P. Jiru

ESR study of Fe3+-zeolites

The ESR signal at g=4.3, recently attributed to Fe3+ which substitute Si, Al in the lattice of glasses and zeolites, can also characterize the charge balancing Fe3+ Td complexes in cavities of Fe3+ HNaY zeolites.AbstractСигнал ЭПР при g=4,3, недавно приписанный Fe+3, замещающему Si, Ql в решетке стекол и цеолитов, также характеризует баланс заряда Td комплексов Fe+3 в ячейках цеолитов Fe+3 HNaY.

Synthesis of ZSM zeolites modified with vanadium and their application in the catalytic oxidation of butadiene

In contrast to ZSM zeolites impregnated with V5+ salts, catalysts prepared by adding V3+ salts during zeolite synthesis exhibited (even when transformed into cristobalite by oxidative activation) higher selectivity to furane in the oxidation of butadiene. Non-oxidative activation preserved the zeolitic structure and increased both the total activity and the selectivity to furane.AbstractВ противоположность цеолитам ZSM, пропитанным солями V5+, катализаторы приготовленные добавлением солей V3+ в ходе синтеза цеолита (даже когда они превращены в кристобалит при окислительной активации) обладают повышенной селективностью к образованию фурана при окислении бутадиена. Неокислительная активация не изменяет структуру цеолита, а повышает как общую активность, так и селективность к образованию фурана.

Synthesis and Characterization of Cr-Modified Silicalite-1

Abstract A series of Cr-modified silicalites-1 was prepared and characterized. Acidic and dehydrogenating properties were observed. Electron-acceptor Cr(III) species were detected by IR adsorption experiments.

Quantum chemical study of the stabilization process of faujasites

The CNDO/2 method is employed in the study of the energetics of the zeolite stabilization process in which skeletal Al atoms are replaced by amorphous Si. It is shown that such a process results in the stabilization of the zeolitic skeleton and that the stabilizing effect increases with decreasing Si: Al ratio as well as with the degree of hydration of the Al-cation formed.AbstractМетод ППДП/2 был использован для изучения энергетики процесса стабилизации на цеолитах, в которых скелетные атомы Al замещаются аморфными Si. Было показано, что такой процесс приводит к стабилизации цеолитного скелета и что стабилизирующий эффект увеличивается с уменьшением отношения Si:Al, а также со степенью гидратации образованного катиона Al.

Surface complexes of cyclohexanone and aqueous solution of NH3 on Ti-silicalite in liquid phase

On the surface of the SiO2 catalyst used in the ammoximation of cyclohexanone to cyclohexanone oxime in the gaseous phase the formation of the imine group (supposed precursor in the reaction) was found previously. The authors investigated the possibilities of the occurence of the imine group on Ti-silicalite used as catalyst in the same reaction when performed in liquid phase. The technique using Ti-silicalite (previously treated with H2O2) suspension in cyclohexanone, NH4OH or their 1∶1 mixture dried on an irtran disc gave the possibility of indicating the formation of surface adsorption complexes by IR spectroscopy. The appearance of a band at 1654 cm−1 corresponding to υ(C=N) after the adsorption of cyclohexanone together with NH4OH indicates the formation of the imine group, whereas the simultaneous lowering of the intensity of the band 970 cm−1 (Ti-O vibration) indicates that the Ti centres take part in this process.

Catalytic Properties of Zeolites in Oxidation and Ammoxidation Reaction

Abstract The catalytic oxidation properties of HY, HZSM5 and HZSM11 zeolites modified by vanadium–phosphorus oxide or vanadium–oxide deposition and of catalysts obtained from V–silicalite precursors are analyzed in the selective conversion of butadiene to furan and maleic anhydride and para–and meta–xylene ammoxidation, and pure ZSM5 zeolites with different Si/Al ratios are tested in the propane conversion to aromatics in the presence of O 2 . In the HY and HZSM5 zeolites the deposited PV clusters interact with protondonor centers giving rise to an inhibition of the maleic anhydride formation from butadiene. This effect is not present in the HZSM11 zeolite. An analogous change in the catalytic behavior is found for the ammoxidation of xylenes. The insertion of V in the framework of silicalite leads to, after activation, the formation of selective sites for furan synthesis from butadiene. Selectivity increases with Si/V atomic ratio. The presence of oxygen in the feed increases the formation of aromatics from propane on the pure zeolites. The oxygen effect is a function of the concentration of OH sites and is attributed to the formation of radical–like surface sites.

Molecular orbital study of the catalytic oxidation of propylene on silver

Analysis of the MINDO/2 reaction coordinates concerning the decomposition of the propylene perepoxide radical anion to propylene oxide and propylene peroxide makes it possible to explain the fundamental differences of ethylene and propylene oxidation on silver catalyst.AbstractАнализ МУПДП/2 реакционных координат разложения анион-радикала перэпоксида пропилена (дающий эпоксид пропилена) дает возможность обБяснить основные различия между окислением этилена и пропилена на серебрянном катализаторе.

Silica as an Ammoximation Catalyst for the Production of Cyclohexanone Oxime

Abstract Amorphous silica samples exhibiting different Bronsted acidities were tested in the gas-phase ammoximation of cyclohexanone with molecular oxygen. Silicalite and titanium silicalite were also tested in the same reaction. The results of the catalytic tests and of the acidity characterizations confirmed the importance of Bronsted sites in order to obtain good activity and showed that the introduction of transition metals into the crystalline framework of silicalite may influence the selectivity considerably and in particular suggested that Ti-silicalite may be a good catalyst for the gas-phase ammoximation of cyclohexanone with O 2 .

Oxidative Transformation of Methanol To Higher Aldehydes Over Zeolite — Oxide Catalysts

Methanol may be in the temperature range 350°–500°C catalytically oxidized in one step to acetaldehyde and benzaldehyde over bifunctional catalysts containing the redox active component Bi-Mo-O together with the HZSM-5 zeolite. In comparison with HZSM-5 zeolite alone (without the redox active component Bi-Mo-O) a 16 times higher selectivity to C 2 + aldehydes was attained. The analysis of the infrared spectra of adsorbed d 3 -acetonitrile and of the surface complexes of methanol formed in its interaction with the proton donor sites of the bifunctional catalyst at 400°C led to the suggestion of the probable mechanism of the oxidative transformation of methanol to higher aldehydes.

Influence of Mo ions and OH groups on l-butene isomerization

It has been shown that loading of silica and silica-alumina with Mo(VI) increases considerably their catalytic activity in 1-butene isomerization to 2-butenes with the preservation of carbocation intermediate mechanism. For the enhancement of catalytic activity the presence of acidic OH groups and Mo(VI) reducible to Mo(V) is necessary.AbstractБыло показано, что добавка Mo(VI) к окислу кремния, а также к окислам кремния и алюминия, значительно увеличивает их каталитическую активность в изомеризации 1-бутена до 2-бутена с сохранением механизма промежуточного карбокатиона. Для повышения катлитической активности необходимо присутствие кислотных OH групп и Mo(VI), восстанавливаемого до Mo(V).