Catalytic in situ infrared spectroscopic study of n-butyraldehyde aldol condensation

摘要

The aldol condensation of n-butyraldehyde on cesium-exchanged zeolites X and Y, mesoporousMCM-41 and silica gel impregnated with cesium salt yields initially 2-ethylhexenal with 100 %selectivity at a high conversion. The catalysts suffer from a fast deactivation, which is probablycaused by a Tishchenko side reaction leading to the formation of butyric acid. Carboxylate ionsstrongly adsorbed on the catalyst surface are detected by in situ infrared spectroscopy. Thecarboxylates cannot be removed from the surface by purging with nitrogen at reaction temperature.They probably poison the active sites and furthermore block the pores of micro- and mesoporouscatalysts. Carboxylate formation can neither be suppressed by carrying out the reaction in ahydrogen atmosphere with a catalyst comprising a hydrogenating component nor by adding watervapor to the feed. However, complete catalyst regeneration can be achieved by heating in nitrogen ataround 350 to 400℃.