Optimization of Redox Functionality Profiles of MoO3–V2O5/ TiO2 Composite Catalysts in Relation to Various Dispersion Patterns

Abstract

Abstract: In the present study, a renewed approach was made to optimize the redox functionality of the well-known catalytic system MoO₃-V₂O₅/ TiO₂ (anatase) in relation to various dispersion patterns. Several types of composite catalysts were considered: xV/T (x of V₂O₅= 2-12 wt %), 6Mo-xV/T co-impregnates, yMo-8V/T co-impregnates (y of MoO₃ = 3-9 wt %), 6Mo-doped 8V/T (coat 1) and 8V-doped Mo/T (coat 2). The samples were characterized by adopting the XRD, FTIR, ESR, TEM, N₂ physisorption, high temperature H₂-chemisorption and high temperature O₂-chemisorptrion (HTOC), techniques. The redox reactivity was estimated in decomposition of H₂O₂ in highly concentrated solution, permitting the formation of several peroxo V intermediates. In xV/T system, the constancy of TON with loading indicated the involvement of single vanadia site, not sensitive to the surface dispersion, but rather depended on the nature of coordination of H₂O₂ molecules to VO_x species. For different co-impregnates of Mo and V, the added molybdena, increasing the Lewis acidity, seemed to undergo a competitive interaction with titania to form non-reducible surface compound, with increased density of surface VOx patches. This was confirmed from H₂-uptakes linked with highly stabilized V⁴⁺ species. The sample of coat 1had the same dispersion and reactivity patterns of the other members of co-impregnated series, with formation of non-reducible surface compound through Mo-O-V bridges. In coat 2 sample, the VOx species existed on the top surface of supported MoO₃/TiO₂ in a better dispersion state, with higher apparent density of surface patches, exhibiting comparable [A] and TON values to those of xV/T samples.