M. V. Abrashev

Nanosize gold catalysts promoted by vanadium oxide supported on titania and zirconia for complete benzene oxidation

Abstract The complete benzene oxidation reaction was used to test the reactivity of the Au-V 2 O 5 /TiO 2 and Au-V 2 O 5 /ZrO 2 catalytic systems. A strong synergistic effect between gold and vanadia was established when molecular oxygen was used as an oxidizing agent. This effect was more pronounced for titania than for the zirconia support. In the presence of gold, predominantly polyvanadate structures are formed on the surface which are more active in the reaction of complete benzene oxidation in comparison with monovanadate species and bulk V 2 O 5 . The deposition of gold leads to a relative lengthening of the VO bond and to a higher electron delocalization. The B and C parameters calculated from ESR spectra showed no differences for the fresh and spent gold-containing samples, i.e. the catalytic systems seemed to be “stabilized” under the working conditions. The effect of gold on the vanadium oxide reducibility, which could be related to the strength of the VO-support bond, results in a considerable lowering of the temperature of the V 5+ → V 3+ transition. With ozone as the oxidizing agent, an additional lowering of the reaction temperature was achieved and very close values of the catalytic activity on all investigated samples were registered. Upon oxidation by molecular oxygen the oxidant activation takes place on the nanosize gold particles while the vanadium oxide surface species are responsible for the activation of benzene. This is in agreement with synergistic effect between the finely dispersed gold and the surface vanadium structures.

Short-range B -site ordering in the inverse spinel ferrite NiFe 2 O 4

. The numberof experimentally observed Raman modes exceeds significantly that expected for a normal spinelstructure and the polarization properties of most of the Raman lines provide evidence for a micro-scopic symmetry lower than that given by the Fd¯3m space group. We argue that the experimentalresults can be explained by considering the short range 1:1 ordering of Ni

Nanosize gold-ceria catalysts promoted by vanadia for complete benzene oxidation

New gold-vanadia-ceria catalysts for complete benzene oxidation were synthesized. A high and stable catalytic activity was established. The influence of the preparation method and the vanadia loading on the catalytic activity was studied. The presence of gold enhances the reducibility and the reactivity of VOx and ceria surface layers which results in the lowering of the reaction temperature. The observed strong synergistic effect between gold and vanadia, when they present simultaneously on ceria, could be related to the specific interaction between gold, vanadia and ceria and the possibility to obtain nanosize gold and ceria particles, being able to produce more active oxygen species.

Role of Jahn-Teller disorder in Raman scattering of mixed-valence manganites

Faculty of Physics, University of Sofia, 1164 Sofia, Bulgaria~Received 14 November 2002; revised manuscript received 29 January 2003; published 20 June 2003!The mixed-valence perovskitelike manganites are characterized by the unique interrelation of Jahn-Tellerdistortions, electric and magnetic properties. The Jahn-Teller distortion follows the Mn

Polarized Raman spectroscopy of nearly tetragonal BiFeO3 thin films

BiFeO

Raman spectra of R2O3 (R—rare earth) sesquioxides with C-type bixbyite crystal structure: A comparative study

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Defect and stress relaxation in HVPE-GaN films using high temperature reactively sputtered AlN buffer

thin films can be epitaxially stabilized in a nearly-tetragonal phase under a high biaxial compressive strain. Here we investigate the polarized Raman spectra of constrained BiFeO

Microwave plasmas applied for the synthesis of free standing graphene sheets

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Raman Study of the Variations of the Jahn-Teller Distortions through the Metal–Insulator Transition in Magnetoresistive La0.7Ca0.3MnO3 Thin Films

films with tetragonal-like (BFO-T), rhombohedral-like (BFO-R) and multiphase (BFO-T+R) structure. Based on analysis of the number and symmetry of the Raman lines, we provide strong experimental evidence that the nearly-tetragonal films are monoclinic (

Raman and infrared studies of La1- ySryMn1- xMxO3 (M=Cr, Co, Cu, Zn, Sc or Ga) : Oxygen disorder and local vibrational modes

Cc