Water catalyst pretreatment

Figure 1. DR UV-vis spectra of hydrated Fe-zeolite catalysts pretreated by calcination in flow of dry oxygen at 540 °C (black curves) and steam-treated in the flow of water vapor at 540 °C (gray curves). A) Fe-sil-12900, B) Fe-MTW-11500, C) Fe-MTW-14700, Fe-MTW-18900.

The lack of information about relative activities of different forms and the unknown dependence of their relative concentrations on catalyst pretreatment and reaction conditions, and the influence of reactants, products (water) and solvents, introduce uncertainty into the interpretation of kinetic measurements. 

The high basicity of Mgo is associated with the presence of surface °2 Cus (cus= coordinatively unsaturated site) their concentration depends on thermal pretreatment and it shows a maximum around 700°C [23]. A sample of Mgo catalyst pretreated at 650°C showed only a negligible enhancement of the amount of condensation products suggesting that 02-cug are not responsible for them (however during the condensation reaction water is produced which could saturate 0 cus) Higher basic strength of surface OH group of CaO and SrO [22] should promote the condensation reactions. 

In 1977 Schrauzer and Guth reported that they had synthesized NH3 from H20 and N2 [1], The process they described involved the use of titanium dioxide-based photocatalysis and UV-visible radiation. The authors reported that Ti02 powders containing chemisorbed water or surface hydroxyls produced H2 and 02 when irradiated in the near UV. The amounts of H2 and 02 so produced were found to be strongly dependent upon the catalyst pretreatment. Experiments demonstrated that N2 at one atmosphere completely inhibited the formation of H2, but had no effect on the yield of 02. The authors were aware of earlier work [57] showing that acetylene is photoreduced under conditions similar to those employed in the water photolysis reactions and they found that acetylene, like nitrogen, completely inhibited H2 production. On the basis of these results, the authors reasoned that photoreduction of N2 could be occurring. They... 

Precipitation catalyst, pretreated at atmospheric pressure, first with hydrogen at 300-400°C. and then with water gas at 245°C. 

One of the features commonly observed for single component oxides is strong dependency of the activity and selectivity on the catalyst pretreatment temperature. Once the surfaces are exposed to air, the surfaces are immediately covered with water and CO2, and lose the catalytic activities. To reveal the basic properties on the surfaces, the oxides need to be pretreated at a high temperature to remove strongly... 

As for the abovementioned steady-state experiments, SSITKA experiments were carried out on catalysts pretreated with water vapor. After reduction, the reactor was cooled down to 453 K in flowing He. The temperature was increased to 523 K before introducing a flow of 1.2 g/h of water vapor, mixed with 2.5 ml/min and 35 ml/min He. After 16 h of water treatment, the catalyst was cooled down to 453 K in flowing He. The further procedure was the same as for the dry catalyst. 

Figure 3. Comparison of the chain length distribution in the hydrocarbon products for the promoted and unpromoted catalyst. T=483 K, P=13 bar. CO conversion is given in Table 1. Solid S3Tnbols catalysts pretreated with water. Open symbols FTS directly after reduction (no water pretreatment). Square symbols before S5mgas/water co-feeding. Circular symbols after syngas/water cofeeding.

The CO conversion and the methane selectivity show the same tendency as for the high pressure experiments. Water treatment reduces both the conversion and the selectivity to methane, either if the water is introduced as a pretreatment procedure, or co-fed with the reaction mixture. Catalysts pretreated with water show no significant difference in behavior before and after the co-feeding. 

Cellulose butyrate is prepared using the anhydride and sulfuric acid as the catalyst. Pretreatment of the cellulose with water and butyric acid is recommended to increase the reaction rate and efficiency. 

The presence of potassium on iron during ammonia pretreatment has no additional effect on the restructuring process when adsorbed alone or when coadsorbed with Al O. Thus, potassium does not seem to affect the structural promotion of ammonia synthesis catalyst either during ammonia or water-vapor pretreatment. However, the presence of potassium on a Al O /Fe surface, during water-vapor pretreatment (Section 4.6), inhibits restructuring. A likely explanation for this observation is that the formation of potassium aluminate blocks the interaction between iron oxide and aluminum oxide. ... 

The effects of water-vapor and ammonia pretreatment on the initial rate of ammonia synthesis over Fe, Al O /Fe, and K/Al O /Fe surfaces can be summarized as follows. The presence of aluminum oxide promotes the restructuring of iron during the water-vapor pretreatment, but it inhibits the ammonia-induced restructuring. The presence of potassium shows no effect in the ammonia pretreatment and it inhibits water-vapor-induced restructuring of iron. These results suggest that to form the most active ammonia synthesis catalyst, the iron should first be restructured in ammonia before aluminum oxide is added. After aluminum oxide is added the surface should be treated in water vapor, and finally potassium should be added to serve as a promoter at high ammonia synthesis reaction conversions. 

The grafting procedure is straightforward, which is a major advantage of this method. The silica was pretreated to remove water from the support, after which it was added to a dichloromethane solution containing the catalyst. After 6 hours of mixing the supported catalyst was isolated by filtration. The remaining solvent was colourless... 

---