Texture mesoporous

Varying KOH ratio in the mixture is a very effective way of controlling porosity development in resultant activated carbons. The trend in the pore volume and BET surface area increase seems to be similar for various precursors (Fig. la). It is interesting to note, however, a sharp widening of pores, resulting in clearly mesoporous texture, when a large excess of KOH is used in reaction with coal semi-coke (Fig. lb). Increase in the reaction temperature within 600-900°C results in a strong development... 

In the present paper, we will focus in a first step, on the results obtained using the same parent support (silica gel) modified by alkyl-dimethyl chlorosilanes of various alkyl chain length 1, 4, 8 and 18 carbon atoms. This material presents a disordered mesoporous texture [8]. 

BJH, Dollimore-Heal and BdB methods were compared for assessment of mesoporosity. Owing to the pore shape of the material used, the first two methods lead to an underestimation of pore size, and hence to an overestimation of total mesoporous surface. The last method is more general, and when the appropriate shape factor is used, a reliable estimation of the mesoporous texture is obtained. The S sdB estimator is almost a perfectly linear function of y, and vanishes in the X(IOO) sample. The external surface area, Xext, computed from the t-plot leads to an overestimation of the true mesoporous surface. 

Low temperature N2 adsorption isotherm gives a reliable information on the mesoporous texture of solids. The adsorption-desorption plot follow the type IV isotherm with hysterisis in the mesopore filling region, the pore size distribution obtained by BJH analysis of nitrogen adsorbed is shown in Fig.3. The pore size distribution is narrow and the maximum is centered around 30 A for all the samples indicating a uniform pore texture of the samples... 

Finally, the nse of Pt-Rn catalysts snpported on a carbon aerogel as an anode for DMFC has been reported by Dn and co-workers [90]. The total metal loading was fixed to 20 wt%, and the Pt/Rn atomic ratio varied from 3 1 to 1 1. Metal particles were dispersed on the snpport nniformly, with a mean size of 3 nm. These anthors fonnd that with mnch less metal loading on the carbon aerogel, the membrane electrode assemblies had the same power density as that of commercial catalysts. This was attributed to the mesopore texture of the carbon aerogel, which facilitated methanol transportation in the electrode. 

The textural and the structural characterisation performed on the Pd/AbOs catalyst prepared by sol-gel method, shows a BET surface area of 270 m /g, a mesoporous texture and a uniform porous distribution with an average pore diameter of 3.3 nm. The metallic dispersion obtained by hydrogen chemisorption is 45 %. This later result is confirmed by the palladium particles diameter varying between 1 and 10 nm with an average of 3 nm obtained form the MET analysis. The palladium content determined by inductively coupled plasma is closely to 1.9 %. No significant BET surface area decrease nor a metallic dispersion loss were observed when the catalyst is aged under catalytic conditions up to the steady state. Since the thermal stability of the catalyst is needed to minimize the modification of the palladium particles structure, the later result justifies the choice of the sol-gel synthesis method and the calcinations temperature (700°C) selection. 

Suh D J, Park T J (2002) Synthesis of high-surface-area zirconia aerogels with a well-developed mesoporous texture using CO2 supercritical drying. Chem Mater 14 1452-1954... 

Subsequently, it was found that the surfactant in the synthesis system can modify the mesoporous textural properties but does not affect the self-formation of the meso-macroporous hierarchy. Zirconium oxides with the similar meso-macropo-rous structure could also be synthesized via the self-formation phenomenon in the absence of a surfactant [131]. The resulting hierarchically meso-macroporous zir-coniiun oxides are mainly tens of micrometers in size with a regular array of parallel or funnel-like macrochannek of 300-800 nm in diameter. The macropore walls are constmcted from mesochannels (around 2.0 nm) with a wormhole-like array. These materials obtained via this self-formation phenomenon present high surface area and pure crystalline phases in meso-macroporous structures. 

Most of the microporous and mesoporous compounds require the use of structure-directing molecules under hydro(solvo)thermal conditions [14, 15, 171, 172]. A serious handicap is the application of high-temperature calcination to develop their porosity. It usually results in inferior textural and acidic properties, and even full structural collapse occurs in the case of open frameworks, (proto) zeolites containing small-crystalline domains, and mesostructures. These materials can show very interesting properties if their structure could be fully maintained. A principal question is, is there any alternative to calcination. There is a manifested interest to find alternatives to calcination to show the potential of new structures. 

The BET surface area values are also reported with the distribution of porosity between microporosity (pore diameter <1.8 nm) deduced from N2 adsorption isotherms (t-curves) and mesoporosity (pore diameter > 1.8 nm). The following trend is observed for high atomic M/HPA ratio used for the precipitation, the precipitates exhibited high surface area mainly due to microporosity. However, depending on the nature of the coxmter cation and also of the previous ratio values, the textural characteristics were not similar. In particular, it is interesting to note the presence of mesopores for (NH4)2.4P, CS2.9P, CS2.7P and Cs2.4Si samples. 

The most active samples for n-C4 isomerization, (NH4)2.4P and Csi.gP, showed opposite reactivities in liquid alkylation. The first one gave rise to a high production of TMP while the second one was only initially slightly active. The main difference between these two samples concerned their porosity (NH4)2.4P was mesoporous while Csi.gP was mainly microporous. Then, one may suggest that the presence of mesoporosity is essential for the accessibility of the reactants to the acid sites and the desorption of the products. As a consequence the catalytic activity seems more governed by the textural features than by the acidity. As a general trend, the samples which were, at the same time, active and stable for the alkylation reaction, exhibited a mesoporosity equivalent to about 40 m. g-i. 

G.J. de A. Soler-Illia, C. Sanchez, B. Lebeau, J. Patari, Chemical strategies to design textured materials from microporous and mesoporous oxides to nanonetworks and hierarchical structures. Chem. Rev. 102 (2002) 4093. 

In conclusion, although the porous texture of these materials is of limited interest for getting high capacitance values, it allows to clearly demonstrate the beneficial effect of mesopores on the capacitor performance. 

Structural and textural characterisation of pure SBA-15 and hybrid GFP/SBA-15 Pure SBA-15 and GFP/SBA-15 hybrid were characterised by X-ray powder diffraction, HRTEM and volumetric analysis. Calcined SBA-15 (Fig. 1, curve A) show the typical XRD pattern of an ordered hexagonal network of mesopores with (10), (11) and (20) reflections. The presence of well resolved (11) and (20) peaks indicate that the calcined material used for the preparation of the hybrid materials have a long-range order. The hexagonal XRD pattern was still clearly observed in the hybrid material (GFP/SBA-15), as all the three main reflections were found (Fig. 1, curve B), indicating that the sonication and the GFP physical adsorption does not affect the framework integrity of the material. 

Figure 1 shows that the catalysts maintain their mesoporous structure with type IV isotherm. It can be observed a reduction in surface area, pore volume and pore diameter and slight increase in textural porosity as the concentration of aluminum increases (Table 1), due to the increase in the wall thickness in the mesoporous material as we have found previously [3],... 

At 9 hours of immersion, instead, isotherms do not show the pore filling associated with mesopores, which in turn appears again between 25 and 26 hours. After 28 hours of soaking, no mesopore filling is observed (figure 3). The DFT pore size distributions also confirm the presence of mesopores (around 2.2 nm) only at 2 hours of immersion and between 25 and 26 hours. The peak at around 5 nm is probably due to the textural interparticles porosity (figure 3 inset). 

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