n-Butyraldehyde self-condensation catalyzed by Ce-modified γ-Al2O3

Abstract

Self-condensation of n-butyraldehyde is an important process for the industrial production of 2-ethylhexanol. The catalytic performance of some solid acids such as γ-Al₂O₃ and molecular sieves for the self-condensation of n-butyraldehyde was investigated and the results showed that γ-Al₂O₃ was the best one. Then the effect of preparation conditions on the catalytic performance of γ-Al₂O₃ and the effect of reaction conditions on the self-condensation of n-butyraldehyde were discussed. In order to improve the catalytic performance, γ-Al₂O₃ was modified by different substances and Ce–Al₂O₃ was found to show the best catalytic performance; the conversion of n-butyraldehyde and the yield of 2-ethyl-2-hexenal could reach 93.8% and 88.6%, respectively. Moreover, the Ce–Al₂O₃ catalyst had excellent reusability. The XPS analysis of Ce3d demonstrated that the valence state of cerium affected the catalytic performance of Ce–Al₂O₃ to some extent but not predominantly. Instead the acid–base property of Ce–Al₂O₃ played a dominant role in the catalytic performance. The reaction components formed over the Ce–Al₂O₃ catalyst were identified by GC-MS and then some side-reactions were speculated and a reaction network for n-butyraldehyde self-condensation catalyzed by Ce–Al₂O₃ was proposed. Subsequently, the research on the intrinsic kinetics of n-butyraldehyde self-condensation catalyzed by Ce–Al₂O₃ showed that both the forward and backward reactions are second order and the corresponding activation energy is separately 79.60 kJ mol⁻¹ and 74.30 kJ mol⁻¹, which is higher than that of the reaction catalyzed by an aqueous base or acid.