Supports pore size

Fig. 18. Cross-sectional scanning electron micrograph of a three-layered alumina membrane/support (pore sizes 0.2, 0.8, and 12 p.m, respectively).

This paper examines the hydrogenation of aniline, /Moluidinc. and 4-fcrt-butylanilinc over a series of 2.5 % Rh/Si02 catalysts, comparing reaction rates and product selectivities. Further studies concentrated on examining support particle size and average metal crystallite size effects on /Moluidinc hydrogenation and the support pore size effects on 4-tert-butylaniline hydrogenation. 

Figure 2. Effect of support pore size on FT reaction rate and hydrocarbon selectivities.

Figure 6 A DIH crystals (crystal size 200nni), B stainless steel support (pore size 60 im-700 im, Stork Veco B.V., The Netherlands), C and D ...

Table 1. Activation energies and permeability ratia for permeation of different gases in a silicalit-1 membrane on a alumina support (pore size 0.15 pm).

Note that the farther away the electric potential of the carbon surface is from the potential of zero charge point ( pzc) l e higher the disjoining pressure is. In principle, this may result in a systematic variation of the support pore size in Me/C catalysts with potential (similar to the electrocapillary curve [96,97]) and consequently the efficiency of metal particle blocking by the pore walls. Such behavior of porous carbons obviously can influence the measurements of the electrochemically active surface area and might be one of the reasons for the observed correlation between the apparent dispersion of Pt/C catalysts, measured by cyclic voltammetry, and pHpzc of the supports [95], whereas no noticeable difference in the particle size has been observed with HRTEM. Undoubtedly, this problem needs further investigation. 

The influence of the type of support (pore size) and the peptising acid on the formation of gel layers during dip-coating, hr all cases the sol contains 1.2 mol A1 (boehmite) per litre. 

The acdvitities of silica-supported phosphonium are support pore size dependent with ca. 100 A typically giving the most active catalysts. This is very similar to more simple physisorbed silica-based supported reagents and seems to support the view that for liquid-phase reactions catalysed by porous solids, a reasonably large pore is required to give a good molecular diffusion rate. 

D. Freilich and G.B. Tanny, Hydrodynamic and microporous support pore size effects on the properties and structure of dynamically formed hydrous Zr(IV)-polyacrylate membranes, Desalination, 1978, 27, 233-251 A.J. van Reenen and R.D. Sanderson, Dynamically formed hydrous zirconium(IV) oxide-polyelectrolyte membranes, VI. Effect of copolymer composition on the stability of poly(acrylic acid - covinyl acetate) and poly(acrylic acid - covinyl alcohol) membranes, Desalination, 1989, 72, 329-338. 

Figure 7.14 Effect of support pore size (D=100, 60, 40 pm) on mineralized nodule formation of rat osteoblast cells cultured in vitro after 28 or 35 days using hydroxylapatite-coated (modified) or uncoated (unmodified) styrene Poly HI PE Polymer cell supports...

Figure 7,15 Effect of pore size on DNA concentration as a function of time in culture of rat osteoblast cells in hydroxyapatite-coated polyHIPE polymer support, illustrating the dependence of cell proliferation rate on support pore size...

Concerning the preparation of thin membranes directly on porous supports, a lower thickness limit seemingly exists for which a dense metal layer can be obtained. This thickness limit increases with increasing surfaee roughness and pore size in the support s top layer." " Clearly, this relation puts strong demands on the support quality in terms of narrow pore size distribution, and the amount of surface defects. Therefore both pore size and roughness of the support surface are often reduced by the application of meso-porous intermediate layers prior to deposition of the permselective metal layer. This procedure facilitates the preparation of thin defect-free membranes beeause it is relatively easier to cover small pores by filling them with metal. It is therefore conceivable that for a certain low Pd-alloy thickness and support pore size, the H2 flux becomes limited by the support resistance. ... 

Kumar et al. [40] reported interesting data for membranes where MCM-48 supports (pore size 2.4 mn) were modified with polyethyleneimine (PEI). They reported an N2/CO2 selectivity of 1.31 ( 293 K) in the absence of water, 17.6 ( 293 K) in the presence of water, and 1.35 ( 363 K) in the presence of water for a feed mixture of 80/20 N2/CO2 and feed pressure of 20 psi (103.4 cm Hg). In the presence of water, the size of the diffusing unit (CO2) increased due to the clustering of water molecules, which in turn reduced the CO2 diffusivity at room temperature, and hence, the PEI-MCM 48 membranes were highly N2 selective in the presence of water. This is opposite to what we and others [10, 12, 13] observe (CO2 selective membrane), and it may be due to the fact that in our case, the amine groups are readily accessible to the CO2 molecules (since they form a brush-like structure) for reactive separation whereas the PEI approach, in contrast, may be dominated by a solution-diffusion mechanism rather than reactive or facilitated transport. 

Dacquin et al. [51] used a method called in situ crystallization in a confined space to prepare a LaNiOs/SBAlO catalyst. As evidenced by TEM analysis, very small nanoparticles of perovskite were generated within the silica porosity with a size between 2 and 5 nm and an average closed to 3 nm. The reduction step performed at 700 °C gives Ni° particles well dispersed within the matrix porosity and their size remained close to the support pore size. The catalytic activity for syngas production was doubled compared to bulk LaNiOs precursor, it remains... 

Membrane Material Presence of support Pore size [p.m] Thickness [p.m] Porosity [%]... 

Support Pore size (nm) Mol. wt exclusion limit foi globular proteins Particle size (gm) Column sizes Length (cm) i.d. (mm) Chemical nature Availability bulk material Manufactured ... 

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