Micro-porous surface area

It can be seen from Table 6.50 that the total micro-pores volume (Vqdr) changes slightly at 1,300°C, while the Vodr changes from 0.33 to 0.036cm g at 1,900°C, and forms a kind of surface structure called as turbulent structure. Therefore, the micro-porous surface area (Sdr) is decreased from 890m to 62m g" ... 

As surface area and pore structure are properties of key importance for any catalyst or support material, we will first describe how these properties can be measured. First, it is useful to draw a clear borderline between roughness and porosity. If most features on a surface are deeper than they are wide, then we call the surface porous (Fig. 5.16). Although it is convenient to think about pores in terms of hollow cylinders, one should realize that pores may have all kinds of shapes. The pore system of zeolites consists of microporous channels and cages, whereas the pores of a silica gel support are formed by the interstices between spheres. Alumina and carbon black, on the other hand, have platelet structures, resulting in slit-shaped pores. All support materials may contain micro, meso and macropores (see text box for definitions). 

GP 2] [R 3a] The performance of one micro reactor with three kinds of catalyst -construction material silver, sputtered silver (dense) on aluminum alloy (AlMg3), and sputtered silver on anodically oxidized (porous) aluminum alloy (AlMg3) -was compared with three fixed beds with the same catalysts [44]. The fixed beds were built up by hackled silver foils, aluminum wires (silver sputtered) and hack-led aluminum foils (anodically oxidized and silver sputtered), all having the same catalytic surface area as the micro channels. Results were compared at the same flow rate per unit surface area. 

GL 18] [R 6a] [P 17] A sol-gel deposited catalyst used in a fixed-bed reactor gave higher conversion than a micro-channel catalyst impregnated on a porous alumina layer [17]. This was due to the higher geometric surface area of the sol-gel deposited catalyst. 

Nowadays synthesis of mesoporous materials with zeolite character has been suggested to overcome the problems of week catalytic activity and poor hydrothermal stability of highly silicious materials. So different approaches for the synthesis of this new generation of bimodal porous materials have been described in the literature like dealumination [4] or desilication [5], use of various carbon forms as templates like carbon black, carbon aerosols, mesoporous carbon or carbon replicas [6] have been applied. These mesoporous zeolites potentially improve the efficiency of zeolitic catalysis via increase in external surface area, accessibility of large molecules due to the mesoporosity and hydrothermal stability due to zeolitic crystalline walls. During past few years various research groups emphasized the importance of the synthesis of siliceous materials with micro- and mesoporosity [7-9]. Microwave synthesis had... 

It is now generally accepted that there is no sound reason why isotherms on micro-porous solids should conform any more closely to the classical Langmuir mechanism than isotherms on non-porous or mesoporous adsorbents. Indeed, a considerable amount of the evidence now available gives strong support to the view that the limiting uptake is controlled rather by the accessible micropore volume than by the internal surface area (Gregg and Sing, 1982). 

The prerequisite for determining meaningful areal enthalpies of immersion is of course an independent assessment of the surface area really wetted by the immersion liquid. This is why, in Table 5, we only give them for the two reference samples which are known to be neither micro- nor meso-porous, ie for which the BET surface area can be expected to be reliable. 

In addition to the design of the solid-gas contactor device, the yield of a desulfurization process directly depends on the physicochemical properties of the used adsorbent crystallite size of the active phase, specific surface area, and porous texture. In the case of a microporous membrane, if the gas flow is forced across the microporosity, it can be expected that the retention will be highly efficient. In return, the low amount of adsorbent restricts the potential applications to the elimination of traces in high-purity gas or to the design of integrated filters for miniaturized devices like micro fuel cells. 

Continuous Pt films at the surface of porous silicon cannot be applicable as catalytic coats for fuel cells electrodes. Quite the contrary, Pt coats should save its porosity to allow an easy penetration of gaseous iuel and to have the effective surface area as high as possible. So, the layers of electrodeposited Pt of about 100 nm in thickness, as illustrated in Fig. Ic, are optimal catalytic Pt films for micro fuel cell electrodes. 

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