Reaction of propionaldehyde over Rh-Y zeolite

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During the desorption of propionaldehyde from the Rh-Y zeolite into a He-CO(10%) stream, the concentration of propionaldehyde decreased with desorption time. n-Propanol formation was enhanced in the desorption of propionaldehyde into a HeH 2(10%) stream, while no appreciable enhancement was observed in the desorption into a HeH 2(10%)-CO(10%) stream. A faster decrease in the concentration of propionaldehyde was observed during the desorption into a helium stream than the desorption into the HeCO stream. In the desorption into the helium stream, formation of pentene was observed. However, no formation of pentene was observed in the desorption into a HeC 2H 6(10%) stream. In the desorption into a HeC 3H 6(10%) stream, the rate of pentene formation was lower than that in the desorption into the helium stream. These results suggest that the pentene is not formed by ethylene-propylene codimerization. The reduced RhCl 3 SiO 2 catalyst which was physically mixed with the Na-Y zeolite showed comparable activity for pentene formation to that of Rh-Y zeolite in the reaction of propionaldehyde. However, neither the RhCl 3 SiO 2 catalyst nor the Na-Y zeolite was effective by itself for pentene formation. The reduced RhCl 3 SiO 2 and Rh-Y zeolite catalysts also showed activity for pentene formation in the reaction of 2-methyl-2-pentenal which is the product of aldol condensation of propionaldehyde. On the basis of the results, two sequential reactions, aldol condensation of propionaldehyde by the zeolite support followed by decarbonylation of 2-methyl-2-pentenal by rhodium metal particles, are proposed as a reaction path for the formation of pentene over the Rh-Y Zeolite.