Drying supported catalyst temperature, effect

The microstructure of a sol, in terms of the nature and concentration of sol particles, significantly affect a membrane s properties such as average pore diameter and pore size distribution. Other critical parameters are the temperature and rate of evaporation used in the drying and calcination steps. Even though it is economical to obtain the final product form quickly, too rapid a drying rate forms cracks in the membrane. Crack formation is also dependent on thickness of the membrane. The work of Cini et al. [49], who prepared supported microporous y-A C membranes as catalyst supports, illustrates many of these effects. 

The mimic is prepared by sequential ion-exchanges with iron(ll) and Pd(ll) tetrammine cations followed by calcinations and reduction of the Pd(ll) to Pd(0) as previously described(14). A material with 2wt% Fe(ll) and 1wt% Pd(0) is used by immersing the dry zeolite solid in neat substrate alkane and then pressuring the reaction vessel with a 3 1 mixture of oxygemhydrogen. After shaking this mixture at room temperature for 4 hours the products are analyzed by capillary GC. As a control to assess the intrinsic selectivity of such a Pd/Fe system in the absence of steric effects of the zeolite, catalysts prepared with amorphous silico-aluminate supports were run for comparison. In these cases all reactions must take place at the particle surface since there is no interior pore structure available. In addition, comparison of reaction selectivities of this catalysts with our zeolite materials allows us to ascertain that the Fe active sites must be actually inside (and not on the exterior surface) of the zeolite crystallites. 

The second series of catalysts was coprecipitated with iron and supported on alumina. The y-Al203 was impregnated with a solution of TiCl3 which contained the desired amount of Fe(N03)2. The mixture was then dried at 120°C, ground, and fired. Iron contents, firing temperatures, and ratios of Ti02 to alumina were the same as for the first series of catalysts. The results from this set of experiments were similar to those from the previous set [65]. All catalysts were reported to produce ammonia. The rate of ammonia production decreased as the iron content increased. The first series of catalysts (surface-loaded catalysts) was more effective than the second series (coprecipitated catalysts) [66], Apparent ammonia production was doubled for one sample of catalyst which had been mixed with aqueous KOH and dried at 120°C [66]. 

Figure 40 The effect of drying temperature on the TPR profiles of alumina supported Pt-Re catalyst prepared by impregnation. The amounts of both Pt and Re were 0.3 wt.-% in all catalysts and the amount of Cl was 0.6 wt. %...

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