Increasing Specific Surface Area

With the aim of further increasing the specific surface area of perovskites, the same authors proposed a process in which an additive was used to increase the surfece area [45]. In this process, the starting oxide precursors were milled for 10-20 h, using a Spex mill, resulting in the synthesis of desired perovskite structure. The milling time in the first step depends on the material composition for 

This process was used to synthesize a number of perovskite formulations, which were then extensively characterized for their catalytic properties such as oxygen storage capacity [49], water vapor sensitivity [50], conversion of CO and exhaust gas emissions [48], sensitivity to CO adsorption [39,40], reduction of NO by propene [51-53], reduction of NO either by CO [54] or by C3H5 [55-58], synthesis of higher alcohols [56,59], CO hydrogenation [60], oxidation of stearic acid [61], and methanol [62]. 

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Another important property is the structure (see Section 4.1) which characterizes the coalescence of primary particles into aggregates resembling chains or bunches of grapes. The dibutyl phthalate (DBP) absorption is commonly accepted as a measure for the carbon black structure. Due to absorption phenomena the DBP number increases with increasing specific surface area. Oil absorption (or, in general, the vehicle demand) is as well an indicator for the structure, but it also depends on the wettability of the black surface. Since linseed oil is a polar system, oil absorption declines as the concentration of surface oxides rises. 

The shape of the micronized particles was irregular and, according to SEM pictures, it was assumed that the particles were porous. With particle-size reduction and, therefore, increased specific surface area (external and internal) the dissolution rate increased to some extent, but the anticipated effective surface area was probably reduced by the drug s hydrophobicity and agglomeration of the particles during and after micronization. 

Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with increasing specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dis-persibihty to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt.% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

It should be added that the method presented here also permits us to obtain adsorbents with an increased specific surface area as compared to the initial carbon-silica adsorbent. This process can be easily accounted for if one takes into consideration the fact that the vapours of the pyrolysed substance transport by the carrier gas, with its adequately high flow rate over the modified carbon-silica adsorbent, may not diffuse into the narrow pores on time but will undergo decomposition either in wide and more easily accessible pores or on active, catalytically acting, corners and walls of the carbon agglomerates formed in the process of pyrolysis of dichloromethane. (Diffusion is a rather slow process, slower than adsorption.) Thus the size of the specific surface area of silica gels modified by dichloromethane may be increased or slightly changed (e.g. Adsorbent X, see Table 7). 

Increased specific surface area would thus increase the rate of hydrolysis. The increase in specific surface area is hkely due to endoglucanase action of fragmenting the cellulose and opening pores thus increasing the amount of enzymes adsorbed. The crystallinity index, on the other hand, increased greatly in the first 12 h but then slowly decreased but not to its initial level. The crystallinity index increased due to the fast removal of the amorphous cellulose in relation to the crystalhne cellulose. 

Ultrafme particles (UFP), defined as being in a size range from a few micrometers down to nanometers, feature natural adhesion tendencies, which strongly increase with decreasing linear dimensions or increasing specific surface area. On the one hand, this may be a disadvantage, because nanosized particles always exist as agglomerates (Fig. 11.1, Chapter 11) and, if individual nanoscale particles are required, special... 

Plasma-induced hydrophobization of cottonfabric in conjunction with increased specific surface area leads to an interesting and practically important effect. Water droplets are able to effectively remove dirt particles from the surface of the cotton fabric. This phenomenon is illustrated in Fig. 9-29 for the case of HMDSO-plasma-treated cotton fabric (Hocker, 2002) and is usually referred to as the Lotus effect. Thus, the highly hydrophobic plasma-treated surface of cotton with specific plasma-modified surface topography is extremely dust- and dirt-repellant in contact with water. As an important consequence, the plasma-treated surface also becomes repellant to bacteria and fungi. The effect is relevant not only to cotton fiber but to some other materials as well. 

The increased specific surface area is very important in heterogeneous catalysis since reactions take place at the gas-solid or liquid-solid interface. For example, the dehydrogenation rate of butane over VN significantly improves with the increasing... 

The total volume of weakly (C ) and strongly (Cuw) bound waters (unfrozen at T < 273 K) at the silica interfaces (Table 38.5) is markedly larger than Vp (but significantly lower than Vemp) with one exception for SI-6 (Table 1). With increasing specific surface area of the first series samples, there is tendency of reduction of the free surface energy (Table 5, js) and the amount of weakly bound water Besides, the AG Cuw)y... 

It follows from all above said that carbon particles interact with the lead active mass, being adsorbed on its surface and/or incorporated in the bulk of the lead skeleton branches. This results in macrostructural changes (reduced median pore radius and increased specific surface area of NAM). Thus, carbon additives alter the very nature of the lead electrode, converting it into a lead—carbon electrode, which will inevitably affect its electrochemical behaviour. The latter will depend on the affinity of carbon to lead, on the electrical conductivity of the carbon additive and on the electrochemical properties of the carbon surface. 

Sphere-packed monolith reactors for catalytic gas/liquid reactions were studied by Bauer et al. [31]. The authors used this concept for a structured trickle bed reactor and observed a significant increase in the reactor performance, which can be explained by an increased specific surface area and a uniform wetting of the particles. This in turn diminishes the risk of local catalyst overheating, which may harm the catalyst stability and the product selechvity. 

Kim and Yang [14] prepared ACNF from electro spun PAN nano fibers activated in steam at 700-800 °C and found that the specific surface area of the ACNF activated at 700 °C was the highest but the Mesopore volume fraction was the lowest. However, the work by Lee et al. [38] showed an opposite result. Song et al. [21] investigated the effect of activation time on the formation of ACNF (ultra-thin PAN fiber based) activated in steam at 1000 °C. Ji et al. [39] made mesoporous ACNF produced from electros-pun PAN nano fibers through physical activation with silica and conducted chemical activations by potassium hydroxide and zinc chloride to increase specific surface area and pore volume of ACNF [40]. It must be pointed out that different methods and conditions of activation lead to very different physical properties and adsorption capacities for ACNF. 

The increased specific surface area clearly indicates that the PTFE film covering the catalyst is removed during the activation process. The removal of the PTFE film at the anode is the rate-determining step in the activation procedure. 

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