ABSTRACT
Alkali cation-containing vanadia solids (M = Li, Na, K, Rb, Cs) were synthesised and used as catalysts in the vapour phase oxidation of toluene, pmethoxytoluene and /7-chlorotoluene to the corresponding aldehydes. Moreover, the effect of the addition of a non-oxidisable base (e.g. pyridine) to the reaction mixture to increase basicity of the reaction mixture was studied. Parent catalyst samples and used specimens were characterised by X-ray diffractometry and infrared spectroscopy. Vanadates and bronze phases of the more bulky alkali metal cations (K, Rb, Cs) are generated during catalyst synthesis and catalytic reaction that may lead to new surface arrangements with vanadia. Aldehyde selectivity up to 60-70 % was reached at high conversions. It could be shown that the formation of the aldehydes strongly depends on nature, strength and concentration of acidic and basic surface sites of the catalysts, the acid-base properties of the reaction mixture and, additionally, on the electronic properties, i.e. nucleophilicity of the reactants.
