Support y-alumina

Catalysts. - Group VIII metals, conventional base metal catalysts (Ni, Co, and Fe) as well as noble metal catalysts (Pt, Ru, Rh, Pd) are active for the SR reaction. These are usually dispersed on various oxide supports. y-Alumina is widely used but a-alumina, magnesium aluminate, calcium aluminate, ceria, magnesia, pervoskites, and zirconia are also used as support materials. The following sections discuss the base metal and noble metal catalysts in detail, focusing on liquid hydrocarbon SR for fuel cell applications. 

A common and well-known method to prepare silica membranes with molecular sieving properties is sol-gel coating [3-5], With this technique, microporous silica layers with a pore-size of about 0.5 nm are dip-coated on top of supported y-alumina membranes. The supports are porous a-alumina disks with pore diameters in the range from 100-200 nm. On top of these macroporous supports a 3 pm thick mesoporous y-alumina layer is coated, with a pore size of 3 nm. 

Ulhom R.J.R., Huis ln t Veld M.H.B.J., Keizer K. and Burggraaf A.J., Synthesis of ceramic membranes. Part 1. synthesis of non-supported and supported y-alumina membranes without defects, J. Mater. ScL 27 527 (1992). 

Fig, 9.18. Permeation and separation factors of supported y-alumina thin film for nitrogen and propylene at 263 K (A,B). Propylene is the preferentially permeating component dashed line gives the relative pressure at which the maximum in the permeation of Fig. 9.18a. occurs. (C) and (D) as (A) md (B) but for a supported film modified with MgO. After Uhlhom et al. [37]. 

In the present paper, results on the influence of reduction temperature on subsequent hydrogen adsorption are reported for platinum supported on three difficult to reduce supports (y-alumina, magnesia and sillcalite). The results indicate that the observed suppression in hydrogen uptakes, after high temperature reduction, are due to poisoning of the platinum surface by species originating from the support. This interpretation is similar to that of Wang et al. (13). 

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... 

Supported membrane concepts that were studied in the past 10 years include 5-p.m-thick dense Pd on supported y-alumina (Pacheco Tanaka et al., 2006), 10-p m-thick dense Lao.sSro.sCoOa.g for O2 purification (van der Haar, 2001), 60-nm thin amorphous silica for small gas molecule separation and water pervaporation (de Vos and Vetweij, 1998), >1 xm-thick MFI zeolite membranes for parajortho-xyicnc isomer separation (Caro et al., 2000), 0.4-2-p.m thick mesoporous y-alumina (Yu et al., 2006), and 4 p,m mesoporous C0AI2O4 for nanofiltration of liquids (Condom et al., 2006). 

Fully nondestractive techniques do not touch the membrane surface and may be used during operation. These requirements make it that such techniques are likely limited to in-line transport measurements and optical reflection measurements. The transport measurements are discussed under quasi nondestructive techniques. Spectroscopic ellipsometry provides the thickness and composition for layers with 0p < 50 nm and X < 5 p,m, mutually independent, for the optically smooth supports and membranes. The composition is in that case obtained from interpretation of the refractive index and may include information about 4>p and the amount of adsorbed molecules. The use of this method was demonstrated first in Benes et al. (2001) for the layer thickness and CO2 sorption in supported amorphous silica membranes, as shown in Figure 34.10, left. Spectroscopic ellipsometry is now used routinely in our laboratory for layer thickness of supported (-y-alumina) membranes. This analysis involves determination of the optical constants of uncoated macroporous AKP15 and AKP30 a-Al203 supports, described in Figure 34.11. As the -y-alumina membranes are optically transparent, the dispersion in refractive index n can be described as a Cauchy type material with the form... 

Mottem, M. L., Oyola, M., Shqau, K., Yu, D., and Verweij, H. (2005). Permeation porometry of membrane supports and thin supported y-alumina membranes. Paper presented at PCM 2005, Brugge, Belgium, Session MP-4, Oct. 20-21, 2005. 

For all experiments, a commercial NiMo-supported y-alumina catalyst was used. Its properties are specific surface area of 175 m /g, mean average pore volume of 0.56 cmVg, mean average pore diameter of 127 A, molybdenum content of 10.66 wt%, and nickel content of 2.88 wt%. The tetralobular commercial catalyst had a diameter of 2.54 mm. 

---