Peculiarities of the vibratioanl spectra of molecules adsorbed on the surface of heterogeneous catalysts: theoretical analysis

The vibrational spectra of adsorption complexes resulting from the adsorption of ammonia on the surface of heterogeneous catalysts are interpreted by computation of frequencies and forms of normal vibrations. The characteristics of normal vibrations are computed from the state of separate fragments of adsorption complexes. It is shown that an interaction of internal coordinates, associated with the adsorption bond, with internal coordinates of the adsorbed molecule leads to a decrease of characteristics of vibrations sensitive to the surface area. A correlation is established between the characteristics of such vibrations and the changes in their frequencies in comparison with the free molecule.     

Acidic properties of fiberglass materials

Acidic properties of fiberglass materials were investigated using the adsorption of NH₃ and the rate of isopropanol dehydration. It is shown that the specific catalytic activity of such materials and amount of the Br?nsted acid sites per their surface unit (100 ?²) exceed considerably those in zeolite HZSM-5.     

Study of the supported zirconocene catalysts by means of UV/vis and DRIFT spectroscopy

UV/vis in diffusion reflection mode (DRS) and DRIFT spectroscopy have been used to study the surface zirconocene species formed at the interaction of Me₂Si(Ind)₂ZrCl₂ and Me₂Si(Ind)₂ZrMe₂ complexes with the MAO/SiO₂ support. Effect of additional activation of these catalysts with TIBA has been studied as well.

Structure of type [Me₂Si(Ind)₂ZrMe]⁺[MeMAO]⁻ (C) is formed at the reaction of Me₂Si(Ind)₂ZrMe₂ complex with MAO/SiO₂ (a.b. at 456 nm in UV/vis spectra). Interaction of this complex with TIBA results in the formation of new structure (D) with a.b. at 496 nm in UV/vis spectra.

The surface species of different composition and structures are formed at interaction of Me₂Si(Ind)₂ZrCl₂ complex with MAO/SiO₂. The ratio between these species depends on the zirconium content in the Me₂Si(Ind)₂ZrCl₂/MAO/SiO₂ catalysts. According to the DRIFTS data (CO and ethylene adsorption) and ethylene polymerization data these catalysts contain active ZrMe bonds but activity of these catalysts at ethylene polymerization is low. Interaction of Me₂Si(Ind)₂ZrCl₂/MAO/SiO₂ with TIBA leads to the formation of the new cationic structure of type (D) with a.b. at 496 nm in UV/vis spectra and great increasing of activity at ethylene polymerization.     

Influence of dehydration conditions on the state of nickel in Y-zeolites

Infrared spectroscopic studies have revealed that the presence of water in dehydrated samples of Ni-containing Y-zeolites rises the number of nickel cations accessible for CO adsorption in NiNH₄Y and leads to their partial screening in NiNaY.

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- , CO NiNH₄Y NiNaY.

     

Infrared spectroscopic studies of H2S adsorption on γ-Al2O3

IR spectra of H₂S adsorbed in various quantities on -Al₂O₃ have been studied. The method of spectral probes has been used to determine the extent of H₂S blocking of Lewis acid and basic centers.

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- , -Al₂O₃. .

     

IR-spectroscopic study of the mechanism of pyridine protomation on the surface of HNaY zeolite

The interaction of pyridine with the surface of Y-type decationized zeolite has been studied by IR spectroscopy over a wide temperature range. It has been shown that the first step of the transfer of a hydroxyl proton to a base is the formation of a strong hydrogen bond. The protonated pyridine exists in free and hydrogen-bonded forms.

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. , . .

     

Effect of additives on acidic and catalytic properties of V?Mo?O catalysts for acrolein oxidation to acrylic acid

Variations of acid-base properties on catalyst surface when modifying V–Mo–O catalyst by various additives changes the reaction course and the catalyst activity.

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- V-Mo-O .

     

Formation of aromatic carbonium ions on V2O5/Al2O3

A comparison of IR spectra of individual toluene, mesitylene, hexamethylbenzene, triene and their carbonium ions with IR spectra of the same molecules adsorbed on V₂O₅/Al₂O₃ has indicated the formation of carbonium ions on catalyst surface.

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- , , , , - , V₂O₅/Al₂O₃ Al₂O₃, t, V₂O₅/Al₂O₃ .

     

Kinetics of Free Radical Generation in the Catalytic Oxidation of Methanol

The formation of free radicals over the surface of platinum-containing catalysts in the methanol oxidation reaction depending on the temperature, the composition of the reaction mixture, and the procedure used for introducing platinum was studied by the matrix isolation method technique. The nature and transformations of surface intermediates depending on the temperature and the presence of oxygen in the gas phase were studied by Fourier transform IR spectroscopy. The main surface intermediate was the methoxy group. The following three types of these groups were stabilized in alumina-based catalysts: (I) CH₃O–Al_oct (_s(–) = 2806 cm^–1), (II) CH₃O–Al_tetr (_s(–) = 2825 cm^–1), and (III) CH₃O < (Al)₂ (_S(–) = 2845 cm^–1, _s(–) = 1460 cm^–1, _s(–) = 1440 cm^–1, r _|| (₃) = 1185 cm^–1, and (–) = 1095 cm^–1). At the same time, isolated methoxy groups (_as(–) = 2997 cm^–1, _as(–) = 2959 cm^–1, _s(–) = 2857 cm^–1, and (₃) = 1450 cm^–1) and hydrogen-bonded groups ((–) = 3400–3550 cm^–1), which resulted from chemisorption at siloxane bridges, were stabilized in silica gel–based catalysts. It was found that CH₃O and CH₃OO radicals were formed only over the surfaces of pure supports (SiO₂ and Al₂O₃) and their mechanical mixtures with platinum. The total concentration of radicals was described by an extremal function of the composition of reactants, whereas the relative concentration depends on the nature of the support. This is conceivably due to the effect of coordinatively unsaturated cations of the support, which are formed by dehydroxylation in the course of catalyst pretreatment. An increase in the rate of formation of gas-phase radicals on mixed catalysts was explained by special properties of the platinum/support interface region, at which surface intermediates were formed in superequilibrium concentrations under reaction conditions.     

IR spectroscopic studies of CO interaction with surface zirconium hydrides

IR spectroscopic studies of CO interaction with surface zirconium hydrides have revealed that it proceeds through a step of CO adsorption on these hydrides at 163–273 K with the subsequent insertion of CO across the Zr-H bonds at T>293 K and the formation of surface formyl compounds.

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CO . , CO 163–273 CO Zr-H 293 .