Pore volume, supports/catalysts after

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). 

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

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. 

The preparation parameters during the sol-gel process are of great influence on properties like pore distribution, pore volume, strength etc. of the end product. It is possible to enlarge the pores in the gelated spheres by applying a hydrothermal treatment after the gelating step [36]. All these parameters can be controlled. So this method makes it is possible to prepare tailor-made supports for catalysts in a reproducible way. 

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... 

The carbon support used was a Norit activated carbon (RX3 extra) having a surface area of 1190 m2.g 1 and a pore volume of 1.0 cm3.g . The Co/C catalyst (4.1 wt% Co) was prepared by pore volume impregnation with an aqueous solution of cobalt nitrate (Merck p.a.) followed by drying in air at 383 K (16 h). The promoted catalyst (1.5 wt% Co, 7.7 wt% Mo) was prepared in a special way to ensure a maximum amount of the Co-Mo-S phase (11). Mossbauer spectroscopy of this promoted catalyst clearly showed that only the Co-Mo-S phase was present after sulfiding (11) and furthermore that this Co-Mo-S is probably a Co-Mo-S type II phase, meaning a minor influence of active phase-support interaction (11,12). The catalytic activity of the sulfided catalysts was determined by a thiophene HDS measurement at 673 K and atmospheric pressure, as described elsewhere (10). The thiophene HDS reaction rate constant kHDg per mol Co present (approximated as a first order reaction) was found to be 17 10 s 1 for Co/C and 61 10 3s 1 for Co-Mo/C. 

Table 3. presents the abatement results of simulated wastewater succinic acid solution with different catalysts in CWO process. The reactions were carried out in an autoclave under the same reaction conditions. The content of Ru in the catalysts is approximately 2%. Among the tested catalyst, Ru/TiOj. S has the highest COD removal rate. This may be due to the contribution of surface treatment on the support. The specific area, pore volume and average pore diameter are enlarged after the treatment, resulting in the Ru concentration increase on the surface of the support and accelerating the reaction speed. Further study on the Ru/TiOjiS is still underway, and new results will be reported elsewhere. 

In excess solution adsorption, the support material is submerged in excess amount of impregnation solution (the volume of impregnation solution is much higher than the pore volume of the support). The excess solution is filtered after adsorption equilibrium is reached. In many cases, competitive adsorption between solvent and solutes and/or between different solutes leads to a nonuniform distribution of active components throughout the support particles. This phenomenon can be utilized to enhance performance (normally selectivity) of certain types of catalysts. The distribution of the active components can also be tailored by the manipulation of the pore structure of the support, pH and viscosity of the solution. ... 

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. 

The textural characteristics of NiMo catalysts are given in Table 2. A significant decrease in BET surface area (Sg), micropore area (S ) and total pore volume (Vp) is observed after metal impregnation. For all NiMo catalysts supported on SBA-15 type materials the decrease of micropore area is much stronger than that which can be explained taking into account the weight of deposited Ni and Mo species. We assume that some obstruction of support pores (principally micropores) by metal oxidic species can take place. No changes were detected in the form of N2 adsorption-desorption isotherms (not shown) after successive incorporation of Mo and Ni species on the SBA-15 support. 

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