Selective Oxidation of Toluene to Benzaldehyde: Investigation of Structure-Reactivity Relationships by in situ-Methods

摘要

(VO)_2P_2O_7 and potassium-doped V_2O_5 catalysts have been studied in the selective oxidation of toluene to benzaldehyde by in situ-EPR, -FTIR, -XRD, -UV/VIS and -XPS. In (VO)_2P_2O_7, Bronsted surface sites formed under reaction conditions favour strong product adsorption and, thus, total oxidation. They can be blocked by adding pyridine, which improves catalystic performance. K-V_2O_5 catalysts are markedly reduced during reaction. Both V~(5+) and V~(4+) species are likely to be active in the catalytic redox cycle. Crystalline K_0.5V_2O_5 formed on the catalyst surface under feed probably lowers the catalytic performance due to structural reasons.