Kazutoshi Chaki

Synthesis of ZSM-5 zeolite with small crystal size and its catalytic performance for ethylene oligomerization

Abstract ZSM-5 zeolites of SiO 2 Al 2 O 3 = 25 with a small crystal size were synthesized under various conditions in order to clarify a relationship between external surface area and catalytic performance, especially lifetime, for the oligomerization of ethylene to higher hydrocarbons of the gasoline range. The measurement of the external surface area, XRD patterns, and FTi.r. spectra of the resulting ZSM-5 zeolites suggested that their crystal grains were very fine. The shapes and sizes of the primary grains of the ZSM-5 zeolites were observed by means of a scanning electron microscopy with a magnification of 300,000. The crystal sizes were in the range of 30–50 nm. In the oligomerization of ethylene, a proton-type zeolite that was synthesized under a high molar ratio of OH SiO 2 showed both high ethylene conversion and high gasoline range selectivity for three times longer on-stream time than those of other zeolites. The external surface area of the zeolite was also three times greater than those of other zeolites, which indicated that the lifetime of ZSM-5 zeolite in the oligomerization of ethylene depended on the external surface area or crystal size.

Oxidative coupling of methane over sodium-doped CaO catalysts prepared by the sol-gel method

Abstract Sodium-doped calcium oxide (Na/CaO) catalysts prepared by the sol-gel method (SGM) show relatively high performance for oxidative coupling of methane (OCM) compared with that prepared by impregnation method (IM). The difference between the performance of these catalysts for OCM seems to come from the difference in morphology and TPD profiles of these catalysts.

Natural Calcium Compounds as Catalysts for Oxidative Coupling of Methane

Oxidative coupling of methane(OCM) over various natural calcium compounds was investigated. Some kinds of shells were found to be good catalysts for OCM. The study of surface properties of the catalysts by XPS revealed that a high performance of the shell catalysts was due to not only morphology but also high concentration of minor components such as sodium on the surface of the catalysts.

Oxidative coupling of methane over natural calcium compounds in fixed- and fluidized-bed reactors

Publisher Summary This chapter presents the catalytic performance of the natural calcium compounds (NCC) catalysts under various reaction conditions, using fixed- and fluidized-bed reactors. In an experiment presented in the chapter, the catalysts were prepared with the help of seashells. Seashells were washed and then dried at 393 K for 24 hours, followed by calcining at 1173K for 10 hours. The obtained materials were then pelletized, crushed, and sieved to grain sizes. The catalysts were tested in a conventional fixed-bed alumina tube reactor of 11 mm i.d. at atmospheric pressure. The catalysts were also tested in a fluidized-bed quartz tube reactor of 22 mm i.d. at atmospheric pressure. The oxidative coupling of methane (OCM) reaction in the fluidized-bed reactor was carried out from the standpoint of the control of reaction temperature. Sodium is one of the effective elements for the OCM reaction; however, sodium-containing catalysts are agglomerated during the reaction, probably because of the melt of sodium on the surface of catalysts. The NCC catalysts have excellent catalytic performance for the OCM reaction in both fixed- and fluidized-bed reactors. The control of reaction temperature in the fluidized-bed OCM reactor is easier than fixed-bed reactor.