Properties and deactivation of the active sites of an MoZSM-5 catalyst for methane dehydroaromatization: Electron microscopic and EPR studies

The MoZSM-5 (4.0 wt % Mo) catalyst has been characterized by high-resolution transmission electron microscopy, EDXA, and EPR. Two types of molybdenum-containing particles are stabilized in the catalyst in the course of nonoxidative methane conversion at 750°C. These are 2-to 10-nm molybdenum carbide particles on the zeolite surface and clusters smaller than 1 nm in zeolite channels. According to EPR data, these clusters contain the oxidized molybdenum form Mo⁵⁺. The surface Mo₂C particles are deactivated at the early stages of the reaction because of graphite condensation on their surface. Methane is mainly activated on oxidized molybdenum clusters located in the open molecular pores of the zeolite. The catalyst is deactivated after the 420-min-long operation because of coke buildup on the zeolite surface and in the zeolite pores.     

ESR study of ordered Ti(III) clusters in frozen solutions

The ESR spectrum of exchange-coupled Ti³⁺ ions of gg_e has been observed in dissolution products of metallic titanium in HCl, evidencing the formation of chloride clusters of mutually ordered Ti³⁺ ions in d_z2-ground state in distorted tetrahedral coordination. The cooperative Jahn-Teller effect (CJTE) defines orbital ordering of the d¹ of Ti³⁺ ions in the cluster.     

ESR studies of the state of Ti3+ and Ti2+ in Ti?Mg catalysts for olefin polymerization

ESR studies have revealed that in Ti–Mg catalysts after interaction with organoaluminium compounds, the Ti³⁺ ions formed are present mainly as TiCl₃ associates. Isolated Ti³⁺ ions of various types are also detected. Part of titanium ions is in the divalent state and provides an ESR signal after oxidation by water to the trivalent state in the form of Ti³⁺ ordered by cooperative Jahn-Teller interaction.

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, - , Ti³⁺ TiCl₃. Ti³⁺ . Ti³⁺ - -.

     

ESR spectra of47Ti-enriched titanium catalysts for polymerization

For the first time ESR spectra of⁴⁷Ti-enriched Ziegler system Ti-TIBA in toluene have been studied. For the ratio Ti/Al1, more accurate h. f. s. constants have been found. For Ti/Al1/15 no h. f. s. have been observed, which is ascribed to ordering due to the cooperative Jahn-Teller effect.

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TiCl₄+ ⁴⁷Ti. Ti/Al1 . Ti/Al1/15 , -.

     

Formation of allyl radicals in the adsorption of propylene on zinc oxide

It has been found by the ESR technique that the adsorption of propylene on zinc oxide leads to the formation of a -allyl radical. It is suggested that the radical species of the surface allyl compound on this catalyst is responsible for its high selectivity in the dehydroaromatization of propylene to benzene.

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, - . , .

     

ESR spectra of copper compounds of α-thiopicoline anilides

ESR spectra are reported for numerous chelates with a Cu-2(N, S) center; the covalent Cu-N bond is found to produce additional hyperfine splitting in solutions and glasses. MOLCAO methods are applied for D_2h symmetry to estimate the degree of covalency of the bonds to N and S, and also the effective degree of covalency of the bonds. Substituents in the pyridine ring do not affect the covalency of the bonds, but they probably affect the covalency of the out-of-plane bonds from the copper to the addends. The steric hindrance produced by the substituents sometimes leads to reduction of the copper, as does the chelation. Substituents in the benzene ring do not affect the copper-addend bonds but do determine the molecular packing.The triaxial anisotropy of the g factor is discussed in relation to details of the crystal structure, including lack of equivalence of the Cu-N and Cu-S bonds.     

Quantum-chemical analysis of the CuCl2 molecule

This paper reports on quantum-chemical analysis of the linear structure of CuCl₂ by Hartree-Fock (HF) and density functional theory (DFT) methods and also by time-dependent HF (TD HF) and DFT (TD DFT) techniques. Using pure DFT exchange correlation functional (B3LYP) yields the best agreement with the experimental electronic spectra of CuCl₂. In this case, the odd electron is delocalized over the molecule, spin density on copper being 0.27. The ground state of the CuCl₂ molecule is ²Π_g with linear geometry.     

EPR study of the nature of active sites and the type of their deactivation in CO hydrogenation on (Ni+Ti)/SiO2 catalysts

As shown by EPR, upon supporting Ni(-C₃H₅)₂ on Ti/SiO₂, the Ni complex is coordinated to Ti³⁺ ions. Deactivation of (Ni+Ti)/SiO₂ catalysts so obtained during CO hydrogenation is due to the oxidation of Ti³⁺ ions and metallic nickel particles by reaction products.

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, Ni(-C₃H₅)₂ Ti/SiO₂ Ni Ti³⁺. , (Ni+Ti)/SiO₂ CO Ti³⁺ .