any of these three materials. 

In Fig. 5 the striking similarity of the isotherms for a virgin DA-5 and a steam-treated DA-5 is apparent. The pore volume and area of the steam-sintered sample are far below those of the virgin, but the isotherm contours are almost identical. A small increase in pore radius is observed. Thus the presence of steam during sintering does not alter significantly the pore structure of the silica-magnesia catalysts studied. It should also be noted here that the isotherms for the DA-5 catalyst... 

The composition of acid-treated natural clay catalysts was more or less duplicated in the synthetic catalyst formulations. TTie main advantage of synthetic catalysts was a reproducible composition with few impurities known to cause deactivation. Both silica/alumina and silica/magnesia formulations were nsed in early tests but, despite good activity, silica/magnesia catalysts were nnstable and difficult to regenerate. 

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