Influence of the texture and acid-base properties of the alumina-containing support on the formation of Co(Ni)-Mo catalysts for deep hydrodesulfurization of the diesel fraction

The influence of the texture of γ-Al₂O₃ on the formation of Co(Ni)-Mo catalysts for hydrodesulfurization of the diesel fraction is studied. As shown by low-temperature N₂ adsorption, X-ray diffraction, IR spectroscopy of adsorbed molecules, and high resolution electron microscopy (HREM), use of a support with a larger specific surface and a lower total concentration of terminal OH groups makes it possible to prepare more active catalysts. The electron density radial distribution method shows that the finely dispersed cobaltcontaining catalyst in its initial state contains CoMoO₄, Al₂(MoO₄)₃, and CoAl₂O₄, the last two phases being present in trace amounts. After the reaction, this catalyst contains cobalt-doped molybdenum sulfide. According to HREM data, the active phase of the cobalt-containing catalyst consists of layered sulfide association species Co_1.3Mo₂S_3.3, which differ in composition from the bulk phase CoMo₂S₄. It is assumed that, out of the 1.3 cobalt atoms in Co_1.3Mo₂S_3.3 0.3 Co occurs at the edges of the association species and 1.0 Co is intercalated into their interlayer space, and 0.7 S at the boundary between the association species and the Al₂O₃ phase is replaced by the corresponding amount of oxygen.     

Surface acidity and basicity of oxide catalysts: From aqueous suspensions to in situ measurements

Our review covers the achievements of recent decades in the investigation of the acid-base properties of oxide catalyst surfaces. Both conventional and new investigation techniques are reviewed, including SSITKA for H/D exchange.     

Effect of thermal treatment conditions on the acid properties of zeolite Beta

The acid properties of zeolite Beta were studied by IR spectroscopy with the use of adsorbed NH₃ and CO probe molecules. It was found that the strength of the Brønsted acid sites (BASs) of zeolite Beta was the same as that of zeolite ZSM-5. Approximately a third of the total amount of BASs participated in the formation of hydrogen bonds at interdomain boundaries; thus, they were inaccessible to molecules larger than the ammonia molecule. The qualitative and quantitative compositions of acid sites in zeolite Beta can be regulated by changing the conditions of calcination of the initial zeolite form (temperature and/or gas atmosphere). Calcination under vacuum conditions afforded the highest acidity of the zeolite with respect to all types of acid sites. Calcination in a flow of air resulted in the lowest acidity of the sample, especially, with respect to the concentration of strong Lewis acid sites, because of the formation of an alumina phase. Calcination in an atmosphere of helium resulted in a decrease (as compared with a vacuum) in the rate of removal of the organic template decomposition products of the initial zeolite form from the channel volume. The resulting ethylene was mainly adsorbed at strong Lewis sites and converted into undesorbed condensation products.     

Mechanism of 1,2-dichloroethane dehydrochlorination on the acid sites of oxide catalysts as studied by IR spectroscopy

Kinetics and Catalysis - The adsorption of 1,2-dichloroethane on zeolite HZSM-5 and γ-Al2O3 at temperatures from 25 to 400°C was studied by Fourier transform IR spectroscopy. The forms of...     

Acetone adsorption on hydroxylated silica gel: Correlation of sorption isotherms and IR spectra

The synthesis of MTBE from methanol and isobutene has been carried out over a ZSM-5 based catalyst, in two types of continuous flow catalytic reactors, fixed-bed and fluidized-bed. We have studied the influence of the molar ratio methanol to isobutene, the temperature and the weight hourly spatial velocity (WHSV) on the yield of MTBE.     

Hydrocarbon specificity in the selective catalytic reduction of NOx over Cu-ZSM-5 and Co-ZSM-5 catalysts

Transformation of surface nitrates under CH₄ (CH₄+O₂) was found to ensure steady-state activity of Co-ZSM-5 in the selective catalytic reduction of nitrogen oxides by methane (CH₄-SCR). For Cu-ZSM-5, such species are mainly converted into NO. Relaxation of the coordination sphere due to oxygen and NO adsorption, stability of C,N-containing intermediates and activation routes of hydrocarbons (methane, propane) were analyzed as factors determining catalytic properties of Cu and Co cations.     

Determination of the strength of aprotic acidic centers on catalyst surfaces from the IR spectra of adsorbed carbon monoxide

Correlations between the adsorption heats of carbon monoxide on aprotic acidic centers and the v _CO values in IR spectra have been studied. In the case of aprotic centers formed by cations of non-transition metals, v _CO is shown to be linearly dependent on the adsorption heat.

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v _CO . , , , v _CO .

     

Acid-base properties of single-phase aluminum oxides

It was found that the surface of single-phase aluminum oxides contains terminal, bridging, and hydrogen-bonded hydroxyl groups, which differ in both concentration and position of related absorption bands. A transition from -Al₂O₃ to -Al₂O₃ does not change the number of absorption bands, but the intensities of these bands decrease. The total concentration of Lewis acid sites in single-phase oxides increases from 2.5 to 5.34 µmol/m² for -Al₂O₃ and -Al₂O₃, respectively. As distinct from other species, -Al₂O₃ contains strong Lewis acid sites ((CO) = 2238 cm^–1). The total concentration of basic sites in aluminum oxides prepared by boehmite dehydration at 600, 800, and 1000°C decreases from 4.86 to 3.72 µmol/m².Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 141–146. Original Russian Text Copyright © 2005 by Kulko, Ivanova, Budneva, Paukshtis.     

Localization of the copper-containing component in the pore volume of zeolite ZSM-5

The distribution of the copper-containing component in the pore volume of zeolite ZSM-5 has been investigated by H₂ and N₂ adsorption at 77 K and IR spectroscopy. Samples were synthesized by ion exchange and incipient wetness impregnation. Copper-containing clusters are mostly located on the surface of the mesopores formed by packed zeolite nanocrystallites. This causes partial blocking of the volume of microporous channels for N₂ molecules, but these channels remain accessible for H₂ molecules. It has been deduced that no considerable amount of copper located in the structural channels of the zeolite. According to IR spectroscopic data, the sorption of copper ions in the Cu/ZSM-5 catalysts takes place on extraframe-work aluminum, which forms Al-OH-Al bridges and terminal Al-OH groups, and on terminal Si-OH groups located on the zeolite crystal surface.