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

Abstract

Mesoporous tungsten-silicates, W-MMM-E, have been prepared following evaporation-induced self-assembly methodology and characterized by elemental analysis, XRD, N 2 adsorption, STEM-HAADF (high angle annular dark field in scanning-TEM mode), DRS UV-vis, and Raman techniques. DRS UV-vis showed the presence of two types of tungsten oxo-species in W-MMM-E samples: isolated tetrahedrally and oligomeric octahedrally coordinated ones, with the ratio depending on the content of tungsten in the catalyst. Materials with lower W loading have a higher contribution from isolated species, regardless of the preparation method. W-MMM-E catalyzes selectively oxidize of a range of alkenes and organic sulfides, including bulky terpene or thianthrene molecules, using green aqueous H 2 O 2 . The selectivity of corresponding epoxides reached 85-99% in up to 80% alkene conversions, while sulfoxides formed with 84-90% selectivity in almost complete sulfide conversions and a 90-100% H 2 O 2 utilization efficiency. The true heterogeneity of catalysis over W-MMM-E was proved by hot filtration tests. Leaching of inactive W species depended on the reaction conditions and initial W loading in the catalyst. After optimization of the catalyst system, it did not exceed 20 ppm and 3 ppm for epoxidation and sulfoxidation reactions, respectively. Elaborated catalysts could be easily retrieved by filtration and reused several times with maintenance of the catalytic behavior.

Alkene Epoxidation and Thioether Oxidation with Hydrogen Peroxide Catalyzed by Mesoporous Zirconium-Silicates

“…Two different methodologies were employed for the catalyst synthesis, namely, evaporation-induced self-assembly (EISA) and solventless dry impregnation of an organometallic Zr precursor onto a commercial mesoporous SiO 2 (OM-DI). Previously, the EISA approach was successfully used for insertion of Ti [27], Nb [32], and W [40] into silicate materials while the OM-DI strategy found application in the preparation of solid oxidic catalysts containing Mo [55,56], Ti and Nb [30,57]. Our present work demonstrated that, regardless of the catalyst preparation method, mesoporous Zr-silicates enable fairly good substrate conversions and product selectivity in the oxidation of bulky alkenes and thioethers.…”

“…However, several research groups demonstrated that Nb-silicates can be more efficient than Ti-ones in the epoxidation of bulky alkenes with H 2 O 2 and, moreover, possess better stability than the latter [28][29][30][31][32][33][34]. Some success has been recorded in the preparation of tungsten-containing silicates and their use in oxidation catalysis; however, partial tungsten leaching under the conditions of liquid-phase oxidation with H 2 O 2 still remains an unresolved problem [35][36][37][38][39][40][41].…”

Recent Developments in Heterogeneous Catalyzed Epoxidation of Styrene to Styrene Oxide

“…Maurya et al reported polymer‐anchored tungsten (VI)(Figure and Figure ) as catalyst for the oxidation of styrene using hydrogen peroxide as oxidant . These polymer‐anchored tungsten (VI) catalysts were prepared by reaction of covalently anchored 2‐(2‐pyridyl)benzimidazole (2‐pybmz) and 2‐(3‐pyridyl)benzimidazole (3‐pybmz) to chloromethylated polystyrene crossed‐linked with 5% divinylbenzene, with metal peroxo species, prepared in situ from WO 3 ⋅H 2 O and an excess of 30% H 2 O 2 .…”

Spongy titanosilicate promotes the catalytic performance and reusability of WO3 in oxidative cleavage of methyl oleate

“…Some transition metal containing catalysts, [13][14][15][16] such as H 2 WO 4 @Al-MCM-41, 12 BaFeO 3Àd , 17,18 Ru(OH) x /g-Al 2 O 3 19 and VO@TiO 2 20 have been proved efficient in catalyzing this reaction with H 2 O 2 as oxidant. Among them, tungsten containing catalysts such as tungsten oxide (WO 3 ), WO 3 nanoparticles, 24 tungstic acid, 25 tungstates and supported WO 3 [26][27][28][29][30] have shown the best catalytic performance. 4,[21][22][23] Although effective in catalytic oxidative cleavage of UFAE, tungsten containing catalyst suffers from active center leaching problem, and thus limits its large scale application.…”

“…Some transition metal containing catalysts, 13–16 such as H 2 WO 4 @Al-MCM-41, 12 BaFeO 3− δ , 17,18 Ru(OH) x /γ-Al 2 O 3 19 and VO@TiO 2 20 have been proved efficient in catalyzing this reaction with H 2 O 2 as oxidant. Among them, tungsten containing catalysts such as tungsten oxide (WO 3 ), WO 3 nanoparticles, 24 tungstic acid, 25 tungstates and supported WO 3 26–30 have shown the best catalytic performance. 4,21–23 …”