Nature of active vanadium nanospecies in MCM-41 type catalysts for olefins oxidation

One-pot synthesis of vanadium-containing silica SBA-3 materials and their catalytic activity for propene oxidation

“…Similar opinion was presented in literature. 32,33 The UVvis spectra of the high loaded samples (>5 wt%) contrary to aforementioned show much higher intensity. Moreover, two additional intense bands with maxima at 330 and 400 nm have appeared.…”

“…The latter bands are assigned to V ions with higher (penta-or hexacoordinated) coordination in oligonuclear V-O-V nano-clusters. 32,34 The comparison of UV-vis spectra recorded for the samples with different V-loading gives rise to the conclusion that along with growing vanadium concentration the signicant increase of the contribution of oligomeric and polymeric vanadium species is observed (Fig. 7, Table S1 †).…”

The design, synthesis and catalytic performance of vanadium-incorporated mesoporous silica with 3D mesoporous structure for propene epoxidation

“…For one-pot synthesized VMCF_3 sample, the vanadium signal was deconvoluted into two binding energies centered at 516.5 eV and 518.1 eV, whereas only one signal at 517.5 eV was registered for VMCF_imp material. According to reports, 36,37 the binding energies of V 4+ species lie between 516.5 and 517.1 eV, while for V 5+ , the values are between 517.2 and 518.2 eV. This suggests that in the impregnated sample, only V 5+ species are present, whereas in the synthesized sample, V 4+ and V 5+ species coexist.…”

“…35 These bands overlap with the bands centered >300 nm attributed to the vanadium atoms on the wall surface and in external clusters. 36 Additionally, for the samples synthesized at pH ¼ 3 (VSBA-12_3), a shoulder at 380 nm appeared, indicating the presence of polymeric V species in octahedral coordination. In the VSBA-12_imp sample, vanadium species are mainly located on the wall surface (UV-vis bands in the range of 250-300 nm) and in the external clusters (bands >300 nm).…”

Ruthenium-doped Titania-pillared Clay for The Selective Catalytic Oxidation of Cyclohexene: Influence of Ru Loading

“…The radical mechanism happens especially in the presence of H2O2 or O2 as oxidant. Both of these reagents are known to generate free radicals [68][69][70].…”