Masami Yamamura

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 ternary metal oxide catalysts consisting of Groups I, III and V elements in the Periodic Table

Abstract Ternary metal oxides consisting of Group I (alkali metals)/Group III/Group V metals with an atomic ratio of 1:1:0.3 were prepared and their catalytic performance for the oxidative coupling of methane as well as their physicochemical properties were investigated. When adding Group V metals to Group I/Group III binary catalysts, a noticeable increase in the conversions of methane and oxygen was observed without any change in C 2+ selectivity. Of the ternary metal oxide catalysts, a Na/La/0.3Nb metal oxide showed the highest performance, viz. a methane conversion of 16.0% and a C 2+ selectivity of 74.1% at 1023 K under atmospheric pressure with a total gas flow-rate of 100 ml NTP/min ( CH 4 /O 2 molar ratio= 9 ). The stability test using a Na/La/0.2Nb catalyst, which was performed under the same conditions as above, showed that the catalyst was very stable with no decrease in methane conversion and C 2+ selectivity for more than 100 h. The crystalline structure, the surface composition and properties of base sites of Na/La/Nb oxide catalysts were investigated using X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) of carbon dioxide. The catalytic performance of the Na/La/Nb mixed oxides depended on the ratio of the two crystalline phases of La 2 O 3 and La 3 NbO 7 . When sodium was added to La 2 O 3 with a La/Na ratio of 1, new base sites were produced, resulting in an increase in the C 2+ selectivity with a significant decrease in methane conversion. The methane conversion was increased by adding a small amount of niobium to the Na/La catalyst, resulting in a change of part of the La 2 O 3 to La 3 NbO 7 . However, when all of the La 2 O 3 was changed to La 3 NbO 7 , the C 2+ selectivity decreased due to the lack of new base sites. A good balance of both crystals (La 2 O 3 and La 3 NbO 7 ) may be obtained at a Nb/Na atomic ratio of 0.15–0.3, which optimizes the catalytic performance of the mixed oxides.

Oxidative coupling of methane over alkali halide- promoted perovskite oxide catalysts

Abstract The catalytic performance of some alkali halide-promoted perovskite oxides as well as that of the perovskite oxides alone for the oxidative coupling of methane were investigated. Although the perovskite oxides alone showed relatively low catalytic activity, a noticeable increase in activity and C2 selectivity was observed when the oxides were promoted by alkali halides. Sodium chloride ( NaCl ) was the most effective promoter among the alkali halides. Of the perovskite oxides examined in the present study, the catalytic activity of PbTiO3 was most remarkably promoted by addition of NaCl, because it showed almost no activity for the reaction in the absence of NaCl. The maximum C2 yield of 28.2% was obtained for an NaCl (0.2 mol against 1 mol of PbTiO3) added PbTiO3 catalyst, where methane conversion and C2 selectivity were 50.7% and 55.7%, respectively, under the conditions;Pch4=10.1 kPa,PO2 = 5.1 kPa,PHe = 86.1 kPa, total gas flow-rate =100 ml STP/min, temperature = 1023 K,W/F= 0.22 g min/ml. The stability test for the 0.2 mol NaCl/PbTiO3 catalyst suggests that the catalyst loses its high activity when most of the NaCI has been removed from the catalyst during the test. However, the same level of activity is recovered when NaCI is added again to the deactivated catalyst. The thermal and temperature-programmed desorption analyses suggest that both high activity and high C2 selectivity for the Nacl-promoted PbTiO3 catalyst can be ascribed to the generation of new basic active sites. These sites must be created through the interaction between NaCl and PbTiO3 on the surface of the catalyst.

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.