Active sites in vanadia/titania catalysts for selective aerial oxidation of β-picoline to nicotinic acid

• Published in: Journal of catalysis 2008-10, Vol.259 (2), p.165-173
• Main Authors: Srinivas, Darbha, Hölderich, Wolfgang F., Kujath, Steffen, Valkenberg, Michael H., Raja, Thirumalaiswamy, Saikia, Lakshi, Hinze, Ramona, Ramaswamy, Veda
• Format: Article
• Language: English
• Subjects: Active vanadium species; Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Nicotinic acid; Oxidation of β-picoline; Selective aerial oxidation; Spectroscopic investigations; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Vanadia/titania
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2008.07.019

Vanadia/titania catalysts with varying vanadium content were prepared by impregnation using three different titania carrier materials of varying surface area. The structure of active vanadium species for β-picoline oxidation was investigated. Vanadium is mainly in the +5 oxidation state as revealed by electron paramagnetic resonance (EPR) and 51V magic-angle spinning nuclear magnetic resonance ( 51V MAS NMR) spectroscopy techniques. Diffuse reflectance UV–visible (DRUV–vis) spectroscopy and spectral deconvolution enabled identification of at least five different types of vanadium oxide species in these catalysts: monomeric tetrahedral VO 3− 4, polymeric distorted tetrahedral VO − 3, square pyramidal V 2O 5, octahedral V 2O 2− 6 and V 4+ oxide species. While both VO 3− 4 and VO − 3 species are active in β-picoline oxidation, the latter having a distorted tetrahedral geometry yielded the desired products—picolinaldehyde and nicotinic acid. High surface area, anatase structure for the support and dispersed, distorted tetrahedral vanadium oxide species are the key parameters determining the activity and selectivity of these oxidation catalysts.