Toward understanding the unusual reactivity of mesoporous niobium silicates in epoxidation of C C bonds with hydrogen peroxide

Selective Formation of Epoxylimonene Catalyzed by Phosphonyl/Arsonyl Derivatives of Trivacant Polyoxotungstates at Low Temperature

“…It was shown that the catalyst efficiency was modulated through the protonation state of POMs (in their case γ‐[SiW 10 O 36 ] 8– ) . In addition, the groups of Kholdeeva and Poblet have recently emphasized the role of protons in heterolytic activation of H 2 O 2 in the case of Nb‐substituted polyoxometalates, as it can be observed for mesoporous niobium silicates or Zr‐Based Metal‐organic frameworks …”

Tungsten-Based Mesoporous Silicates W-MMM-E as Heterogeneous Catalysts for Liquid-Phase Oxidations with Aqueous H2O2

“…Cyclohexene also produced allylic oxidation products-cyclohexenyl hydroperoxide, 2-cyclohexene-1-ol, and 2-cyclohexene-1-one (totally 15-17%)-as well as 1,2-trans-cyclohexane diol and its overoxidation product, 2-hydroxycyclohexane-1-one. However, compared to Ti-and Nb-containing MMM-E (Table 3, entries 7, 8 and 11, 12), W-MMM-E materials were more selective during epoxidation of cyclohexene and styrene [59]. As with the other known tungsten-silicates, W-HMS gave only 2-cyclohexenol and 2-cyclohexenone during cyclohexene oxidation with a three-fold excess of 37% H 2 O 2 [38], while the reaction over W-SBA-16 yielded a 56% epoxidation selectivity with 36% conversion (1 equivalent of 30% H 2 O 2 , 50 • C, 6 h) [23].…”

“…Other products: 2-cyclohexene-1-ol (6%), 2-cyclohexene-1-one (6%), cyclohexenyl hydroperoxide (3%); h Heterolytic pathway selectivity = Σ(cyclohexene oxide (33%) + 2-hydroxy-cyclohexane-1-one (17%) + 1,2-trans-cyclohexane diol (33%)). Other products: 2-cyclohexene-1-ol (7%), 2-cyclohexene-1-one (7%), cyclohexenyl hydroperoxide (3%); i Total selectivity of heterolytic oxidation products (cyclohexene oxide + trans-cyclohexane-1,2-diol + 2-hydroxycyclohexanone) [59].…”

Niobium oxide prepared through a novel supercritical-CO2-assisted method as a highly active heterogeneous catalyst for the synthesis of azoxybenzene from aniline

“…Different mechanisms have been proposed for the activation of hydrogen peroxide by Nb 2 O 5 catalysts, involving the formation of active oxygen species, among which metal (hydroxy)peroxo species and hydroxyl radicals are the most common. 46,50 In order to gain more insight into how Nb 2 O 5 -scCO 2 activates H 2 O 2 towards the oxidation of aniline, a control experiment was conducted under the optimum reaction conditions but with the addition of TEMPO (1 mol% relative to H 2 O 2 ), which has been widely reported to act as a hydroxyl radical scavenger. 51,52 A drastic decrease in the conversion of aniline to 5% was observed (Table 1, entry 7).…”

“…The catalytic cycle most likely starts with the formation of niobium hydroperoxo (Nb-OOH) species through the reaction between surface niobium-hydroxyls (Nb-OH) and H 2 O 2 . 46,50 Then, the interaction between Nb-OOH and H 2 O 2 can generate highly reactive hydroxyl radicals ( • OH) and hydroperoxo radicals ( • OOH) and/or niobium peroxo radicals (NbO 2…”