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Publisher Summary This chapter discusses catalytic in situ infrared spectroscopic study of n -butyraldehyde aldol condensation. Aldol condensation of n -butyraldehyde on cesium-exchanged zeolites X and Y, mesoporous MCM-41, and silica gel impregnated with cesium salt yield initially 2-ethylhexenal with 100% selectivity at a high conversion. The active catalysts suffer from fast deactivation, which is probably caused by a Tishchenko side reaction leading to the formation of butyric acid. A carboxylate ion strongly adsorbed on the catalyst surface is detected by in situ infrared spectroscopy. It probably poisons the active sites and blocks the pores of micro and mesoporous catalysts. Carboxylate formation cannot be suppressed by carrying out the reaction in hydrogen or by adding water to the feed. However, complete catalyst regeneration can be achieved by heating in nitrogen at around 350 to 400°C. |
