A Chain Catalytic Reaction Involving Pd Cluster as Chain Carrier

   α−Alkyl- and α,α′-dialkyl-substituted benzylic alcohols PhCR′R′′OH (R′=H, Me, Et, Bu; R′′=H, Me) are transformed to the corresponding dilbenzylic ethers and water in acid-free neat substrate media shortly after the addition of the palladium(I) cluster [Pd₄(CO)₄(OAc)₄] (1). During the catalytic reaction occurring under anaerobic conditions, cluster 1 is gradually decomposed to form Pd black, whereas neither original cluster 1 nor Pd black is responsible for the observed reaction. The true reaction catalyst is generated from cluster 1 after a short induction period. On the basis of the reaction kinetics and the HREM, X-ray diffraction, DTA-TG, and elemental analysis data, the catalytic dehydration is suggested to occur through a nonradical chain mechanism involving an unstable intermediate Pd cluster as the chain carrier.

Influence of radiation defects on the hyperfine magnetic field at181Ta in (Zr0.9Hf0.1)Fe2

TDPAC measurements for the 133–482 keV -ray cascade in¹⁸¹Ta were performed with¹⁸¹Hf sources in the ferromagnetic Laves intermetallic compound (Zr_0.9Hf_0.1)Fe₂. Two samples, annealed and not annealed after activation of¹⁸¹Hf in a reactor, were investigated. It was shown that in the annealed sample practically all the¹⁸¹Ta daughters occupied regular sites in the cubic Zr(Hf) sublattice and experienced a unique magnetic hyperfine fieldH _h.f.(Ta)=–6.38(14) T. In the unannealed source the regular precession was observed only for 50% of¹⁸¹Ta nuclei, another half of them were located at some unobservable sites due, obviously, to a recoil after the (n, ) reaction. Possible reasons for discrepancies in the results onH _h.f.(Ta) reported in the literature are discussed.     

Effect of the Conditions of Thermal Treatment of Molybdenum–Titanium and Vanadium–Molybdenum–Titanium Oxide Catalysts on Pore Structure Formation

The effect of the conditions of thermal treatment on the texture formation in molybdenum–titanium oxide (Mo–Ti–O) and vanadium–molybdenum–titanium oxide (V–Mo–Ti–O) catalysts was studied. It was found that the presence of MoO₃ in the Mo–Ti–O catalyst resulted in the stabilization of the surface area of anatase and in the retention of the fine pore structure upon thermal treatment because of the insertion of highly dispersed molybdenum crystallites into the aggregates of anatase crystallites, preventing from their agglomeration over a wide range of temperatures. In the presence of MoO₃ and V₂O₅ in the catalyst, anatase particles underwent agglomeration as the temperature was increased. This resulted in a more drastic decrease in the specific surface area and an increase in the pore size, as compared with binary samples, because of the formation of a thermally labile vanadium–molybdenum compound at the surface of anatase.     

Nature of the active oxygen of Co3O4

The differentiation of surface oxygen forms of Co₃O₄ by energy, reactivity and centers of adsorption has been carried out.

---

Co₃O₄ , .

     

Critical phenomena in particle dissolution in the melt during electron-beam surfacing

A model for the electron-beam surfacing process is proposed that takes into account the dissolution of the modifying particles in the melt. Critical conditions are determined for various modes of surfacing resulting in nearly homogeneous or composite coatings. A detailed parametric study of the one-dimensional version of the model is performed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 131–142, January–February, 2007.     

Investigation of nonstoichiometric spinels by method of full-profile analysis

Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 3, pp. 18–25, May–June, 1991.     

Effect of structural disorder on the catalytic activity of mixed La?Sr?Co?Fr?O perovskites

For a perovskite system La_0.7Sr_0.3Co_1-xFe_xO₃, the effect of partial substitution of Co by Fe on the particle microstructure and chemical composition of the surface layer has been studied. Iron incorporation was found to cause a structure rearrangement from the hexagonal (at x<0.05) to the cubic (atx>0.05) type, which was not accompanied by any appreciable variation of the surface layer composition. A transient sample with x=0.05 was characterized by a high degree of misorientation of microblocks and had the highest activity in the CO catalytic oxidation.     

Atomic structure of polycrystalline vanadium molybdate

Catalysis Institute, Siberian Branch, Academy of Sciences of the USSR. Translated from zhurnal Strukturnoi Khimii, Vol. 32, No. 1, pp. 110–115, January–February, 1991.     

Reactivity of Extra‐framework Species of USY Zeolites in Alkaline Medium

Zeolites of type USY (ultra‐stable Y) were obtained by steaming of NH₄NaY modification. Samples were modified by subsequent alkaline treatment in KOH solution. USY and USY‐KOH were characterised by chemical element analysis, XRD, IR, ²⁹Al and ²⁹Si MAS NMR spectroscopic measurements. Correct silicon to aluminium ratios (Si/Al) were determined by XRD and IR (double ring vibration w_DR) data whereas values calculated according to data of ²⁹Si MAS NMR and IR spectroscopy (asymmetrical TOT valence vibration w_TOT) appeared to be too high., In the latter case, the signals of the zeolite framework were strongly superimposed by that of extra‐framework silica gel (EFSi) formed during steaming. It was found that alkaline leaching induces desilication of silicon‐rich area of the zeolite framework and partial dissolution of EFSi. Silicate ions of both react with likewise dissolved extra‐framework aluminium (EFAl) to form X‐ray amorphous aluminosilicate. Consequently, the superposition of the ²⁹Si MAS NMR signals of the zeolite framework by silica gel was reduced for Q⁴(0Al) but increased for Q⁴ (2Al) and Q⁴(3Al) structure units. A reinsertion of EFAl into the zeolite framework has not been observed.