Highly porous support

Interpretation of pubhshed data is often comphcated by the fact that rather complex catalytic materials are utilized, namely, poly disperse nonuniform metal particles, highly porous supports, etc., where various secondary effects may influence or even submerge PSEs. These include mass transport and discrete particle distribution effects in porous layers, as confirmed by Gloaguen, Antoine, and co-workers [Gloaguen et al., 1994, 1998 Antoine et al., 1998], and diffusion-readsorption effects, as shown by Jusys and co-workers for the MOR and by Chen and Kucemak for the ORR [Jusys et al., 2003 Chen and Kucemak, 2004a, b]. Novel approaches to the design of ordered nanoparticle arrays where nanoparticle size and interparticle distances can be varied independently are expected to shed hght on PSEs in complex multistep multielectron processes such as the MOR and the ORR. 

A rather new concept for biphasic reactions with ionic liquids is the supported ionic liquid phase (SILP) concept [115]. The SILP catalyst consists of a dissolved homogeneous catalyst in ionic liquid, which covers a highly porous support material (Fig. 41.13). Based on the surface area of the solid support and the amount of the ionic liquid medium, an average ionic liquid layer thickness of between 2 and 10 A can be estimated. This means that the mass transfer limitations in the fluid/ionic liquid system are greatly reduced. Furthermore, the amount of ionic liquid required in these systems is very small, and the reaction can be carried in classical fixed-bed reactors. 

A thin layer of skeletal catalyst precursor alloy can be coated on a supporting material prior to leaching. Referring to the literature, discuss (1) why is a coating used, and (2) what processes are used to achieve this coating, both for a flat surface and for a highly porous support ... 

To understand heterogeneous catalysis it is necessary to characterize the surface of the catalyst, where reactants bond and chemical transformations subsequently take place. The activity of a solid catalyst scales directly with the number of exposed active sites on the surface, and the activity is optimized by dispersing the active material as nanometer-sized particles onto highly porous supports with surface areas often in excess of 500m /g. When the dimensions of the catalytic material become sufficiently small, the properties become size-dependent, and it is often insufficient to model a catalytically active material from its macroscopic properties. The structural complexity of the materials, combined with the high temperatures and pressures of catalysis, may limit the possibilities for detailed structural characterization of real catalysts. 

Ultrafiltration is the application of pressure or suction to force the solvent and small particles across a membrane while the larger particles are retained. The membrane is normally supported between fine wire screens or deposited in a highly porous support such as a sintered glass disc. An important application of ultrafiltration is the so-called reverse osmosis method of water desalination25. 

L Highly porous support J layer with negligible... 

B. Molecular sieving (zeolite or carbon) Reverse selective skin Iayer o Highly porous support (wide range of sizes morphologies ... 

To allow a more efficient utilization of the precious metals, the latter are dispersed on thermally stable (refractory), nonmetallic supports. A very large initial dispersion (the ratio of the surface atoms exposed to the chemical atmosphere to total atoms of the active component) is usually obtained by using highly porous supports, such as alumina, silica, zeolites, etc., which provide a... 

The catalytic wall reactor with channel diameter in the range of 50-1000 pm and a length dependent on the reaction time required circumvents the shortcomings of micro packed beds. This is discussed in more detail in Section 6.5.4. However, in most of the cases, the catalytic surface area provided by the walls alone is insufficient for the chemical transformation and, therefore, the SSA has to be increased by the chemical treatment of the channel walls, or by coating them with highly porous support layers. The thickness of the layer 5 3, depends on catalytic activity. In general, the layer thickness is sufficiently small to avoid internal heat and mass transfer influences. Catalytic layers can be obtained by using a... 

EXPERIMENTS ON IMPREGNATION AND DRYING OF HIGHLY POROUS SUPPORTS... 

J. Lee, J.H. Jang, H.-R. Chae, S.H. Lee, C.-H. Lee, P.-K. Park, Y.-J. Won, I.-C. Kim, A facile route to enhance the water flux of a thin-film composite reverse osmosis membrane incorporating thickness-controUed graphene oxide into a highly porous support layer, Journal of Materials Chemistry A (44) (2015). 

Note The membrane thickness corresponds to that of a thin layer, having the required pore size and porosity, on top of a thicker highly porous support layer having at least an order of magnimde larger pore size therefore the support layer resistance may be neglected. 

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