GAS-PHASE ALDOL CONDENSATION OF N-BUTYRALDEHYDE TO 2-ETHYLHEXENAL

Aldol condensation of n-butyraldehyde to produce 2-ethylhexenal in gas-phase over solid catalysts based on niobium, tantalum or tungsten oxide supported on silica was studied. The catalysts were prepared by different procedures based on co-precipitation or impregnation methods and characterized by X-ray fluorescence, scanning electron microscopy and specific surface-area determinations. The self-condensation of n-butyraldehyde in the temperature range 150-350-degrees-C, at contact times of 1-8 s, and through a continuous-flow microreactor at atmospheric pressure, was investigated. Supported niobium oxide, either co-precipitated or impregnated, gave better yields than both tantalum and tungsten oxide, with selectivities to 2-ethylhexenal higher than 95% up to 250-degrees-C. The performances of the niobium oxide-supported catalyst were also much better than those hitherto stated in the literature for a catalyst based on reduced tin supported on silica gel.