SBA-15 ordered mesoporous silicas were synthesized using the method reported by Zhao et al. The structures of these materials were characterized using powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nitrogen adsorption. The samples were found to exhibit structural properties similar to those reported earlier. Our study confirmed that the size of primary mesopores of SBA-15 can be tailored by the choice of synthesis temperature and that SBA-15 exhibits a significant amount of disordered micropores and small mesopores. The volume and size of these complementary pores were found to be dependent to some extent on the synthesis/aging temperature. It was shown that the washing of as-synthesized SBA-15 in water or ethanol was accompanied by an appreciable structural shrinkage and led to the removal of a significant part of the polymeric template. Therefore, washing needs to be avoided if one wants to isolate SBA-15 without appreciable loss of the template. It was confirmed that water-washed SBA-15 samples have fully accessible primary mesopores. Ethanol-washed samples also were found to exhibit accessible porosity. Despite an appreciable content of the template in the water-and ethanol-washed samples, their pore sizes were usually larger than those of the calcined materials. The observed structural properties of SBA-15 and their dependence on the synthesis temperature and washing were attributed to the changes in the degree of penetration of the poly(ethylene oxide) chains of the triblock copolymer template within the siliceous walls of SBA-15.

Microporosity and connectivity of ordered mesopores of SBA-15 silica were studied using nitrogen adsorption and novel methods based on selective pore blocking via organosilane modification, and on the imaging of inverse platinum replica of ordered mesoporous structure. It was found that SBA-15 exhibits a relation between the pore size, pore volume and specific surface area which is significantly different from that for cylindrical or hexagonal pores, which suggests that the SBA-15 structure is more complex than an array of hexagonally ordered channels, even if they are corrugated. Nitrogen and argon adsorption measurements provided evidence that large mesopores are accompanied by a certain amount of significantly smaller pores (of the size below about 3.4 nm) with a broad distribution primarily in the micropore/small-mesopore range. The modification of SBA-15 via chemical bonding of small trimethylsilyl ligands partially blocked the complementary pores, and the bonding of larger octyldimethylsilyl groups made them essentially fully inaccessible to nitrogen molecules, which manifested itself in dramatic changes in the relation between the pore size, pore volume, and specific surface area. After dissolution of the SBA-15 framework, platinum wires grown inside the porous structure formed bundles, as seen from transmission electron microscopy. These results provided strong and unambiguous evidence that large ordered mesopores of SBA-15 are accompanied by much smaller disordered pores and that an appreciable fraction of the latter is located in the pore walls, providing connectivity between the ordered large-pore channels. The complementary pores are suggested to form as a result of penetration of poly(ethylene oxide) chains of the triblock copolymer template within the silica framework of as-synthesized SBA-15. We also studied thermal stability of SBA-15 structure and its complementary porosity. As inferred from nitrogen adsorption data, the complementary porosity was retained to a significant extent even after calcination at 1173 K, but most likely completely disappeared at 1273 K. The heat treatment was accompanied not only by a significant decrease in the specific surface area and pore volume but also by narrowing the pore size distribution at temperatures up to 1173 K. Thus, we were able to demonstrate for the first time that the SBA-15 sample with nitrogen adsorption properties similar to those of MCM-41 can be obtained via calcination at 1273 K, although the pore volume and specific surface area of such SBA-15 material is relatively low.

Highly ordered MCM-41 materials were synthesized using single or mixed alkyltrimethylammonium and alkyltriethylammonium surfactants of alkyl chain lengths from 12 to 22. As determined using combined adsorption/powder X-ray diffraction (XRD) analysis, the obtained samples exhibited pore sizes from 3.2 to 4.8 nm with about 0.3 nm increments. Nitrogen adsorption isotherms for the samples under study exhibited remarkably sharp capillary condensation steps. The adsorption isotherm for the highly ordered 4.8 nm MCM-41 featured a narrow hysteresis loop with parallel adsorption and desorption branches. This behavior is probably a feature of nitrogen adsorption in ideal cylindrical pores of this size and is distinctly different from the previously reported behavior of MCM-41 with pore sizes in the range 4-5.5 nm, which had triangular hysteresis loops on their nitrogen adsorption isotherms. All MCM-41 materials had remarkably narrow pore size distributions, which showed that fine-tuning of the pore size is easily achievable for the synthesis procedure used. The pore wall thickness was found to increase as the pore size increased. The pore wall thickness determined using transmission electron microscopy (TEM) was somewhat larger than that obtained using the combined XRD/adsorption analysis, which was attributed to inherent features of these determination methods. TEM images showed that pores of MCM-41 samples were approximately hexagonal rather than circular, thus providing structural information especially important for application of MCM-41 as a model adsorbent. Low-pressure adsorption studies of uncalcined ethanol-washed MCM-41 samples revealed that external surfaces of their particles were covered by relatively dense layers of surfactant ions. This behavior is consistent with the generally accepted mechanism of the MCM-41 formation via self-assembly of silicate-surfactant ion pairs. Comparison of adsorption isotherms for uncalcined and calcined samples allowed us to exclude the possibility of any appreciable structural degradation during calcination, although TEM provided some indication of the lowering of structural ordering upon calcination.

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Transmission electron micrographic images of platinum wires, incorporated into the channels of mesoporous molecular sieves, show that one-dimensional channels are arranged parallel in MCM-41 while the channels are threedimensionally interconnected in other types of mesoporous molecular sieves constructed with silica frameworks.

Carbon-based adsorbents with controlled porosity were prepared to investigate the adsorption capacity of refractory sulfur compounds. The porosity of carbon-based adsorbents was controlled by thermal treatment at 1173 K in CO 2 environment. The equilibrium sulfur adsorption capacities of each adsorbent were measured for both model and commercial diesel. Pore widening of carbon-based adsorbents by CO 2 activation increased BET surface area, total pore volume, micropore volume, and sulfur adsorption capacity. However, the sulfur adsorption capacity did not increase linearly according to the increase of BET surface area, total pore volume, and BJH pore volume, which included the properties of meso-and macropores. Specific micropore volume, whose pore diameters range from 0.63 to 1.2 nm, showed good linear relationship with sulfur adsorption capacity for commercial diesel. Model diesel adsorption tests supported that adsorbents with proper pore size for target sulfur molecules should be prepared for the enhancement of sulfur adsorption capacity.

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