S. Imamura

State of titanium in Ti-containing silica and silicalite catalysts in relation to their oxidation activity

The nature of active titanium species for epoxidation of olefins with H2O2 and t-butyl hydroperoxide has been investigated for titanium silicalite (TS-1), titania silica (TiO2/SiO2) prepared by a sol-gel method, and titanium oxide supported on silica by a CVD method (TiO2/SiO2-CVD). IR and XANES analyses suggested that Ti in TiO2/SiO2 and TiO2/SiO2-CVD has a tetrahedral configuration bonded to SiO2 and that in TS-1 has a configuration composed of >Ti=O or related to it. Their configurations are closely related to their reactivities for epoxidation of olefins in which the former works with t-butyl hydroperoxide and the latter with H2O2.

Acid-base properties of supported vanadium oxide catalyst

Reduction of V2O5/Al2O3 and V2O5/silica-alumina produced Lewis acid sites which could strongly adsorb CO (heat of adsorption: 90 kJ/mol). Such strong acid sites were not formed in the cases of V2O5/SiO2 and V2O5/MgO. V2O5 loaded on Al2O3 interacted with the basic sites of alumina but not with the acidic sites, while the V2O5 on silica-alumina interacted with the acidic sites of the silica-alumina and decreased its acidity.AbstractВосстановление V2O5/Al2O3 и V2O5/SiO2−Al2O3 приводит к образованию центров льюисовских кислот, которые способны сильно адсорбировать CO (теплота адсорбции 90 кДж/моль). В случае V2O5/SiO2 и V2O5/MgO таких сильных кислот не образуется. V2O5, нанесенный на Al2O3, взаимодействует с основными центрами алюмозема, а не с кислыми центрами, в то время как V2O5 на SiO2−Al2O3 взаимодействует с кислыми центрами кремнезема-алюмозема и тем самым уменьшает их кислотность.

DECOMPOSITION OF N2O ON RH-LOADED ZEOLITES

N2O was decomposed over Rh supported on NaY zeolite and ZSM5. With low Rh-loading (≤0.1 wt.%) the activity of Rh was much higher than that supported on SiO2 and CeO2. On the contrary, the activity of Rh-loaded zeolites (0.1 wt.%) was not so high or even lower than that on SiO2 for the oxidation of toluene, which has a larger molecular size than N2O. Thus the Rh present inside the zeolite cavity was especially effective in the decomposition of N2O.

Ethylene polymerization on lewis acid sites of a reduced V2O5/Al2O3 catalyst

The reduced V2O5/Al2O3 and V2O5/silica-alumina catalyst pretreated at 670°C showed high C2H4 polymerization activity at 70°C while the polymerization scarcely occurred on SiO2-supported catalyst and did not occur on MgO-supported catalyst. The activities of the catalysts were closely related to the amounts of strong Lewis acid sites.AbstractПредварительно восстановленные при 670°C катализаторы V2O5/Al2O3 и V2O5/силикагель-кремнезем проявляли высокую активность к полимеризации C2H4 при 70°C, в то время как полимеризация едва протекала на катализаторах, нанесенных на SiO2, и совсем не была обнаружена при использовании MgO в качестве носителя. Активность катализаторов находится в строгой зависимости с числом сильно кислых центров типа Льюиса.

ADSORPTION OF CARBON MONOXIDE ON LEWIS ACID SITES OF ALUMINA

It has been found that carbon monoxide is adsorbed on Lewis acid sites of a high acid strength. Potential applicability of carbon monoxide as a gaseous base to determine the strength and amount of acid sites is suggested.AbstractНайдено, что моноокись углерода адсорбируется на льюисовских центрах созначительно высокой кислотной силой. Предложен метод использования CO, как газового основания, для определения силы и количества кислых центров.

Kinetics of C2H4 polymerization on reduced V2O5/Al2O3 catalyst

Kinetic study of C2H4 polymerization on reduced V2O5/Al2O3 catalysts revealed that the rate equation can be expressed as Vρ=k exp (-αYρ) KaPE/(1+KaPE) in the temperature range of −20 to 70°C. The deactivation constant, α, was found to have a close relation with the yield and molecular weight of the polymer.AbstractНа основе кинетических исследований полимеоризации C2H4 на восстановленны х каталиааторах V2O5/Al2O3 в интервале температур−20 ≐ +70°C было выведено следующее уравнение скорости: Vp=k·exp(-αYp)·KaPe/(1+KaPe). Константа дезактивации α находится в завсимости с конверсий и молекулярным весом полимера.

Active site for hydrogenation on reduced V2O5/Al2O3 catalyst

Active sites for C2H4 hydrogenation produced by reduction of V2O5/Al2O3 catalyst pretreated at 450°C were found to be composed of both strong Lewis acid sites associated with V4+ and basic sites of Al2O3. C2H4 polymerization concurrent with hydrogenation was assumed to occur on Lewis acid sites with higher acid strengths than those of the hydrogenation sites.AbstractАктивные центры гидрогенизации C2H4, образующиеся при восстановлении катализатора V2O5/Al2O3, предварительно обработанного при 450°C, содержат как сильно кислые льюисовские центры, так и основные центры Al2O3. Полагали, что на центрах льюисовской кислоты с силой, превышающей необходимую для гидрогенизации, конкурентно протекает полимеризация C2H4.

Properties of χ-alumina as related to catalysis

Abstractχ-Alumina was synthesized by thermal decomposition of aluminium(III) isopropoxide, and its properties were investigated. The change in its surface area with increasing calcination temperature resembled that of γ-alumina. Both aluminas had the same acid strength, and their activities in isomerization of 1-butene were the same. χ-Alumina as a support for molybdenum catalyst in the epoxidation of allyl alcohol also behavedin the same manner as γ-alumina. Thus χ-alumina has almost the same catalytic properties as γ-alumina.

Preparation of heat-resistant BaAl12O19 combustion catalyst by solid-state reaction combined with sub-micron grinding

Heat-resistant barium hexaaluminate combustion catalyst was prepared by a conventional solid-state reaction combined with sub-micron grinding. The barium hexaaluminate thus prepared retained almost the same high surface area at high temperatures as the one prepared by the alkoxide method, exhibiting high activity in the catalytic combustion of methane.

Oxidation of CO on Ag-based composite oxides

Thermal stability of the oxidized state of silver was increased in the Cr, Mn, Fe and Co oxides. However, Ni and Cu oxides did not stabilize Ag, leading to its aggregation to form metallic Ag at 400°C. The Ag in the former group exhibited high catalytic activity in the oxidation of CO due to the formation of composite oxides with these transition metals.AbstractТермическую стабильность к окислению серебра повышали окислами Cr, Mn, Fe и Co. Однако, окислы Ni и Cu не стабилизируют Ag, приводя к его агрегации в металлическую форму при 400°C. В такой смеси Ag обладает высокой каталитической активностью в окислении CO, вследствие образования композитных окислов с этими переходными металлами.