Calcined catalysts surface areas

Impacts of Catalyst Preparation and Activation on Surface Area. Studies have been performed to determine the effects of catalyst preparation and activation procedures and Si addition to the support on catalyst surface area. This work was performed with Pd HTO catalysts, which also show an increase in activity with Si addition to the support. Figure 4a shows the effects of the Ti Si ratio in the support and the acidification pH during catalyst preparation on the surface areas of Pd HTO catalysts that have been calcined at 30QoC in air. The presence of a 6 1 TirSi mole ratio results in a 2- to 3-fold increase in surface area with respect to Pd HTO without Si addition. When the Si content is increased to give a Ti Si ratio of 2, any discernible enhancement in surface area compared to catalyst without Si is small and is limited to materials formed at the lower pHs. The effect of pH on the surface areas of catalysts prepared on the same supports is more difficult to discern. There appears to be a general trend whereby the surface areas of samples acidified at pH 4 and 5 are slightly enhanced with respect to materials that either were not acidified (pH>6) or were prepared at pH 2. 

Increasing the calcination temperature to 500 C (Figure 4b) shows similar trends to those observed at 30(JoC. As would be expected, the higher temperature resulted in decreases in catalyst surface areas. The results of this... 

The differences between the behaviour of these catalysts is not only caused by the differences in the surface area, since the variation of the relative activity (i.e. mol of CH4 converted per min and m of catalyst surface area) does not follow any clear trend with the calcining temperature. So, at 400°C, the relative activities are 0.225 pmol/min-m for the catalyst calcined at 400 C, 0.717 pmol/min-m for the catalyst calcined at 600 C and 0.471 pmoEmin-m for the catalyst calcined at 800 C. These results suggest that different active... 

Influence of the calcination on H -up-take and surface area of colloid embedded catalysts Catalyst Surface area, m g H2-uptake, cm g ... 

The crystal morphology of (VO)2P207 can be determined by control of the pseudomorphic precursor VOH17O4.0.5H2O. The standard method of preparation and calcination shows that the primary factor is the nature of alcohol used for reflux, which influences crystallinity and shape of secondary particles of precursor and catalyst. Surface area depends mainly on thickness and width of plates, the later being related to selectivity in oxidation of butane to maleic anhydride. 

Early catalysts were produced from calcined ferric oxide, potassium carbonate, a binder when required, and usually chromium oxide. Subsequently a wide range of other oxides replaced the chromium oxide typical compositions are shown in Table 7.5. The paste was extruded or granulated to produce a suitable shape and then calcined at a high temperature in the range 900°-950°C. Solid solutions of a-hematite and chromium oxide (the active catalyst precursors) were formed and these also contained potassium carbonate to inhibit coke formation. Catalyst surface area and pore volume were controlled by calcination conditions. It has been confirmed by X-ray diffraction studies that a-hematite is reduced to magnetite and that there is some combination of potash and the chromium oxide stabilizer. There is little change in the physical properties of the catalyst during reduction and subsequent operation. 

Catalyst performance depends on composition, the method of preparation, support, and calcination conditions. Other key properties include, in addition to chemical performance requkements, surface area, porosity, density, pore size distribution, hardness, strength, and resistance to mechanical attrition. 

Preparation of Pillared Clay Catalysts. PAG products are used for the preparation of zeolite-like catalysts by intercalation, the insertion of Al polycations molecules between the alurninosiHcate sheets of clay (3,33). Aqueous clay suspensions are slowly added to vigorously stirred PAG solutions, and the reaction mixture is aged for several hours. The clay is separated from the PAG solution and washed free of chloride ion. The treated clay is first dried at low temperature and then calcined in air at 450—500°G, producing a high surface area material having a regular-sized pore opening of about 0.6 to... 

Table 1. Specific surface area and acidity of Ni0-Ti02/15-W03 catalysts containing different NiO contents and calcined at 400"C for 1.5 h...

By coprecipitating the catalytically active component and the support to give a mixture that is subsequently dried, calcined (heated in air), and reduced to yield a porous material with a high surface area. This procedure is followed when materials are cheap and obtaining the optimum catalytic activity per unit volume of catalyst is the main consideration. 

Extensive data on the charaaerization and the thermal evolution of the different catalysts have been reported elsewhere [9-14]. Phase composition, cell parameters and surface area of the final materials are summarized in Table 1. The XRD data indicate that for all the hexaaluminate-type samples the formation of the final phase begins at 1273 -1373 K and requires calcination temperatures of 1473-1573 K to be completed. 

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