Yasunori Oumi

Mesoporous materials prepared using coal fly ash as the silicon and aluminium source

Coal fly ash was converted into two types of porous materials, MCM-41 and SBA-15 (both of hexagonal structure), using the supernatant of the fly ash. It was found that most of the Si and Al components in the fly ash could be effectively transformed into mesoporous materials, depending on the hydrothermal conditions, and that fusion is essential. Investigation by 29Si and 27Al MAS NMR demonstrated that fusion plays an important role in enhancing the hydrothermal conditions for synthesis of these materials. A high concentration of Na ions in the supernatant of the fused fly ash was not found to be critical in the formation of Al-MCM-41 when prepared under controlled pH conditions. Pyridine adsorption experiments on Al-MCM-41 prepared from coal fly ash revealed the presence of Bronsted and Lewis acid sites. It was also found that the catalytic activity in the cumene cracking reaction is linked only to the accessible aluminium, and not to the total incorporated aluminium present in the Al-MCM-41.

Characterization of AlSBA-15 prepared by post-synthesisalumination with trimethylaluminium

The mesoporous siliceous SBA-15 molecular sieve was synthesized and post-synthesis alumination was carried out using trimethylaluminium (TMA). It was found that the aluminium could be easily incorporated into the siliceous framework of SBA-15 without serious structure deformation. From detailed characterization of the prepared aluminium-containing SBA-15 (AlSBA-15) it was also found that it is difficult to keep the aluminium in the framework position after calcination. The hydrothermal stability of SBA-15 was considerably improved by the TMA processing. The results of the cumene cracking reactions and the pyridine adsorption experiments indicated that the Bronsted acid sites of AlSBA-15 are stronger than those of AlMCM-41 prepared by the same method.

Reversibility of dealumination–realumination process of BEA zeolite

Abstract The reversibility of dealumination–realumination process of BEA zeolite by pH control was investigated by means of nitrogen adsorption, XRD, 27 Al MAS NMR and FT-IR. Aluminum species in the solution, which were eliminated from the framework of BEA zeolite by HCl treatment, were easily reinserted into the framework by controlling the pH value of the suspension below 7. The amount of reinserted framework aluminum increased with an increase in the pH value. The realumination efficiency was also studied by evaluating the change in the cracking activity of cumene. The activity of the BEA zeolite realuminated at pH 5.1 was comparable to that of parent BEA zeolite.

Novel post-synthesis alumination method for MCM-41 using trimethylaluminum

Post-synthesis alumination of purely siliceous MCM-41 was carried out using trimethylaluminum (TMA). The present alumination showed that aluminum can be inserted into tetrahedral positions within the framework at room temperature, namely no further calcination is required. It was found that TMA is an efficient aluminum source for the post-synthesis alumination.

Influences of aliphatic alcohols on crystallization of large mordenite crystals and their sorption properties

The influences of aliphatic alcohols (ROH) on the synthesis of mordenite (MOR) type zeolite were investigated using a starting synthesis mixture with the chemical compositions (0–3 ROH∶0.035 Na2O∶0.005–0.01 Al2O3∶SiO2∶40 H2O). Highly crystalline single crystals of MOR were successfully synthesized using ethanol, 1-propanol and 1-butanol. Under well-optimized conditions, pure uniform and large single crystals up to ca. 50 μm in length were obtained. From sorption experiments of nitrogen, water, benzene and Se, it was found that the single large MOR obtained is not the large-port type MOR and that the effective sorption capacity is markedly influenced by the carbon chain length of aliphatic alcohol used in the crystallization.

Effect of the framework structure on the dealumination–realumination behavior of zeolite

Abstract The dealumination–realumination processes of MOR, MFI, FER and BEA zeolites were investigated by means of XRD, 27 Al MAS NMR, FT-IR and N2 adsorption. Framework aluminums of BEA zeolite were easily removed from the framework by HCl treatment. Dealumination of MOR zeolite was performed by a combination of calcination in air and HCl treatment. However, in the case of MFI and FER zeolites, although the aluminums were taken out of their frameworks by calcination, they remained in the zeolites even after subsequent HCl treatment. This indicates that the structure type is one of the major factors that influence the dealumination behavior. From realumination of various dealuminated zeolites by pH control in solution, it was also found that aluminum species in the solution, which are eliminated from the frameworks of BEA and MOR zeolites by HCl treatment, are easily reinserted into the frameworks by controlling the pH value of the suspension below 7. The amount of incorporated aluminums increased with an increase in the pH value. However, in the case of MOR zeolite, all of incorporated aluminums were not necessarily responsible for generation of tetrahedral coordinated sites. Reinsertion of non-framework aluminums into the dealuminated MFI and FER zeolites hardly occurred.

Direct hydrothermal synthesis and stabilization of high-silica mordenite (Si∶Al = 25) using tetraethylammonium and fluoride ions

The direct crystallization of high-silica mordenite (MOR) zeolite using both tetraethylammonium and fluoride ions was investigated by varying the primary variables of the hydrothermal synthesis such as Si∶Al and H2O∶SiO2 ratios in the starting synthesis mixture. Under well-optimized conditions, highly crystalline MOR zeolites with a Si∶Al ratio of approximately 25 were successfully prepared. From evaluation of the thermal stabilities of the MOR zeolites obtained, it was also found that there is a good relationship between the thermal stability and the bulk Si∶Al ratio of MOR zeolites and that any NaF remaining in the zeolite crystals considerably reduces the thermal stability.

Binary mixture adsorption of water and ethanol on silicalite

Single component and binary mixture adsorption behaviors of water (H 2 O) and ethanol (EtOH) were investigated on silicalites with different crystallinity (structure-defects) by a combination of volumetric and gravimetric methods. No influence of the crystallinity of silicalite on the pure EtOH adsorption was observed. On the other hand, the amount of H 2 O adsorbed on the silicalite with less structure-defects was significantly smaller. The total adsorption amount in the binary mixture adsorption was strongly dependent on the EtOH/H 2 O ratio in the initial mixture. From the analysis of the binary adsorption data, it became clear that EtOH molecules adsorb preferentially on silicalite with less structure-defects and that more selective adsorption of EtOH takes place under the lower equilibrium pressure.

Effective activation of metallocene catalyst with AlMCM-41 in propylene polymerization

AlMCM-41 was prepared by a post-synthesis alumination of MCM-41 and applied to propylene polymerization with rac-ethylene(bisindenyl)zirconium dichloride and triisobutylaluminium. The resulting catalyst system gave selectively isotactic polypropylene and the polymer yield was strongly dependent upon the evacuation temperature in the pretreatment of the AlMCM-41 before use. From the linear relationship between the polymer yield and the number of Lewis acid sites on the AlMCM-41 evaluated by pyridine adsorption, it was found that Lewis acid sites on AlMCM-41 are able to activate effectively the metallocene compound, resulting in the formation of active species.

Application of porous inorganic materials to adsorptive separation of methylalumoxane used as co-catalyst in olefin polymerization

Abstract Inorganic siliceous porous materials with different average pore diameters were applied to the adsorptive separation of methylalumoxane (MAO) used as co-catalyst in α-olefin polymerization. The co-catalytic performance of the separated MAO was investigated by propylene polymerization with rac-ethylene(bisindenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2). The polymerization activity and the stereoregularity of the resulting polymer were markedly dependent upon the pore size of the porous material used for adsorptive separation. From the results obtained by the solvent extraction of the produced polymers, it was suggested that the adsorptive separation of MAO by porous materials is helpful in the characterization of MAO, and at least two different species of MAO are present.