Activity after steam treatment

The steam treatment does however affect the Al-surroundings in the zeolite crystal. As seen in Fig. 2b, the intensity of both the tetragonally (at 0 ppm) and octahedrally (at 55 ppm) coordinated aluminum species decreases considerably after steam treatments for more than 4 h. Steam treatment for more than 8 h did not lead to a further decrease in the signal intensities. The decreases confirm that aluminum is extracted from the framework during the steaming process, as was also concluded from the 29Si MAS-NMR spectra (Fig. 1 b). This may lead to the formation of additional (micro) porosity, but the aluminum extraction could negatively affect the catalytic activity. 

C30MPARISC 1 OF GAS OIL C3 CKING ACTIVITIES OF AMORFHCUS AND CRYSTALLINE HIGH-AIDMINA SILTCA-AIDMINAS AFTER STEAM TREATMENT... 

A sample of Si02/Al203-pillared montmorillonite was tested as catalyst for catalytic cracking after steam treatment at 750 C for 18 hr. The MAT activity and the surface area, both given in Table I, indicate an almost complete collapse of the material upon steaming. 

The stability of mesoporous material SBA-15 and Al-SBA-15 was investigated under steaming treatment (100 % H2O) at 800 °C for different time. Al-SBA-15 catalyst has been prepared via post-synthesis procedure. The results show that the mesostructure of SBA-15 and Al-SBA-15 can be retained at 800 °C steaming for 8 h, while MCM-41 totally loses its mesostructure under the same condition just for 2 h. Moreover, Al-SBA-15 still has cracking activity of n-hexadecane and Pt/Al-SBA-15 has hydroisomerization activity of n-dodecane to some extent even after steaming treatment at 800 °C for 8 h. Meanwhile, Al-MCM-41and Pt/Al-MCM-41 catalysts totally lose their activity under the same treatment condition just for 2h. 

In terms of chemical modifications, treatment of ZSM-5 with phosphorus compounds [42,43] seems to be an interesting route to enhance the selectivity to light olefins in cracking reactions. It has been demonstrated that after phosphorus treatment, the strong acid sites of the original zeolite are replaced by an increased number of weaker acid sites, whose concentration increases after steam treatment. Finally, the combined treatment phosphorus/ REs [44] results in an improvement in both stability and activity. Apparently, REs reduce aromatics formation on the external surface area of the zeolite, whereas phosphorus reduces the loss in activity caused by dealumination. 

The opposite behavior was observed after the treatment of the two catalysts in the steam-containing stream, at 380°C. The catalyst P/V 1.06 did not show any change of catalytic performance, whereas in the case of P/V 1.00 the treatment rendered the catalyst less active but more selective than the sample equilibrated in the reactive atmosphere at 380°C. This means that with P/V 1.00, the active layer is not fully hydrolyzed under reaction conditions, and that a hydrolyzed surface is more selective than the active surface of the equilibrated P/V 1.00 catalyst. On the contrary, the active surface of catalyst P/V 1.06 either was already hydrolyzed under... 

VANADIUM DEACTIVATION UNDER SIMULATED CONDITIONS. The degree of catalyst deactivation was measured by comparing the activity of the catalyst or catalyst/passivator blend containing 5000 ppm V to that of the corresponding sample with no V added after similar treatment conditions (Table II). For the USY catalyst (catalyst A), steaming with VgO at 1450 F resulted in a 6855 decline in activitjr ... 

Fig. 18. Correlation between cracking activity and surface area of Si/Al catalyst after various steam treatments.

One of the major current challenges is the structural investigation of the benzene to phenol oxidation catalyst. The Fe-MFl material used for this application was suggested to work only after activation by steaming or high-temperature treatment. 

Figure 4. Generation of porosity in powdered activated carbon by steam treatment. Note For clarity, all planes are oriented in such a way that they are viewed from the edge. In reality, any orientation will be found. A. Structure of carbonized raw material showing basal planes (B) and active basal planes (AB). B. Development of microporosity after active basal planes are gasified. C. Subsequent thermal treatment generates additional active basal planes. D. Development of mesoporosity and additional microporosity after more active basal planes are gasified. B = basal plane AB= active basal plane xp = micropore Mp = mesopores. (Courtesy Norit Nederland B.V.)...

The effect of the steaming temperature on stabflity and activity of zeohte samples is demonstrated in Table 1. CrystaUinity for all samples decreases noticeably after steaming at 500-700°C. Hydrothermal treatment at 800°C results in the coUapse of FAU and EMT. Although the initial EMT sample has a higher Si/Al ratio, it demonstrates a somewhat lower stabflity than FAU, which is perhaps due to the higher symmetry assodated with the structure of Y zeohte. Indeed, EMO, which possesses the structure of cubic Y zeohte and has a Si/Al ratio similar to that of the EMT sample, is the most stable among these three catalysts. It should be noted that A1 distribution can also affect stabflity of the zeohtes. 

The activities in oxidation at 200°C (fig. 4) and steam reforming at 300°C (fig 5) are determined for the two bimetallic catalysts before and after thermal treatments. These figures show the following points ... 

During the rich or lean excursions, the two catalysts containing NiAl204 seem to present a very good stability of Rh with a minimal loss of steam reforming activity after regeneration in H2. But for those catalysts, platinum oxidative activity is very affected by a reducing treatment. 

Hilman et al. [20, 21] have shown that addition of high-pressure steam (6.5 bar) to the syngas feed causes a substantial loss of activity for C0/AI2O3 and CoRe/AhOs FT catalysts when steam addition is ceased, a slight recovery in activity is observed. Loss of catalytic activity was attributed to surfaee cobalt oxidation although loss of chemisorption surface area and formation of hard to reduce cobalt-aluminate were also observed after the steam treatment. 

The first thing we did after we were satisfied with test conditions was to set up a series of standard curves. These are shown in Figure 3. We have plotted the C5+ gasoline, total C4 s, dry gas and coke yields against the volume percent conversion of the gas oil. The conversion was controlled by varying the activity of the standard silica-alumina gel catalyst. This was done by controlled steam treatment. 

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