Silica-alumina, impregnated, coke

Figure 2. Kinetics of steam gasification at 1500°F of coke deposited on silica-alumina impregnated with oxides of copper (A), vanadium ( Z ), iron (VI, and nickel (O, 3, , [various preparations]).

The intracrystalline pore volume of the catalysts was evaluated by n-hexane sorption as shown in Fig. 6. Sorption capacities for samples SI to S3 are comparable to that of the zeolite before Ga impregnation and correspond to the value expected for an unaltered ZSM-5 type material (S10). Sorption capacity decreases for samples S3, S4, S5, and S6, because of intracrystalline volume blockage by coke deposits and possibly also (silica)-alumina debris [6] in the aged catalyt S6. In addition, the sorption rate for S6 is about twice the rate observed for the other samples, suggesting that adsorption occurs mostly at the external surface of the S6 catalyst crystallites. Thus, it appears that coke deposited on S6, probably as polyaromatic species, has almost blocked the channel pore mouths and/or practically occupied the whole intracrystalline pore volume. It explains the poor catalytic performance of S6. 

For experiments involving metal-containing substrates, samples of the Durabead silica-alumina were impregnated with the nitrate salts of copper, iron, or nickel, or with vanadyl sulfate, at a level of 5 wt % metal, and then calcined in air for 10 hrs at 1000°F. The resulting metal oxide-containing materials were then subjected to the coking procedure described below without further treatment. 

The steam-carbon reaction is known to be catalyzed by metals, particularly transition metals (3,4.). In an effort to improve the rate of gasification, separate samples of the silica-alumina (Durabead) catalyst were impregnated with one of various metals prior to coke deposition, and the results for the subsequent steam-carbon reaction at 1500°F over these materials are shown in Figure 2 and Table IV. The effects of the deposited metal oxides can be summarized as follows ... 

Coke/Steam Reaction Rates on Metal-Impregnated Durabead (Silica-Alumina) TCC Catalysts at 1500°F... 

In marked contrast to the effects observed with iron, vanadium and copper oxides, prior impregnation of silica-alumina with nickel oxide led to a considerable increase in the initial rate of subsequent coke gasification, up to a coke conversion level of a>30% (Figure 2). 

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