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Synthesis of molybdenum-incorporated mesoporous silicates by evaporation-induced self-assembly: Insights into surface oxide species and corresponding olefin metathesis activity

ABSTRACT

Molybdenum-incorporated mesoporous silicates with different Si/Mo ratios were synthesized via the Evaporation Induced Self-Assembly (EISA) method. SAXS and nitrogen physisorption results confirm the ordered mesoporosity. The BET surface area, pore volume and pore size distribution generally decrease with Mo loading while preserving the mesoporosity. Highly dispersed monomeric and oligomeric MoOx species (Mo6+ oxidation state) were evident from diffuse reflectance UV–Vis and XPS spectra. H2-TPR results confirm the existence of polymeric MoOx and bulk crystalline MoO3 species. At lower loadings, Mo exits in both tetrahedral and octahedral symmetry as established by Mo L3-edge XANES studies. Mo-EISA catalysts with highly dispersed isolated MoOx sites display stable activity for 2-butene + ethylene metathesis that is comparable to those reported for WO3/SiO2 catalysts.

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