Hirotoshi Sakagami

Isomerization of heptane on molybdenum oxides treated with hydrogen

Isomerization of heptane was carried out at 573 K under atmospheric pressure using molybdenum oxides as catalysts. MoO3 was inactive for this reaction. H2 reduction of MoO3 at 623 K, however, enhanced the isomerization activity and selectivity, which became almost constant after the reduction for 24 h. The reduced MoO3 exhibited a higher isomerization activity than a typical bifunctional catalyst, 0.5 wt%Pt/USY zeolite, while there was no appreciable difference in product distribution between these two catalysts. These results indicate that the reduced MoO3 catalyzed the isomerization of heptane via a conventional bifunctional mechanism.

Catalytic properties of H2-reduced MoO3 and Pt/zeolites for the isomerization of pentane, hexane, and heptane

Abstract The catalytic properties of H 2 -reduced MoO 3 for the isomerization of C 5 –C 7 alkanes were compared to those of Pt/HY and Pt/Hβ zeolites. The pentane isomerization activity decreased in the following order: Pt/Hβ>H 2 -reduced MoO 3 >Pt/HY. In contrast, H 2 -reduced MoO 3 exhibited the lowest activity for heptane isomerization among the catalysts tested. H 2 -reduced MoO 3 catalyzed the isomerization of heptane more selectively than other catalysts, although no appreciable difference appeared in the selectivity for pentane isomerization. Kinetic parameters on H 2 -reduced MoO 3 were identical with those on Pt/zeolites, suggesting that isomerization reactions on H 2 -reduced MoO 3 proceeded via the bifunctional mechanism. We suggested from the results of 2-propanol conversion that the low dehydrogenation–hydrogenation activity of H 2 -reduced MoO 3 was a reason for its low isomerization activity. Adsorption of heptane was found to be restricted on H 2 -reduced MoO 3 , leading to the low activity for heptane isomerization.

Hydrate‐bearing structures in the Sea of Okhotsk

Gas hydrates are natural gas reservoirs in ice-like crystalline solids, and are stable in pore spaces of submarine sediments in water depths greater than about 300–500 m. They have been recovered in many of the worlds oceans, both at larger sub-bottom depths (up to 450 m) by drilling and near the seafloor in shallow cores by gravity-coring. In the latter case, the gas hydrates are related to the sites of enhanced seepage such as cold seeps and mud volcanoes [Ginsburg and Soloviev, 1998]. Multidisciplinary field investigations during the two cruises have revealed new, large hydrate-bearing seepage structures in the Sea of Okhotsk, a northwestern marginal sea of the Pacific Ocean (Figure l). The Derugin Basin at the central part of the Sea of Okhotsk, the zone of intensive gas seepage and hydrate accumulation, was studied during two cruises of the R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS), in August and October 2003 within the framework of the CHAOS project (hydroCarbon Hydrate Accumulations in the Okhotsk Sea) supported by funding agencies in five nations.

Catalytic properties of MoO3 reduced at different temperatures for the conversions of heptane and 2-propanol

Abstract Conversions of heptane and 2-propanol were carried out using H 2 -reduced MoO 3 . The catalytic activity of H 2 -reduced MoO 3 for the isomerization of heptane increased in proportion to the extent of reduction, irrespective of reduction temperature. When MoO 3 samples reduced at different temperatures were compared at a definite extent of reduction, however, MoO 3 reduced at 573 and 623 K exhibited higher isomerization activities than that at 673 K. The dehydration and dehydrogenation of 2-propanol proceeded simultaneously on H 2 -reduced MoO 3 catalysts, indicating the presence of the dual sites. MoO 3 reduced at 623 K was most active for the dehydration to yield propene, while the highest dehydrogenation activity was obtained after reduction at 673 K. There was a good relationship between the isomerization activity and the rate of propene formation.

Effect of reduction temperature on the transformation of MoO3 to MoOx with a large surface area

Abstract The surface area of MoO 3 was enlarged by H 2 reduction. When the samples reduced at different temperatures were compared at a certain extent of reduction, MoO 3 reduced at 573 and 623 K exhibited much larger surface areas than that at 673 K. MoO 3 reduced at temperature below 623 K had a surface area of 170–180 m 2 g −1 and pores with the diameter of 0.6–3.0 nm when the reduction degree was about 50%. Since the surface area and the porous structure of MoO 3 reduced at 623 K changed little by treatment at 673 K in an N 2 atmosphere, the small surface area of MoO 3 reduced at 673 K cannot be elucidated by thermal stability. XRD studies showed that reduction of MoO 3 at temperature below 623 K proceeded via the formation of hydrogen molybdenum bronze, H x MoO 3 , while the H x MoO 3 phase was not observed at 673 K. We suggest from these results that the enlargement of surface area and the formation of micropores can occur only when reduction of MoO 3 proceeds via the H x MoO 3 phase.

Comparison of the catalytic properties of H2-reduced Pt/MoO3 and of Pt/zeolites for the conversions of pentane and heptane

Abstract The catalytic properties of H 2 -reduced Pt/MoO 3 for the isomerization of pentane and heptane were compared to those of Pt/zeolites. H 2 -reduced Pt/MoO 3 was more active for pentane isomerization than Pt/Hβ and Pt/USY. In contrast, the heptane isomerization activity decreased in the following order: Pt/Hβ>H 2 -reduced Pt/MoO 3 >Pt/USY. All of the catalysts gave negative kinetic orders toward hydrogen in both pentane and heptane isomerization. The reaction order toward pentane was positive in all cases. The reaction order toward heptane on H 2 -reduced Pt/MoO 3 was found to be −0.3, whereas those on Pt/Hβ and Pt/USY were zero and positive, respectively. These results indicate that heptane was more strongly adsorbed on H 2 -reduced Pt/MoO 3 , resulting in the low heptane isomerization activity. Adsorption studies showed that interaction of heptane with the surface of H 2 -reduced Pt/MoO 3 was hindered, probably by its porous structure. We suggest from these results that the low catalytic activity of H 2 -reduced Pt/MoO 3 for heptane isomerization can be caused by steric effects as well as by the strong adsorption of heptane.

H2-reduction of Pt/MoO3 to MoOx with a large surface area and its catalytic activities for the conversions of heptane and propan-2-ol

The surface area of H2-reduced 0.01 mol.% Pt/MoO3 increased in proportion to the extent of reduction, and reached the maximum value of 250 m2 g−1 at a reduction degree of 60–70%. In the case of H2-reduced MoO3, the relationship between the surface area and the reduction degree was dependent on reduction temperature. MoO3 reduced at 673 K exhibited a much smaller surface area than that at 623 K even when the reduction degree was comparable. XRD studies showed that reduction of Pt/MoO3 proceeded ia the formation of HxMoO3 phase, irrespective of reduction temperature. In the reduction of MoO3 without Pt, however, the HxMoO3 phase was formed at temperature below 623 K. The heptane isomerization activity of H2-reduced MoO3 and Pt/MoO3 was similarly dependent on the reduction degree as the surface area. H2-reduced MoO3 and Pt/MoO3 catalyzed the dehydrogenation and dehydration of propan-2-ol simultaneously, indicating the presence of dual sites. There were good relationships between the isomerization activity and the dehydration activity. We suggest from these results that the surface area and the catalytic activities can be enlarged when reduction of MoO3 proceeds through the formation of a HxMoO3 phase.

distribution of butane in the host water cage of structure II clathrate hydrates.

To understand host-guest interactions of hydrocarbon clathrate hydrates, we investigated the crystal structure of simple and binary clathrate hydrates including butane (n-C4 H10 or iso-C4 H10 ) as the guest. Powder X-ray diffraction (PXRD) analysis using the information on the conformation of C4 H10 molecules obtained by molecular dynamics (MD) simulations was performed. It was shown that the guest n-C4 H10 molecule tends to change to the gauche conformation within host water cages. Any distortion of the large 5(12) 6(4) cage and empty 5(12) cage for the simple iso-C4 H10 hydrate was not detected, and it was revealed that dynamic disorder of iso-C4 H10 and gauche-nC4 H10 were spherically extended within the large 5(12) 6(4) cages. It was indicated that structural isomers of hydrocarbon molecules with different van der Waals diameters are enclathrated within water cages in the same way owing to conformational change and dynamic disorder of the molecules. Furthermore, these results show that the method reported herein is applicable to structure analysis of other host-guest materials including guest molecules that could change molecular conformations.

13C Chemical Shifts of Propane Molecules Encaged in Structure II Clathrate Hydrate

Experimental NMR measurements for (13)C chemical shifts of propane molecules encaged in 16-hedral cages of structure II clathrate hydrate were conducted to investigate the effects of guest-host interaction of pure propane clathrate on the (13)C chemical shifts of propane guests. Experimental (13)C NMR measurements revealed that the clathrate hydration of propane reverses the (13)C chemical shifts of methyl and methylene carbons in propane guests to gaseous propane at room temperature and atmospheric pressure or isolated propane, suggesting a change in magnetic environment around the propane guest by the clathrate hydration. Inversion of the (13)C chemical shifts of propane clathrate suggests that the deshielding effect of the water cage on the methyl carbons of the propane molecule encaged in the 16-hedral cage is greater than that on its methylene carbon.

Chemical Shift Changes and Line Narrowing in 13C NMR Spectra of Hydrocarbon Clathrate Hydrates

The solid-state (13)C NMR spectra of various guest hydrocarbons (methane, ethane, propane, adamantane) in clathrate hydrates were measured to elucidate the local structural environments around hydrocarbon molecules isolated in guest-host frameworks of clathrate hydrates. The results show that, depending on the cage environment, the trends in the (13)C chemical shift and line width change as a function of temperature. Shielding around the carbons of the guest normal alkanes in looser cage environments tends to decrease with increasing temperature, whereas shielding in tighter cage environments tends to increase continuously with increasing temperature. Furthermore, the (13)C NMR line widths suggest, because of the reorientation of the guest alkanes, that the local structures in structure II are more averaged than those in structure I. The differences between structures I and II tend to be very large in the lower temperature range examined in this study. The (13)C NMR spectra of adamantane guest molecules in structure H hydrate show that the local structures around adamantane guests trapped in structure H hydrate cages are averaged at the same level as in the α phase of solid adamantane.