Sepiolite Surface area

The broad line 2H NMR results, combined with the H and 29Si MAS-NMR results, confirm that acetone-d6 molecules are able to penetrate into the microporous channels of sepiolite, and cannot be removed by heating to only 60°C. This result is in agreement with a previous study that found, on the basis of BET surface area measurements, that molecules such water, ammonia, ethanol, benzene and pyridine were small enough to fit inside the microporous channels [10],... 

Table 2 summarises the main textural properties of the five titania-sepiolite, 50 50, wt/wt, supports (named after the titania type used in their preparation). The BET sur ce area gives the total surface area, while the MIP sur ce area is due to pores larger than 7 nm in diameter. Thus, the differences between both areas were due to narrow mesopores of less than 7 nm diameter. Characteristic mesopores of the sepiolite [12] were detected for A, B and E, which also showed a bimodal MIP pore size distribution. 

From the MIP curves of support A heat treated at 500 and 800°C (not shown), although the total pore volume was maintained, the mesopores associated with sepiolite (18 nm) were lost and a shift in the pore size of the wider pores due to titania (65 to 90 nm) was observed. An associated fall in the MIP and BET surface areas from 95 to 46 m /g and 133 to 60 m /g, respectively, was found. These changes in the support would explain the decrease in activity, pointing out the importance, not only of the surface area, but also of the pore size distribution and the presence of sepiolite mesopores. A change in the available titania surface in the support should not affect the ft dispersion as indicated by the results with different titania contents in Section 3.1. 

The results presented in this study on Pt-titania-sepiolite monolithic catalysts indicated that their activity in the reduction of nitrogen oxides with propene in the presence of 10% oxygen was strongly affected by the properties of the titania selected for the support s preparation. Thus, different industrially produced titanias had different textural properties, and these differences affected the textural properties of the titania-sepiolite monoliths (MIP total pore volume, MIP surface area, MIP pore size distribution and BET surface area) and the NOx... 

XRD, TG-DSC and MIP results showed that the fall in activity produced by heat treating the support of catalyst A at 500 and 800°C should not be due to phase changes in either the titania or sepiolite, but to sintering of the materials which reduced the surface areas and changed the pore size distribution, although the support s total pore volume was maintained. 

The measurement of BET surface areas and pore volumes were carried out on pure sepiolite support and also on Mo03/sepiolite catalysts. The surface area decreases as a function of Mo-loading on sepiolite see in figure 1 (a) and the corresponding data is presented in table 1... 

Sepiolite/ Palygorskite Phyllosilicates Marine sediments, arid soils, high Si and Mg levels R Moderately high CEC.15 surface area, and sorptive properties... 

Taking as a reference the textural characteristics of the heat treated sepiolite support "ST", the data in Table 1 indicated that washing this natural silicate with an acid solution produced an appreciable increase in tlie BET surface area but had little effect on the surface area and pore volume measured by merciuy porosimetry. Thus, this increase must have been in pores of between 1 and 3nm radius, since evaluation of the adsorption isotlierm by use of the t-plot... 

The catalysts prepared on these supports had similar properties to those corresponding to the support used. From the results presented in Table 1 the modifications in the properties which were caused by the introduction of the active phase on the supports may be seen. Thus, on the introduction of the active phases on the acid washed sepiolite, SLCuNi, the BET surface area was reduced, probably due to blocking of the narrower mesopores. Due to the deposition of the active phases on the pore walls the areas calculated from the intrusion curves of... 

One of the questions that can be answered with the help of adsorption measurements concerns the microtexture of natural clay minerals. Several idealized models for the texture of soil clays (see [5]) have been considered, but rather than assuming one model a priori, one should try to gain useful information from experimental relationships between the size of clay particles and apparent density or surface area and internal porosity, as described in Sections 6.1 and 6.2.1. Experiments aiming at the evaluation of the microtextures of clay minerals were carried out by Ben Ohoud and van Damme [95], who studied kaolinite, sepiolite, palygorskite and 20 monoionic montmorillonite samples. The accessible surface area S of consecutive fractions of size r was measured by N2 adsorption using the classical BET method, whereas the open porosity P was measured from the amounts of adsorbed N2 at a relative vapor... 

Both, sepiolite and palygorskite exhibit an elevated specific surface area, as measured from nitrogen adsorption isotherms, with BET values that are in the order... 

The initially high surface areas of the samples after pretreatment at 110 C were thus mainly due to the presence of microporosity. The loss of microporosity on heating to 500°C halved the surface areas in samples containing sepiolite and reduced the titania monolith to less than a third. Heat treatment at 800°C forther reduced the surface areas, especially in the titania monolith. After treatment at 1000°C the surface areas were very low for all of the materials. Thus, although the surface areas of all the materials were reduced with heat treatment, the inclusion of sepiolite even at only 20 wt% was enough to retard the loss of surface area. 

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