Pore volume, supports/catalysts after calcination

BET Surface Area, Pore Volume, and Average Pore Diameter of the Supports and Catalysts after Calcination at 623 K... 

Table 1. BET surface area, mean pore diameter, and pore volume for the supports and catalysts after calcination. For the nitrogen sorption data, the experimental error ( 2ff) is 5 m /g for the surface areas, 0.2 nm for the mean pore diameters, and 0.02 cm /g for the pore volumes.

Although the dopant dissolves in the ceria lattice, we cannot rule out the presence of an amorphous dopant-rich phase at the surface of the catalyst (even after severe calcining). XPS + XRD measurements show a dopant-lean bulk and a dopant-rich surface. The structural similarity of the different catalysts is supported by the surface area-pore volume relationship (Figure 3). 

Impregnation of Supports and Drying. Most obvious is incipient wetness impregnation of a support with a solution of an active precursor and subsequent drying and calcination of the thus loaded support [6], Incipient wetness or pore-volume impregnation is especially attractive with preshaped support bodies. When the active component has to be in the metallic state, reduction can be carried out after the calcination step. Often, the catalyst is reduced after loading into the reactor to prevent a separate passivation step, in which the surface of the pyrophoric reduced catalyst is carefully oxidized. However, to achieve reproducible catalysts the catalyst manufacturer usually reduces the catalyst and delivers the passivated catalyst, which then only needs a short additional reduction. 

Alumina-supported Co- and Ni-promoted molybdenum sulphide hydrotreating catalysts are the main workhorses in many refineries and have, therefore, attracted a lot of attention from catalytic chemists. They are usually prepared via co-impregnation, i.e. pore-volume impregnation with both Mo and the promoter atom present in solution. After drying and calcining, the catalyst manufacture is complete, but it has to be sulphided before use. Traditionally, this is done in situ... 

Catalyst preparation. Chloroplatinic acid, in such amounts as to obtain the desired concentration of Pt in the catalysts, was added to previously prepared w/o microemulsions. Two types of catalytic supports, y-alumina in the form of full pellets (diameter 5 mm) and 0-alumina in the form of hollow pellets (diameter 5 mm, hole 2 mm), both manufactured in Chemopetrol Litvinov, Czech Republic, were chosen for catalysts preparation. After calcination at 500 °C y-alumina had Sbet=166 m /g, pore volume 0.459 ml/g, mean pore radius 7.0 nm and water absorption capacity 40 %. After calcination at 900 °C 0-alumina showed Sbet=145 m /g, pore volume 0.445 ml/g, mean pore radius 8.1 nm and water absorption capacity 50 %. The catalysts with 0.3 and 0.1 wt. % Pt were prepared by impregnation with HaPtCle water solutions (denoted as I) or Pt microemulsions (denoted as M). The catalysts were dried 2 h at 120-160°C and calcined 2 h in air at 550 °C. Characterization of microemulsions... 

Various promoted Ni/MgO catalysts have been prepared by multiple successive impregnation of the MgO support. Tlie support used, which was calcined at 1450°C, had the following characteristics macroporous spherical granules having diameter of about 20 mm, BET surface area of 0.25 m and specific pore volume of 0.145 cmV -Aqueous solutions of Ni-nitrate and nitrate of the corresponding promoter, with atomic ratio 10 1, respectively, were used. All the impregnation steps were performed at 25°C, with the ratio of solution volume to support mass of 3 cmV. and the solution/support contact time of 30 min. After each impregnation the catalyst precursors were subsequently dried at 110°C for Ih and calcined at 400°C for 2h to convert nitrate salts onto oxides. 

Two catalysts were prepared by impregnation of the alumina support in question with an aqueous nickel nitrate solution. The concentration of this solution was such as to result in a metal loading of approximately 11 wt.X (prior to calcination or reduction) after saturation of the pore volume of the support by submersion and subsequent filtration. A commercial gamma-alumina was used for one catalyst an alpha-alumina support was prepared from this carrier by calcination at lllO C for 2 hours. 

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