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The N2-adsorption isotherms of porous solids are received in the form V = f(P/Po). If such data are depicted in the form V(1 − P/Po) = f(P/Po) or V(1 − P/Po)/(P/Po) = f(V(1 − P/Po)), they show an identical inversion point (I-point, Inversion or Inflection point), which corresponds exactly to the monolayer volume Vm. As a result the value of specific surface area S is determined with unique precision via the trivial relationship S (m2 g−1) = 4.356Vm (cm3 g−1) without any use of the classic BET treatment. The derivates dV/d[(P/Po)] vs. (P/Po) and d(V[1 − (P/Po)])/d[(P/Po)] vs. (P/Po) exhibit maxima exactly at the same pressure (P/Po), while the second order derivative d2V/d[(P/Po)]2 vs. (P/Po) exhibits a minimum exactly at the same pressure (P/Po) with the I-point. As a consequence the specific surface area of solids can be determined just from experimental raw (P/Po), V data without any use, neither of linear BET treatment nor the Inversion or Inflection type graphs. For some MCM-41 type mesoporous materials, the I-plots show not one but two Inversion points/I-points. The first inversion/inflection point at lower (P/Po) values, “ILP-point”, corresponds to the completion of the adsorption procedure on the bare surface and the formation of monolayer and is useful for the determination of specific surface area S. The second inversion/inflection point at higher (P/Po) values, “IHP-point”, corresponds to the completion of the pore filling via condensation and may be useful for the determination of mesopore volume.

In the present study two synthetic mesoporous carbons, a highly ordered CMK-3 sample with hexagonal structure and a disordered mesoporous carbon (denoted DMC) were investigated for the sorption of Remazol Red 3BS (C.I. 239) dye in comparison to three commercial activated carbons and a HMS mesoporous silica with a wormhole pore structure. The structural, porosity and surface characteristics of the materials were evaluated using XRD, TEM, N 2 porosimetry, FT-IR spectroscopy and zeta-potential measurements. Optimal dye sorption occurred at pH ∼2. Equilibrium sorption data followed the Langmuir model and showed that the two synthetic mesoporous carbons exhibit higher sorption capacities ( q max ∼ 500–580 mg/g at 25 °C) in comparison to the commercial activated carbons which possessed either microporous (Takeda 5A and Calgon carbon) or combined micro-/mesoporous (Norit SAE-2) structures and to the HMS mesoporous silica. Thermodynamic parameters as the change in free energy, enthalpy, and entropy of sorption were also estimated. Kinetic studies were carried out and showed a rapid sorption of dye in the first ca. 30 min while equilibrium was reached after ca. 3 h. The sorption kinetics of dye was best described by a second-order kinetic model. A surfactant enhanced carbon regeneration (SECR) technique was used to regenerate the dye-loaded carbon sorbents.

The effect of the textural properties and morphology of zeolite Y, used as support of iron (Fe) or cobalt (Co) oxides, on the quantity and quality of the multi-wall carbon nanotubes (MWNTs) synthesized by catalytic chemical vapour deposition (CCVD) of acetylene was studied. The parent zeolite Y was modified by various dealumination procedures, namely hydrothermal treatment (steaming), treatment with ammonium hexafluorosilicate (AHFS) and combined steaming-AHFS. The ion-exchange and wet impregnation methods were used for supporting the metals on the zeolite Y samples, with the latter method providing the most effective catalysts for carbon nanotube (CNT) formation. Severe dealumination of zeolite-Y by steaming, which induced the formation of secondary meso/macropores and of relatively large particles/aggregates, resulted in significant decrease in the formation of CNTs compared to the catalysts based on the parent zeolite-Y. Post-treatment of the steamed samples with AHFS had no beneficial effect on the catalysts' activity. Moderate dealumination of the parent zeolite Y by AHFS also inhibited the formation of CNTs, but to a lesser extent compared to the catalysts based on steamed zeolite Y. The TGA studies revealed the presence of carbon phases with different thermal stability in the zeolite-CNT composites, ranging from amorphous carbon to well-graphitized MWNTs. TEM images and micro-Raman spectra taken right after growth confirmed the formation of high quality MWNTs with a low degree of disorder irrespective of the catalysts used, the degree of dealumination of the zeolite Y and the textural and morphological characteristics of the zeolitic support. (c) 2007 Elsevier Inc. All rights reserved. Microporous and Mesoporous Materials

The present study focuses on the synthesis and characterization of vanadia catalysts supported on non-porous (SiO2), microporous (silicalite), mesoporous (MCM-41, HMS, SBA-15) and ultra-large mesoporous (MCF) silicate materials. The structure and porosity characteristics of the above mesoporous supports were verified by means of XRD, N2 porosimetry and HR-TEM studies. Vanadium was introduced in the porous materials via wet impregnation of vanadium oxalate complex in strongly acidic aqueous media. No crystalline V2O5 phases were found on the surface of all the above mesoporous supports for V loadings as high as 8 wt.%, in contrast to microporous zeolite silicalite and non-porous SiO2 on which V2O5 crystals were formed as evidenced by XRD. Increasing addition of vanadium under the strongly acidic impregnation conditions followed by typical calcination of the catalyst, resulted in partial structure breakdown and loss of surface area of the mesoporous supports which was more pronounced in the case of SBA-15 and MCF materials. The most active catalysts for the formation of propene in the oxidative dehydrogenation of propane (ODP) at reaction temperatures 500–600 °C were those supported on HMS and MCM-41 mesoporous materials showing high propene yields up to 19% at about 600 °C. The vanadia catalysts based on SBA-15 and MCF were less active in the production of propene (yields up to 13%) compared to the MCM-41 and HMS based catalysts. The SiO2 and silicalite based catalysts showed much lower yields of propene (

The in situ upgrading of biomass pyrolysis vapors with two mesoporous aluminosilicate materials (MSU-S BEA ) assembled from zeolite Beta (BEA) seeds was tested in the present study, in comparison to conventional Al-MCM-41 and to non-catalytic biomass pyrolysis. The first sample (MSU-S/H BEA ) exhibited an hexagonal mesopore structure while the second one (MSU-S/W BEA ) possessed a wormhole-like mesopore structure with high textural porosity. The catalytic tests were performed on a fixed-bed reactor, the reaction temperature was 500 °C and the feed was a lignocellulosic biomass based on beech wood. The use of the MSU-S catalytic materials led to significantly lower organic phase in the produced bio-oil and also to higher coke and char yields, compared to non-catalytic pyrolysis and to the use of Al-MCM-41 which induced a small increase in the yields of liquid oil and coke. Pyrolysis gases were also affected by all mesoporous catalysts. The MSU-S catalytic materials were very selective towards polycyclic aromatic hydrocarbons (PAHs) and heavy fractions, while they produced negligible amounts of acids, alcohols and carbonyls, and very few phenols. The MSU-S materials appeared to possess stronger acid sites than Al-MCM-41, resulting in enhanced yields of aromatics, PAHs and coke, as well as propylene in the pyrolysis gases.