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

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 O2chemisorptrion (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 VOx 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 V 4+ 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.