The vapor-phase reaction of citronellal (CTN) at 220°C and atmospheric pressure has been studied using mesoporous molecular sieves and zeolites in a fixed-bed reactor. The primary products included isopulegol (IPG), menthone, and pulegol with subsequent reactions to form cyclic hydrocarbons. The CTN conversion and the product selectivity depend on the acidity and the textural property of catalysts. Lewis and/or Brönsted acid sites are essential for catalyzing this reaction. An increase of SiO2/Al2O3 mol ratio diminishes the acid amount of all catalysts and enhances both the surface area and the structural order of MCM-41. The catalytic activity follows the order of MCM-41 > HZSM-5 ³ Hb > USY, in accordance with the relative total acid amount except that of MCM-41. Despite its low acidity, Si-MCM-41 exhibits the best catalytic performance due to its uniform mesopores, large surface area and good stability; the CTN conversion and the IPG yield attain 91.9% and 58.6%, respectively, after at least 25 h time-on-stream.
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